Table of Contents
The MySQL Performance Schema is a feature for monitoring MySQL Server execution at a low level. The Performance Schema has these characteristics:
The Performance Schema provides a way to inspect internal
execution of the server at runtime. It is implemented using the
PERFORMANCE_SCHEMA
storage engine
and the performance_schema
database. The
Performance Schema focuses primarily on performance data. This
differs from INFORMATION_SCHEMA
, which serves
for inspection of metadata.
The Performance Schema monitors server events. An “event” is anything the server does that takes time and has been instrumented so that timing information can be collected. In general, an event could be a function call, a wait for the operating system, a stage of an SQL statement execution such as parsing or sorting, or an entire statement or group of statements. Event collection provides access to information about synchronization calls (such as for mutexes) file and table I/O, table locks, and so forth for the server and for several storage engines.
Performance Schema events are distinct from events written to the server's binary log (which describe data modifications) and Event Scheduler events (which are a type of stored program).
Performance Schema events are specific to a given instance of the MySQL Server. Performance Schema tables are considered local to the server, and changes to them are not replicated or written to the binary log.
Current events are available, as well as event histories and summaries. This enables you to determine how many times instrumented activities were performed and how much time they took. Event information is available to show the activities of specific threads, or activity associated with particular objects such as a mutex or file.
The PERFORMANCE_SCHEMA
storage
engine collects event data using “instrumentation
points” in server source code.
Collected events are stored in tables in the
performance_schema
database. These tables can
be queried using SELECT
statements like other tables.
Performance Schema configuration can be modified dynamically by
updating tables in the performance_schema
database through SQL statements. Configuration changes affect
data collection immediately.
Tables in the Performance Schema are in-memory tables that use no persistent on-disk storage. The contents are repopulated beginning at server startup and discarded at server shutdown.
Monitoring is available on all platforms supported by MySQL.
Some limitations might apply: The types of timers might vary per platform. Instruments that apply to storage engines might not be implemented for all storage engines. Instrumentation of each third-party engine is the responsibility of the engine maintainer. See also Section 25.21, “Restrictions on Performance Schema”.
Data collection is implemented by modifying the server source code to add instrumentation. There are no separate threads associated with the Performance Schema, unlike other features such as replication or the Event Scheduler.
The Performance Schema is intended to provide access to useful information about server execution while having minimal impact on server performance. The implementation follows these design goals:
Activating the Performance Schema causes no changes in server
behavior. For example, it does not cause thread scheduling to
change, and it does not cause query execution plans (as shown by
EXPLAIN
) to change.
Server monitoring occurs continuously and unobtrusively with very little overhead. Activating the Performance Schema does not make the server unusable.
The parser is unchanged. There are no new keywords or statements.
Execution of server code proceeds normally even if the Performance Schema fails internally.
When there is a choice between performing processing during event collection initially or during event retrieval later, priority is given to making collection faster. This is because collection is ongoing whereas retrieval is on demand and might never happen at all.
It is easy to add new instrumentation points.
Instrumentation is versioned. If the instrumentation implementation changes, previously instrumented code will continue to work. This benefits developers of third-party plugins because it is not necessary to upgrade each plugin to stay synchronized with the latest Performance Schema changes.
The MySQL sys
schema is a set of objects that
provides convenient access to data collected by the Performance
Schema. The sys
schema is installed by default.
For usage instructions, see Chapter 26, MySQL sys Schema.
This section briefly introduces the Performance Schema with examples that show how to use it. For additional examples, see Section 25.19, “Using the Performance Schema to Diagnose Problems”.
The Performance Schema is enabled by default. To enable or disable
it explicitly, start the server with the
performance_schema
variable set
to an appropriate value. For example, use these lines in the
server my.cnf
file:
[mysqld] performance_schema=ON
When the server starts, it sees
performance_schema
and attempts
to initialize the Performance Schema. To verify successful
initialization, use this statement:
mysql> SHOW VARIABLES LIKE 'performance_schema';
+--------------------+-------+
| Variable_name | Value |
+--------------------+-------+
| performance_schema | ON |
+--------------------+-------+
A value of ON
means that the Performance Schema
initialized successfully and is ready for use. A value of
OFF
means that some error occurred. Check the
server error log for information about what went wrong.
The Performance Schema is implemented as a storage engine. If this
engine is available (which you should already have checked
earlier), you should see it listed with a
SUPPORT
value of YES
in the
output from the
INFORMATION_SCHEMA.ENGINES
table or
the SHOW ENGINES
statement:
mysql>SELECT * FROM INFORMATION_SCHEMA.ENGINES
WHERE ENGINE='PERFORMANCE_SCHEMA'\G
*************************** 1. row *************************** ENGINE: PERFORMANCE_SCHEMA SUPPORT: YES COMMENT: Performance Schema TRANSACTIONS: NO XA: NO SAVEPOINTS: NO mysql>SHOW ENGINES\G
... Engine: PERFORMANCE_SCHEMA Support: YES Comment: Performance Schema Transactions: NO XA: NO Savepoints: NO ...
The PERFORMANCE_SCHEMA
storage engine
operates on tables in the performance_schema
database. You can make performance_schema
the
default database so that references to its tables need not be
qualified with the database name:
mysql> USE performance_schema;
Performance Schema tables are stored in the
performance_schema
database. Information about
the structure of this database and its tables can be obtained, as
for any other database, by selecting from the
INFORMATION_SCHEMA
database or by using
SHOW
statements. For example, use
either of these statements to see what Performance Schema tables
exist:
mysql>SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES
WHERE TABLE_SCHEMA = 'performance_schema';
+------------------------------------------------------+ | TABLE_NAME | +------------------------------------------------------+ | accounts | | cond_instances | ... | events_stages_current | | events_stages_history | | events_stages_history_long | | events_stages_summary_by_account_by_event_name | | events_stages_summary_by_host_by_event_name | | events_stages_summary_by_thread_by_event_name | | events_stages_summary_by_user_by_event_name | | events_stages_summary_global_by_event_name | | events_statements_current | | events_statements_history | | events_statements_history_long | ... | file_instances | | file_summary_by_event_name | | file_summary_by_instance | | host_cache | | hosts | | memory_summary_by_account_by_event_name | | memory_summary_by_host_by_event_name | | memory_summary_by_thread_by_event_name | | memory_summary_by_user_by_event_name | | memory_summary_global_by_event_name | | metadata_locks | | mutex_instances | | objects_summary_global_by_type | | performance_timers | | replication_connection_configuration | | replication_connection_status | | replication_applier_configuration | | replication_applier_status | | replication_applier_status_by_coordinator | | replication_applier_status_by_worker | | rwlock_instances | | session_account_connect_attrs | | session_connect_attrs | | setup_actors | | setup_consumers | | setup_instruments | | setup_objects | | setup_timers | | socket_instances | | socket_summary_by_event_name | | socket_summary_by_instance | | table_handles | | table_io_waits_summary_by_index_usage | | table_io_waits_summary_by_table | | table_lock_waits_summary_by_table | | threads | | users | +------------------------------------------------------+ mysql>SHOW TABLES FROM performance_schema;
+------------------------------------------------------+ | Tables_in_performance_schema | +------------------------------------------------------+ | accounts | | cond_instances | | events_stages_current | | events_stages_history | | events_stages_history_long | ...
The number of Performance Schema tables increases over time as implementation of additional instrumentation proceeds.
The name of the performance_schema
database is
lowercase, as are the names of tables within it. Queries should
specify the names in lowercase.
To see the structure of individual tables, use
SHOW CREATE TABLE
:
mysql> SHOW CREATE TABLE performance_schema.setup_consumers\G
*************************** 1. row ***************************
Table: setup_consumers
Create Table: CREATE TABLE `setup_consumers` (
`NAME` varchar(64) NOT NULL,
`ENABLED` enum('YES','NO') NOT NULL
) ENGINE=PERFORMANCE_SCHEMA DEFAULT CHARSET=utf8
Table structure is also available by selecting from tables such as
INFORMATION_SCHEMA.COLUMNS
or by
using statements such as SHOW
COLUMNS
.
Tables in the performance_schema
database can
be grouped according to the type of information in them: Current
events, event histories and summaries, object instances, and setup
(configuration) information. The following examples illustrate a
few uses for these tables. For detailed information about the
tables in each group, see
Section 25.12, “Performance Schema Table Descriptions”.
Initially, not all instruments and consumers are enabled, so the performance schema does not collect all events. To turn all of these on and enable event timing, execute two statements (the row counts may differ depending on MySQL version):
mysql>UPDATE performance_schema.setup_instruments
SET ENABLED = 'YES', TIMED = 'YES';
Query OK, 560 rows affected (0.04 sec) mysql>UPDATE performance_schema.setup_consumers
SET ENABLED = 'YES';
Query OK, 10 rows affected (0.00 sec)
To see what the server is doing at the moment, examine the
events_waits_current
table. It
contains one row per thread showing each thread's most recent
monitored event:
mysql>SELECT *
FROM performance_schema.events_waits_current\G
*************************** 1. row *************************** THREAD_ID: 0 EVENT_ID: 5523 END_EVENT_ID: 5523 EVENT_NAME: wait/synch/mutex/mysys/THR_LOCK::mutex SOURCE: thr_lock.c:525 TIMER_START: 201660494489586 TIMER_END: 201660494576112 TIMER_WAIT: 86526 SPINS: NULL OBJECT_SCHEMA: NULL OBJECT_NAME: NULL INDEX_NAME: NULL OBJECT_TYPE: NULL OBJECT_INSTANCE_BEGIN: 142270668 NESTING_EVENT_ID: NULL NESTING_EVENT_TYPE: NULL OPERATION: lock NUMBER_OF_BYTES: NULL FLAGS: 0 ...
This event indicates that thread 0 was waiting for 86,526
picoseconds to acquire a lock on
THR_LOCK::mutex
, a mutex in the
mysys
subsystem. The first few columns provide
the following information:
The ID columns indicate which thread the event comes from and the event number.
EVENT_NAME
indicates what was instrumented
and SOURCE
indicates which source file
contains the instrumented code.
The timer columns show when the event started and stopped and
how long it took. If an event is still in progress, the
TIMER_END
and TIMER_WAIT
values are NULL
. Timer values are
approximate and expressed in picoseconds. For information
about timers and event time collection, see
Section 25.4.1, “Performance Schema Event Timing”.
The history tables contain the same kind of rows as the
current-events table but have more rows and show what the server
has been doing “recently” rather than
“currently.” The
events_waits_history
and
events_waits_history_long
tables
contain the most recent 10 events per thread and most recent
10,000 events, respectively. For example, to see information for
recent events produced by thread 13, do this:
mysql>SELECT EVENT_ID, EVENT_NAME, TIMER_WAIT
FROM performance_schema.events_waits_history
WHERE THREAD_ID = 13
ORDER BY EVENT_ID;
+----------+-----------------------------------------+------------+ | EVENT_ID | EVENT_NAME | TIMER_WAIT | +----------+-----------------------------------------+------------+ | 86 | wait/synch/mutex/mysys/THR_LOCK::mutex | 686322 | | 87 | wait/synch/mutex/mysys/THR_LOCK_malloc | 320535 | | 88 | wait/synch/mutex/mysys/THR_LOCK_malloc | 339390 | | 89 | wait/synch/mutex/mysys/THR_LOCK_malloc | 377100 | | 90 | wait/synch/mutex/sql/LOCK_plugin | 614673 | | 91 | wait/synch/mutex/sql/LOCK_open | 659925 | | 92 | wait/synch/mutex/sql/THD::LOCK_thd_data | 494001 | | 93 | wait/synch/mutex/mysys/THR_LOCK_malloc | 222489 | | 94 | wait/synch/mutex/mysys/THR_LOCK_malloc | 214947 | | 95 | wait/synch/mutex/mysys/LOCK_alarm | 312993 | +----------+-----------------------------------------+------------+
As new events are added to a history table, older events are discarded if the table is full.
Summary tables provide aggregated information for all events over
time. The tables in this group summarize event data in different
ways. To see which instruments have been executed the most times
or have taken the most wait time, sort the
events_waits_summary_global_by_event_name
table on the COUNT_STAR
or
SUM_TIMER_WAIT
column, which correspond to a
COUNT(*)
or SUM(TIMER_WAIT)
value, respectively, calculated over all events:
mysql>SELECT EVENT_NAME, COUNT_STAR
FROM performance_schema.events_waits_summary_global_by_event_name
ORDER BY COUNT_STAR DESC LIMIT 10;
+---------------------------------------------------+------------+ | EVENT_NAME | COUNT_STAR | +---------------------------------------------------+------------+ | wait/synch/mutex/mysys/THR_LOCK_malloc | 6419 | | wait/io/file/sql/FRM | 452 | | wait/synch/mutex/sql/LOCK_plugin | 337 | | wait/synch/mutex/mysys/THR_LOCK_open | 187 | | wait/synch/mutex/mysys/LOCK_alarm | 147 | | wait/synch/mutex/sql/THD::LOCK_thd_data | 115 | | wait/io/file/myisam/kfile | 102 | | wait/synch/mutex/sql/LOCK_global_system_variables | 89 | | wait/synch/mutex/mysys/THR_LOCK::mutex | 89 | | wait/synch/mutex/sql/LOCK_open | 88 | +---------------------------------------------------+------------+ mysql>SELECT EVENT_NAME, SUM_TIMER_WAIT
FROM performance_schema.events_waits_summary_global_by_event_name
ORDER BY SUM_TIMER_WAIT DESC LIMIT 10;
+----------------------------------------+----------------+ | EVENT_NAME | SUM_TIMER_WAIT | +----------------------------------------+----------------+ | wait/io/file/sql/MYSQL_LOG | 1599816582 | | wait/synch/mutex/mysys/THR_LOCK_malloc | 1530083250 | | wait/io/file/sql/binlog_index | 1385291934 | | wait/io/file/sql/FRM | 1292823243 | | wait/io/file/myisam/kfile | 411193611 | | wait/io/file/myisam/dfile | 322401645 | | wait/synch/mutex/mysys/LOCK_alarm | 145126935 | | wait/io/file/sql/casetest | 104324715 | | wait/synch/mutex/sql/LOCK_plugin | 86027823 | | wait/io/file/sql/pid | 72591750 | +----------------------------------------+----------------+
These results show that the THR_LOCK_malloc
mutex is “hot,” both in terms of how often it is used
and amount of time that threads wait attempting to acquire it.
The THR_LOCK_malloc
mutex is used only in
debug builds. In production builds it is not hot because it is
nonexistent.
Instance tables document what types of objects are instrumented.
An instrumented object, when used by the server, produces an
event. These tables provide event names and explanatory notes or
status information. For example, the
file_instances
table lists instances
of instruments for file I/O operations and their associated files:
mysql>SELECT *
FROM performance_schema.file_instances\G
*************************** 1. row *************************** FILE_NAME: /opt/mysql-log/60500/binlog.000007 EVENT_NAME: wait/io/file/sql/binlog OPEN_COUNT: 0 *************************** 2. row *************************** FILE_NAME: /opt/mysql/60500/data/mysql/tables_priv.MYI EVENT_NAME: wait/io/file/myisam/kfile OPEN_COUNT: 1 *************************** 3. row *************************** FILE_NAME: /opt/mysql/60500/data/mysql/columns_priv.MYI EVENT_NAME: wait/io/file/myisam/kfile OPEN_COUNT: 1 ...
Setup tables are used to configure and display monitoring
characteristics. For example,
setup_instruments
lists the set of
instruments for which events can be collected and shows which of
them are enabled:
mysql> SELECT * FROM performance_schema.setup_instruments;
+---------------------------------------------------+---------+-------+
| NAME | ENABLED | TIMED |
+---------------------------------------------------+---------+-------+
...
| stage/sql/end | NO | NO |
| stage/sql/executing | NO | NO |
| stage/sql/init | NO | NO |
| stage/sql/insert | NO | NO |
...
| statement/sql/load | YES | YES |
| statement/sql/grant | YES | YES |
| statement/sql/check | YES | YES |
| statement/sql/flush | YES | YES |
...
| wait/synch/mutex/sql/LOCK_global_read_lock | YES | YES |
| wait/synch/mutex/sql/LOCK_global_system_variables | YES | YES |
| wait/synch/mutex/sql/LOCK_lock_db | YES | YES |
| wait/synch/mutex/sql/LOCK_manager | YES | YES |
...
| wait/synch/rwlock/sql/LOCK_grant | YES | YES |
| wait/synch/rwlock/sql/LOGGER::LOCK_logger | YES | YES |
| wait/synch/rwlock/sql/LOCK_sys_init_connect | YES | YES |
| wait/synch/rwlock/sql/LOCK_sys_init_slave | YES | YES |
...
| wait/io/file/sql/binlog | YES | YES |
| wait/io/file/sql/binlog_index | YES | YES |
| wait/io/file/sql/casetest | YES | YES |
| wait/io/file/sql/dbopt | YES | YES |
...
To understand how to interpret instrument names, see Section 25.6, “Performance Schema Instrument Naming Conventions”.
To control whether events are collected for an instrument, set its
ENABLED
value to YES
or
NO
. For example:
mysql>UPDATE performance_schema.setup_instruments
SET ENABLED = 'NO'
WHERE NAME = 'wait/synch/mutex/sql/LOCK_mysql_create_db';
The Performance Schema uses collected events to update tables in
the performance_schema
database, which act as
“consumers” of event information. The
setup_consumers
table lists the
available consumers and which are enabled:
mysql> SELECT * FROM performance_schema.setup_consumers;
+----------------------------------+---------+
| NAME | ENABLED |
+----------------------------------+---------+
| events_stages_current | NO |
| events_stages_history | NO |
| events_stages_history_long | NO |
| events_statements_current | YES |
| events_statements_history | YES |
| events_statements_history_long | NO |
| events_transactions_current | NO |
| events_transactions_history | NO |
| events_transactions_history_long | NO |
| events_waits_current | NO |
| events_waits_history | NO |
| events_waits_history_long | NO |
| global_instrumentation | YES |
| thread_instrumentation | YES |
| statements_digest | YES |
+----------------------------------+---------+
To control whether the Performance Schema maintains a consumer as
a destination for event information, set its
ENABLED
value.
For more information about the setup tables and how to use them to control event collection, see Section 25.4.2, “Performance Schema Event Filtering”.
There are some miscellaneous tables that do not fall into any of
the previous groups. For example,
performance_timers
lists the
available event timers and their characteristics. For information
about timers, see Section 25.4.1, “Performance Schema Event Timing”.
The Performance Schema is mandatory and always compiled in. It is possible to exclude certain parts of the Performance Schema instrumentation. For example, to exclude stage and statement instrumentation, do this:
shell>cmake . \
-DDISABLE_PSI_STAGE=1 \
-DDISABLE_PSI_STATEMENT=1
For more information, see the descriptions of the
DISABLE_PSI_
CMake options in
Section 2.9.7, “MySQL Source-Configuration Options”.
XXX
If you install MySQL over a previous installation that was configured without the Performance Schema (or with an older version of the Performance Schema that has missing or out-of-date tables). One indication of this issue is the presence of messages such as the following in the error log:
[ERROR] Native table 'performance_schema'.'events_waits_history' has the wrong structure [ERROR] Native table 'performance_schema'.'events_waits_history_long' has the wrong structure ...
To correct that problem, perform the MySQL upgrade procedure. See Section 2.11, “Upgrading MySQL”.
To verify whether a server was built with Performance Schema
support, check its help output. If the Performance Schema is
available, the output will mention several variables with names
that begin with performance_schema
:
shell> mysqld --verbose --help
...
--performance_schema
Enable the performance schema.
--performance_schema_events_waits_history_long_size=#
Number of rows in events_waits_history_long.
...
You can also connect to the server and look for a line that names
the PERFORMANCE_SCHEMA
storage engine
in the output from SHOW ENGINES
:
mysql> SHOW ENGINES\G
...
Engine: PERFORMANCE_SCHEMA
Support: YES
Comment: Performance Schema
Transactions: NO
XA: NO
Savepoints: NO
...
If the Performance Schema was not configured into the server at
build time, no row for
PERFORMANCE_SCHEMA
will appear in the
output from SHOW ENGINES
. You might
see performance_schema
listed in the output
from SHOW DATABASES
, but it will
have no tables and you will not be able to use it.
A line for PERFORMANCE_SCHEMA
in the
SHOW ENGINES
output means that the
Performance Schema is available, not that it is enabled. To enable
it, you must do so at server startup, as described in the next
section.
To use the MySQL Performance Schema, it must be enabled at server startup to enable event collection to occur.
Assuming that the Performance Schema is available, it is enabled
by default. To enable or disable it explicitly, start the server
with the performance_schema
variable set to an appropriate value. For example, use these lines
in your my.cnf
file:
[mysqld] performance_schema=ON
If the server is unable to allocate any internal buffer during
Performance Schema initialization, the Performance Schema disables
itself and sets
performance_schema
to
OFF
, and the server runs without
instrumentation.
The Performance Schema also permits instrument and consumer configuration at server startup.
To control an instrument at server startup, use an option of this form:
--performance-schema-instrument='instrument_name
=value
'
Here, instrument_name
is an instrument
name such as wait/synch/mutex/sql/LOCK_open
,
and value
is one of these values:
OFF
, FALSE
, or
0
: Disable the instrument
ON
, TRUE
, or
1
: Enable and time the instrument
COUNTED
: Enable and count (rather than
time) the instrument
Each
--performance-schema-instrument
option can specify only one instrument name, but multiple
instances of the option can be given to configure multiple
instruments. In addition, patterns are permitted in instrument
names to configure instruments that match the pattern. To
configure all condition synchronization instruments as enabled and
counted, use this option:
--performance-schema-instrument='wait/synch/cond/%=COUNTED'
To disable all instruments, use this option:
--performance-schema-instrument='%=OFF'
Exception: The memory/performance_schema/%
instruments are built in and cannot be disabled at startup.
Longer instrument name strings take precedence over shorter pattern names, regardless of order. For information about specifying patterns to select instruments, see Section 25.4.9, “Naming Instruments or Consumers for Filtering Operations”.
An unrecognized instrument name is ignored. It is possible that a plugin installed later may create the instrument, at which time the name is recognized and configured.
To control a consumer at server startup, use an option of this form:
--performance-schema-consumer-consumer_name
=value
Here, consumer_name
is a consumer name
such as events_waits_history
, and
value
is one of these values:
OFF
, FALSE
, or
0
: Do not collect events for the consumer
ON
, TRUE
, or
1
: Collect events for the consumer
For example, to enable the events_waits_history
consumer, use this option:
--performance-schema-consumer-events-waits-history=ON
The permitted consumer names can be found by examining the
setup_consumers
table. Patterns are
not permitted. Consumer names in the
setup_consumers
table use
underscores, but for consumers set at startup, dashes and
underscores within the name are equivalent.
The Performance Schema includes several system variables that provide configuration information:
mysql> SHOW VARIABLES LIKE 'perf%';
+--------------------------------------------------------+---------+
| Variable_name | Value |
+--------------------------------------------------------+---------+
| performance_schema | ON |
| performance_schema_accounts_size | 100 |
| performance_schema_digests_size | 200 |
| performance_schema_events_stages_history_long_size | 10000 |
| performance_schema_events_stages_history_size | 10 |
| performance_schema_events_statements_history_long_size | 10000 |
| performance_schema_events_statements_history_size | 10 |
| performance_schema_events_waits_history_long_size | 10000 |
| performance_schema_events_waits_history_size | 10 |
| performance_schema_hosts_size | 100 |
| performance_schema_max_cond_classes | 80 |
| performance_schema_max_cond_instances | 1000 |
...
The performance_schema
variable
is ON
or OFF
to indicate
whether the Performance Schema is enabled or disabled. The other
variables indicate table sizes (number of rows) or memory
allocation values.
With the Performance Schema enabled, the number of Performance Schema instances affects the server memory footprint, perhaps to a large extent. The Performance Schema autoscales many parameters to use memory only as required; see Section 25.17, “The Performance Schema Memory-Allocation Model”.
To change the value of Performance Schema system variables, set
them at server startup. For example, put the following lines in a
my.cnf
file to change the sizes of the
history tables for wait events:
[mysqld] performance_schema performance_schema_events_waits_history_size=20 performance_schema_events_waits_history_long_size=15000
The Performance Schema automatically sizes the values of several of its parameters at server startup if they are not set explicitly. For example, it sizes the parameters that control the sizes of the events waits tables this way. the Performance Schema allocates memory incrementally, scaling its memory use to actual server load, instead of allocating all the memory it needs during server startup. Consequently, many sizing parameters need not be set at all. To see which parameters are autosized or autoscaled, use mysqld --verbose --help and examine the option descriptions, or see Section 25.15, “Performance Schema System Variables”.
For each autosized parameter that is not set at server startup, the Performance Schema determines how to set its value based on the value of the following system values, which are considered as “hints” about how you have configured your MySQL server:
max_connections open_files_limit table_definition_cache table_open_cache
To override autosizing or autoscaling for a given parameter, set it to a value other than −1 at startup. In this case, the Performance Schema assigns it the specified value.
At runtime, SHOW VARIABLES
displays
the actual values that autosized parameters were set to.
Autoscaled parameters display with a value of −1.
If the Performance Schema is disabled, its autosized and
autoscaled parameters remain set to −1 and
SHOW VARIABLES
displays −1.
Specific Performance Schema features can be enabled at runtime to control which types of event collection occur.
Performance Schema setup tables contain information about monitoring configuration:
mysql>SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES
WHERE TABLE_SCHEMA = 'performance_schema'
AND TABLE_NAME LIKE 'setup%';
+-------------------+ | TABLE_NAME | +-------------------+ | setup_actors | | setup_consumers | | setup_instruments | | setup_objects | | setup_timers | +-------------------+
You can examine the contents of these tables to obtain information
about Performance Schema monitoring characteristics. If you have
the UPDATE
privilege, you can
change Performance Schema operation by modifying setup tables to
affect how monitoring occurs. For additional details about these
tables, see Section 25.12.2, “Performance Schema Setup Tables”.
To see which event timers are selected, query the
setup_timers
tables:
mysql> SELECT * FROM performance_schema.setup_timers;
+-------------+-------------+
| NAME | TIMER_NAME |
+-------------+-------------+
| idle | MICROSECOND |
| wait | CYCLE |
| stage | NANOSECOND |
| statement | NANOSECOND |
| transaction | NANOSECOND |
+-------------+-------------+
The NAME
value indicates the type of instrument
to which the timer applies, and TIMER_NAME
indicates which timer applies to those instruments. The timer
applies to instruments where their name begins with a component
matching the NAME
value.
To change the timer, update the NAME
value. For
example, to use the NANOSECOND
timer for the
wait
timer:
mysql>UPDATE performance_schema.setup_timers
SET TIMER_NAME = 'NANOSECOND'
WHERE NAME = 'wait';
mysql>SELECT * FROM performance_schema.setup_timers;
+-------------+-------------+ | NAME | TIMER_NAME | +-------------+-------------+ | idle | MICROSECOND | | wait | NANOSECOND | | stage | NANOSECOND | | statement | NANOSECOND | | transaction | NANOSECOND | +-------------+-------------+
For discussion of timers, see Section 25.4.1, “Performance Schema Event Timing”.
The setup_instruments
and
setup_consumers
tables list the
instruments for which events can be collected and the types of
consumers for which event information actually is collected,
respectively. Other setup tables enable further modification of
the monitoring configuration.
Section 25.4.2, “Performance Schema Event Filtering”, discusses how you
can modify these tables to affect event collection.
If there are Performance Schema configuration changes that must be
made at runtime using SQL statements and you would like these
changes to take effect each time the server starts, put the
statements in a file and start the server with the
init_file
system variable set to
name the file. This strategy can also be useful if you have
multiple monitoring configurations, each tailored to produce a
different kind of monitoring, such as casual server health
monitoring, incident investigation, application behavior
troubleshooting, and so forth. Put the statements for each
monitoring configuration into their own file and specify the
appropriate file as the init_file
value when you start the server.
Events are collected by means of instrumentation added to the server source code. Instruments time events, which is how the Performance Schema provides an idea of how long events take. It is also possible to configure instruments not to collect timing information. This section discusses the available timers and their characteristics, and how timing values are represented in events.
Two Performance Schema tables provide timer information:
performance_timers
lists the
available timers and their characteristics.
setup_timers
indicates which
timers are used for which instruments.
Each timer row in setup_timers
must refer to one of the timers listed in
performance_timers
.
Timers vary in precision and amount of overhead. To see what
timers are available and their characteristics, check the
performance_timers
table:
mysql> SELECT * FROM performance_schema.performance_timers;
+-------------+-----------------+------------------+----------------+
| TIMER_NAME | TIMER_FREQUENCY | TIMER_RESOLUTION | TIMER_OVERHEAD |
+-------------+-----------------+------------------+----------------+
| CYCLE | 2389029850 | 1 | 72 |
| NANOSECOND | 1000000000 | 1 | 112 |
| MICROSECOND | 1000000 | 1 | 136 |
| MILLISECOND | 1036 | 1 | 168 |
| TICK | 105 | 1 | 2416 |
+-------------+-----------------+------------------+----------------+
If the values associated with a given timer name are
NULL
, that timer is not supported on your
platform. The rows that do not contain NULL
indicate which timers you can use in
setup_timers
.
The columns have these meanings:
The TIMER_NAME
column shows the names
of the available timers. CYCLE
refers
to the timer that is based on the CPU (processor) cycle
counter. The timers in
setup_timers
that you can use
are those that do not have NULL
in the
other columns. If the values associated with a given timer
name are NULL
, that timer is not
supported on your platform.
TIMER_FREQUENCY
indicates the number of
timer units per second. For a cycle timer, the frequency
is generally related to the CPU speed. The value shown was
obtained on a system with a 2.4GHz processor. The other
timers are based on fixed fractions of seconds. For
TICK
, the frequency may vary by
platform (for example, some use 100 ticks/second, others
1000 ticks/second).
TIMER_RESOLUTION
indicates the number
of timer units by which timer values increase at a time.
If a timer has a resolution of 10, its value increases by
10 each time.
TIMER_OVERHEAD
is the minimal number of
cycles of overhead to obtain one timing with the given
timer. The overhead per event is twice the value displayed
because the timer is invoked at the beginning and end of
the event.
To see which timers are in effect or to change timers, access
the setup_timers
table:
mysql>SELECT * FROM performance_schema.setup_timers;
+-------------+-------------+ | NAME | TIMER_NAME | +-------------+-------------+ | idle | MICROSECOND | | wait | CYCLE | | stage | NANOSECOND | | statement | NANOSECOND | | transaction | NANOSECOND | +-------------+-------------+ mysql>UPDATE performance_schema.setup_timers
SET TIMER_NAME = 'MICROSECOND'
WHERE NAME = 'idle';
mysql>SELECT * FROM performance_schema.setup_timers;
+-------------+-------------+ | NAME | TIMER_NAME | +-------------+-------------+ | idle | MICROSECOND | | wait | CYCLE | | stage | NANOSECOND | | statement | NANOSECOND | | transaction | NANOSECOND | +-------------+-------------+
By default, the Performance Schema uses the best timer available for each instrument type, but you can select a different one.
To time wait events, the most important criterion is to reduce
overhead, at the possible expense of the timer accuracy, so
using the CYCLE
timer is the best.
The time a statement (or stage) takes to execute is in general
orders of magnitude larger than the time it takes to execute a
single wait. To time statements, the most important criterion
is to have an accurate measure, which is not affected by
changes in processor frequency, so using a timer which is not
based on cycles is the best. The default timer for statements
is NANOSECOND
. The extra
“overhead” compared to the
CYCLE
timer is not significant, because the
overhead caused by calling a timer twice (once when the
statement starts, once when it ends) is orders of magnitude
less compared to the CPU time used to execute the statement
itself. Using the CYCLE
timer has no
benefit here, only drawbacks.
The precision offered by the cycle counter depends on
processor speed. If the processor runs at 1 GHz (one billion
cycles/second) or higher, the cycle counter delivers
sub-nanosecond precision. Using the cycle counter is much
cheaper than getting the actual time of day. For example, the
standard gettimeofday()
function can take
hundreds of cycles, which is an unacceptable overhead for data
gathering that may occur thousands or millions of times per
second.
Cycle counters also have disadvantages:
End users expect to see timings in wall-clock units, such as fractions of a second. Converting from cycles to fractions of seconds can be expensive. For this reason, the conversion is a quick and fairly rough multiplication operation.
Processor cycle rate might change, such as when a laptop goes into power-saving mode or when a CPU slows down to reduce heat generation. If a processor's cycle rate fluctuates, conversion from cycles to real-time units is subject to error.
Cycle counters might be unreliable or unavailable
depending on the processor or the operating system. For
example, on Pentiums, the instruction is
RDTSC
(an assembly-language rather than
a C instruction) and it is theoretically possible for the
operating system to prevent user-mode programs from using
it.
Some processor details related to out-of-order execution or multiprocessor synchronization might cause the counter to seem fast or slow by up to 1000 cycles.
MySQL works with cycle counters on x386 (Windows, macOS, Linux, Solaris, and other Unix flavors), PowerPC, and IA-64.
Rows in Performance Schema tables that store current events
and historical events have three columns to represent timing
information: TIMER_START
and
TIMER_END
indicate when an event started
and finished, and TIMER_WAIT
indicates
event duration.
The setup_instruments
table has
an ENABLED
column to indicate the
instruments for which to collect events. The table also has a
TIMED
column to indicate which instruments
are timed. If an instrument is not enabled, it produces no
events. If an enabled instrument is not timed, events produced
by the instrument have NULL
for the
TIMER_START
, TIMER_END
,
and TIMER_WAIT
timer values. This in turn
causes those values to be ignored when calculating aggregate
time values in summary tables (sum, minimum, maximum, and
average).
Internally, times within events are stored in units given by the timer in effect when event timing begins. For display when events are retrieved from Performance Schema tables, times are shown in picoseconds (trillionths of a second) to normalize them to a standard unit, regardless of which timer is selected.
Modifications to the setup_timers
table affect monitoring immediately. Events already in
progress may use the original timer for the begin time and the
new timer for the end time. To avoid unpredictable results
after you make timer changes, use
TRUNCATE TABLE
to reset
Performance Schema statistics.
The timer baseline (“time zero”) occurs at
Performance Schema initialization during server startup.
TIMER_START
and
TIMER_END
values in events represent
picoseconds since the baseline. TIMER_WAIT
values are durations in picoseconds.
Picosecond values in events are approximate. Their accuracy is
subject to the usual forms of error associated with conversion
from one unit to another. If the CYCLE
timer is used and the processor rate varies, there might be
drift. For these reasons, it is not reasonable to look at the
TIMER_START
value for an event as an
accurate measure of time elapsed since server startup. On the
other hand, it is reasonable to use
TIMER_START
or
TIMER_WAIT
values in ORDER
BY
clauses to order events by start time or
duration.
The choice of picoseconds in events rather than a value such
as microseconds has a performance basis. One implementation
goal was to show results in a uniform time unit, regardless of
the timer. In an ideal world this time unit would look like a
wall-clock unit and be reasonably precise; in other words,
microseconds. But to convert cycles or nanoseconds to
microseconds, it would be necessary to perform a division for
every instrumentation. Division is expensive on many
platforms. Multiplication is not expensive, so that is what is
used. Therefore, the time unit is an integer multiple of the
highest possible TIMER_FREQUENCY
value,
using a multiplier large enough to ensure that there is no
major precision loss. The result is that the time unit is
“picoseconds.” This precision is spurious, but
the decision enables overhead to be minimized.
While a wait, stage, statement, or transaction event is executing, the respective current-event tables display current-event timing information:
events_waits_current events_stages_current events_statements_current events_transactions_current
To make it possible to determine how long a not-yet-completed event has been running, the timer columns are set as follows:
TIMER_START
is populated.
TIMER_END
is populated with the current
timer value.
TIMER_WAIT
is populated with the time
elapsed so far (TIMER_END
−
TIMER_START
).
Events that have not yet completed have an
END_EVENT_ID
value of
NULL
. To assess time elapsed so far for an
event, use the TIMER_WAIT
column.
Therefore, to identify events that have not yet completed and
have taken longer than N
picoseconds thus far, monitoring applications can use this
expression in queries:
WHERE END_EVENT_ID IS NULL AND TIMER_WAIT > N
Event identification as just described assumes that the
corresponding instruments have ENABLED
and
TIMED
set to YES
and
that the relevant consumers are enabled.
Events are processed in a producer/consumer fashion:
Instrumented code is the source for events and produces
events to be collected. The
setup_instruments
table lists
the instruments for which events can be collected, whether
they are enabled, and (for enabled instruments) whether to
collect timing information:
mysql> SELECT * FROM performance_schema.setup_instruments;
+---------------------------------------------------+---------+-------+
| NAME | ENABLED | TIMED |
+---------------------------------------------------+---------+-------+
...
| wait/synch/mutex/sql/LOCK_global_read_lock | YES | YES |
| wait/synch/mutex/sql/LOCK_global_system_variables | YES | YES |
| wait/synch/mutex/sql/LOCK_lock_db | YES | YES |
| wait/synch/mutex/sql/LOCK_manager | YES | YES |
...
The setup_instruments
table
provides the most basic form of control over event
production. To further refine event production based on the
type of object or thread being monitored, other tables may
be used as described in
Section 25.4.3, “Event Pre-Filtering”.
Performance Schema tables are the destinations for events
and consume events. The
setup_consumers
table lists the
types of consumers to which event information can be sent
and whether they are enabled:
mysql> SELECT * FROM performance_schema.setup_consumers;
+----------------------------------+---------+
| NAME | ENABLED |
+----------------------------------+---------+
| events_stages_current | NO |
| events_stages_history | NO |
| events_stages_history_long | NO |
| events_statements_current | YES |
| events_statements_history | YES |
| events_statements_history_long | NO |
| events_transactions_current | NO |
| events_transactions_history | NO |
| events_transactions_history_long | NO |
| events_waits_current | NO |
| events_waits_history | NO |
| events_waits_history_long | NO |
| global_instrumentation | YES |
| thread_instrumentation | YES |
| statements_digest | YES |
+----------------------------------+---------+
Filtering can be done at different stages of performance monitoring:
Pre-filtering. This is done by modifying Performance Schema configuration so that only certain types of events are collected from producers, and collected events update only certain consumers. To do this, enable or disable instruments or consumers. Pre-filtering is done by the Performance Schema and has a global effect that applies to all users.
Reasons to use pre-filtering:
To reduce overhead. Performance Schema overhead should be minimal even with all instruments enabled, but perhaps you want to reduce it further. Or you do not care about timing events and want to disable the timing code to eliminate timing overhead.
To avoid filling the current-events or history tables with events in which you have no interest. Pre-filtering leaves more “room” in these tables for instances of rows for enabled instrument types. If you enable only file instruments with pre-filtering, no rows are collected for nonfile instruments. With post-filtering, nonfile events are collected, leaving fewer rows for file events.
To avoid maintaining some kinds of event tables. If you disable a consumer, the server does not spend time maintaining destinations for that consumer. For example, if you do not care about event histories, you can disable the history table consumers to improve performance.
Post-filtering.
This involves the use of WHERE
clauses
in queries that select information from Performance Schema
tables, to specify which of the available events you want
to see. Post-filtering is performed on a per-user basis
because individual users select which of the available
events are of interest.
Reasons to use post-filtering:
To avoid making decisions for individual users about which event information is of interest.
To use the Performance Schema to investigate a performance issue when the restrictions to impose using pre-filtering are not known in advance.
The following sections provide more detail about pre-filtering and provide guidelines for naming instruments or consumers in filtering operations. For information about writing queries to retrieve information (post-filtering), see Section 25.5, “Performance Schema Queries”.
Pre-filtering is done by the Performance Schema and has a global effect that applies to all users. Pre-filtering can be applied to either the producer or consumer stage of event processing:
To configure pre-filtering at the producer stage, several tables can be used:
setup_instruments
indicates
which instruments are available. An instrument disabled
in this table produces no events regardless of the
contents of the other production-related setup tables.
An instrument enabled in this table is permitted to
produce events, subject to the contents of the other
tables.
setup_objects
controls
whether the Performance Schema monitors particular table
and stored program objects.
threads
indicates whether
monitoring is enabled for each server thread.
setup_actors
determines the
initial monitoring state for new foreground threads.
To configure pre-filtering at the consumer stage, modify the
setup_consumers
table. This
determines the destinations to which events are sent.
setup_consumers
also implicitly
affects event production. If a given event will not be sent
to any destination (that is, will not be consumed), the
Performance Schema does not produce it.
Modifications to any of these tables affect monitoring immediately, with some exceptions:
Modifications to some instruments in the
setup_instruments
table are
effective only at server startup; changing them at runtime
has no effect. This affects primarily mutexes, conditions,
and rwlocks in the server, although there may be other
instruments for which this is true. This restriction is
lifted as of MySQL 5.7.12.
Modifications to the
setup_actors
table affect only
foreground threads created subsequent to the modification,
not existing threads.
When you change the monitoring configuration, the Performance
Schema does not flush the history tables. Events already
collected remain in the current-events and history tables until
displaced by newer events. If you disable instruments, you might
need to wait a while before events for them are displaced by
newer events of interest. Alternatively, use
TRUNCATE TABLE
to empty the
history tables.
After making instrumentation changes, you might want to truncate
the summary tables. Generally, the effect is to reset the
summary columns to 0 or NULL
, not to remove
rows. This enables you to clear collected values and restart
aggregation. That might be useful, for example, after you have
made a runtime configuration change. Exceptions to this
truncation behavior are noted in individual summary table
sections.
The following sections describe how to use specific tables to control Performance Schema pre-filtering.
The setup_instruments
table lists
the available instruments:
mysql> SELECT * FROM performance_schema.setup_instruments;
+---------------------------------------------------+---------+-------+
| NAME | ENABLED | TIMED |
+---------------------------------------------------+---------+-------+
...
| stage/sql/end | NO | NO |
| stage/sql/executing | NO | NO |
| stage/sql/init | NO | NO |
| stage/sql/insert | NO | NO |
...
| statement/sql/load | YES | YES |
| statement/sql/grant | YES | YES |
| statement/sql/check | YES | YES |
| statement/sql/flush | YES | YES |
...
| wait/synch/mutex/sql/LOCK_global_read_lock | YES | YES |
| wait/synch/mutex/sql/LOCK_global_system_variables | YES | YES |
| wait/synch/mutex/sql/LOCK_lock_db | YES | YES |
| wait/synch/mutex/sql/LOCK_manager | YES | YES |
...
| wait/synch/rwlock/sql/LOCK_grant | YES | YES |
| wait/synch/rwlock/sql/LOGGER::LOCK_logger | YES | YES |
| wait/synch/rwlock/sql/LOCK_sys_init_connect | YES | YES |
| wait/synch/rwlock/sql/LOCK_sys_init_slave | YES | YES |
...
| wait/io/file/sql/binlog | YES | YES |
| wait/io/file/sql/binlog_index | YES | YES |
| wait/io/file/sql/casetest | YES | YES |
| wait/io/file/sql/dbopt | YES | YES |
...
To control whether an instrument is enabled, set its
ENABLED
column to YES
or
NO
. To configure whether to collect timing
information for an enabled instrument, set its
TIMED
value to YES
or
NO
. Setting the TIMED
column affects Performance Schema table contents as described in
Section 25.4.1, “Performance Schema Event Timing”.
Modifications to most
setup_instruments
rows affect
monitoring immediately. For some instruments, modifications are
effective only at server startup; changing them at runtime has
no effect. This affects primarily mutexes, conditions, and
rwlocks in the server, although there may be other instruments
for which this is true.
The setup_instruments
table
provides the most basic form of control over event production.
To further refine event production based on the type of object
or thread being monitored, other tables may be used as described
in Section 25.4.3, “Event Pre-Filtering”.
The following examples demonstrate possible operations on the
setup_instruments
table. These
changes, like other pre-filtering operations, affect all users.
Some of these queries use the LIKE
operator and a pattern match instrument names. For additional
information about specifying patterns to select instruments, see
Section 25.4.9, “Naming Instruments or Consumers for Filtering Operations”.
Disable all instruments:
UPDATE performance_schema.setup_instruments SET ENABLED = 'NO';
Now no events will be collected.
Disable all file instruments, adding them to the current set of disabled instruments:
UPDATE performance_schema.setup_instruments SET ENABLED = 'NO' WHERE NAME LIKE 'wait/io/file/%';
Disable only file instruments, enable all other instruments:
UPDATE performance_schema.setup_instruments SET ENABLED = IF(NAME LIKE 'wait/io/file/%', 'NO', 'YES');
Enable all but those instruments in the
mysys
library:
UPDATE performance_schema.setup_instruments SET ENABLED = CASE WHEN NAME LIKE '%/mysys/%' THEN 'YES' ELSE 'NO' END;
Disable a specific instrument:
UPDATE performance_schema.setup_instruments SET ENABLED = 'NO' WHERE NAME = 'wait/synch/mutex/mysys/TMPDIR_mutex';
To toggle the state of an instrument, “flip”
its ENABLED
value:
UPDATE performance_schema.setup_instruments SET ENABLED = IF(ENABLED = 'YES', 'NO', 'YES') WHERE NAME = 'wait/synch/mutex/mysys/TMPDIR_mutex';
Disable timing for all events:
UPDATE performance_schema.setup_instruments SET TIMED = 'NO';
The setup_objects
table controls
whether the Performance Schema monitors particular table and
stored program objects. The initial
setup_objects
contents look like
this:
mysql> SELECT * FROM performance_schema.setup_objects;
+-------------+--------------------+-------------+---------+-------+
| OBJECT_TYPE | OBJECT_SCHEMA | OBJECT_NAME | ENABLED | TIMED |
+-------------+--------------------+-------------+---------+-------+
| EVENT | mysql | % | NO | NO |
| EVENT | performance_schema | % | NO | NO |
| EVENT | information_schema | % | NO | NO |
| EVENT | % | % | YES | YES |
| FUNCTION | mysql | % | NO | NO |
| FUNCTION | performance_schema | % | NO | NO |
| FUNCTION | information_schema | % | NO | NO |
| FUNCTION | % | % | YES | YES |
| PROCEDURE | mysql | % | NO | NO |
| PROCEDURE | performance_schema | % | NO | NO |
| PROCEDURE | information_schema | % | NO | NO |
| PROCEDURE | % | % | YES | YES |
| TABLE | mysql | % | NO | NO |
| TABLE | performance_schema | % | NO | NO |
| TABLE | information_schema | % | NO | NO |
| TABLE | % | % | YES | YES |
| TRIGGER | mysql | % | NO | NO |
| TRIGGER | performance_schema | % | NO | NO |
| TRIGGER | information_schema | % | NO | NO |
| TRIGGER | % | % | YES | YES |
+-------------+--------------------+-------------+---------+-------+
Modifications to the setup_objects
table affect object monitoring immediately.
The OBJECT_TYPE
column indicates the type of
object to which a row applies. TABLE
filtering affects table I/O events
(wait/io/table/sql/handler
instrument) and
table lock events
(wait/lock/table/sql/handler
instrument).
The OBJECT_SCHEMA
and
OBJECT_NAME
columns should contain a literal
schema or object name, or '%'
to match any
name.
The ENABLED
column indicates whether matching
objects are monitored, and TIMED
indicates
whether to collect timing information. Setting the
TIMED
column affects Performance Schema table
contents as described in
Section 25.4.1, “Performance Schema Event Timing”.
The effect of the default object configuration is to instrument
all objects except those in the mysql
,
INFORMATION_SCHEMA
, and
performance_schema
databases. (Tables in the
INFORMATION_SCHEMA
database are not
instrumented regardless of the contents of
setup_objects
; the row for
information_schema.%
simply makes this
default explicit.)
When the Performance Schema checks for a match in
setup_objects
, it tries to find
more specific matches first. For rows that match a given
OBJECT_TYPE
, the Performance Schema checks
rows in this order:
Rows with
OBJECT_SCHEMA='
and
literal
'OBJECT_NAME='
.
literal
'
Rows with
OBJECT_SCHEMA='
and literal
'OBJECT_NAME='%'
.
Rows with OBJECT_SCHEMA='%'
and
OBJECT_NAME='%'
.
For example, with a table db1.t1
, the
Performance Schema looks in TABLE
rows for a
match for 'db1'
and 't1'
,
then for 'db1'
and '%'
,
then for '%'
and '%'
. The
order in which matching occurs matters because different
matching setup_objects
rows can
have different ENABLED
and
TIMED
values.
For table-related events, the Performance Schema combines the
contents of setup_objects
with
setup_instruments
to determine
whether to enable instruments and whether to time enabled
instruments:
For tables that match a row in
setup_objects
, table
instruments produce events only if
ENABLED
is YES
in both
setup_instruments
and
setup_objects
.
The TIMED
values in the two tables are
combined, so that timing information is collected only when
both values are YES
.
For stored program objects, the Performance Schema takes the
ENABLED
and TIMED
columns
directly from the setup_objects
row. There is no combining of values with
setup_instruments
.
Suppose that setup_objects
contains
the following TABLE
rows that apply to
db1
, db2
, and
db3
:
+-------------+---------------+-------------+---------+-------+ | OBJECT_TYPE | OBJECT_SCHEMA | OBJECT_NAME | ENABLED | TIMED | +-------------+---------------+-------------+---------+-------+ | TABLE | db1 | t1 | YES | YES | | TABLE | db1 | t2 | NO | NO | | TABLE | db2 | % | YES | YES | | TABLE | db3 | % | NO | NO | | TABLE | % | % | YES | YES | +-------------+---------------+-------------+---------+-------+
If an object-related instrument in
setup_instruments
has an
ENABLED
value of NO
,
events for the object are not monitored. If the
ENABLED
value is YES
,
event monitoring occurs according to the
ENABLED
value in the relevant
setup_objects
row:
db1.t1
events are monitored
db1.t2
events are not monitored
db2.t3
events are monitored
db3.t4
events are not monitored
db4.t5
events are monitored
Similar logic applies for combining the TIMED
columns from the setup_instruments
and setup_objects
tables to
determine whether to collect event timing information.
If a persistent table and a temporary table have the same name,
matching against setup_objects
rows
occurs the same way for both. It is not possible to enable
monitoring for one table but not the other. However, each table
is instrumented separately.
The threads
table contains a row
for each server thread. Each row contains information about a
thread and indicates whether monitoring is enabled for it. For
the Performance Schema to monitor a thread, these things must be
true:
The thread_instrumentation
consumer in
the setup_consumers
table must
be YES
.
The threads.INSTRUMENTED
column must be
YES
.
Monitoring occurs only for those thread events produced from
instruments that are enabled in the
setup_instruments
table.
The threads
table also indicates
for each server thread whether to perform historical event
logging. This includes wait, stage, statement, and transaction
events and affects logging to these tables:
events_waits_history events_waits_history_long events_stages_history events_stages_history_long events_statements_history events_statements_history_long events_transactions_history events_transactions_history_long
For historical event logging to occur, these things must be true:
The appropriate history-related consumers in the
setup_consumers
table must be
enabled. For example, wait event logging in the
events_waits_history
and
events_waits_history_long
tables requires the corresponding
events_waits_history
and
events_waits_history_long
consumers to be
YES
.
The threads.HISTORY
column must be
YES
.
Logging occurs only for those thread events produced from
instruments that are enabled in the
setup_instruments
table.
For foreground threads (resulting from client connections), the
initial values of the INSTRUMENTED
and
HISTORY
columns in
threads
table rows are determined
by whether the user account associated with a thread matches any
row in the setup_actors
table. The
values come from the ENABLED
and
HISTORY
columns of the matching
setup_actors
table row.
For background threads, there is no associated user.
INSTRUMENTED
and HISTORY
are YES
by default and
setup_actors
is not consulted.
The initial setup_actors
contents
look like this:
mysql> SELECT * FROM performance_schema.setup_actors;
+------+------+------+---------+---------+
| HOST | USER | ROLE | ENABLED | HISTORY |
+------+------+------+---------+---------+
| % | % | % | YES | YES |
+------+------+------+---------+---------+
The HOST
and USER
columns
should contain a literal host or user name, or
'%'
to match any name.
The ENABLED
and HISTORY
columns indicate whether to enable instrumentation and
historical event logging for matching threads, subject to the
other conditions described previously.
When the Performance Schema checks for a match for each new
foreground thread in setup_actors
, it tries
to find more specific matches first, using the
USER
and HOST
columns
(ROLE
is unused):
Rows with
USER='
and
literal
'HOST='
.
literal
'
Rows with
USER='
and literal
'HOST='%'
.
Rows with USER='%'
and
HOST='
.
literal
'
Rows with USER='%'
and
HOST='%'
.
The order in which matching occurs matters because different
matching setup_actors
rows can have
different USER
and HOST
values. This enables instrumenting and historical event logging
to be applied selectively per host, user, or account (user and
host combination), based on the ENABLED
and
HISTORY
column values:
When the best match is a row with
ENABLED=YES
, the
INSTRUMENTED
value for the thread becomes
YES
. When the best match is a row with
HISTORY=YES
, the
HISTORY
value for the thread becomes
YES
.
When the best match is a row with
ENABLED=NO
, the
INSTRUMENTED
value for the thread becomes
NO
. When the best match is a row with
HISTORY=NO
, the
HISTORY
value for the thread becomes
NO
.
When no match is found, the INSTRUMENTED
and HISTORY
values for the thread become
NO
.
The ENABLED
and HISTORY
columns in setup_actors
rows can be
set to YES
or NO
independent of one another. This means you can enable
instrumentation separately from whether you collect historical
events.
By default, monitoring and historical event collection are
enabled for all new foreground threads because the
setup_actors
table initially
contains a row with '%'
for both
HOST
and USER
. To perform
more limited matching such as to enable monitoring only for some
foreground threads, you must change this row because it matches
any connection, and add rows for more specific
HOST
/USER
combinations.
Suppose that you modify
setup_actors
as follows:
UPDATE performance_schema.setup_actors SET ENABLED = 'NO', HISTORY = 'NO' WHERE HOST = '%' AND USER = '%'; INSERT INTO performance_schema.setup_actors (HOST,USER,ROLE,ENABLED,HISTORY) VALUES('localhost','joe','%','YES','YES'); INSERT INTO performance_schema.setup_actors (HOST,USER,ROLE,ENABLED,HISTORY) VALUES('hosta.example.com','joe','%','YES','NO'); INSERT INTO performance_schema.setup_actors (HOST,USER,ROLE,ENABLED,HISTORY) VALUES('%','sam','%','NO','YES');
The UPDATE
statement changes the
default match to disable instrumentation and historical event
collection. The INSERT
statements
add rows for more specific matches.
Now the Performance Schema determines how to set the
INSTRUMENTED
and HISTORY
values for new connection threads as follows:
If joe
connects from the local host, the
connection matches the first inserted row. The
INSTRUMENTED
and
HISTORY
values for the thread become
YES
.
If joe
connects from
hosta.example.com
, the connection matches
the second inserted row. The INSTRUMENTED
value for the thread becomes YES
and the
HISTORY
value becomes
NO
.
If joe
connects from any other host,
there is no match. The INSTRUMENTED
and
HISTORY
values for the thread become
NO
.
If sam
connects from any host, the
connection matches the third inserted row. The
INSTRUMENTED
value for the thread becomes
NO
and the HISTORY
value becomes YES
.
For any other connection, the row with
HOST
and USER
set to
'%'
matches. This row now has
ENABLED
and HISTORY
set to NO
, so the
INSTRUMENTED
and
HISTORY
values for the thread become
NO
.
Modifications to the setup_actors
table affect only foreground threads created subsequent to the
modification, not existing threads. To affect existing threads,
modify the INSTRUMENTED
and
HISTORY
columns of
threads
table rows.
The setup_consumers
table lists the
available consumer types and which are enabled:
mysql> SELECT * FROM performance_schema.setup_consumers;
+----------------------------------+---------+
| NAME | ENABLED |
+----------------------------------+---------+
| events_stages_current | NO |
| events_stages_history | NO |
| events_stages_history_long | NO |
| events_statements_current | YES |
| events_statements_history | YES |
| events_statements_history_long | NO |
| events_transactions_current | NO |
| events_transactions_history | NO |
| events_transactions_history_long | NO |
| events_waits_current | NO |
| events_waits_history | NO |
| events_waits_history_long | NO |
| global_instrumentation | YES |
| thread_instrumentation | YES |
| statements_digest | YES |
+----------------------------------+---------+
Modify the setup_consumers
table to
affect pre-filtering at the consumer stage and determine the
destinations to which events are sent. To enable or disable a
consumer, set its ENABLED
value to
YES
or NO
.
Modifications to the
setup_consumers
table affect
monitoring immediately.
If you disable a consumer, the server does not spend time maintaining destinations for that consumer. For example, if you do not care about historical event information, disable the history consumers:
UPDATE performance_schema.setup_consumers SET ENABLED = 'NO' WHERE NAME LIKE '%history%';
The consumer settings in the
setup_consumers
table form a
hierarchy from higher levels to lower. The following principles
apply:
Destinations associated with a consumer receive no events unless the Performance Schema checks the consumer and the consumer is enabled.
A consumer is checked only if all consumers it depends on (if any) are enabled.
If a consumer is not checked, or is checked but is disabled, other consumers that depend on it are not checked.
Dependent consumers may have their own dependent consumers.
If an event would not be sent to any destination, the Performance Schema does not produce it.
The following lists describe the available consumer values. For discussion of several representative consumer configurations and their effect on instrumentation, see Section 25.4.8, “Example Consumer Configurations”.
global_instrumentation
is the highest
level consumer. If
global_instrumentation
is
NO
, it disables global instrumentation.
All other settings are lower level and are not checked; it
does not matter what they are set to. No global or per
thread information is maintained and no individual events
are collected in the current-events or event-history
tables. If global_instrumentation
is
YES
, the Performance Schema maintains
information for global states and also checks the
thread_instrumentation
consumer.
thread_instrumentation
is checked only
if global_instrumentation
is
YES
. Otherwise, if
thread_instrumentation
is
NO
, it disables thread-specific
instrumentation and all lower-level settings are ignored.
No information is maintained per thread and no individual
events are collected in the current-events or
event-history tables. If
thread_instrumentation
is
YES
, the Performance Schema maintains
thread-specific information and also checks
events_
consumers.
xxx
_current
These consumers require both
global_instrumentation
and
thread_instrumentation
to be
YES
or they are not checked. If checked,
they act as follows:
events_waits_current
, if
NO
, disables collection of individual
wait events in the
events_waits_current
table.
If YES
, it enables wait event
collection and the Performance Schema checks the
events_waits_history
and
events_waits_history_long
consumers.
events_waits_history
is not checked if
event_waits_current
is
NO
. Otherwise, an
events_waits_history
value of
NO
or YES
disables
or enables collection of wait events in the
events_waits_history
table.
events_waits_history_long
is not
checked if event_waits_current
is
NO
. Otherwise, an
events_waits_history_long
value of
NO
or YES
disables
or enables collection of wait events in the
events_waits_history_long
table.
These consumers require both
global_instrumentation
and
thread_instrumentation
to be
YES
or they are not checked. If checked,
they act as follows:
events_stages_current
, if
NO
, disables collection of individual
stage events in the
events_stages_current
table.
If YES
, it enables stage event
collection and the Performance Schema checks the
events_stages_history
and
events_stages_history_long
consumers.
events_stages_history
is not checked if
event_stages_current
is
NO
. Otherwise, an
events_stages_history
value of
NO
or YES
disables
or enables collection of stage events in the
events_stages_history
table.
events_stages_history_long
is not
checked if event_stages_current
is
NO
. Otherwise, an
events_stages_history_long
value of
NO
or YES
disables
or enables collection of stage events in the
events_stages_history_long
table.
These consumers require both
global_instrumentation
and
thread_instrumentation
to be
YES
or they are not checked. If checked,
they act as follows:
events_statements_current
, if
NO
, disables collection of individual
statement events in the
events_statements_current
table. If YES
, it enables statement
event collection and the Performance Schema checks the
events_statements_history
and
events_statements_history_long
consumers.
events_statements_history
is not
checked if events_statements_current
is
NO
. Otherwise, an
events_statements_history
value of
NO
or YES
disables
or enables collection of statement events in the
events_statements_history
table.
events_statements_history_long
is not
checked if events_statements_current
is
NO
. Otherwise, an
events_statements_history_long
value of
NO
or YES
disables
or enables collection of statement events in the
events_statements_history_long
table.
These consumers require both
global_instrumentation
and
thread_instrumentation
to be
YES
or they are not checked. If checked,
they act as follows:
events_transactions_current
, if
NO
, disables collection of individual
transaction events in the
events_transactions_current
table. If YES
, it enables transaction
event collection and the Performance Schema checks the
events_transactions_history
and
events_transactions_history_long
consumers.
events_transactions_history
is not
checked if events_transactions_current
is NO
. Otherwise, an
events_transactions_history
value of
NO
or YES
disables
or enables collection of transaction events in the
events_transactions_history
table.
events_transactions_history_long
is not
checked if events_transactions_current
is NO
. Otherwise, an
events_transactions_history_long
value
of NO
or YES
disables or enables collection of transaction events in
the
events_transactions_history_long
table.
The statements_digest
consumer requires
global_instrumentation
to be
YES
or it is not checked. There is no
dependency on the statement event consumers, so you can obtain
statistics per digest without having to collect statistics in
events_statements_current
, which
is advantageous in terms of overhead. Conversely, you can get
detailed statements in
events_statements_current
without
digests (the DIGEST
and
DIGEST_TEXT
columns will be
NULL
).
For more information about statement digesting, see Section 25.10, “Performance Schema Statement Digests”.
The consumer settings in the
setup_consumers
table form a
hierarchy from higher levels to lower. The following discussion
describes how consumers work, showing specific configurations
and their effects as consumer settings are enabled progressively
from high to low. The consumer values shown are representative.
The general principles described here apply to other consumer
values that may be available.
The configuration descriptions occur in order of increasing functionality and overhead. If you do not need the information provided by enabling lower-level settings, disable them and the Performance Schema will execute less code on your behalf and you will have less information to sift through.
The setup_consumers
table contains
the following hierarchy of values:
global_instrumentation thread_instrumentation events_waits_current events_waits_history events_waits_history_long events_stages_current events_stages_history events_stages_history_long events_statements_current events_statements_history events_statements_history_long events_transactions_current events_transactions_history events_transactions_history_long statements_digest
In the consumer hierarchy, the consumers for waits, stages, statements, and transactions are all at the same level. This differs from the event nesting hierarchy, for which wait events nest within stage events, which nest within statement events, which nest within transaction events.
If a given consumer setting is NO
, the
Performance Schema disables the instrumentation associated with
the consumer and ignores all lower-level settings. If a given
setting is YES
, the Performance Schema
enables the instrumentation associated with it and checks the
settings at the next lowest level. For a description of the
rules for each consumer, see
Section 25.4.7, “Pre-Filtering by Consumer”.
For example, if global_instrumentation
is
enabled, thread_instrumentation
is checked.
If thread_instrumentation
is enabled, the
events_
consumers are checked. If of these
xxx
_currentevents_waits_current
is enabled,
events_waits_history
and
events_waits_history_long
are checked.
Each of the following configuration descriptions indicates which setup elements the Performance Schema checks and which output tables it maintains (that is, for which tables it collects information).
Server configuration state:
mysql> SELECT * FROM performance_schema.setup_consumers;
+---------------------------+---------+
| NAME | ENABLED |
+---------------------------+---------+
| global_instrumentation | NO |
...
+---------------------------+---------+
In this configuration, nothing is instrumented.
Setup elements checked:
Table setup_consumers
,
consumer global_instrumentation
Output tables maintained:
None
Server configuration state:
mysql> SELECT * FROM performance_schema.setup_consumers;
+---------------------------+---------+
| NAME | ENABLED |
+---------------------------+---------+
| global_instrumentation | YES |
| thread_instrumentation | NO |
...
+---------------------------+---------+
In this configuration, instrumentation is maintained only for global states. Per-thread instrumentation is disabled.
Additional setup elements checked, relative to the preceding configuration:
Table setup_consumers
,
consumer thread_instrumentation
Table setup_instruments
Table setup_objects
Table setup_timers
Additional output tables maintained, relative to the preceding configuration:
Server configuration state:
mysql> SELECT * FROM performance_schema.setup_consumers;
+----------------------------------+---------+
| NAME | ENABLED |
+----------------------------------+---------+
| global_instrumentation | YES |
| thread_instrumentation | YES |
| events_waits_current | NO |
...
| events_stages_current | NO |
...
| events_statements_current | NO |
...
| events_transactions_current | NO |
...
+----------------------------------+---------+
In this configuration, instrumentation is maintained globally and per thread. No individual events are collected in the current-events or event-history tables.
Additional setup elements checked, relative to the preceding configuration:
Table setup_consumers
,
consumers
events_
,
where xxx
_currentxxx
is
waits
, stages
,
statements
,
transactions
Table setup_actors
Column threads.instrumented
Additional output tables maintained, relative to the preceding configuration:
events_
,
where xxx
_summary_by_yyy
_by_event_namexxx
is
waits
, stages
,
statements
,
transactions
; and
yyy
is
thread
, user
,
host
, account
Server configuration state:
mysql> SELECT * FROM performance_schema.setup_consumers;
+----------------------------------+---------+
| NAME | ENABLED |
+----------------------------------+---------+
| global_instrumentation | YES |
| thread_instrumentation | YES |
| events_waits_current | YES |
| events_waits_history | NO |
| events_waits_history_long | NO |
| events_stages_current | YES |
| events_stages_history | NO |
| events_stages_history_long | NO |
| events_statements_current | YES |
| events_statements_history | NO |
| events_statements_history_long | NO |
| events_transactions_current | YES |
| events_transactions_history | NO |
| events_transactions_history_long | NO |
...
+----------------------------------+---------+
In this configuration, instrumentation is maintained globally and per thread. Individual events are collected in the current-events table, but not in the event-history tables.
Additional setup elements checked, relative to the preceding configuration:
Consumers
events_
,
where xxx
_historyxxx
is
waits
, stages
,
statements
,
transactions
Consumers
events_
,
where xxx
_history_longxxx
is
waits
, stages
,
statements
,
transactions
Additional output tables maintained, relative to the preceding configuration:
events_
,
where xxx
_currentxxx
is
waits
, stages
,
statements
,
transactions
The preceding configuration collects no event history because
the
events_
and
xxx
_historyevents_
consumers are disabled. Those consumers can be enabled
separately or together to collect event history per thread,
globally, or both.
xxx
_history_long
This configuration collects event history per thread, but not globally:
mysql> SELECT * FROM performance_schema.setup_consumers;
+----------------------------------+---------+
| NAME | ENABLED |
+----------------------------------+---------+
| global_instrumentation | YES |
| thread_instrumentation | YES |
| events_waits_current | YES |
| events_waits_history | YES |
| events_waits_history_long | NO |
| events_stages_current | YES |
| events_stages_history | YES |
| events_stages_history_long | NO |
| events_statements_current | YES |
| events_statements_history | YES |
| events_statements_history_long | NO |
| events_transactions_current | YES |
| events_transactions_history | YES |
| events_transactions_history_long | NO |
...
+----------------------------------+---------+
Event-history tables maintained for this configuration:
events_
,
where xxx
_historyxxx
is
waits
, stages
,
statements
,
transactions
This configuration collects event history globally, but not per thread:
mysql> SELECT * FROM performance_schema.setup_consumers;
+----------------------------------+---------+
| NAME | ENABLED |
+----------------------------------+---------+
| global_instrumentation | YES |
| thread_instrumentation | YES |
| events_waits_current | YES |
| events_waits_history | NO |
| events_waits_history_long | YES |
| events_stages_current | YES |
| events_stages_history | NO |
| events_stages_history_long | YES |
| events_statements_current | YES |
| events_statements_history | NO |
| events_statements_history_long | YES |
| events_transactions_current | YES |
| events_transactions_history | NO |
| events_transactions_history_long | YES |
...
+----------------------------------+---------+
Event-history tables maintained for this configuration:
events_
,
where xxx
_history_longxxx
is
waits
, stages
,
statements
,
transactions
This configuration collects event history per thread and globally:
mysql> SELECT * FROM performance_schema.setup_consumers;
+----------------------------------+---------+
| NAME | ENABLED |
+----------------------------------+---------+
| global_instrumentation | YES |
| thread_instrumentation | YES |
| events_waits_current | YES |
| events_waits_history | YES |
| events_waits_history_long | YES |
| events_stages_current | YES |
| events_stages_history | YES |
| events_stages_history_long | YES |
| events_statements_current | YES |
| events_statements_history | YES |
| events_statements_history_long | YES |
| events_transactions_current | YES |
| events_transactions_history | YES |
| events_transactions_history_long | YES |
...
+----------------------------------+---------+
Event-history tables maintained for this configuration:
events_
,
where xxx
_historyxxx
is
waits
, stages
,
statements
,
transactions
events_
,
where xxx
_history_longxxx
is
waits
, stages
,
statements
,
transactions
Names given for filtering operations can be as specific or general as required. To indicate a single instrument or consumer, specify its name in full:
UPDATE performance_schema.setup_instruments SET ENABLED = 'NO' WHERE NAME = 'wait/synch/mutex/myisammrg/MYRG_INFO::mutex'; UPDATE performance_schema.setup_consumers SET ENABLED = 'NO' WHERE NAME = 'events_waits_current';
To specify a group of instruments or consumers, use a pattern that matches the group members:
UPDATE performance_schema.setup_instruments SET ENABLED = 'NO' WHERE NAME LIKE 'wait/synch/mutex/%'; UPDATE performance_schema.setup_consumers SET ENABLED = 'NO' WHERE NAME LIKE '%history%';
If you use a pattern, it should be chosen so that it matches all the items of interest and no others. For example, to select all file I/O instruments, it is better to use a pattern that includes the entire instrument name prefix:
... WHERE NAME LIKE 'wait/io/file/%';
A pattern of '%/file/%'
will match other
instruments that have a component of '/file/'
anywhere in the name. Even less suitable is the pattern
'%file%'
because it will match instruments
with 'file'
anywhere in the name, such as
wait/synch/mutex/innodb/file_open_mutex
.
To check which instrument or consumer names a pattern matches, perform a simple test:
SELECT NAME FROM performance_schema.setup_instruments WHERE NAME LIKE 'pattern
'; SELECT NAME FROM performance_schema.setup_consumers WHERE NAME LIKE 'pattern
';
For information about the types of names that are supported, see Section 25.6, “Performance Schema Instrument Naming Conventions”.
It is always possible to determine what instruments the
Performance Schema includes by checking the
setup_instruments
table. For
example, to see what file-related events are instrumented for
the InnoDB
storage engine, use this query:
mysql>SELECT * FROM performance_schema.setup_instruments
WHERE NAME LIKE 'wait/io/file/innodb/%';
+--------------------------------------+---------+-------+ | NAME | ENABLED | TIMED | +--------------------------------------+---------+-------+ | wait/io/file/innodb/innodb_data_file | YES | YES | | wait/io/file/innodb/innodb_log_file | YES | YES | | wait/io/file/innodb/innodb_temp_file | YES | YES | +--------------------------------------+---------+-------+
An exhaustive description of precisely what is instrumented is not given in this documentation, for several reasons:
What is instrumented is the server code. Changes to this code occur often, which also affects the set of instruments.
It is not practical to list all the instruments because there are hundreds of them.
As described earlier, it is possible to find out by querying
the setup_instruments
table.
This information is always up to date for your version of
MySQL, also includes instrumentation for instrumented
plugins you might have installed that are not part of the
core server, and can be used by automated tools.
Pre-filtering limits which event information is collected and is
independent of any particular user. By contrast, post-filtering is
performed by individual users through the use of queries with
appropriate WHERE
clauses that restrict what
event information to select from the events available after
pre-filtering has been applied.
In Section 25.4.3, “Event Pre-Filtering”, an example
showed how to pre-filter for file instruments. If the event tables
contain both file and nonfile information, post-filtering is
another way to see information only for file events. Add a
WHERE
clause to queries to restrict event
selection appropriately:
mysql>SELECT THREAD_ID, NUMBER_OF_BYTES
FROM performance_schema.events_waits_history
WHERE EVENT_NAME LIKE 'wait/io/file/%'
AND NUMBER_OF_BYTES IS NOT NULL;
+-----------+-----------------+ | THREAD_ID | NUMBER_OF_BYTES | +-----------+-----------------+ | 11 | 66 | | 11 | 47 | | 11 | 139 | | 5 | 24 | | 5 | 834 | +-----------+-----------------+
An instrument name consists of a sequence of components separated
by '/'
characters. Example names:
wait/io/file/myisam/log wait/io/file/mysys/charset wait/lock/table/sql/handler wait/synch/cond/mysys/COND_alarm wait/synch/cond/sql/BINLOG::update_cond wait/synch/mutex/mysys/BITMAP_mutex wait/synch/mutex/sql/LOCK_delete wait/synch/rwlock/sql/Query_cache_query::lock stage/sql/closing tables stage/sql/Sorting result statement/com/Execute statement/com/Query statement/sql/create_table statement/sql/lock_tables
The instrument name space has a tree-like structure. The components of an instrument name from left to right provide a progression from more general to more specific. The number of components a name has depends on the type of instrument.
The interpretation of a given component in a name depends on the
components to the left of it. For example,
myisam
appears in both of the following names,
but myisam
in the first name is related to file
I/O, whereas in the second it is related to a synchronization
instrument:
wait/io/file/myisam/log wait/synch/cond/myisam/MI_SORT_INFO::cond
Instrument names consist of a prefix with a structure defined by
the Performance Schema implementation and a suffix defined by the
developer implementing the instrument code. The top-level
component of an instrument prefix indicates the type of
instrument. This component also determines which event timer in
the setup_timers
table applies to the
instrument. For the prefix part of instrument names, the top level
indicates the type of instrument.
The suffix part of instrument names comes from the code for the instruments themselves. Suffixes may include levels such as these:
A name for the major component (a server module such as
myisam
, innodb
,
mysys
, or sql
) or a
plugin name.
The name of a variable in the code, in the form
XXX
(a global variable) or
(a member CCC
::MMM
MMM
in class
CCC
). Examples:
COND_thread_cache
,
THR_LOCK_myisam
,
BINLOG::LOCK_index
.
idle
: An instrumented idle event. This
instrument has no further components.
memory
: An instrumented memory event.
stage
: An instrumented stage event.
statement
: An instrumented statement
event.
transaction
: An instrumented transaction
event. This instrument has no further components.
wait
: An instrumented wait event.
The idle
instrument is used for idle events,
which The Performance Schema generates as discussed in the
description of the socket_instances.STATE
column in Section 25.12.3.5, “The socket_instances Table”.
Most memory instrumentation is disabled by default, and can be
enabled or disabled at startup, or dynamically at runtime by
updating the ENABLED
column of the relevant
instruments in the
setup_instruments
table. Memory
instruments have names of the form
memory/
where code_area
/instrument_name
code_area
is a value such as
sql
or myisam
, and
instrument_name
is the instrument
detail.
Instruments named with the prefix
memory/performance_schema/
expose how much
memory is allocated for internal buffers in the Performance
Schema. The memory/performance_schema/
instruments are built in, always enabled, and cannot be disabled
at startup or runtime. Built-in memory instruments are displayed
only in the
memory_summary_global_by_event_name
table. For more information, see
Section 25.17, “The Performance Schema Memory-Allocation Model”.
Stage instruments have names of the form
stage/
,
where code_area
/stage_name
code_area
is a value such as
sql
or myisam
, and
stage_name
indicates the stage of
statement processing, such as Sorting result
or Sending data
. Stages correspond to the
thread states displayed by SHOW
PROCESSLIST
or that are visible in the
INFORMATION_SCHEMA.PROCESSLIST
table.
statement/abstract/*
: An abstract
instrument for statement operations. Abstract instruments
are used during the early stages of statement classification
before the exact statement type is known, then changed to a
more specific statement instrument when the type is known.
For a description of this process, see
Section 25.12.6, “Performance Schema Statement Event Tables”.
statement/com
: An instrumented command
operation. These have names corresponding to
COM_
operations (see the xxx
mysql_com.h
header
file and sql/sql_parse.cc
. For example,
the statement/com/Connect
and
statement/com/Init DB
instruments
correspond to the COM_CONNECT
and
COM_INIT_DB
commands.
statement/scheduler/event
: A single
instrument to track all events executed by the Event
Scheduler. This instrument comes into play when a scheduled
event begins executing.
statement/sp
: An instrumented internal
instruction executed by a stored program. For example, the
statement/sp/cfetch
and
statement/sp/freturn
instruments are used
cursor fetch and function return instructions.
statement/sql
: An instrumented SQL
statement operation. For example, the
statement/sql/create_db
and
statement/sql/select
instruments are used
for CREATE DATABASE
and
SELECT
statements.
wait/io
An instrumented I/O operation.
wait/io/file
An instrumented file I/O operation. For files, the wait
is the time waiting for the file operation to complete
(for example, a call to fwrite()
).
Due to caching, the physical file I/O on the disk might
not happen within this call.
wait/io/socket
An instrumented socket operation. Socket instruments
have names of the form
wait/io/socket/sql/
.
The server has a listening socket for each network
protocol that it supports. The instruments associated
with listening sockets for TCP/IP or Unix socket file
connections have a
socket_type
socket_type
value of
server_tcpip_socket
or
server_unix_socket
, respectively.
When a listening socket detects a connection, the server
transfers the connection to a new socket managed by a
separate thread. The instrument for the new connection
thread has a socket_type
value of client_connection
.
wait/io/table
An instrumented table I/O operation. These include row-level accesses to persistent base tables or temporary tables. Operations that affect rows are fetch, insert, update, and delete. For a view, waits are associated with base tables referenced by the view.
Unlike most waits, a table I/O wait can include other
waits. For example, table I/O might include file I/O or
memory operations. Thus,
events_waits_current
for a
table I/O wait usually has two rows. For more
information, see
Section 25.8, “Performance Schema Atom and Molecule Events”.
Some row operations might cause multiple table I/O waits. For example, an insert might activate a trigger that causes an update.
wait/lock
An instrumented lock operation.
wait/lock/table
An instrumented table lock operation.
wait/lock/metadata/sql/mdl
An instrumented metadata lock operation.
wait/synch
An instrumented synchronization object. For synchronization
objects, the TIMER_WAIT
time includes the
amount of time blocked while attempting to acquire a lock on
the object, if any.
wait/synch/cond
A condition is used by one thread to signal to other threads that something they were waiting for has happened. If a single thread was waiting for a condition, it can wake up and proceed with its execution. If several threads were waiting, they can all wake up and compete for the resource for which they were waiting.
wait/synch/mutex
A mutual exclusion object used to permit access to a resource (such as a section of executable code) while preventing other threads from accessing the resource.
wait/synch/rwlock
A read/write lock object used to lock a specific variable for access while preventing its use by other threads. A shared read lock can be acquired simultaneously by multiple threads. An exclusive write lock can be acquired by only one thread at a time.
wait/synch/sxlock
A shared-exclusive (SX) lock is a type of
rwlock lock object
that provides write access to a common resource while
permitting inconsistent reads by other threads.
sxlocks
optimize concurrency and
improve scalability for read-write workloads.
There are several status variables associated with the Performance Schema:
mysql> SHOW STATUS LIKE 'perf%';
+-----------------------------------------------+-------+
| Variable_name | Value |
+-----------------------------------------------+-------+
| Performance_schema_accounts_lost | 0 |
| Performance_schema_cond_classes_lost | 0 |
| Performance_schema_cond_instances_lost | 0 |
| Performance_schema_digest_lost | 0 |
| Performance_schema_file_classes_lost | 0 |
| Performance_schema_file_handles_lost | 0 |
| Performance_schema_file_instances_lost | 0 |
| Performance_schema_hosts_lost | 0 |
| Performance_schema_locker_lost | 0 |
| Performance_schema_memory_classes_lost | 0 |
| Performance_schema_metadata_lock_lost | 0 |
| Performance_schema_mutex_classes_lost | 0 |
| Performance_schema_mutex_instances_lost | 0 |
| Performance_schema_nested_statement_lost | 0 |
| Performance_schema_program_lost | 0 |
| Performance_schema_rwlock_classes_lost | 0 |
| Performance_schema_rwlock_instances_lost | 0 |
| Performance_schema_session_connect_attrs_lost | 0 |
| Performance_schema_socket_classes_lost | 0 |
| Performance_schema_socket_instances_lost | 0 |
| Performance_schema_stage_classes_lost | 0 |
| Performance_schema_statement_classes_lost | 0 |
| Performance_schema_table_handles_lost | 0 |
| Performance_schema_table_instances_lost | 0 |
| Performance_schema_thread_classes_lost | 0 |
| Performance_schema_thread_instances_lost | 0 |
| Performance_schema_users_lost | 0 |
+-----------------------------------------------+-------+
The Performance Schema status variables provide information about instrumentation that could not be loaded or created due to memory constraints. Names for these variables have several forms:
Performance_schema_
indicates how many instruments of type
xxx
_classes_lostxxx
could not be loaded.
Performance_schema_
indicates how many instances of object type
xxx
_instances_lostxxx
could not be created.
Performance_schema_
indicates how many instances of object type
xxx
_handles_lostxxx
could not be opened.
Performance_schema_locker_lost
indicates
how many events are “lost” or not recorded.
For example, if a mutex is instrumented in the server source but
the server cannot allocate memory for the instrumentation at
runtime, it increments
Performance_schema_mutex_classes_lost
.
The mutex still functions as a synchronization object (that is,
the server continues to function normally), but performance data
for it will not be collected. If the instrument can be allocated,
it can be used for initializing instrumented mutex instances. For
a singleton mutex such as a global mutex, there will be only one
instance. Other mutexes have an instance per connection, or per
page in various caches and data buffers, so the number of
instances varies over time. Increasing the maximum number of
connections or the maximum size of some buffers will increase the
maximum number of instances that might be allocated at once. If
the server cannot create a given instrumented mutex instance, it
increments
Performance_schema_mutex_instances_lost
.
Suppose that the following conditions hold:
The server was started with the
--performance_schema_max_mutex_classes=200
option and thus has room for 200 mutex instruments.
150 mutex instruments have been loaded already.
The plugin named plugin_a
contains 40 mutex
instruments.
The plugin named plugin_b
contains 20 mutex
instruments.
The server allocates mutex instruments for the plugins depending on how many they need and how many are available, as illustrated by the following sequence of statements:
INSTALL PLUGIN plugin_a
The server now has 150+40 = 190 mutex instruments.
UNINSTALL PLUGIN plugin_a;
The server still has 190 instruments. All the historical data generated by the plugin code is still available, but new events for the instruments are not collected.
INSTALL PLUGIN plugin_a;
The server detects that the 40 instruments are already defined, so no new instruments are created, and previously assigned internal memory buffers are reused. The server still has 190 instruments.
INSTALL PLUGIN plugin_b;
The server has room for 200-190 = 10 instruments (in this case,
mutex classes), and sees that the plugin contains 20 new
instruments. 10 instruments are loaded, and 10 are discarded or
“lost.” The
Performance_schema_mutex_classes_lost
indicates the number of instruments (mutex classes) lost:
mysql> SHOW STATUS LIKE "perf%mutex_classes_lost";
+---------------------------------------+-------+
| Variable_name | Value |
+---------------------------------------+-------+
| Performance_schema_mutex_classes_lost | 10 |
+---------------------------------------+-------+
1 row in set (0.10 sec)
The instrumentation still works and collects (partial) data for
plugin_b
.
When the server cannot create a mutex instrument, these results occur:
No row for the instrument is inserted into the
setup_instruments
table.
Performance_schema_mutex_classes_lost
increases by 1.
Performance_schema_mutex_instances_lost
does not change. (When the mutex instrument is not created, it
cannot be used to create instrumented mutex instances later.)
The pattern just described applies to all types of instruments, not just mutexes.
A value of
Performance_schema_mutex_classes_lost
greater than 0 can happen in two cases:
To save a few bytes of memory, you start the server with
--performance_schema_max_mutex_classes=
,
where N
N
is less than the default
value. The default value is chosen to be sufficient to load
all the plugins provided in the MySQL distribution, but this
can be reduced if some plugins are never loaded. For example,
you might choose not to load some of the storage engines in
the distribution.
You load a third-party plugin that is instrumented for the
Performance Schema but do not allow for the plugin's
instrumentation memory requirements when you start the server.
Because it comes from a third party, the instrument memory
consumption of this engine is not accounted for in the default
value chosen for
performance_schema_max_mutex_classes
.
If the server has insufficient resources for the plugin's
instruments and you do not explicitly allocate more using
--performance_schema_max_mutex_classes=
,
loading the plugin leads to starvation of instruments.
N
If the value chosen for
performance_schema_max_mutex_classes
is too small, no error is reported in the error log and there is
no failure at runtime. However, the content of the tables in the
performance_schema
database will miss events.
The
Performance_schema_mutex_classes_lost
status variable is the only visible sign to indicate that some
events were dropped internally due to failure to create
instruments.
If an instrument is not lost, it is known to the Performance
Schema, and is used when instrumenting instances. For example,
wait/synch/mutex/sql/LOCK_delete
is the name of
a mutex instrument in the
setup_instruments
table. This single
instrument is used when creating a mutex in the code (in
THD::LOCK_delete
) however many instances of the
mutex are needed as the server runs. In this case,
LOCK_delete
is a mutex that is per connection
(THD
), so if a server has 1000 connections,
there are 1000 threads, and 1000 instrumented
LOCK_delete
mutex instances
(THD::LOCK_delete
).
If the server does not have room for all these 1000 instrumented
mutexes (instances), some mutexes are created with
instrumentation, and some are created without instrumentation. If
the server can create only 800 instances, 200 instances are lost.
The server continues to run, but increments
Performance_schema_mutex_instances_lost
by 200 to indicate that instances could not be created.
A value of
Performance_schema_mutex_instances_lost
greater than 0 can happen when the code initializes more mutexes
at runtime than were allocated for
--performance_schema_max_mutex_instances=
.
N
The bottom line is that if
SHOW STATUS LIKE
'perf%'
says that nothing was lost (all values are
zero), the Performance Schema data is accurate and can be relied
upon. If something was lost, the data is incomplete, and the
Performance Schema could not record everything given the
insufficient amount of memory it was given to use. In this case,
the specific
Performance_schema_
variable indicates the problem area.
xxx
_lost
It might be appropriate in some cases to cause deliberate instrument starvation. For example, if you do not care about performance data for file I/O, you can start the server with all Performance Schema parameters related to file I/O set to 0. No memory will be allocated for file-related classes, instances, or handles, and all file events will be lost.
Use SHOW ENGINE
PERFORMANCE_SCHEMA STATUS
to inspect the internal
operation of the Performance Schema code:
mysql> SHOW ENGINE PERFORMANCE_SCHEMA STATUS\G
...
*************************** 3. row ***************************
Type: performance_schema
Name: events_waits_history.size
Status: 76
*************************** 4. row ***************************
Type: performance_schema
Name: events_waits_history.count
Status: 10000
*************************** 5. row ***************************
Type: performance_schema
Name: events_waits_history.memory
Status: 760000
...
*************************** 57. row ***************************
Type: performance_schema
Name: performance_schema.memory
Status: 26459600
...
This statement is intended to help the DBA understand the effects that different Performance Schema options have on memory requirements. For a description of the field meanings, see Section 13.7.5.15, “SHOW ENGINE Statement”.
For a table I/O event, there are usually two rows in
events_waits_current
, not one. For
example, a row fetch might result in rows like this:
Row# EVENT_NAME TIMER_START TIMER_END ---- ---------- ----------- --------- 1 wait/io/file/myisam/dfile 10001 10002 2 wait/io/table/sql/handler 10000 NULL
The row fetch causes a file read. In the example, the table I/O
fetch event started before the file I/O event but has not finished
(its TIMER_END
value is
NULL
). The file I/O event is
“nested” within the table I/O event.
This occurs because, unlike other “atomic” wait
events such as for mutexes or file I/O, table I/O events are
“molecular” and include (overlap with) other events.
In events_waits_current
, the table
I/O event usually has two rows:
One row for the most recent table I/O wait event
One row for the most recent wait event of any kind
Usually, but not always, the “of any kind” wait event
differs from the table I/O event. As each subsidiary event
completes, it disappears from
events_waits_current
. At this point,
and until the next subsidiary event begins, the table I/O wait is
also the most recent wait of any kind.
For wait, stage, statement, and transaction events, the
Performance Schema can monitor and store current events. In
addition, when events end, the Performance Schema can store them
in history tables. For each event type, the Performance Schema
uses three tables for storing current and historical events. The
tables have names of the following forms, where
xxx
indicates the event type
(waits
, stages
,
statements
, transactions
):
events_
:
The “current events” table stores the current
monitored event for each thread (one row per thread).
xxx
_current
events_
:
The “recent history” table stores the most recent
events that have ended per thread (up to a maximum number of
rows per thread).
xxx
_history
events_
:
The “long history” table stores the most recent
events that have ended globally (across all threads, up to a
maximum number of rows per table).
xxx
_history_long
The _current
table for each event type contains
one row per thread, so there is no system variable for configuring
its maximum size. The Performance Schema autosizes the history
tables, or the sizes can be configured explicitly at server
startup using table-specific system variables, as indicated in the
sections that describe the individual history tables. Typical
autosized values are 10 rows per thread for
_history
tables, and 10,000 rows total for
_history_long
tables.
For each event type, the _current
,
_history
, and _history_long
tables have the same columns.
The _current
tables show what is currently
happening within the server. When a current event ends, it is
removed from its _current
table.
The _history
and
_history_long
tables show what has happened in
the recent past. When the history tables become full, old events
are discarded as new events are added. Rows expire from the
_history
and _history_long
tables in different ways because the tables serve different
purposes:
_history
is meant to investigate individual
threads, independently of the global server load.
_history_long
is meant to investigate the
server globally, not each thread.
The difference between the two types of history tables relates to the data retention policy. Both tables contains the same data when an event is first seen. However, data within each table expires differently over time, so that data might be preserved for a longer or shorter time in each table:
For _history
, when the table contains the
maximum number of rows for a given thread, the oldest thread
row is discarded when a new row for that thread is added.
For _history_long
, when the table becomes
full, the oldest row is discarded when a new row is added,
regardless of which thread generated either row.
When a thread ends, all its rows are discarded from the
_history
table but not from the
_history_long
table.
The following example illustrates the differences in how events are added to and discarded from the two types of history tables. The principles apply equally to all event types. The example is based on these assumptions:
The Performance Schema is configured to retain 10 rows per
thread in the _history
table and 10,000
rows total in the _history_long
table.
Thread A generates 1 event per second.
Thread B generates 100 events per second.
No other threads are running.
After 5 seconds of execution:
A and B have generated 5 and 500 events, respectively.
_history
contains 5 rows for A and 10 rows
for B. Because storage per thread is limited to 10 rows, no
rows have been discarded for A, whereas 490 rows have been
discarded for B.
_history_long
contains 5 rows for A and 500
rows for B. Because the table has a maximum size of 10,000
rows, no rows have been discarded for either thread.
After 5 minutes (300 seconds) of execution:
A and B have generated 300 and 30,000 events, respectively.
_history
contains 10 rows for A and 10 rows
for B. Because storage per thread is limited to 10 rows, 290
rows have been discarded for A, whereas 29,990 rows have been
discarded for B. Rows for A include data up to 10 seconds old,
whereas rows for B include data up to only .1 seconds old.
_history_long
contains 10,000 rows. Because
A and B together generate 101 events per second, the table
contains data up to approximately 10,000/101 = 99 seconds old,
with a mix of rows approximately 100 to 1 from B as opposed to
A.
The MySQL server is capable of maintaining statement digest information. The digesting process converts each SQL statement to normalized form (the statement digest) and computes an MD5 hash value (the digest hash value) from the normalized result. Normalization permits statements that are similar to be grouped and summarized to expose information about the types of statements the server is executing and how often they occur. This section describes how statement digesting occurs and how it can be useful.
Digesting occurs in the parser regardless of whether the Performance Schema is available, so that other server components such as MySQL Enterprise Firewall and query rewrite plugins have access to statement digests.
When the parser receives an SQL statement, it computes a statement digest if that digest is needed, which is true if any of the following conditions are true:
Performance Schema digest instrumentation is enabled
MySQL Enterprise Firewall is enabled
A Query Rewrite Plugin is enabled
The max_digest_length
system
variable value determines the maximum number of bytes available
per session for computation of normalized statement digests.
Once that amount of space is used during digest computation,
truncation occurs: no further tokens from a parsed statement are
collected or figure into its digest value. Statements that
differ only after that many bytes of parsed tokens produce the
same normalized statement digest and are considered identical if
compared or if aggregated for digest statistics.
After the normalized statement has been computed, an MD5 hash value is computed from it. In addition:
If MySQL Enterprise Firewall is enabled, it is called and the digest as computed is available to it.
If any Query Rewrite Plugin is enabled, it is called and the statement digest and digest value are available to it.
If the Performance Schema has digest instrumentation
enabled, it makes a copy of the normalized statement digest,
allocating a maximum of
performance_schema_max_digest_length
bytes for it. Consequently, if
performance_schema_max_digest_length
is less than
max_digest_length
, the copy
is truncated relative to the original. The copy of the
normalized statement digest is stored in the appropriate
Performance Schema tables, along with the MD5 hash value
computed from the original normalized statement. (If the
Performance Schema truncates its copy of the normalized
statement digest relative to the original, it does not
recompute the MD5 hash value.)
Statement normalization transforms the statement text to a more standardized digest string representation that preserves the general statement structure while removing information not essential to the structure:
Object identifiers such as database and table names are preserved.
Literal values are converted to parameter markers. A normalized statement does not retain information such as names, passwords, dates, and so forth.
Comments are removed and whitespace is adjusted.
Consider these statements:
SELECT * FROM orders WHERE customer_id=10 AND quantity>20 SELECT * FROM orders WHERE customer_id = 20 AND quantity > 100
To normalize these statements, the parser replaces data values
by ?
and adjusts whitespace. Both statements
yield the same normalized form and thus are considered
“the same”:
SELECT * FROM orders WHERE customer_id = ? AND quantity > ?
The normalized statement contains less information but is still representative of the original statement. Other similar statements that have different data values have the same normalized form.
Now consider these statements:
SELECT * FROM customers WHERE customer_id = 1000 SELECT * FROM orders WHERE customer_id = 1000
In this case, the normalized statements differ because the object identifiers differ:
SELECT * FROM customers WHERE customer_id = ? SELECT * FROM orders WHERE customer_id = ?
If normalization produces a statement that exceeds the space
available in the digest buffer (as determined by
max_digest_length
), truncation
occurs and the text ends with “...”. Long
normalized statements that differ only in the part that occurs
following the “...” are considered the same.
Consider these statements:
SELECT * FROM mytable WHERE cola = 10 AND colb = 20 SELECT * FROM mytable WHERE cola = 10 AND colc = 20
If the cutoff happens to be right after the
AND
, both statements have this normalized
form:
SELECT * FROM mytable WHERE cola = ? AND ...
In this case, the difference in the second column name is lost and both statements are considered the same.
In the Performance Schema, statement digesting involves these components:
A statements_digest
consumer in the
setup_consumers
table controls
whether the Performance Schema maintains digest information.
See
Statement Digest Consumer.
The statement event tables
(events_statements_current
,
events_statements_history
, and
events_statements_history_long
)
have columns for storing normalized statement digests and
the corresponding digest MD5 hash values:
DIGEST_TEXT
is the text of the
normalized statement digest. This is a copy of the
original normalized statement that was computed to a
maximum of
max_digest_length
bytes, further truncated as necessary to
performance_schema_max_digest_length
bytes.
DIGEST
is the digest MD5 hash value
computed from the original normalized statement.
See Section 25.12.6, “Performance Schema Statement Event Tables”.
The
events_statements_summary_by_digest
summary table provides aggregated statement digest
information. This table aggregates information for
statements per SCHEMA_NAME
and
DIGEST
combination. The Performance
Schema uses MD5 hash values for aggregation because they are
fast to compute and have a favorable statistical
distribution that minimizes collisions. See
Section 25.12.15.3, “Statement Summary Tables”.
The statement event tables also have an
SQL_TEXT
column that contains the original
SQL statement. The maximum space available for statement display
is 1024 bytes by default. To change this value, set the
performance_schema_max_sql_text_length
system variable at server startup.
The
performance_schema_max_digest_length
system variable determines the maximum number of bytes available
per statement for digest value storage in the Performance
Schema. However, the display length of statement digests may be
longer than the available buffer size due to internal encoding
of statement components such as keywords and literal values.
Consequently, values selected from the
DIGEST_TEXT
column of statement event tables
may appear to exceed the
performance_schema_max_digest_length
value.
The
events_statements_summary_by_digest
summary table provides a profile of the statements executed by
the server. It shows what kinds of statements an application is
executing and how often. An application developer can use this
information together with other information in the table to
assess the application's performance characteristics. For
example, table columns that show wait times, lock times, or
index use may highlight types of queries that are inefficient.
This gives the developer insight into which parts of the
application need attention.
The
events_statements_summary_by_digest
summary table has a fixed size. By default the Performance
Schema estimates the size to use at startup. To specify the
table size explicitly, set the
performance_schema_digests_size
system variable at server startup. If the table becomes full,
the Performance Schema groups statements that have
SCHEMA_NAME
and DIGEST
values not matching existing values in the table in a special
row with SCHEMA_NAME
and
DIGEST
set to NULL
. This
permits all statements to be counted. However, if the special
row accounts for a significant percentage of the statements
executed, it might be desirable to increase the summary table
size by increasing
performance_schema_digests_size
.
For applications that generate very long statements that differ
only at the end, increasing
max_digest_length
enables
computation of digests that distinguish statements that would
otherwise aggregate to the same digest. Conversely, decreasing
max_digest_length
causes the
server to devote less memory to digest storage but increases the
likelihood of longer statements aggregating to the same digest.
Administrators should keep in mind that larger values result in
correspondingly increased memory requirements, particularly for
workloads that involve large numbers of simultaneous sessions
(the server allocates
max_digest_length
bytes per
session).
As described previously, normalized statement digests as
computed by the parser are constrained to a maximum of
max_digest_length
bytes,
whereas normalized statement digests stored in the Performance
Schema use
performance_schema_max_digest_length
bytes. The following memory-use considerations apply regarding
the relative values of
max_digest_length
and
performance_schema_max_digest_length
:
If max_digest_length
is
less than
performance_schema_max_digest_length
:
Server components other than the Performance Schema use
normalized statement digests that take up to
max_digest_length
bytes.
The Performance Schema does not further truncate
normalized statement digests that it stores, but
allocates more memory than
max_digest_length
bytes
per digest, which is unnecessary.
If max_digest_length
equals
performance_schema_max_digest_length
:
Server components other than the Performance Schema use
normalized statement digests that take up to
max_digest_length
bytes.
The Performance Schema does not further truncate
normalized statement digests that it stores, and
allocates the same amount of memory as
max_digest_length
bytes
per digest.
If max_digest_length
is
greater than
performance_schema_max_digest_length
:
Server components other than the Performance Schema use
normalized statement digests that take up to
max_digest_length
bytes.
The Performance Schema further truncates normalized
statement digests that it stores, and allocates less
memory than
max_digest_length
bytes
per digest.
Because the Performance Schema statement event tables might
store many digests, setting
performance_schema_max_digest_length
smaller than max_digest_length
enables administrators to balance these factors:
The need to have long normalized statement digests available for server components outside the Performance Schema
Many concurrent sessions, each of which allocates digest-computation memory
The need to limit memory consumption by the Performance Schema statement event tables when storing many statement digests
The
performance_schema_max_digest_length
setting is not per session, it is per statement, and a session
can store multiple statements in the
events_statements_history
table. A
typical number of statements in this table is 10 per session, so
each session will consume 10 times the memory indicated by the
performance_schema_max_digest_length
value, for this table alone.
Also, there are many statements (and digests) collected
globally, most notably in the
events_statements_history_long
table. Here, too, N
statements stored
will consume N
times the memory
indicated by the
performance_schema_max_digest_length
value.
To assess the amount of memory used for SQL statement storage
and digest computation, use the
SHOW ENGINE
PERFORMANCE_SCHEMA STATUS
statement, or monitor these
instruments:
mysql>SELECT NAME
FROM performance_schema.setup_instruments
WHERE NAME LIKE '%.sqltext';
+------------------------------------------------------------------+ | NAME | +------------------------------------------------------------------+ | memory/performance_schema/events_statements_history.sqltext | | memory/performance_schema/events_statements_current.sqltext | | memory/performance_schema/events_statements_history_long.sqltext | +------------------------------------------------------------------+ mysql>SELECT NAME
FROM performance_schema.setup_instruments
WHERE NAME LIKE 'memory/performance_schema/%.tokens';
+----------------------------------------------------------------------+ | NAME | +----------------------------------------------------------------------+ | memory/performance_schema/events_statements_history.tokens | | memory/performance_schema/events_statements_current.tokens | | memory/performance_schema/events_statements_summary_by_digest.tokens | | memory/performance_schema/events_statements_history_long.tokens | +----------------------------------------------------------------------+
The name of the performance_schema
database is
lowercase, as are the names of tables within it. Queries should
specify the names in lowercase.
Many tables in the performance_schema
database
are read only and cannot be modified:
mysql> TRUNCATE TABLE performance_schema.setup_instruments;
ERROR 1683 (HY000): Invalid performance_schema usage.
Some of the setup tables have columns that can be modified to
affect Performance Schema operation; some also permit rows to be
inserted or deleted. Truncation is permitted to clear collected
events, so TRUNCATE TABLE
can be
used on tables containing those kinds of information, such as
tables named with a prefix of events_waits_
.
Summary tables can be truncated with TRUNCATE
TABLE
. Generally, the effect is to reset the summary
columns to 0 or NULL
, not to remove rows. This
enables you to clear collected values and restart aggregation.
That might be useful, for example, after you have made a runtime
configuration change. Exceptions to this truncation behavior are
noted in individual summary table sections.
Privileges are as for other databases and tables:
Because only a limited set of privileges apply to Performance
Schema tables, attempts to use GRANT ALL
as
shorthand for granting privileges at the database or table leval
fail with an error:
mysql>GRANT ALL ON performance_schema.*
TO 'u1'@'localhost';
ERROR 1044 (42000): Access denied for user 'root'@'localhost' to database 'performance_schema' mysql>GRANT ALL ON performance_schema.setup_instruments
TO 'u2'@'localhost';
ERROR 1044 (42000): Access denied for user 'root'@'localhost' to database 'performance_schema'
Instead, grant exactly the desired privileges:
mysql>GRANT SELECT ON performance_schema.*
TO 'u1'@'localhost';
Query OK, 0 rows affected (0.03 sec) mysql>GRANT SELECT, UPDATE ON performance_schema.setup_instruments
TO 'u2'@'localhost';
Query OK, 0 rows affected (0.02 sec)
Tables in the performance_schema
database can
be grouped as follows:
Setup tables. These tables are used to configure and display monitoring characteristics.
Current events tables. The
events_waits_current
table
contains the most recent event for each thread. Other similar
tables contain current events at different levels of the event
hierarchy: events_stages_current
for stage events,
events_statements_current
for
statement events, and
events_transactions_current
for
transaction events.
History tables. These tables have the same structure as the
current events tables, but contain more rows. For example, for
wait events, events_waits_history
table contains the most recent 10 events per thread.
events_waits_history_long
contains the most recent 10,000 events. Other similar tables
exist for stage, statement, and transaction histories.
To change the sizes of the history tables, set the appropriate
system variables at server startup. For example, to set the
sizes of the wait event history tables, set
performance_schema_events_waits_history_size
and
performance_schema_events_waits_history_long_size
.
Summary tables. These tables contain information aggregated over groups of events, including those that have been discarded from the history tables.
Instance tables. These tables document what types of objects are instrumented. An instrumented object, when used by the server, produces an event. These tables provide event names and explanatory notes or status information.
Miscellaneous tables. These do not fall into any of the other table groups.
The following table lists each Performance Schema table and provides a short description of each one.
Table 25.1 Performance Schema Tables
Table Name | Description |
---|---|
accounts |
Connection statistics per client account |
cond_instances |
synchronization object instances |
events_stages_current |
Current stage events |
events_stages_history |
Most recent stage events per thread |
events_stages_history_long |
Most recent stage events overall |
events_stages_summary_by_account_by_event_name |
Stage events per account and event name |
events_stages_summary_by_host_by_event_name |
Stage events per host name and event name |
events_stages_summary_by_thread_by_event_name |
Stage waits per thread and event name |
events_stages_summary_by_user_by_event_name |
Stage events per user name and event name |
events_stages_summary_global_by_event_name |
Stage waits per event name |
events_statements_current |
Current statement events |
events_statements_history |
Most recent statement events per thread |
events_statements_history_long |
Most recent statement events overall |
events_statements_summary_by_account_by_event_name |
Statement events per account and event name |
events_statements_summary_by_digest |
Statement events per schema and digest value |
events_statements_summary_by_host_by_event_name |
Statement events per host name and event name |
events_statements_summary_by_program |
Statement events per stored program |
events_statements_summary_by_thread_by_event_name |
Statement events per thread and event name |
events_statements_summary_by_user_by_event_name |
Statement events per user name and event name |
events_statements_summary_global_by_event_name |
Statement events per event name |
events_transactions_current |
Current transaction events |
events_transactions_history |
Most recent transaction events per thread |
events_transactions_history_long |
Most recent transaction events overall |
events_transactions_summary_by_account_by_event_name |
Transaction events per account and event name |
events_transactions_summary_by_host_by_event_name |
Transaction events per host name and event name |
events_transactions_summary_by_thread_by_event_name |
Transaction events per thread and event name |
events_transactions_summary_by_user_by_event_name |
Transaction events per user name and event name |
events_transactions_summary_global_by_event_name |
Transaction events per event name |
events_waits_current |
Current wait events |
events_waits_history |
Most recent wait events per thread |
events_waits_history_long |
Most recent wait events overall |
events_waits_summary_by_account_by_event_name |
Wait events per account and event name |
events_waits_summary_by_host_by_event_name |
Wait events per host name and event name |
events_waits_summary_by_instance |
Wait events per instance |
events_waits_summary_by_thread_by_event_name |
Wait events per thread and event name |
events_waits_summary_by_user_by_event_name |
Wait events per user name and event name |
events_waits_summary_global_by_event_name |
Wait events per event name |
file_instances |
File instances |
file_summary_by_event_name |
File events per event name |
file_summary_by_instance |
File events per file instance |
global_status |
Global status variables |
global_variables |
Global system variables |
host_cache |
Information from the internal host cache |
hosts |
Connection statistics per client host name |
memory_summary_by_account_by_event_name |
Memory operations per account and event name |
memory_summary_by_host_by_event_name |
Memory operations per host and event name |
memory_summary_by_thread_by_event_name |
Memory operations per thread and event name |
memory_summary_by_user_by_event_name |
Memory operations per user and event name |
memory_summary_global_by_event_name |
Memory operations globally per event name |
metadata_locks |
Metadata locks and lock requests |
mutex_instances |
Mutex synchronization object instances |
objects_summary_global_by_type |
Object summaries |
performance_timers |
Which event timers are available |
prepared_statements_instances |
Prepared statement instances and statistics |
replication_applier_configuration |
Configuration parameters for the transaction applier on the slave |
replication_applier_status |
Current status of the transaction applier on the slave |
replication_applier_status_by_coordinator |
SQL or coordinator thread applier status |
replication_applier_status_by_worker |
Worker thread applier status (empty unless slave is multithreaded) |
replication_connection_configuration |
Configuration parameters for connecting to the master |
replication_connection_status |
Current status of the connection to the master |
rwlock_instances |
Lock synchronization object instances |
session_account_connect_attrs |
Connection attributes per for the current session |
session_connect_attrs |
Connection attributes for all sessions |
session_status |
Status variables for current session |
session_variables |
System variables for current session |
setup_actors |
How to initialize monitoring for new foreground threads |
setup_consumers |
Consumers for which event information can be stored |
setup_instruments |
Classes of instrumented objects for which events can be collected |
setup_objects |
Which objects should be monitored |
setup_timers |
Current event timer |
socket_instances |
Active connection instances |
socket_summary_by_event_name |
Socket waits and I/O per event name |
socket_summary_by_instance |
Socket waits and I/O per instance |
status_by_account |
Session status variables per account |
status_by_host |
Session status variables per host name |
status_by_thread |
Session status variables per session |
status_by_user |
Session status variables per user name |
table_handles |
Table locks and lock requests |
table_io_waits_summary_by_index_usage |
Table I/O waits per index |
table_io_waits_summary_by_table |
Table I/O waits per table |
table_lock_waits_summary_by_table |
Table lock waits per table |
threads |
Information about server threads |
user_variables_by_thread |
User-defined variables per thread |
users |
Connection statistics per client user name |
variables_by_thread |
Session system variables per session |
The setup tables provide information about the current
instrumentation and enable the monitoring configuration to be
changed. For this reason, some columns in these tables can be
changed if you have the UPDATE
privilege.
The use of tables rather than individual variables for setup information provides a high degree of flexibility in modifying Performance Schema configuration. For example, you can use a single statement with standard SQL syntax to make multiple simultaneous configuration changes.
These setup tables are available:
setup_actors
: How to initialize
monitoring for new foreground threads
setup_consumers
: The
destinations to which event information can be sent and
stored
setup_instruments
: The classes
of instrumented objects for which events can be collected
setup_objects
: Which objects
should be monitored
setup_timers
: The current event
timer
The setup_actors
table contains
information that determines whether to enable monitoring and
historical event logging for new foreground server threads
(threads associated with client connections). This table has a
maximum size of 100 rows by default. To change the table size,
modify the
performance_schema_setup_actors_size
system variable at server startup.
For each new foreground thread, the Performance Schema matches
the user and host for the thread against the rows of the
setup_actors
table. If a row from
that table matches, its ENABLED
and
HISTORY
column values are used to set the
INSTRUMENTED
and HISTORY
columns, respectively, of the
threads
table row for the thread.
This enables instrumenting and historical event logging to be
applied selectively per host, user, or account (user and host
combination). If there is no match, the
INSTRUMENTED
and HISTORY
columns for the thread are set to NO
.
For background threads, there is no associated user.
INSTRUMENTED
and HISTORY
are YES
by default and
setup_actors
is not consulted.
The initial contents of the
setup_actors
table match any user
and host combination, so monitoring and historical event
collection are enabled by default for all foreground threads:
mysql> SELECT * FROM performance_schema.setup_actors;
+------+------+------+---------+---------+
| HOST | USER | ROLE | ENABLED | HISTORY |
+------+------+------+---------+---------+
| % | % | % | YES | YES |
+------+------+------+---------+---------+
For information about how to use the
setup_actors
table to affect
event monitoring, see
Section 25.4.6, “Pre-Filtering by Thread”.
Modifications to the setup_actors
table affect only foreground threads created subsequent to the
modification, not existing threads. To affect existing
threads, modify the INSTRUMENTED
and
HISTORY
columns of
threads
table rows.
The setup_actors
table has these
columns:
HOST
The host name. This should be a literal name, or
'%'
to mean “any host.”
USER
The user name. This should be a literal name, or
'%'
to mean “any user.”
ROLE
Unused.
ENABLED
Whether to enable instrumentation for foreground threads
matched by the row. The value is YES
or
NO
.
HISTORY
Whether to log historical events for foreground threads
matched by the row. The value is YES
or
NO
.
TRUNCATE TABLE
is permitted for
the setup_actors
table. It
removes the rows.
The setup_consumers
table lists
the types of consumers for which event information can be
stored and which are enabled:
mysql> SELECT * FROM performance_schema.setup_consumers;
+----------------------------------+---------+
| NAME | ENABLED |
+----------------------------------+---------+
| events_stages_current | NO |
| events_stages_history | NO |
| events_stages_history_long | NO |
| events_statements_current | YES |
| events_statements_history | YES |
| events_statements_history_long | NO |
| events_transactions_current | NO |
| events_transactions_history | NO |
| events_transactions_history_long | NO |
| events_waits_current | NO |
| events_waits_history | NO |
| events_waits_history_long | NO |
| global_instrumentation | YES |
| thread_instrumentation | YES |
| statements_digest | YES |
+----------------------------------+---------+
The consumer settings in the
setup_consumers
table form a
hierarchy from higher levels to lower. For detailed
information about the effect of enabling different consumers,
see Section 25.4.7, “Pre-Filtering by Consumer”.
Modifications to the
setup_consumers
table affect
monitoring immediately.
The setup_consumers
table has
these columns:
NAME
The consumer name.
ENABLED
Whether the consumer is enabled. The value is
YES
or NO
. This
column can be modified. If you disable a consumer, the
server does not spend time adding event information to it.
TRUNCATE TABLE
is not permitted
for the setup_consumers
table.
The setup_instruments
table lists
classes of instrumented objects for which events can be
collected:
mysql> SELECT * FROM performance_schema.setup_instruments;
+---------------------------------------------------+---------+-------+
| NAME | ENABLED | TIMED |
+---------------------------------------------------+---------+-------+
...
| stage/sql/end | NO | NO |
| stage/sql/executing | NO | NO |
| stage/sql/init | NO | NO |
| stage/sql/insert | NO | NO |
...
| statement/sql/load | YES | YES |
| statement/sql/grant | YES | YES |
| statement/sql/check | YES | YES |
| statement/sql/flush | YES | YES |
...
| wait/synch/mutex/sql/LOCK_global_read_lock | YES | YES |
| wait/synch/mutex/sql/LOCK_global_system_variables | YES | YES |
| wait/synch/mutex/sql/LOCK_lock_db | YES | YES |
| wait/synch/mutex/sql/LOCK_manager | YES | YES |
...
| wait/synch/rwlock/sql/LOCK_grant | YES | YES |
| wait/synch/rwlock/sql/LOGGER::LOCK_logger | YES | YES |
| wait/synch/rwlock/sql/LOCK_sys_init_connect | YES | YES |
| wait/synch/rwlock/sql/LOCK_sys_init_slave | YES | YES |
...
| wait/io/file/sql/binlog | YES | YES |
| wait/io/file/sql/binlog_index | YES | YES |
| wait/io/file/sql/casetest | YES | YES |
| wait/io/file/sql/dbopt | YES | YES |
...
Each instrument added to the source code provides a row for
the setup_instruments
table, even
when the instrumented code is not executed. When an instrument
is enabled and executed, instrumented instances are created,
which are visible in the
tables, such as xxx
_instancesfile_instances
or
rwlock_instances
.
Modifications to most
setup_instruments
rows affect
monitoring immediately. For some instruments, modifications
are effective only at server startup; changing them at runtime
has no effect. This affects primarily mutexes, conditions, and
rwlocks in the server, although there may be other instruments
for which this is true.
For more information about the role of the
setup_instruments
table in event
filtering, see
Section 25.4.3, “Event Pre-Filtering”.
The setup_instruments
table has
these columns:
NAME
The instrument name. Instrument names may have multiple
parts and form a hierarchy, as discussed in
Section 25.6, “Performance Schema Instrument Naming Conventions”.
Events produced from execution of an instrument have an
EVENT_NAME
value that is taken from the
instrument NAME
value. (Events do not
really have a “name,” but this provides a way
to associate events with instruments.)
ENABLED
Whether the instrument is enabled. The value is
YES
or NO
. A
disabled instrument produces no events. This column can be
modified, although setting ENABLED
has
no effect for instruments that have already been created.
TIMED
Whether the instrument is timed. The value is
YES
or NO
. This
column can be modified, although setting
TIMED
has no effect for instruments
that have already been created.
For memory instruments, the TIMED
column in setup_instruments
is ignored because memory operations are not timed.
If an enabled instrument is not timed, the instrument code
is enabled, but the timer is not. Events produced by the
instrument have NULL
for the
TIMER_START
,
TIMER_END
, and
TIMER_WAIT
timer values. This in turn
causes those values to be ignored when calculating the
sum, minimum, maximum, and average time values in summary
tables.
TRUNCATE TABLE
is not permitted
for the setup_instruments
table.
The setup_objects
table controls
whether the Performance Schema monitors particular objects.
This table has a maximum size of 100 rows by default. To
change the table size, modify the
performance_schema_setup_objects_size
system variable at server startup.
The initial setup_objects
contents look like this:
mysql> SELECT * FROM performance_schema.setup_objects;
+-------------+--------------------+-------------+---------+-------+
| OBJECT_TYPE | OBJECT_SCHEMA | OBJECT_NAME | ENABLED | TIMED |
+-------------+--------------------+-------------+---------+-------+
| EVENT | mysql | % | NO | NO |
| EVENT | performance_schema | % | NO | NO |
| EVENT | information_schema | % | NO | NO |
| EVENT | % | % | YES | YES |
| FUNCTION | mysql | % | NO | NO |
| FUNCTION | performance_schema | % | NO | NO |
| FUNCTION | information_schema | % | NO | NO |
| FUNCTION | % | % | YES | YES |
| PROCEDURE | mysql | % | NO | NO |
| PROCEDURE | performance_schema | % | NO | NO |
| PROCEDURE | information_schema | % | NO | NO |
| PROCEDURE | % | % | YES | YES |
| TABLE | mysql | % | NO | NO |
| TABLE | performance_schema | % | NO | NO |
| TABLE | information_schema | % | NO | NO |
| TABLE | % | % | YES | YES |
| TRIGGER | mysql | % | NO | NO |
| TRIGGER | performance_schema | % | NO | NO |
| TRIGGER | information_schema | % | NO | NO |
| TRIGGER | % | % | YES | YES |
+-------------+--------------------+-------------+---------+-------+
Modifications to the
setup_objects
table affect object
monitoring immediately.
For object types listed in
setup_objects
, the Performance
Schema uses the table to how to monitor them. Object matching
is based on the OBJECT_SCHEMA
and
OBJECT_NAME
columns. Objects for which
there is no match are not monitored.
The effect of the default object configuration is to
instrument all tables except those in the
mysql
,
INFORMATION_SCHEMA
, and
performance_schema
databases. (Tables in
the INFORMATION_SCHEMA
database are not
instrumented regardless of the contents of
setup_objects
; the row for
information_schema.%
simply makes this
default explicit.)
When the Performance Schema checks for a match in
setup_objects
, it tries to find
more specific matches first. For example, with a table
db1.t1
, it looks for a match for
'db1'
and 't1'
, then for
'db1'
and '%'
, then for
'%'
and '%'
. The order
in which matching occurs matters because different matching
setup_objects
rows can have
different ENABLED
and
TIMED
values.
Rows can be inserted into or deleted from
setup_objects
by users with the
INSERT
or
DELETE
privilege on the table.
For existing rows, only the ENABLED
and
TIMED
columns can be modified, by users
with the UPDATE
privilege on
the table.
For more information about the role of the
setup_objects
table in event
filtering, see
Section 25.4.3, “Event Pre-Filtering”.
The setup_objects
table has these
columns:
OBJECT_TYPE
The type of object to instrument. The value is one of
'EVENT'
(Event Scheduler event),
'FUNCTION'
(stored function),
'PROCEDURE'
(stored procedure),
'TABLE'
(base table), or
'TRIGGER'
(trigger).
TABLE
filtering affects table I/O
events (wait/io/table/sql/handler
instrument) and table lock events
(wait/lock/table/sql/handler
instrument).
OBJECT_SCHEMA
The schema that contains the object. This should be a
literal name, or '%'
to mean “any
schema.”
OBJECT_NAME
The name of the instrumented object. This should be a
literal name, or '%'
to mean “any
object.”
ENABLED
Whether events for the object are instrumented. The value
is YES
or NO
. This
column can be modified.
TIMED
Whether events for the object are timed. The value is
YES
or NO
. This
column can be modified.
TRUNCATE TABLE
is permitted for
the setup_objects
table. It
removes the rows.
The setup_timers
table shows the
currently selected event timers:
mysql> SELECT * FROM performance_schema.setup_timers;
+-------------+-------------+
| NAME | TIMER_NAME |
+-------------+-------------+
| idle | MICROSECOND |
| wait | CYCLE |
| stage | NANOSECOND |
| statement | NANOSECOND |
| transaction | NANOSECOND |
+-------------+-------------+
As of MySQL 5.7.21, the Performance Schema
setup_timers
table is
deprecated and is removed in MySQL 8.0, as is the
TICKS
row in the
performance_timers
table.
The setup_timers.TIMER_NAME
value can be
changed to select a different timer. The value can be any of
the values in the
performance_timers.TIMER_NAME
column. For
an explanation of how event timing occurs, see
Section 25.4.1, “Performance Schema Event Timing”.
Modifications to the setup_timers
table affect monitoring immediately. Events already in
progress may use the original timer for the begin time and the
new timer for the end time. To avoid unpredictable results
after you make timer changes, use
TRUNCATE TABLE
to reset
Performance Schema statistics.
The setup_timers
table has these
columns:
NAME
The type of instrument the timer is used for.
TIMER_NAME
The timer that applies to the instrument type. This column can be modified.
TRUNCATE TABLE
is not permitted
for the setup_timers
table.
Instance tables document what types of objects are instrumented. They provide event names and explanatory notes or status information:
cond_instances
: Condition
synchronization object instances
file_instances
: File instances
mutex_instances
: Mutex
synchronization object instances
rwlock_instances
: Lock
synchronization object instances
socket_instances
: Active
connection instances
These tables list instrumented synchronization objects, files,
and connections. There are three types of synchronization
objects: cond
, mutex
, and
rwlock
. Each instance table has an
EVENT_NAME
or NAME
column
to indicate the instrument associated with each row. Instrument
names may have multiple parts and form a hierarchy, as discussed
in Section 25.6, “Performance Schema Instrument Naming Conventions”.
The mutex_instances.LOCKED_BY_THREAD_ID
and
rwlock_instances.WRITE_LOCKED_BY_THREAD_ID
columns are extremely important for investigating performance
bottlenecks or deadlocks. For examples of how to use them for
this purpose, see Section 25.19, “Using the Performance Schema to Diagnose Problems”
The cond_instances
table lists
all the conditions seen by the Performance Schema while the
server executes. A condition is a synchronization mechanism
used in the code to signal that a specific event has happened,
so that a thread waiting for this condition can resume work.
When a thread is waiting for something to happen, the condition name is an indication of what the thread is waiting for, but there is no immediate way to tell which other thread, or threads, will cause the condition to happen.
The cond_instances
table has
these columns:
NAME
The instrument name associated with the condition.
OBJECT_INSTANCE_BEGIN
The address in memory of the instrumented condition.
TRUNCATE TABLE
is not permitted
for the cond_instances
table.
The file_instances
table lists
all the files seen by the Performance Schema when executing
file I/O instrumentation. If a file on disk has never been
opened, it will not be in
file_instances
. When a file is
deleted from the disk, it is also removed from the
file_instances
table.
The file_instances
table has
these columns:
FILE_NAME
The file name.
EVENT_NAME
The instrument name associated with the file.
OPEN_COUNT
The count of open handles on the file. If a file was
opened and then closed, it was opened 1 time, but
OPEN_COUNT
will be 0. To list all the
files currently opened by the server, use WHERE
OPEN_COUNT > 0
.
TRUNCATE TABLE
is not permitted
for the file_instances
table.
The mutex_instances
table lists
all the mutexes seen by the Performance Schema while the
server executes. A mutex is a synchronization mechanism used
in the code to enforce that only one thread at a given time
can have access to some common resource. The resource is said
to be “protected” by the mutex.
When two threads executing in the server (for example, two user sessions executing a query simultaneously) do need to access the same resource (a file, a buffer, or some piece of data), these two threads will compete against each other, so that the first query to obtain a lock on the mutex will cause the other query to wait until the first is done and unlocks the mutex.
The work performed while holding a mutex is said to be in a “critical section,” and multiple queries do execute this critical section in a serialized way (one at a time), which is a potential bottleneck.
The mutex_instances
table has
these columns:
NAME
The instrument name associated with the mutex.
OBJECT_INSTANCE_BEGIN
The address in memory of the instrumented mutex.
LOCKED_BY_THREAD_ID
When a thread currently has a mutex locked,
LOCKED_BY_THREAD_ID
is the
THREAD_ID
of the locking thread,
otherwise it is NULL
.
TRUNCATE TABLE
is not permitted
for the mutex_instances
table.
For every mutex instrumented in the code, the Performance Schema provides the following information.
The setup_instruments
table
lists the name of the instrumentation point, with the
prefix wait/synch/mutex/
.
When some code creates a mutex, a row is added to the
mutex_instances
table. The
OBJECT_INSTANCE_BEGIN
column is a
property that uniquely identifies the mutex.
When a thread attempts to lock a mutex, the
events_waits_current
table
shows a row for that thread, indicating that it is waiting
on a mutex (in the EVENT_NAME
column),
and indicating which mutex is waited on (in the
OBJECT_INSTANCE_BEGIN
column).
When a thread succeeds in locking a mutex:
events_waits_current
shows that the wait on the mutex is completed (in the
TIMER_END
and
TIMER_WAIT
columns)
The completed wait event is added to the
events_waits_history
and
events_waits_history_long
tables
mutex_instances
shows
that the mutex is now owned by the thread (in the
THREAD_ID
column).
When a thread unlocks a mutex,
mutex_instances
shows that
the mutex now has no owner (the
THREAD_ID
column is
NULL
).
When a mutex object is destroyed, the corresponding row is
removed from mutex_instances
.
By performing queries on both of the following tables, a monitoring application or a DBA can detect bottlenecks or deadlocks between threads that involve mutexes:
events_waits_current
, to see
what mutex a thread is waiting for
mutex_instances
, to see which
other thread currently owns a mutex
The rwlock_instances
table lists
all the rwlock (read write
lock) instances seen by the Performance Schema while the
server executes. An rwlock
is a
synchronization mechanism used in the code to enforce that
threads at a given time can have access to some common
resource following certain rules. The resource is said to be
“protected” by the rwlock
. The
access is either shared (many threads can have a read lock at
the same time), exclusive (only one thread can have a write
lock at a given time), or shared-exclusive (a thread can have
a write lock while permitting inconsistent reads by other
threads). Shared-exclusive access is otherwise known as an
sxlock
and optimizes concurrency and
improves scalability for read-write workloads.
Depending on how many threads are requesting a lock, and the nature of the locks requested, access can be either granted in shared mode, exclusive mode, shared-exclusive mode or not granted at all, waiting for other threads to finish first.
The rwlock_instances
table has
these columns:
NAME
The instrument name associated with the lock.
OBJECT_INSTANCE_BEGIN
The address in memory of the instrumented lock.
WRITE_LOCKED_BY_THREAD_ID
When a thread currently has an rwlock
locked in exclusive (write) mode,
WRITE_LOCKED_BY_THREAD_ID
is the
THREAD_ID
of the locking thread,
otherwise it is NULL
.
READ_LOCKED_BY_COUNT
When a thread currently has an rwlock
locked in shared (read) mode,
READ_LOCKED_BY_COUNT
is incremented by
1. This is a counter only, so it cannot be used directly
to find which thread holds a read lock, but it can be used
to see whether there is a read contention on an
rwlock
, and see how many readers are
currently active.
TRUNCATE TABLE
is not permitted
for the rwlock_instances
table.
By performing queries on both of the following tables, a monitoring application or a DBA may detect some bottlenecks or deadlocks between threads that involve locks:
events_waits_current
, to see
what rwlock
a thread is waiting for
rwlock_instances
, to see
which other thread currently owns an
rwlock
There is a limitation: The
rwlock_instances
can be used only
to identify the thread holding a write lock, but not the
threads holding a read lock.
The socket_instances
table
provides a real-time snapshot of the active connections to the
MySQL server. The table contains one row per TCP/IP or Unix
socket file connection. Information available in this table
provides a real-time snapshot of the active connections to the
server. (Additional information is available in socket summary
tables, including network activity such as socket operations
and number of bytes transmitted and received; see
Section 25.12.15.8, “Socket Summary Tables”).
mysql> SELECT * FROM performance_schema.socket_instances\G
*************************** 1. row ***************************
EVENT_NAME: wait/io/socket/sql/server_unix_socket
OBJECT_INSTANCE_BEGIN: 4316619408
THREAD_ID: 1
SOCKET_ID: 16
IP:
PORT: 0
STATE: ACTIVE
*************************** 2. row ***************************
EVENT_NAME: wait/io/socket/sql/client_connection
OBJECT_INSTANCE_BEGIN: 4316644608
THREAD_ID: 21
SOCKET_ID: 39
IP: 127.0.0.1
PORT: 55233
STATE: ACTIVE
*************************** 3. row ***************************
EVENT_NAME: wait/io/socket/sql/server_tcpip_socket
OBJECT_INSTANCE_BEGIN: 4316699040
THREAD_ID: 1
SOCKET_ID: 14
IP: 0.0.0.0
PORT: 50603
STATE: ACTIVE
Socket instruments have names of the form
wait/io/socket/sql/
and are used like this:
socket_type
The server has a listening socket for each network
protocol that it supports. The instruments associated with
listening sockets for TCP/IP or Unix socket file
connections have a socket_type
value of server_tcpip_socket
or
server_unix_socket
, respectively.
When a listening socket detects a connection, the server
transfers the connection to a new socket managed by a
separate thread. The instrument for the new connection
thread has a socket_type
value
of client_connection
.
When a connection terminates, the row in
socket_instances
corresponding to it is deleted.
The socket_instances
table has
these columns:
EVENT_NAME
The name of the wait/io/socket/*
instrument that produced the event. This is a
NAME
value from the
setup_instruments
table.
Instrument names may have multiple parts and form a
hierarchy, as discussed in
Section 25.6, “Performance Schema Instrument Naming Conventions”.
OBJECT_INSTANCE_BEGIN
This column uniquely identifies the socket. The value is the address of an object in memory.
THREAD_ID
The internal thread identifier assigned by the server. Each socket is managed by a single thread, so each socket can be mapped to a thread which can be mapped to a server process.
SOCKET_ID
The internal file handle assigned to the socket.
IP
The client IP address. The value may be either an IPv4 or IPv6 address, or blank to indicate a Unix socket file connection.
PORT
The TCP/IP port number, in the range from 0 to 65535.
STATE
The socket status, either IDLE
or
ACTIVE
. Wait times for active sockets
are tracked using the corresponding socket instrument.
Wait times for idle sockets are tracked using the
idle
instrument.
A socket is idle if it is waiting for a request from the
client. When a socket becomes idle, the event row in
socket_instances
that is
tracking the socket switches from a status of
ACTIVE
to IDLE
. The
EVENT_NAME
value remains
wait/io/socket/*
, but timing for the
instrument is suspended. Instead, an event is generated in
the events_waits_current
table with an EVENT_NAME
value of
idle
.
When the next request is received, the
idle
event terminates, the socket
instance switches from IDLE
to
ACTIVE
, and timing of the socket
instrument resumes.
TRUNCATE TABLE
is not permitted
for the socket_instances
table.
The IP:PORT
column combination value
identifies the connection. This combination value is used in
the OBJECT_NAME
column of the
events_waits_
tables, to identify the connection from which socket events
come:
xxx
For the Unix domain listener socket
(server_unix_socket
), the port is 0,
and the IP is ''
.
For client connections via the Unix domain listener
(client_connection
), the port is 0, and
the IP is ''
.
For the TCP/IP server listener socket
(server_tcpip_socket
), the port is
always the master port (for example, 3306), and the IP is
always 0.0.0.0
.
For client connections via the TCP/IP listener
(client_connection
), the port is
whatever the server assigns, but never 0. The IP is the IP
of the originating host (127.0.0.1
or
::1
for the local host)
The Performance Schema instruments waits, which are events that take time. Within the event hierarchy, wait events nest within stage events, which nest within statement events, which nest within transaction events.
These tables store wait events:
events_waits_current
: The
current wait event for each thread.
events_waits_history
: The most
recent wait events that have ended per thread.
events_waits_history_long
: The
most recent wait events that have ended globally (across all
threads).
The following sections describe the wait event tables. There are also summary tables that aggregate information about wait events; see Section 25.12.15.1, “Wait Event Summary Tables”.
For more information about the relationship between the three wait event tables, see Section 25.9, “Performance Schema Tables for Current and Historical Events”.
To control whether to collect wait events, set the state of the relevant instruments and consumers:
The setup_instruments
table
contains instruments with names that begin with
wait
. Use these instruments to enable or
disable collection of individual wait event classes.
The setup_consumers
table
contains consumer values with names corresponding to the
current and historical wait event table names. Use these
consumers to filter collection of wait events.
Some wait instruments are enabled by default; others are disabled. For example:
mysql>SELECT * FROM performance_schema.setup_instruments
WHERE NAME LIKE 'wait/io/file/innodb%';
+--------------------------------------+---------+-------+ | NAME | ENABLED | TIMED | +--------------------------------------+---------+-------+ | wait/io/file/innodb/innodb_data_file | YES | YES | | wait/io/file/innodb/innodb_log_file | YES | YES | | wait/io/file/innodb/innodb_temp_file | YES | YES | +--------------------------------------+---------+-------+ mysql>SELECT *
FROM performance_schema.setup_instruments WHERE
NAME LIKE 'wait/io/socket/%';
+----------------------------------------+---------+-------+ | NAME | ENABLED | TIMED | +----------------------------------------+---------+-------+ | wait/io/socket/sql/server_tcpip_socket | NO | NO | | wait/io/socket/sql/server_unix_socket | NO | NO | | wait/io/socket/sql/client_connection | NO | NO | +----------------------------------------+---------+-------+
The wait consumers are disabled by default:
mysql>SELECT *
FROM performance_schema.setup_consumers
WHERE NAME LIKE 'events_waits%';
+---------------------------+---------+ | NAME | ENABLED | +---------------------------+---------+ | events_waits_current | NO | | events_waits_history | NO | | events_waits_history_long | NO | +---------------------------+---------+
To control wait event collection at server startup, use lines
like these in your my.cnf
file:
Enable:
[mysqld] performance-schema-instrument='wait/%=ON' performance-schema-consumer-events-waits-current=ON performance-schema-consumer-events-waits-history=ON performance-schema-consumer-events-waits-history-long=ON
Disable:
[mysqld] performance-schema-instrument='wait/%=OFF' performance-schema-consumer-events-waits-current=OFF performance-schema-consumer-events-waits-history=OFF performance-schema-consumer-events-waits-history-long=OFF
To control wait event collection at runtime, update the
setup_instruments
and
setup_consumers
tables:
Enable:
UPDATE performance_schema.setup_instruments SET ENABLED = 'YES', TIMED = 'YES' WHERE NAME = 'wait/%'; UPDATE performance_schema.setup_consumers SET ENABLED = 'YES' WHERE NAME LIKE 'events_waits%';
Disable:
UPDATE performance_schema.setup_instruments SET ENABLED = 'NO', TIMED = 'NO' WHERE NAME = 'wait/%'; UPDATE performance_schema.setup_consumers SET ENABLED = 'NO' WHERE NAME LIKE 'events_waits%';
To collect only specific wait events, enable only the corresponding wait instruments. To collect wait events only for specific wait event tables, enable the wait instruments but only the wait consumers corresponding to the desired tables.
The setup_timers
table contains a
row with a NAME
value of
wait
that indicates the unit for wait event
timing. The default unit is CYCLE
:
mysql>SELECT *
FROM performance_schema.setup_timers
WHERE NAME = 'wait';
+------+------------+ | NAME | TIMER_NAME | +------+------------+ | wait | CYCLE | +------+------------+
To change the timing unit, modify the
TIMER_NAME
value:
UPDATE performance_schema.setup_timers SET TIMER_NAME = 'NANOSECOND' WHERE NAME = 'wait';
For additional information about configuring event collection, see Section 25.3, “Performance Schema Startup Configuration”, and Section 25.4, “Performance Schema Runtime Configuration”.
The events_waits_current
table
contains current wait events. The table stores one row per
thread showing the current status of the thread's most recent
monitored wait event, so there is no system variable for
configuring the table size.
Of the tables that contain wait event rows,
events_waits_current
is the most
fundamental. Other tables that contain wait event rows are
logically derived from the current events. For example, the
events_waits_history
and
events_waits_history_long
tables
are collections of the most recent wait events that have
ended, up to a maximum number of rows per thread and globally
across all threads, respectively.
For more information about the relationship between the three wait event tables, see Section 25.9, “Performance Schema Tables for Current and Historical Events”.
For information about configuring whether to collect wait events, see Section 25.12.4, “Performance Schema Wait Event Tables”.
The events_waits_current
table
has these columns:
THREAD_ID
, EVENT_ID
The thread associated with the event and the thread
current event number when the event starts. The
THREAD_ID
and
EVENT_ID
values taken together uniquely
identify the row. No two rows have the same pair of
values.
END_EVENT_ID
This column is set to NULL
when the
event starts and updated to the thread current event
number when the event ends.
EVENT_NAME
The name of the instrument that produced the event. This
is a NAME
value from the
setup_instruments
table.
Instrument names may have multiple parts and form a
hierarchy, as discussed in
Section 25.6, “Performance Schema Instrument Naming Conventions”.
SOURCE
The name of the source file containing the instrumented code that produced the event and the line number in the file at which the instrumentation occurs. This enables you to check the source to determine exactly what code is involved. For example, if a mutex or lock is being blocked, you can check the context in which this occurs.
TIMER_START
,
TIMER_END
,
TIMER_WAIT
Timing information for the event. The unit for these
values is picoseconds (trillionths of a second). The
TIMER_START
and
TIMER_END
values indicate when event
timing started and ended. TIMER_WAIT
is
the event elapsed time (duration).
If an event has not finished, TIMER_END
is the current timer value and
TIMER_WAIT
is the time elapsed so far
(TIMER_END
−
TIMER_START
).
If an event is produced from an instrument that has
TIMED = NO
, timing information is not
collected, and TIMER_START
,
TIMER_END
, and
TIMER_WAIT
are all
NULL
.
For discussion of picoseconds as the unit for event times and factors that affect time values, see Section 25.4.1, “Performance Schema Event Timing”.
SPINS
For a mutex, the number of spin rounds. If the value is
NULL
, the code does not use spin rounds
or spinning is not instrumented.
OBJECT_SCHEMA
,
OBJECT_NAME
,
OBJECT_TYPE
,
OBJECT_INSTANCE_BEGIN
These columns identify the object “being acted on.” What that means depends on the object type.
For a synchronization object (cond
,
mutex
, rwlock
):
OBJECT_SCHEMA
,
OBJECT_NAME
, and
OBJECT_TYPE
are
NULL
.
OBJECT_INSTANCE_BEGIN
is the
address of the synchronization object in memory.
For a file I/O object:
OBJECT_SCHEMA
is
NULL
.
OBJECT_NAME
is the file name.
OBJECT_TYPE
is
FILE
.
OBJECT_INSTANCE_BEGIN
is an address
in memory.
For a socket object:
OBJECT_NAME
is the
IP:PORT
value for the socket.
OBJECT_INSTANCE_BEGIN
is an address
in memory.
For a table I/O object:
OBJECT_SCHEMA
is the name of the
schema that contains the table.
OBJECT_NAME
is the table name.
OBJECT_TYPE
is
TABLE
for a persistent base table
or TEMPORARY TABLE
for a temporary
table.
OBJECT_INSTANCE_BEGIN
is an address
in memory.
An OBJECT_INSTANCE_BEGIN
value itself
has no meaning, except that different values indicate
different objects.
OBJECT_INSTANCE_BEGIN
can be used for
debugging. For example, it can be used with GROUP
BY OBJECT_INSTANCE_BEGIN
to see whether the load
on 1,000 mutexes (that protect, say, 1,000 pages or blocks
of data) is spread evenly or just hitting a few
bottlenecks. This can help you correlate with other
sources of information if you see the same object address
in a log file or another debugging or performance tool.
INDEX_NAME
The name of the index used. PRIMARY
indicates the table primary index. NULL
means that no index was used.
NESTING_EVENT_ID
The EVENT_ID
value of the event within
which this event is nested.
NESTING_EVENT_TYPE
The nesting event type. The value is
TRANSACTION
,
STATEMENT
, STAGE
, or
WAIT
.
OPERATION
The type of operation performed, such as
lock
, read
, or
write
.
NUMBER_OF_BYTES
The number of bytes read or written by the operation. For
table I/O waits (events for the
wait/io/table/sql/handler
instrument),
NUMBER_OF_BYTES
indicates the number of
rows. If the value is greater than 1, the event is for a
batch I/O operation. The following discussion describes
the difference between exclusively single-row reporting
and reporting that reflects batch I/O.
MySQL executes joins using a nested-loop implementation.
The job of the Performance Schema instrumentation is to
provide row count and accumulated execution time per table
in the join. Assume a join query of the following form
that is executed using a table join order of
t1
, t2
,
t3
:
SELECT ... FROM t1 JOIN t2 ON ... JOIN t3 ON ...
Table “fanout” is the increase or decrease in
number of rows from adding a table during join processing.
If the fanout for table t3
is greater
than 1, the majority of row-fetch operations are for that
table. Suppose that the join accesses 10 rows from
t1
, 20 rows from t2
per row from t1
, and 30 rows from
t3
per row of table
t2
. With single-row reporting, the
total number of instrumented operations is:
10 + (10 * 20) + (10 * 20 * 30) = 6210
A significant reduction in the number of instrumented
operations is achievable by aggregating them per scan
(that is, per unique combination of rows from
t1
and t2
). With
batch I/O reporting, the Performance Schema produces an
event for each scan of the innermost table
t3
rather than for each row, and the
number of instrumented row operations reduces to:
10 + (10 * 20) + (10 * 20) = 410
That is a reduction of 93%, illustrating how the batch-reporting strategy significantly reduces Performance Schema overhead for table I/O by reducing the number of reporting calls. The tradeoff is lesser accuracy for event timing. Rather than time for an individual row operation as in per-row reporting, timing for batch I/O includes time spent for operations such as join buffering, aggregation, and returning rows to the client.
For batch I/O reporting to occur, these conditions must be true:
Query execution accesses the innermost table of a query block (for a single-table query, that table counts as innermost)
Query execution does not request a single row from the
table (so, for example,
eq_ref
access
prevents use of batch reporting)
Query execution does not evaluate a subquery containing table access for the table
FLAGS
Reserved for future use.
TRUNCATE TABLE
is permitted for
the events_waits_current
table.
It removes the rows.
The events_waits_history
table
contains the N
most recent wait
events that have ended per thread. Wait events are not added
to the table until they have ended. When the table contains
the maximum number of rows for a given thread, the oldest
thread row is discarded when a new row for that thread is
added. When a thread ends, all its rows are discarded.
The Performance Schema autosizes the value of
N
during server startup. To set the
number of rows per thread explicitly, set the
performance_schema_events_waits_history_size
system variable at server startup.
The events_waits_history
table
has the same columns as
events_waits_current
. See
Section 25.12.4.1, “The events_waits_current Table”.
TRUNCATE TABLE
is permitted for
the events_waits_history
table.
It removes the rows.
For more information about the relationship between the three wait event tables, see Section 25.9, “Performance Schema Tables for Current and Historical Events”.
For information about configuring whether to collect wait events, see Section 25.12.4, “Performance Schema Wait Event Tables”.
The events_waits_history_long
table contains N
the most recent
wait events that have ended globally, across all threads. Wait
events are not added to the table until they have ended. When
the table becomes full, the oldest row is discarded when a new
row is added, regardless of which thread generated either row.
The Performance Schema autosizes the value of
N
during server startup. To set the
table size explicitly, set the
performance_schema_events_waits_history_long_size
system variable at server startup.
The events_waits_history_long
table has the same columns as
events_waits_current
. See
Section 25.12.4.1, “The events_waits_current Table”.
TRUNCATE TABLE
is permitted for
the events_waits_history_long
table. It removes the rows.
For more information about the relationship between the three wait event tables, see Section 25.9, “Performance Schema Tables for Current and Historical Events”.
For information about configuring whether to collect wait events, see Section 25.12.4, “Performance Schema Wait Event Tables”.
The Performance Schema instruments stages, which are steps
during the statement-execution process, such as parsing a
statement, opening a table, or performing a
filesort
operation. Stages correspond to the
thread states displayed by SHOW
PROCESSLIST
or that are visible in the
INFORMATION_SCHEMA.PROCESSLIST
table. Stages begin and end when state values change.
Within the event hierarchy, wait events nest within stage events, which nest within statement events, which nest within transaction events.
These tables store stage events:
events_stages_current
: The
current stage event for each thread.
events_stages_history
: The most
recent stage events that have ended per thread.
events_stages_history_long
: The
most recent stage events that have ended globally (across
all threads).
The following sections describe the stage event tables. There are also summary tables that aggregate information about stage events; see Section 25.12.15.2, “Stage Summary Tables”.
For more information about the relationship between the three stage event tables, see Section 25.9, “Performance Schema Tables for Current and Historical Events”.
To control whether to collect stage events, set the state of the relevant instruments and consumers:
The setup_instruments
table
contains instruments with names that begin with
stage
. Use these instruments to enable or
disable collection of individual stage event classes.
The setup_consumers
table
contains consumer values with names corresponding to the
current and historical stage event table names. Use these
consumers to filter collection of stage events.
Other than those instruments that provide statement progress information, the stage instruments are disabled by default. For example:
mysql>SELECT *
FROM performance_schema.setup_instruments
WHERE NAME RLIKE 'stage/sql/[a-c]';
+----------------------------------------------------+---------+-------+ | NAME | ENABLED | TIMED | +----------------------------------------------------+---------+-------+ | stage/sql/After create | NO | NO | | stage/sql/allocating local table | NO | NO | | stage/sql/altering table | NO | NO | | stage/sql/committing alter table to storage engine | NO | NO | | stage/sql/Changing master | NO | NO | | stage/sql/Checking master version | NO | NO | | stage/sql/checking permissions | NO | NO | | stage/sql/checking privileges on cached query | NO | NO | | stage/sql/checking query cache for query | NO | NO | | stage/sql/cleaning up | NO | NO | | stage/sql/closing tables | NO | NO | | stage/sql/Connecting to master | NO | NO | | stage/sql/converting HEAP to MyISAM | NO | NO | | stage/sql/Copying to group table | NO | NO | | stage/sql/Copying to tmp table | NO | NO | | stage/sql/copy to tmp table | NO | NO | | stage/sql/Creating sort index | NO | NO | | stage/sql/creating table | NO | NO | | stage/sql/Creating tmp table | NO | NO | +----------------------------------------------------+---------+-------+
Stage event instruments that provide statement progress information are enabled and timed by default:
mysql>SELECT *
FROM performance_schema.setup_instruments
WHERE ENABLED='YES' AND NAME LIKE "stage/%";
+------------------------------------------------------+---------+-------+ | NAME | ENABLED | TIMED | +------------------------------------------------------+---------+-------+ | stage/sql/copy to tmp table | YES | YES | | stage/innodb/alter table (end) | YES | YES | | stage/innodb/alter table (flush) | YES | YES | | stage/innodb/alter table (insert) | YES | YES | | stage/innodb/alter table (log apply index) | YES | YES | | stage/innodb/alter table (log apply table) | YES | YES | | stage/innodb/alter table (merge sort) | YES | YES | | stage/innodb/alter table (read PK and internal sort) | YES | YES | | stage/innodb/buffer pool load | YES | YES | +------------------------------------------------------+---------+-------+
The stage consumers are disabled by default:
mysql>SELECT *
FROM performance_schema.setup_consumers
WHERE NAME LIKE 'events_stages%';
+----------------------------+---------+ | NAME | ENABLED | +----------------------------+---------+ | events_stages_current | NO | | events_stages_history | NO | | events_stages_history_long | NO | +----------------------------+---------+
To control stage event collection at server startup, use lines
like these in your my.cnf
file:
Enable:
[mysqld] performance-schema-instrument='stage/%=ON' performance-schema-consumer-events-stages-current=ON performance-schema-consumer-events-stages-history=ON performance-schema-consumer-events-stages-history-long=ON
Disable:
[mysqld] performance-schema-instrument='stage/%=OFF' performance-schema-consumer-events-stages-current=OFF performance-schema-consumer-events-stages-history=OFF performance-schema-consumer-events-stages-history-long=OFF
To control stage event collection at runtime, update the
setup_instruments
and
setup_consumers
tables:
Enable:
UPDATE performance_schema.setup_instruments SET ENABLED = 'YES', TIMED = 'YES' WHERE NAME = 'stage/%'; UPDATE performance_schema.setup_consumers SET ENABLED = 'YES' WHERE NAME LIKE 'events_stages%';
Disable:
UPDATE performance_schema.setup_instruments SET ENABLED = 'NO', TIMED = 'NO' WHERE NAME = 'stage/%'; UPDATE performance_schema.setup_consumers SET ENABLED = 'NO' WHERE NAME LIKE 'events_stages%';
To collect only specific stage events, enable only the corresponding stage instruments. To collect stage events only for specific stage event tables, enable the stage instruments but only the stage consumers corresponding to the desired tables.
The setup_timers
table contains a
row with a NAME
value of
stage
that indicates the unit for stage event
timing. The default unit is NANOSECOND
:
mysql>SELECT *
FROM performance_schema.setup_timers
WHERE NAME = 'stage';
+-------+------------+ | NAME | TIMER_NAME | +-------+------------+ | stage | NANOSECOND | +-------+------------+
To change the timing unit, modify the
TIMER_NAME
value:
UPDATE performance_schema.setup_timers SET TIMER_NAME = 'MICROSECOND' WHERE NAME = 'stage';
For additional information about configuring event collection, see Section 25.3, “Performance Schema Startup Configuration”, and Section 25.4, “Performance Schema Runtime Configuration”.
The Performance Schema stage event tables contain two columns that, taken together, provide a stage progress indicator for each row:
WORK_COMPLETED
: The number of work units
completed for the stage
WORK_ESTIMATED
: The number of work units
expected for the stage
Each column is NULL
if no progress
information is provided for an instrument. Interpretation of the
information, if it is available, depends entirely on the
instrument implementation. The Performance Schema tables provide
a container to store progress data, but make no assumptions
about the semantics of the metric itself:
A “work unit” is an integer metric that increases over time during execution, such as the number of bytes, rows, files, or tables processed. The definition of “work unit” for a particular instrument is left to the instrumentation code providing the data.
The WORK_COMPLETED
value can increase one
or many units at a time, depending on the instrumented code.
The WORK_ESTIMATED
value can change
during the stage, depending on the instrumented code.
Instrumentation for a stage event progress indicator can implement any of the following behaviors:
No progress instrumentation
This is the most typical case, where no progress data is
provided. The WORK_COMPLETED
and
WORK_ESTIMATED
columns are both
NULL
.
Unbounded progress instrumentation
Only the WORK_COMPLETED
column is
meaningful. No data is provided for the
WORK_ESTIMATED
column, which displays 0.
By querying the
events_stages_current
table for
the monitored session, a monitoring application can report
how much work has been performed so far, but cannot report
whether the stage is near completion. Currently, no stages
are instrumented like this.
Bounded progress instrumentation
The WORK_COMPLETED
and
WORK_ESTIMATED
columns are both
meaningful.
This type of progress indicator is appropriate for an
operation with a defined completion criterion, such as the
table-copy instrument described later. By querying the
events_stages_current
table for
the monitored session, a monitoring application can report
how much work has been performed so far, and can report the
overall completion percentage for the stage, by computing
the WORK_COMPLETED
/
WORK_ESTIMATED
ratio.
The stage/sql/copy to tmp table
instrument
illustrates how progress indicators work. During execution of an
ALTER TABLE
statement, the
stage/sql/copy to tmp table
stage is used,
and this stage can execute potentially for a long time,
depending on the size of the data to copy.
The table-copy task has a defined termination (all rows copied),
and the stage/sql/copy to tmp table
stage is
instrumented to provided bounded progress information: The work
unit used is number of rows copied,
WORK_COMPLETED
and
WORK_ESTIMATED
are both meaningful, and their
ratio indicates task percentage complete.
To enable the instrument and the relevant consumers, execute these statements:
UPDATE performance_schema.setup_instruments SET ENABLED='YES' WHERE NAME='stage/sql/copy to tmp table'; UPDATE performance_schema.setup_consumers SET ENABLED='YES' WHERE NAME LIKE 'events_stages_%';
To see the progress of an ongoing ALTER
TABLE
statement, select from the
events_stages_current
table.
The events_stages_current
table
contains current stage events. The table stores one row per
thread showing the current status of the thread's most recent
monitored stage event, so there is no system variable for
configuring the table size.
Of the tables that contain stage event rows,
events_stages_current
is the most
fundamental. Other tables that contain stage event rows are
logically derived from the current events. For example, the
events_stages_history
and
events_stages_history_long
tables
are collections of the most recent stage events that have
ended, up to a maximum number of rows per thread and globally
across all threads, respectively.
For more information about the relationship between the three stage event tables, see Section 25.9, “Performance Schema Tables for Current and Historical Events”.
For information about configuring whether to collect stage events, see Section 25.12.5, “Performance Schema Stage Event Tables”.
The events_stages_current
table
has these columns:
THREAD_ID
, EVENT_ID
The thread associated with the event and the thread
current event number when the event starts. The
THREAD_ID
and
EVENT_ID
values taken together uniquely
identify the row. No two rows have the same pair of
values.
END_EVENT_ID
This column is set to NULL
when the
event starts and updated to the thread current event
number when the event ends.
EVENT_NAME
The name of the instrument that produced the event. This
is a NAME
value from the
setup_instruments
table.
Instrument names may have multiple parts and form a
hierarchy, as discussed in
Section 25.6, “Performance Schema Instrument Naming Conventions”.
SOURCE
The name of the source file containing the instrumented code that produced the event and the line number in the file at which the instrumentation occurs. This enables you to check the source to determine exactly what code is involved.
TIMER_START
,
TIMER_END
,
TIMER_WAIT
Timing information for the event. The unit for these
values is picoseconds (trillionths of a second). The
TIMER_START
and
TIMER_END
values indicate when event
timing started and ended. TIMER_WAIT
is
the event elapsed time (duration).
If an event has not finished, TIMER_END
is the current timer value and
TIMER_WAIT
is the time elapsed so far
(TIMER_END
−
TIMER_START
).
If an event is produced from an instrument that has
TIMED = NO
, timing information is not
collected, and TIMER_START
,
TIMER_END
, and
TIMER_WAIT
are all
NULL
.
For discussion of picoseconds as the unit for event times and factors that affect time values, see Section 25.4.1, “Performance Schema Event Timing”.
WORK_COMPLETED
,
WORK_ESTIMATED
These columns provide stage progress information, for
instruments that have been implemented to produce such
information. WORK_COMPLETED
indicates
how many work units have been completed for the stage, and
WORK_ESTIMATED
indicates how many work
units are expected for the stage. For more information,
see Stage Event Progress Information.
NESTING_EVENT_ID
The EVENT_ID
value of the event within
which this event is nested. The nesting event for a stage
event is usually a statement event.
NESTING_EVENT_TYPE
The nesting event type. The value is
TRANSACTION
,
STATEMENT
, STAGE
, or
WAIT
.
TRUNCATE TABLE
is permitted for
the events_stages_current
table.
It removes the rows.
The events_stages_history
table
contains the N
most recent stage
events that have ended per thread. Stage events are not added
to the table until they have ended. When the table contains
the maximum number of rows for a given thread, the oldest
thread row is discarded when a new row for that thread is
added. When a thread ends, all its rows are discarded.
The Performance Schema autosizes the value of
N
during server startup. To set the
number of rows per thread explicitly, set the
performance_schema_events_stages_history_size
system variable at server startup.
The events_stages_history
table
has the same columns as
events_stages_current
. See
Section 25.12.5.1, “The events_stages_current Table”.
TRUNCATE TABLE
is permitted for
the events_stages_history
table.
It removes the rows.
For more information about the relationship between the three stage event tables, see Section 25.9, “Performance Schema Tables for Current and Historical Events”.
For information about configuring whether to collect stage events, see Section 25.12.5, “Performance Schema Stage Event Tables”.
The events_stages_history_long
table contains the N
most recent
stage events that have ended globally, across all threads.
Stage events are not added to the table until they have ended.
When the table becomes full, the oldest row is discarded when
a new row is added, regardless of which thread generated
either row.
The Performance Schema autosizes the value of
N
during server startup. To set the
table size explicitly, set the
performance_schema_events_stages_history_long_size
system variable at server startup.
The events_stages_history_long
table has the same columns as
events_stages_current
. See
Section 25.12.5.1, “The events_stages_current Table”.
TRUNCATE TABLE
is permitted for
the events_stages_history_long
table. It removes the rows.
For more information about the relationship between the three stage event tables, see Section 25.9, “Performance Schema Tables for Current and Historical Events”.
For information about configuring whether to collect stage events, see Section 25.12.5, “Performance Schema Stage Event Tables”.
The Performance Schema instruments statement execution. Statement events occur at a high level of the event hierarchy. Within the event hierarchy, wait events nest within stage events, which nest within statement events, which nest within transaction events.
These tables store statement events:
events_statements_current
: The
current statement event for each thread.
events_statements_history
: The
most recent statement events that have ended per thread.
events_statements_history_long
:
The most recent statement events that have ended globally
(across all threads).
prepared_statements_instances
:
Prepared statement instances and statistics
The following sections describe the statement event tables. There are also summary tables that aggregate information about statement events; see Section 25.12.15.3, “Statement Summary Tables”.
For more information about the relationship between the three
events_statements_
event tables, see
Section 25.9, “Performance Schema Tables for Current and Historical Events”.
xxx
To control whether to collect statement events, set the state of the relevant instruments and consumers:
The setup_instruments
table
contains instruments with names that begin with
statement
. Use these instruments to
enable or disable collection of individual statement event
classes.
The setup_consumers
table
contains consumer values with names corresponding to the
current and historical statement event table names, and the
statement digest consumer. Use these consumers to filter
collection of statement events and statement digesting.
The statement instruments are enabled by default, and the
events_statements_current
,
events_statements_history
, and
statements_digest
statement consumers are
enabled by default:
mysql>SELECT *
FROM performance_schema.setup_instruments
WHERE NAME LIKE 'statement/%';
+---------------------------------------------+---------+-------+ | NAME | ENABLED | TIMED | +---------------------------------------------+---------+-------+ | statement/sql/select | YES | YES | | statement/sql/create_table | YES | YES | | statement/sql/create_index | YES | YES | ... | statement/sp/stmt | YES | YES | | statement/sp/set | YES | YES | | statement/sp/set_trigger_field | YES | YES | | statement/scheduler/event | YES | YES | | statement/com/Sleep | YES | YES | | statement/com/Quit | YES | YES | | statement/com/Init DB | YES | YES | ... | statement/abstract/Query | YES | YES | | statement/abstract/new_packet | YES | YES | | statement/abstract/relay_log | YES | YES | +---------------------------------------------+---------+-------+
mysql>SELECT *
FROM performance_schema.setup_consumers
WHERE NAME LIKE '%statements%';
+--------------------------------+---------+ | NAME | ENABLED | +--------------------------------+---------+ | events_statements_current | YES | | events_statements_history | YES | | events_statements_history_long | NO | | statements_digest | YES | +--------------------------------+---------+
To control statement event collection at server startup, use
lines like these in your my.cnf
file:
Enable:
[mysqld] performance-schema-instrument='statement/%=ON' performance-schema-consumer-events-statements-current=ON performance-schema-consumer-events-statements-history=ON performance-schema-consumer-events-statements-history-long=ON performance-schema-consumer-statements-digest=ON
Disable:
[mysqld] performance-schema-instrument='statement/%=OFF' performance-schema-consumer-events-statements-current=OFF performance-schema-consumer-events-statements-history=OFF performance-schema-consumer-events-statements-history-long=OFF performance-schema-consumer-statements-digest=OFF
To control statement event collection at runtime, update the
setup_instruments
and
setup_consumers
tables:
Enable:
UPDATE performance_schema.setup_instruments SET ENABLED = 'YES', TIMED = 'YES' WHERE NAME LIKE 'statement/%'; UPDATE performance_schema.setup_consumers SET ENABLED = 'YES' WHERE NAME LIKE '%statements%';
Disable:
UPDATE performance_schema.setup_instruments SET ENABLED = 'NO', TIMED = 'NO' WHERE NAME LIKE 'statement/%'; UPDATE performance_schema.setup_consumers SET ENABLED = 'NO' WHERE NAME LIKE '%statements%';
To collect only specific statement events, enable only the corresponding statement instruments. To collect statement events only for specific statement event tables, enable the statement instruments but only the statement consumers corresponding to the desired tables.
The setup_timers
table contains a
row with a NAME
value of
statement
that indicates the unit for
statement event timing. The default unit is
NANOSECOND
:
mysql>SELECT *
FROM performance_schema.setup_timers
WHERE NAME = 'statement';
+-----------+------------+ | NAME | TIMER_NAME | +-----------+------------+ | statement | NANOSECOND | +-----------+------------+
To change the timing unit, modify the
TIMER_NAME
value:
UPDATE performance_schema.setup_timers SET TIMER_NAME = 'MICROSECOND' WHERE NAME = 'statement';
For additional information about configuring event collection, see Section 25.3, “Performance Schema Startup Configuration”, and Section 25.4, “Performance Schema Runtime Configuration”.
Statement monitoring begins from the moment the server sees that activity is requested on a thread, to the moment when all activity has ceased. Typically, this means from the time the server gets the first packet from the client to the time the server has finished sending the response. Statements within stored programs are monitored like other statements.
When the Performance Schema instruments a request (server command or SQL statement), it uses instrument names that proceed in stages from more general (or “abstract”) to more specific until it arrives at a final instrument name.
Final instrument names correspond to server commands and SQL statements:
Server commands correspond to the
COM_
defined in the xxx
codesmysql_com.h
header file
and processed in sql/sql_parse.cc
.
Examples are COM_PING
and
COM_QUIT
. Instruments for commands have
names that begin with statement/com
, such
as statement/com/Ping
and
statement/com/Quit
.
SQL statements are expressed as text, such as
DELETE FROM t1
or SELECT * FROM
t2
. Instruments for SQL statements have names that
begin with statement/sql
, such as
statement/sql/delete
and
statement/sql/select
.
Some final instrument names are specific to error handling:
statement/com/Error
accounts for messages
received by the server that are out of band. It can be used
to detect commands sent by clients that the server does not
understand. This may be helpful for purposes such as
identifying clients that are misconfigured or using a
version of MySQL more recent than that of the server, or
clients that are attempting to attack the server.
statement/sql/error
accounts for SQL
statements that fail to parse. It can be used to detect
malformed queries sent by clients. A query that fails to
parse differs from a query that parses but fails due to an
error during execution. For example, SELECT *
FROM
is malformed, and the
statement/sql/error
instrument is used.
By contrast, SELECT *
parses but fails
with a No tables used
error. In this
case, statement/sql/select
is used and
the statement event contains information to indicate the
nature of the error.
A request can be obtained from any of these sources:
As a command or statement request from a client, which sends the request as packets
As a statement string read from the relay log on a replication slave
As an event from the Event Scheduler
The details for a request are not initially known and the Performance Schema proceeds from abstract to specific instrument names in a sequence that depends on the source of the request.
For a request received from a client:
When the server detects a new packet at the socket level, a
new statement is started with an abstract instrument name of
statement/abstract/new_packet
.
When the server reads the packet number, it knows more about
the type of request received, and the Performance Schema
refines the instrument name. For example, if the request is
a COM_PING
packet, the instrument name
becomes statement/com/Ping
and that is
the final name. If the request is a
COM_QUERY
packet, it is known to
correspond to an SQL statement but not the particular type
of statement. In this case, the instrument changes from one
abstract name to a more specific but still abstract name,
statement/abstract/Query
, and the request
requires further classification.
If the request is a statement, the statement text is read
and given to the parser. After parsing, the exact statement
type is known. If the request is, for example, an
INSERT
statement, the
Performance Schema refines the instrument name from
statement/abstract/Query
to
statement/sql/insert
, which is the final
name.
For a request read as a statement from the relay log on a replication slave:
Statements in the relay log are stored as text and are read
as such. There is no network protocol, so the
statement/abstract/new_packet
instrument
is not used. Instead, the initial instrument is
statement/abstract/relay_log
.
When the statement is parsed, the exact statement type is
known. If the request is, for example, an
INSERT
statement, the
Performance Schema refines the instrument name from
statement/abstract/Query
to
statement/sql/insert
, which is the final
name.
The preceding description applies only for statement-based replication. For row-based replication, table I/O done on the slave as it processes row changes can be instrumented, but row events in the relay log do not appear as discrete statements.
For a request received from the Event Scheduler:
The event execution is instrumented using the name
statement/scheduler/event
. This is the final
name.
Statements executed within the event body are instrumented using
statement/sql/*
names, without use of any
preceding abstract instrument. An event is a stored program, and
stored programs are precompiled in memory before execution.
Consequently, there is no parsing at runtime and the type of
each statement is known by the time it executes.
Statements executed within the event body are child statements.
For example, if an event executes an
INSERT
statement, execution of
the event itself is the parent, instrumented using
statement/scheduler/event
, and the
INSERT
is the child, instrumented
using statement/sql/insert
. The parent/child
relationship holds between separate
instrumented operations. This differs from the sequence of
refinement that occurs within a single
instrumented operation, from abstract to final instrument names.
For statistics to be collected for statements, it is not
sufficient to enable only the final
statement/sql/*
instruments used for
individual statement types. The abtract
statement/abstract/*
instruments must be
enabled as well. This should not normally be an issue because
all statement instruments are enabled by default. However, an
application that enables or disables statement instruments
selectively must take into account that disabling abstract
instruments also disables statistics collection for the
individual statement instruments. For example, to collect
statistics for INSERT
statements,
statement/sql/insert
must be enabled, but
also statement/abstract/new_packet
and
statement/abstract/Query
. Similarly, for
replicated statements to be instrumented,
statement/abstract/relay_log
must be enabled.
No statistics are aggregated for abstract instruments such as
statement/abstract/Query
because no statement
is ever classified with an abstract instrument as the final
statement name.
The events_statements_current
table contains current statement events. The table stores one
row per thread showing the current status of the thread's most
recent monitored statement event, so there is no system
variable for configuring the table size.
Of the tables that contain statement event rows,
events_statements_current
is the
most fundamental. Other tables that contain statement event
rows are logically derived from the current events. For
example, the
events_statements_history
and
events_statements_history_long
tables are collections of the most recent statement events
that have ended, up to a maximum number of rows per thread and
globally across all threads, respectively.
For more information about the relationship between the three
events_statements_
event tables, see
Section 25.9, “Performance Schema Tables for Current and Historical Events”.
xxx
For information about configuring whether to collect statement events, see Section 25.12.6, “Performance Schema Statement Event Tables”.
The events_statements_current
table has these columns:
THREAD_ID
, EVENT_ID
The thread associated with the event and the thread
current event number when the event starts. The
THREAD_ID
and
EVENT_ID
values taken together uniquely
identify the row. No two rows have the same pair of
values.
END_EVENT_ID
This column is set to NULL
when the
event starts and updated to the thread current event
number when the event ends.
EVENT_NAME
The name of the instrument from which the event was
collected. This is a NAME
value from
the setup_instruments
table.
Instrument names may have multiple parts and form a
hierarchy, as discussed in
Section 25.6, “Performance Schema Instrument Naming Conventions”.
For SQL statements, the EVENT_NAME
value initially is statement/com/Query
until the statement is parsed, then changes to a more
appropriate value, as described in
Section 25.12.6, “Performance Schema Statement Event Tables”.
SOURCE
The name of the source file containing the instrumented code that produced the event and the line number in the file at which the instrumentation occurs. This enables you to check the source to determine exactly what code is involved.
TIMER_START
,
TIMER_END
,
TIMER_WAIT
Timing information for the event. The unit for these
values is picoseconds (trillionths of a second). The
TIMER_START
and
TIMER_END
values indicate when event
timing started and ended. TIMER_WAIT
is
the event elapsed time (duration).
If an event has not finished, TIMER_END
is the current timer value and
TIMER_WAIT
is the time elapsed so far
(TIMER_END
−
TIMER_START
).
If an event is produced from an instrument that has
TIMED = NO
, timing information is not
collected, and TIMER_START
,
TIMER_END
, and
TIMER_WAIT
are all
NULL
.
For discussion of picoseconds as the unit for event times and factors that affect time values, see Section 25.4.1, “Performance Schema Event Timing”.
LOCK_TIME
The time spent waiting for table locks. This value is computed in microseconds but normalized to picoseconds for easier comparison with other Performance Schema timers.
SQL_TEXT
The text of the SQL statement. For a command not
associated with an SQL statement, the value is
NULL
.
The maximum space available for statement display is 1024
bytes by default. To change this value, set the
performance_schema_max_sql_text_length
system variable at server startup.
DIGEST
The statement digest MD5 value as a string of 32
hexadecimal characters, or NULL
if the
statements_digest
consumer is
no
. For more information about
statement digesting, see
Section 25.10, “Performance Schema Statement Digests”.
DIGEST_TEXT
The normalized statement digest text, or
NULL
if the
statements_digest
consumer is
no
. For more information about
statement digesting, see
Section 25.10, “Performance Schema Statement Digests”.
The
performance_schema_max_digest_length
system variable determines the maximum number of bytes
available per session for digest value storage. However,
the display length of statement digests may be longer than
the available buffer size due to encoding of statement
components such as keywords and literal values in digest
buffer. Consequently, values selected from the
DIGEST_TEXT
column of statement event
tables may appear to exceed the
performance_schema_max_digest_length
value.
CURRENT_SCHEMA
The default database for the statement,
NULL
if there is none.
OBJECT_SCHEMA
,
OBJECT_NAME
,
OBJECT_TYPE
For nested statements (stored programs), these columns
contain information about the parent statement. Otherwise
they are NULL
.
OBJECT_INSTANCE_BEGIN
This column identifies the statement. The value is the address of an object in memory.
MYSQL_ERRNO
The statement error number, from the statement diagnostics area.
RETURNED_SQLSTATE
The statement SQLSTATE value, from the statement diagnostics area.
MESSAGE_TEXT
The statement error message, from the statement diagnostics area.
ERRORS
Whether an error occurred for the statement. The value is
0 if the SQLSTATE value begins with 00
(completion) or 01
(warning). The value
is 1 is the SQLSTATE value is anything else.
WARNINGS
The number of warnings, from the statement diagnostics area.
ROWS_AFFECTED
The number of rows affected by the statement. For a description of the meaning of “affected,” see Section 27.7.6.1, “mysql_affected_rows()”.
ROWS_SENT
The number of rows returned by the statement.
ROWS_EXAMINED
The number of rows examined by the server layer (not counting any processing internal to storage engines).
CREATED_TMP_DISK_TABLES
Like the
Created_tmp_disk_tables
status variable, but specific to the statement.
CREATED_TMP_TABLES
Like the
Created_tmp_tables
status variable, but specific to the statement.
SELECT_FULL_JOIN
Like the
Select_full_join
status
variable, but specific to the statement.
SELECT_FULL_RANGE_JOIN
Like the
Select_full_range_join
status variable, but specific to the statement.
SELECT_RANGE
Like the Select_range
status variable, but specific to the statement.
SELECT_RANGE_CHECK
Like the
Select_range_check
status variable, but specific to the statement.
SELECT_SCAN
Like the Select_scan
status variable, but specific to the statement.
SORT_MERGE_PASSES
Like the
Sort_merge_passes
status
variable, but specific to the statement.
SORT_RANGE
Like the Sort_range
status variable, but specific to the statement.
SORT_ROWS
Like the Sort_rows
status variable, but specific to the statement.
SORT_SCAN
Like the Sort_scan
status variable, but specific to the statement.
NO_INDEX_USED
1 if the statement performed a table scan without using an index, 0 otherwise.
NO_GOOD_INDEX_USED
1 if the server found no good index to use for the
statement, 0 otherwise. For additional information, see
the description of the Extra
column
from EXPLAIN
output for the
Range checked for each record
value in
Section 8.8.2, “EXPLAIN Output Format”.
NESTING_EVENT_ID
,
NESTING_EVENT_TYPE
,
NESTING_EVENT_LEVEL
These three columns are used with other columns to provide information as follows for top-level (unnested) statements and nested statements (executed within a stored program).
For top level statements:
OBJECT_TYPE = NULL OBJECT_SCHEMA = NULL OBJECT_NAME = NULL NESTING_EVENT_ID = NULL NESTING_EVENT_TYPE = NULL NESTING_LEVEL = 0
For nested statements:
OBJECT_TYPE = the parent statement object type OBJECT_SCHEMA = the parent statement object schema OBJECT_NAME = the parent statement object name NESTING_EVENT_ID = the parent statement EVENT_ID NESTING_EVENT_TYPE = 'STATEMENT' NESTING_LEVEL = the parent statement NESTING_LEVEL plus one
TRUNCATE TABLE
is permitted for
the events_statements_current
table. It removes the rows.
The events_statements_history
table contains the N
most recent
statement events that have ended per thread. Statement events
are not added to the table until they have ended. When the
table contains the maximum number of rows for a given thread,
the oldest thread row is discarded when a new row for that
thread is added. When a thread ends, all its rows are
discarded.
The Performance Schema autosizes the value of
N
during server startup. To set the
number of rows per thread explicitly, set the
performance_schema_events_statements_history_size
system variable at server startup.
The events_statements_history
table has the same columns as
events_statements_current
. See
Section 25.12.6.1, “The events_statements_current Table”.
TRUNCATE TABLE
is permitted for
the events_statements_history
table. It removes the rows.
For more information about the relationship between the three
events_statements_
event tables, see
Section 25.9, “Performance Schema Tables for Current and Historical Events”.
xxx
For information about configuring whether to collect statement events, see Section 25.12.6, “Performance Schema Statement Event Tables”.
The
events_statements_history_long
table contains the N
most recent
statement events that have ended globally, across all threads.
Statement events are not added to the table until they have
ended. When the table becomes full, the oldest row is
discarded when a new row is added, regardless of which thread
generated either row.
The value of N
is autosized at
server startup. To set the table size explicitly, set the
performance_schema_events_statements_history_long_size
system variable at server startup.
The
events_statements_history_long
table has the same columns as
events_statements_current
. See
Section 25.12.6.1, “The events_statements_current Table”.
TRUNCATE TABLE
is permitted for
the
events_statements_history_long
table. It removes the rows.
For more information about the relationship between the three
events_statements_
event tables, see
Section 25.9, “Performance Schema Tables for Current and Historical Events”.
xxx
For information about configuring whether to collect statement events, see Section 25.12.6, “Performance Schema Statement Event Tables”.
The Performance Schema provides instrumentation for prepared statements, for which there are two protocols:
The binary protocol. This is accessed through the MySQL C API and maps onto underlying server commands as shown in the following table.
C API Function | Corresponding Server Command |
---|---|
mysql_stmt_prepare() |
COM_STMT_PREPARE |
mysql_stmt_execute() |
COM_STMT_EXECUTE |
mysql_stmt_close() |
COM_STMT_CLOSE |
The text protocol. This is accessed using SQL statements and maps onto underlying server commands as shown in the following table.
SQL Statement | Corresponding Server Command |
---|---|
PREPARE |
SQLCOM_PREPARE |
EXECUTE |
SQLCOM_EXECUTE |
DEALLOCATE PREPARE ,
DROP
PREPARE |
SQLCOM_DEALLOCATE PREPARE |
Performance Schema prepared statement instrumentation covers both protocols. The following discussion refers to the server commands rather than the C API functions or SQL statements.
Information about prepared statements is available in the
prepared_statements_instances
table. This table enables inspection of prepared statements
used in the server and provides aggregated statistics about
them. To control the size of this table, set the
performance_schema_max_prepared_statements_instances
system variable at server startup.
Collection of prepared statement information depends on the
statement instruments shown in the following table. These
instruments are enabled by default. To modify them, update the
setup_instruments
table.
Instrument | Server Command |
---|---|
statement/com/Prepare |
COM_STMT_PREPARE |
statement/com/Execute |
COM_STMT_EXECUTE |
statement/sql/prepare_sql |
SQLCOM_PREPARE |
statement/sql/execute_sql |
SQLCOM_EXECUTE |
The Performance Schema manages the contents of the
prepared_statements_instances
table as follows:
Statement preparation
A COM_STMT_PREPARE
or
SQLCOM_PREPARE
command creates a
prepared statement in the server. If the statement is
successfully instrumented, a new row is added to the
prepared_statements_instances
table. If the statement cannot be instrumented,
Performance_schema_prepared_statements_lost
status variable is incremented.
Prepared statement execution
Execution of a COM_STMT_EXECUTE
or
SQLCOM_PREPARE
command for an
instrumented prepared statement instance updates the
corresponding
prepared_statements_instances
table row.
Prepared statement deallocation
Execution of a COM_STMT_CLOSE
or
SQLCOM_DEALLOCATE_PREPARE
command for
an instrumented prepared statement instance removes the
corresponding
prepared_statements_instances
table row. To avoid resource leaks, removal occurs even if
the prepared statement instruments described previously
are disabled.
The prepared_statements_instances
table has these columns:
OBJECT_INSTANCE_BEGIN
The address in memory of the instrumented prepared statement.
STATEMENT_ID
The internal statement ID assigned by the server. The text and binary protocols both use statement IDs.
STATEMENT_NAME
For the binary protocol, this column is
NULL
. For the text protocol, this
column is the external statement name assigned by the
user. For example, for the following SQL statement, the
name of the prepared statement is stmt
:
PREPARE stmt FROM 'SELECT 1';
SQL_TEXT
The prepared statement text, with ?
placeholder markers.
OWNER_THREAD_ID
,
OWNER_EVENT_ID
These columns indicate the event that created the prepared statement.
OWNER_OBJECT_TYPE
,
OWNER_OBJECT_SCHEMA
,
OWNER_OBJECT_NAME
For a prepared statement created by a client session,
these columns are NULL
. For a prepared
statement created by a stored program, these columns point
to the stored program. A typical user error is forgetting
to deallocate prepared statements. These columns can be
used to find stored programs that leak prepared
statements:
SELECT OWNER_OBJECT_TYPE, OWNER_OBJECT_SCHEMA, OWNER_OBJECT_NAME, STATEMENT_NAME, SQL_TEXT FROM performance_schema.prepared_statements_instances WHERE OWNER_OBJECT_TYPE IS NOT NULL;
TIMER_PREPARE
The time spent executing the statement preparation itself.
COUNT_REPREPARE
The number of times the statement was reprepared internally (see Section 8.10.4, “Caching of Prepared Statements and Stored Programs”). Timing statistics for repreparation are not available because it is counted as part of statement execution, not as a separate operation.
COUNT_EXECUTE
,
SUM_TIMER_EXECUTE
,
MIN_TIMER_EXECUTE
,
AVG_TIMER_EXECUTE
,
MAX_TIMER_EXECUTE
Aggregated statistics for executions of the prepared statement.
SUM_
xxx
The remaining
SUM_
columns are the same as for the statement summary tables
(see Section 25.12.15.3, “Statement Summary Tables”).
xxx
TRUNCATE TABLE
resets the
statistics columns of the
prepared_statements_instances
table.
The Performance Schema instruments transactions. Within the event hierarchy, wait events nest within stage events, which nest within statement events, which nest within transaction events.
These tables store transaction events:
events_transactions_current
:
The current transaction event for each thread.
events_transactions_history
:
The most recent transaction events that have ended per
thread.
events_transactions_history_long
:
The most recent transaction events that have ended globally
(across all threads).
The following sections describe the transaction event tables. There are also summary tables that aggregate information about transaction events; see Section 25.12.15.4, “Transaction Summary Tables”.
For more information about the relationship between the three transaction event tables, see Section 25.9, “Performance Schema Tables for Current and Historical Events”.
To control whether to collect transaction events, set the state of the relevant instruments and consumers:
The setup_instruments
table
contains an instrument named transaction
.
Use this instrument to enable or disable collection of
individual transaction event classes.
The setup_consumers
table
contains consumer values with names corresponding to the
current and historical transaction event table names. Use
these consumers to filter collection of transaction events.
The transaction
instrument and the
transaction consumers are disabled by default:
mysql>SELECT *
FROM performance_schema.setup_instruments
WHERE NAME = 'transaction';
+-------------+---------+-------+ | NAME | ENABLED | TIMED | +-------------+---------+-------+ | transaction | NO | NO | +-------------+---------+-------+ mysql>SELECT *
FROM performance_schema.setup_consumers
WHERE NAME LIKE 'events_transactions%';
+----------------------------------+---------+ | NAME | ENABLED | +----------------------------------+---------+ | events_transactions_current | NO | | events_transactions_history | NO | | events_transactions_history_long | NO | +----------------------------------+---------+
To control transaction event collection at server startup, use
lines like these in your my.cnf
file:
Enable:
[mysqld] performance-schema-instrument='transaction=ON' performance-schema-consumer-events-transactions-current=ON performance-schema-consumer-events-transactions-history=ON performance-schema-consumer-events-transactions-history-long=ON
Disable:
[mysqld] performance-schema-instrument='transaction=OFF' performance-schema-consumer-events-transactions-current=OFF performance-schema-consumer-events-transactions-history=OFF performance-schema-consumer-events-transactions-history-long=OFF
To control transaction event collection at runtime, update the
setup_instruments
and
setup_consumers
tables:
Enable:
UPDATE performance_schema.setup_instruments SET ENABLED = 'YES', TIMED = 'YES' WHERE NAME = 'transaction'; UPDATE performance_schema.setup_consumers SET ENABLED = 'YES' WHERE NAME LIKE 'events_transactions%';
Disable:
UPDATE performance_schema.setup_instruments SET ENABLED = 'NO', TIMED = 'NO' WHERE NAME = 'transaction'; UPDATE performance_schema.setup_consumers SET ENABLED = 'NO' WHERE NAME LIKE 'events_transactions%';
To collect transaction events only for specific transaction
event tables, enable the transaction
instrument but only the transaction consumers corresponding to
the desired tables.
The setup_timers
table contains a
row with a NAME
value of
transaction
that indicates the unit for
transaction event timing. The default unit is
NANOSECOND
:
mysql>SELECT *
FROM performance_schema.setup_timers
WHERE NAME = 'transaction';
+-------------+------------+ | NAME | TIMER_NAME | +-------------+------------+ | transaction | NANOSECOND | +-------------+------------+
To change the timing unit, modify the
TIMER_NAME
value:
UPDATE performance_schema.setup_timers SET TIMER_NAME = 'MICROSECOND' WHERE NAME = 'transaction';
For additional information about configuring event collection, see Section 25.3, “Performance Schema Startup Configuration”, and Section 25.4, “Performance Schema Runtime Configuration”.
In MySQL Server, transactions start explicitly with these statements:
START TRANSACTION | BEGIN | XA START | XA BEGIN
Transactions also start implicitly. For example, when the
autocommit
system variable is
enabled, the start of each statement starts a new transaction.
When autocommit
is disabled,
the first statement following a committed transaction marks the
start of a new transaction. Subsequent statements are part of
the transaction until it is committed.
Transactions explicitly end with these statements:
COMMIT | ROLLBACK | XA COMMIT | XA ROLLBACK
Transactions also end implicitly, by execution of DDL statements, locking statements, and server administration statements.
In the following discussion, references to
START
TRANSACTION
also apply to
BEGIN
,
XA
START
, and
XA
BEGIN
. Similarly, references to
COMMIT
and
ROLLBACK
apply
to XA
COMMIT
and
XA
ROLLBACK
, respectively.
The Performance Schema defines transaction boundaries similarly to that of the server. The start and end of a transaction event closely match the corresponding state transitions in the server:
For an explicitly started transaction, the transaction event
starts during processing of the
START
TRANSACTION
statement.
For an implicitly started transaction, the transaction event starts on the first statement that uses a transactional engine after the previous transaction has ended.
For any transaction, whether explicitly or implicitly ended,
the transaction event ends when the server transitions out
of the active transaction state during the processing of
COMMIT
or
ROLLBACK
.
There are subtle implications to this approach:
Transaction events in the Performance Schema do not fully
include the statement events associated with the
corresponding START
TRANSACTION
,
COMMIT
, or
ROLLBACK
statements. There is a trivial amount of timing overlap
between the transaction event and these statements.
Statements that work with nontransactional engines have no
effect on the transaction state of the connection. For
implicit transactions, the transaction event begins with the
first statement that uses a transactional engine. This means
that statements operating exclusively on nontransactional
tables are ignored, even following
START
TRANSACTION
.
To illustrate, consider the following scenario:
1. SET autocommit = OFF; 2. CREATE TABLE t1 (a INT) ENGINE = InnoDB; 3. START TRANSACTION; -- Transaction 1 START 4. INSERT INTO t1 VALUES (1), (2), (3); 5. CREATE TABLE t2 (a INT) ENGINE = MyISAM; -- Transaction 1 COMMIT -- (implicit; DDL forces commit) 6. INSERT INTO t2 VALUES (1), (2), (3); -- Update nontransactional table 7. UPDATE t2 SET a = a + 1; -- ... and again 8. INSERT INTO t1 VALUES (4), (5), (6); -- Write to transactional table -- Transaction 2 START (implicit) 9. COMMIT; -- Transaction 2 COMMIT
From the perspective of the server, Transaction 1 ends when
table t2
is created. Transaction 2 does not
start until a transactional table is accessed, despite the
intervening updates to nontransactional tables.
From the perspective of the Performance Schema, Transaction 2 starts when the server transitions into an active transaction state. Statements 6 and 7 are not included within the boundaries of Transaction 2, which is consistent with how the server writes transactions to the binary log.
Three attributes define transactions:
Access mode (read only, read write)
Isolation level
(SERIALIZABLE
,
REPEATABLE READ
, and so
forth)
Implicit (autocommit
enabled) or explicit
(autocommit
disabled)
To reduce complexity of the transaction instrumentation and to ensure that the collected transaction data provides complete, meaningful results, all transactions are instrumented independently of access mode, isolation level, or autocommit mode.
To selectively examine transaction history, use the attribute
columns in the transaction event tables:
ACCESS_MODE
,
ISOLATION_LEVEL
, and
AUTOCOMMIT
.
The cost of transaction instrumentation can be reduced various ways, such as enabling or disabling transaction instrumentation according to user, account, host, or thread (client connection).
The parent of a transaction event is the event that initiated
the transaction. For an explicitly started transaction, this
includes the START
TRANSACTION
and
COMMIT AND
CHAIN
statements. For an implicitly started
transaction, it is the first statement that uses a transactional
engine after the previous transaction ends.
In general, a transaction is the top-level parent to all events
initiated during the transaction, including statements that
explicitly end the transaction such as
COMMIT
and
ROLLBACK
.
Exceptions are statements that implicitly end a transaction,
such as DDL statements, in which case the current transaction
must be committed before the new statement is executed.
Transactions and stored program events are related as follows:
Stored Procedures
Stored procedures operate independently of transactions. A stored procedure can be started within a transaction, and a transaction can be started or ended from within a stored procedure. If called from within a transaction, a stored procedure can execute statements that force a commit of the parent transaction and then start a new transaction.
If a stored procedure is started within a transaction, that transaction is the parent of the stored procedure event.
If a transaction is started by a stored procedure, the stored procedure is the parent of the transaction event.
Stored Functions
Stored functions are restricted from causing an explicit or implicit commit or rollback. Stored function events can reside within a parent transaction event.
Triggers
Triggers activate as part of a statement that accesses the table with which it is associated, so the parent of a trigger event is always the statement that activates it.
Triggers cannot issue statements that cause an explicit or implicit commit or rollback of a transaction.
Scheduled Events
The execution of the statements in the body of a scheduled event takes place in a new connection. Nesting of a scheduled event within a parent transaction is not applicable.
Savepoint statements are recorded as separate statement events.
Transaction events include separate counters for
SAVEPOINT
,
ROLLBACK TO
SAVEPOINT
, and
RELEASE
SAVEPOINT
statements issued during the transaction.
Errors and warnings that occur within a transaction are recorded in statement events, but not in the corresponding transaction event. This includes transaction-specific errors and warnings, such as a rollback on a nontransactional table or GTID consistency errors.
The events_transactions_current
table contains current transaction events. The table stores
one row per thread showing the current status of the thread's
most recent monitored transaction event, so there is no system
variable for configuring the table size. For example:
mysql>SELECT *
FROM performance_schema.events_transactions_current LIMIT 1\G
*************************** 1. row *************************** THREAD_ID: 26 EVENT_ID: 7 END_EVENT_ID: NULL EVENT_NAME: transaction STATE: ACTIVE TRX_ID: NULL GTID: 3E11FA47-71CA-11E1-9E33-C80AA9429562:56 XID: NULL XA_STATE: NULL SOURCE: transaction.cc:150 TIMER_START: 420833537900000 TIMER_END: NULL TIMER_WAIT: NULL ACCESS_MODE: READ WRITE ISOLATION_LEVEL: REPEATABLE READ AUTOCOMMIT: NO NUMBER_OF_SAVEPOINTS: 0 NUMBER_OF_ROLLBACK_TO_SAVEPOINT: 0 NUMBER_OF_RELEASE_SAVEPOINT: 0 OBJECT_INSTANCE_BEGIN: NULL NESTING_EVENT_ID: 6 NESTING_EVENT_TYPE: STATEMENT
Of the tables that contain transaction event rows,
events_transactions_current
is
the most fundamental. Other tables that contain transaction
event rows are logically derived from the current events. For
example, the
events_transactions_history
and
events_transactions_history_long
tables are collections of the most recent transaction events
that have ended, up to a maximum number of rows per thread and
globally across all threads, respectively.
For more information about the relationship between the three transaction event tables, see Section 25.9, “Performance Schema Tables for Current and Historical Events”.
For information about configuring whether to collect transaction events, see Section 25.12.7, “Performance Schema Transaction Tables”.
The events_transactions_current
table has these columns:
THREAD_ID
, EVENT_ID
The thread associated with the event and the thread
current event number when the event starts. The
THREAD_ID
and
EVENT_ID
values taken together uniquely
identify the row. No two rows have the same pair of
values.
END_EVENT_ID
This column is set to NULL
when the
event starts and updated to the thread current event
number when the event ends.
EVENT_NAME
The name of the instrument from which the event was
collected. This is a NAME
value from
the setup_instruments
table.
Instrument names may have multiple parts and form a
hierarchy, as discussed in
Section 25.6, “Performance Schema Instrument Naming Conventions”.
STATE
The current transaction state. The value is
ACTIVE
(after
START
TRANSACTION
or
BEGIN
),
COMMITTED
(after
COMMIT
), or ROLLED
BACK
(after
ROLLBACK
).
TRX_ID
Unused.
GTID
The GTID column contains the value of
gtid_next
, which can be
one of ANONYMOUS
,
AUTOMATIC
, or a GTID using the format
UUID:NUMBER
. For transactions that use
gtid_next=AUTOMATIC
,
which is all normal client transactions, the GTID column
changes when the transaction commits and the actual GTID
is assigned. If gtid_mode
is either ON
or
ON_PERMISSIVE
, the GTID column changes
to the transaction's GTID. If gtid_mode
is either OFF
or
OFF_PERMISSIVE
, the GTID column changes
to ANONYMOUS
.
XID_FORMAT_ID
,
XID_GTRID
, and
XID_BQUAL
The components of the XA transaction identifier. They have the format described in Section 13.3.7.1, “XA Transaction SQL Statements”.
XA_STATE
The state of the XA transaction. The value is
ACTIVE
(after
XA
START
), IDLE
(after
XA
END
), PREPARED
(after
XA
PREPARE
), ROLLED BACK
(after
XA
ROLLBACK
), or COMMITTED
(after XA
COMMIT
).
On a replication slave, the same XA transaction can appear
in the
events_transactions_current
table with different states on different threads. This is
because immediately after the XA transaction is prepared,
it is detached from the slave applier thread, and can be
committed or rolled back by any thread on the slave. The
events_transactions_current
table displays the current status of the most recent
monitored transaction event on the thread, and does not
update this status when the thread is idle. So the XA
transaction can still be displayed in the
PREPARED
state for the original applier
thread, after it has been processed by another thread. To
positively identify XA transactions that are still in the
PREPARED
state and need to be
recovered, use the
XA
RECOVER
statement rather than the Performance
Schema transaction tables.
SOURCE
The name of the source file containing the instrumented code that produced the event and the line number in the file at which the instrumentation occurs. This enables you to check the source to determine exactly what code is involved.
TIMER_START
,
TIMER_END
,
TIMER_WAIT
Timing information for the event. The unit for these
values is picoseconds (trillionths of a second). The
TIMER_START
and
TIMER_END
values indicate when event
timing started and ended. TIMER_WAIT
is
the event elapsed time (duration).
If an event has not finished, TIMER_END
is the current timer value and
TIMER_WAIT
is the time elapsed so far
(TIMER_END
−
TIMER_START
).
If an event is produced from an instrument that has
TIMED = NO
, timing information is not
collected, and TIMER_START
,
TIMER_END
, and
TIMER_WAIT
are all
NULL
.
For discussion of picoseconds as the unit for event times and factors that affect time values, see Section 25.4.1, “Performance Schema Event Timing”.
ACCESS_MODE
The transaction access mode. The value is READ
WRITE
or READ ONLY
.
ISOLATION_LEVEL
The transaction isolation level. The value is
REPEATABLE READ
,
READ COMMITTED
,
READ UNCOMMITTED
, or
SERIALIZABLE
.
AUTOCOMMIT
Whether autcommit mode was enabled when the transaction started.
NUMBER_OF_SAVEPOINTS
,
NUMBER_OF_ROLLBACK_TO_SAVEPOINT
,
NUMBER_OF_RELEASE_SAVEPOINT
The number of SAVEPOINT
,
ROLLBACK TO
SAVEPOINT
, and
RELEASE
SAVEPOINT
statements issued during the
transaction.
OBJECT_INSTANCE_BEGIN
Unused.
NESTING_EVENT_ID
The EVENT_ID
value of the event within
which this event is nested.
NESTING_EVENT_TYPE
The nesting event type. The value is
TRANSACTION
,
STATEMENT
, STAGE
, or
WAIT
. (TRANSACTION
will not appear because transactions cannot be nested.)
TRUNCATE TABLE
is permitted for
the events_transactions_current
table. It removes the rows.
The events_transactions_history
table contains the N
most recent
transaction events that have ended per thread. Transaction
events are not added to the table until they have ended. When
the table contains the maximum number of rows for a given
thread, the oldest thread row is discarded when a new row for
that thread is added. When a thread ends, all its rows are
discarded.
The Performance Schema autosizes the value of
N
during server startup. To set the
number of rows per thread explicitly, set the
performance_schema_events_transactions_history_size
system variable at server startup.
The events_transactions_history
table has the same columns as
events_transactions_current
. See
Section 25.12.7.1, “The events_transactions_current Table”.
TRUNCATE TABLE
is permitted for
the events_transactions_history
table. It removes the rows.
For more information about the relationship between the three transaction event tables, see Section 25.9, “Performance Schema Tables for Current and Historical Events”.
For information about configuring whether to collect transaction events, see Section 25.12.7, “Performance Schema Transaction Tables”.
The
events_transactions_history_long
table contains the N
most recent
transaction events that have ended globally, across all
threads. Transaction events are not added to the table until
they have ended. When the table becomes full, the oldest row
is discarded when a new row is added, regardless of which
thread generated either row.
The Performance Schema autosizes the value of
N
is autosized at server startup.
To set the table size explicitly, set the
performance_schema_events_transactions_history_long_size
system variable at server startup.
The
events_transactions_history_long
table has the same columns as
events_transactions_current
. See
Section 25.12.7.1, “The events_transactions_current Table”.
TRUNCATE TABLE
is permitted for
the
events_transactions_history_long
table. It removes the rows.
For more information about the relationship between the three transaction event tables, see Section 25.9, “Performance Schema Tables for Current and Historical Events”.
For information about configuring whether to collect transaction events, see Section 25.12.7, “Performance Schema Transaction Tables”.
When a client connects to the MySQL server, it does so under a particular user name and from a particular host. The Performance Schema provides statistics about these connections, tracking them per account (user and host combination) as well as separately per user name and host name, using these tables:
The meaning of “account” in the connection tables
is similar to its meaning in the MySQL grant tables in the
mysql
system database, in the sense that the
term refers to a combination of user and host values. They
differ in that, for grant tables, the host part of an account
can be a pattern, whereas for Performance Schema tables, the
host value is always a specific nonpattern host name.
Each connection table has CURRENT_CONNECTIONS
and TOTAL_CONNECTIONS
columns to track the
current and total number of connections per “tracking
value” on which its statistics are based. The tables
differ in what they use for the tracking value. The
accounts
table has
USER
and HOST
columns to
track connections per user and host combination. The
users
and
hosts
tables have a
USER
and HOST
column,
respectively, to track connections per user name and host name.
The Performance Schema also counts internal threads and threads
for user sessions that failed to authenticate, using rows with
USER
and HOST
column
values of NULL
.
Suppose that clients named user1
and
user2
each connect one time from
hosta
and hostb
. The
Performance Schema tracks the connections as follows:
The accounts
table has four
rows, for the
user1
/hosta
,
user1
/hostb
,
user2
/hosta
, and
user2
/hostb
account
values, each row counting one connection per account.
The hosts
table has two rows,
for hosta
and hostb
,
each row counting two connections per host name.
The users
table has two rows,
for user1
and user2
,
each row counting two connections per user name.
When a client connects, the Performance Schema determines which
row in each connection table applies, using the tracking value
appropriate to each table. If there is no such row, one is
added. Then the Performance Schema increments by one the
CURRENT_CONNECTIONS
and
TOTAL_CONNECTIONS
columns in that row.
When a client disconnects, the Performance Schema decrements by
one the CURRENT_CONNECTIONS
column in the row
and leaves the TOTAL_CONNECTIONS
column
unchanged.
TRUNCATE TABLE
is permitted for
connection tables. It has these effects:
Rows are removed for accounts, hosts, or users that have no
current connections (rows with CURRENT_CONNECTIONS
= 0
).
Nonremoved rows are reset to count only current connections:
For rows with CURRENT_CONNECTIONS > 0
,
TOTAL_CONNECTIONS
is reset to
CURRENT_CONNECTIONS
.
Summary tables that depend on the connection table are implicitly truncated, as described later in this section.
The Performance Schema maintains summary tables that aggregate
connection statistics for various event types by account, host,
or user. These tables have
_summary_by_account
,
_summary_by_host
, or
_summary_by_user
in the name. To identify
them, use this query:
mysql>SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES
WHERE TABLE_SCHEMA = 'performance_schema'
AND TABLE_NAME REGEXP '_summary_by_(account|host|user)'
ORDER BY TABLE_NAME;
+------------------------------------------------------+ | TABLE_NAME | +------------------------------------------------------+ | events_stages_summary_by_account_by_event_name | | events_stages_summary_by_host_by_event_name | | events_stages_summary_by_user_by_event_name | | events_statements_summary_by_account_by_event_name | | events_statements_summary_by_host_by_event_name | | events_statements_summary_by_user_by_event_name | | events_transactions_summary_by_account_by_event_name | | events_transactions_summary_by_host_by_event_name | | events_transactions_summary_by_user_by_event_name | | events_waits_summary_by_account_by_event_name | | events_waits_summary_by_host_by_event_name | | events_waits_summary_by_user_by_event_name | | memory_summary_by_account_by_event_name | | memory_summary_by_host_by_event_name | | memory_summary_by_user_by_event_name | +------------------------------------------------------+
For details about individual connection summary tables, consult the section that describes tables for the summarized event type:
Wait event summaries: Section 25.12.15.1, “Wait Event Summary Tables”
Stage event summaries: Section 25.12.15.2, “Stage Summary Tables”
Statement event summaries: Section 25.12.15.3, “Statement Summary Tables”
Transaction event summaries: Section 25.12.15.4, “Transaction Summary Tables”
Memory event summaries: Section 25.12.15.9, “Memory Summary Tables”
TRUNCATE TABLE
is permitted for
connection summary tables. It removes rows for accounts, hosts,
or users with no connections, and resets the summary columns to
zero for the remaining rows. In addition, each summary table
that is aggregated by account, host, user, or thread is
implicitly truncated by truncation of the connection table on
which it depends. The following table describes the relationship
between connection table truncation and implicitly truncated
tables.
Table 25.2 Implicit Effects of Connection Table Truncation
Truncated Connection Table | Implicitly Truncated Summary Tables |
---|---|
accounts |
Tables with names containing _summary_by_account ,
_summary_by_thread |
hosts |
Tables with names containing _summary_by_account ,
_summary_by_host ,
_summary_by_thread |
users |
Tables with names containing _summary_by_account ,
_summary_by_user ,
_summary_by_thread |
Truncating a _summary_global
summary table
also implicitly truncates its corresponding connection and
thread summary tables. For example, truncating
events_waits_summary_global_by_event_name
implicitly truncates the wait event summary tables that are
aggregated by account, host, user, or thread.
The accounts
table contains a row
for each account that has connected to the MySQL server. For
each account, the table counts the current and total number of
connections. The table size is autosized at server startup. To
set the table size explicitly, set the
performance_schema_accounts_size
system variable at server startup. To disable account
statistics, set this variable to 0.
The accounts
table has the
following columns. For a description of how the Performance
Schema maintains rows in this table, including the effect of
TRUNCATE TABLE
, see
Section 25.12.8, “Performance Schema Connection Tables”.
USER
The client user name for the connection. This is
NULL
for an internal thread, or for a
user session that failed to authenticate.
HOST
The host from which the client connected. This is
NULL
for an internal thread, or for a
user session that failed to authenticate.
CURRENT_CONNECTIONS
The current number of connections for the account.
TOTAL_CONNECTIONS
The total number of connections for the account.
The hosts
table contains a row
for each host from which clients have connected to the MySQL
server. For each host name, the table counts the current and
total number of connections. The table size is autosized at
server startup. To set the table size explicitly, set the
performance_schema_hosts_size
system variable at server startup. To disable host statistics,
set this variable to 0.
The hosts
table has the following
columns. For a description of how the Performance Schema
maintains rows in this table, including the effect of
TRUNCATE TABLE
, see
Section 25.12.8, “Performance Schema Connection Tables”.
HOST
The host from which the client connected. This is
NULL
for an internal thread, or for a
user session that failed to authenticate.
CURRENT_CONNECTIONS
The current number of connections for the host.
TOTAL_CONNECTIONS
The total number of connections for the host.
The users
table contains a row
for each user who has connected to the MySQL server. For each
user name, the table counts the current and total number of
connections. The table size is autosized at server startup. To
set the table size explicitly, set the
performance_schema_users_size
system variable at server startup. To disable user statistics,
set this variable to 0.
The users
table has the following
columns. For a description of how the Performance Schema
maintains rows in this table, including the effect of
TRUNCATE TABLE
, see
Section 25.12.8, “Performance Schema Connection Tables”.
USER
The client user name for the connection. This is
NULL
for an internal thread, or for a
user session that failed to authenticate.
CURRENT_CONNECTIONS
The current number of connections for the user.
TOTAL_CONNECTIONS
The total number of connections for the user.
Connection attributes are key-value pairs that application
programs can pass to the server at connect time. For
applications based on the C API implemented by the
libmysqlclient
client library, the
mysql_options()
and
mysql_options4()
functions
define the connection attribute set. Other MySQL Connectors may
provide their own attribute-definition methods.
These Performance Schema tables expose attribute information:
session_account_connect_attrs
:
Connection attributes for the current session, and other
sessions associated with the session account
session_connect_attrs
:
Connection attributes for all sessions
Attribute names that begin with an underscore
(_
) are reserved for internal use and should
not be created by application programs. This convention permits
new attributes to be introduced by MySQL without colliding with
application attributes, and enables application programs to
define their own attributes that do not collide with internal
attributes.
The set of connection attributes visible within a given connection varies depending on factors such as your platform, MySQL Connector used to establish the connection, or client program.
The libmysqlclient
client library sets these
attributes:
_client_name
: The client name
(libmysql
for the client library).
_client_version
: The client library
version.
_os
: The operating system (for example,
Linux
, Win64
).
_pid
: The client process ID.
_platform
: The machine platform (for
example, x86_64
).
_thread
: The client thread ID (Windows
only).
Other MySQL Connectors may define their own connection attributes.
MySQL Connector/J defines these attributes:
_client_license
: The connector license
type.
_runtime_vendor
: The Java runtime
environment (JRE) vendor.
_runtime_version
: The Java runtime
environment (JRE) version.
MySQL Connector/NET defines these attributes:
_client_version
: The client library
version.
_os
: The operating system (for example,
Linux
, Win64
).
_pid
: The client process ID.
_platform
: The machine platform (for
example, x86_64
).
_program_name
: The client name.
_thread
: The client thread ID (Windows
only).
PHP defines attributes that depend on how it was compiled:
Compiled using libmysqlclient
: The
standard libmysqlclient
attributes,
described previously.
Compiled using mysqlnd
: Only the
_client_name
attribute, with a value of
mysqlnd
.
Many MySQL client programs set a program_name
attribute with a value equal to the client name. For example,
mysqladmin and mysqldump
set program_name
to
mysqladmin
and mysqldump
,
respectively.
Some MySQL client programs define additional attributes:
_client_role
:
binary_log_listener
Replication slave connections:
program_name
:
mysqld
_client_role
:
binary_log_listener
_client_replication_channel_name
: The
channel name.
FEDERATED
storage engine
connections:
program_name
:
mysqld
_client_role
:
federated_storage
There are limits on the amount of connection attribute data transmitted from client to server:
A fixed limit imposed by the client prior to connect time.
A fixed limit imposed by the server at connect time.
A configurable limit imposed by the Performance Schema at connect time.
For connections initiated using the C API, the
libmysqlclient
library imposes a limit of
64KB on the aggregate size of connection attribute data on the
client side: Calls to
mysql_options()
that cause this
limit to be exceeded produce a
CR_INVALID_PARAMETER_NO
error.
Other MySQL Connectors may impose their own client-side limits
on how much connection attribute data can be transmitted to the
server.
On the server side, these size checks on connection attribute data occur:
The server imposes a limit of 64KB on the aggregate size of connection attribute data it will accept. If a client attempts to send more than 64KB of attribute data, the server rejects the connection.
For accepted connections, the Performance Schema checks
aggregate attribute size against the value of the
performance_schema_session_connect_attrs_size
system variable. If attribute size exceeds this value, these
actions take place:
The Performance Schema truncates the attribute data and
increments the
Performance_schema_session_connect_attrs_lost
status variable, which indicates the number of
connections for which attribute truncation occurred.
The Performance Schema writes a message to the error log
if the
log_error_verbosity
system variable is greater than 1:
[Warning] Connection attributes of length N
were truncated
Application programs can provide key-value connection attributes to be passed to the server at connect time. For descriptions of common attributes, see Section 25.12.9, “Performance Schema Connection Attribute Tables”.
The session_account_connect_attrs
table contains connection attributes only for the current
session, and other sessions associated with the session
account. To see connection attributes for all sessions, use
the session_connect_attrs
table.
The session_account_connect_attrs
table contains these columns:
PROCESSLIST_ID
The connection identifier for the session.
ATTR_NAME
The attribute name.
ATTR_VALUE
The attribute value.
ORDINAL_POSITION
The order in which the attribute was added to the set of connection attributes.
TRUNCATE TABLE
is not permitted
for the
session_account_connect_attrs
table.
Application programs can provide key-value connection attributes to be passed to the server at connect time. For descriptions of common attributes, see Section 25.12.9, “Performance Schema Connection Attribute Tables”.
The session_connect_attrs
table
contains connection attributes for all sessions. To see
connection attributes only for the current session, and other
sessions associated with the session account, use the
session_account_connect_attrs
table.
The session_connect_attrs
table
contains these columns:
PROCESSLIST_ID
The connection identifier for the session.
ATTR_NAME
The attribute name.
ATTR_VALUE
The attribute value.
ORDINAL_POSITION
The order in which the attribute was added to the set of connection attributes.
TRUNCATE TABLE
is not permitted
for the session_connect_attrs
table.
The Performance Schema provides a
user_variables_by_thread
table that
exposes user-defined variables. These are variables defined
within a specific session and include a @
character preceding the name; see
Section 9.4, “User-Defined Variables”.
The user_variables_by_thread
table
contains these columns:
THREAD_ID
The thread identifier of the session in which the variable is defined.
VARIABLE_NAME
The variable name, without the leading @
character.
VARIABLE_VALUE
The variable value.
TRUNCATE TABLE
is not permitted
for the user_variables_by_thread
table.
The Performance Schema provides tables that expose replication
information. This is similar to the information available from
the SHOW SLAVE STATUS
statement,
but representation in table form is more accessible and has
usability benefits:
SHOW SLAVE STATUS
output is
useful for visual inspection, but not so much for
programmatic use. By contrast, using the Performance Schema
tables, information about slave status can be searched using
general SELECT
queries,
including complex WHERE
conditions,
joins, and so forth.
Query results can be saved in tables for further analysis, or assigned to variables and thus used in stored procedures.
The replication tables provide better diagnostic
information. For multithreaded slave operation,
SHOW SLAVE STATUS
reports all
coordinator and worker thread errors using the
Last_SQL_Errno
and
Last_SQL_Error
fields, so only the most
recent of those errors is visible and information can be
lost. The replication tables store errors on a per-thread
basis without loss of information.
The last seen transaction is visible in the replication
tables on a per-worker basis. This is information not
avilable from SHOW SLAVE
STATUS
.
Developers familiar with the Performance Schema interface can extend the replication tables to provide additional information by adding rows to the tables.
The Performance Schema provides the following replication-related tables:
Tables that contain information about the connection of the slave server to the master server:
replication_connection_configuration
:
Configuration parameters for connecting to the master
replication_connection_status
:
Current status of the connection to the master
Tables that contain general (not thread-specific) information about the transaction applier:
replication_applier_configuration
:
Configuration parameters for the transaction applier on
the slave.
replication_applier_status
:
Current status of the transaction applier on the slave.
Tables that contain information about specific threads responsible for applying transactions received from the master:
replication_applier_status_by_coordinator
:
Status of the coordinator thread (empty unless the slave
is multithreaded).
replication_applier_status_by_worker
:
Status of the applier thread or worker threads if the
slave is multithreaded.
Tables that contain information about replication group members:
replication_group_members
:
Provides network and status information for group
members.
replication_group_member_stats
:
Provides statistical information about group members and
transaction in which they participate.
The following sections describe each replication table in more
detail, including the correspondence between the columns
produced by SHOW SLAVE STATUS
and
the replication table columns in which the same information
appears.
The remainder of this introduction to the replication tables
describes how the Performance Schema populates them and which
fields from SHOW SLAVE STATUS
are
not represented in the tables.
The Performance Schema populates the replication tables as follows:
Prior to execution of CHANGE MASTER
TO
, the tables are empty.
After CHANGE MASTER TO
, the
configuration parameters can be seen in the tables. At this
time, there are no active slave threads, so the
THREAD_ID
columns are
NULL
and the
SERVICE_STATE
columns have a value of
OFF
.
After START SLAVE
,
non-NULL
THREAD_ID
values can be seen. Threads that are idle or active have a
SERVICE_STATE
value of
ON
. The thread that connects to the
master server has a value of CONNECTING
while it establishes the connection, and
ON
thereafter as long as the connection
lasts.
After STOP SLAVE
, the
THREAD_ID
columns become
NULL
and the
SERVICE_STATE
columns for threads that no
longer exist have a value of OFF
.
The tables are preserved after STOP
SLAVE
or threads dying due to an error.
The
replication_applier_status_by_worker
table is nonempty only when the slave is operating in
multithreaded mode. That is, if the
slave_parallel_workers
system variable is greater than 0, this table is populated
when START SLAVE
is executed,
and the number of rows shows the number of workers.
The information in the Performance Schema replication tables
differs somewhat from the information available from
SHOW SLAVE STATUS
because the
tables are oriented toward use of global transaction identifiers
(GTIDs), not file names and positions, and they represent server
UUID values, not server ID values. Due to these differences,
several SHOW SLAVE STATUS
columns
are not preserved in the Performance Schema replication tables,
or are represented a different way:
The following fields refer to file names and positions and are not preserved:
Master_Log_File Read_Master_Log_Pos Relay_Log_File Relay_Log_Pos Relay_Master_Log_File Exec_Master_Log_Pos Until_Condition Until_Log_File Until_Log_Pos
The Master_Info_File
field is not
preserved. It refers to the master.info
file, which has been superseded by crash-safe slave tables.
The following fields are based on
server_id
, not
server_uuid
, and are not
preserved:
Master_Server_Id Replicate_Ignore_Server_Ids
The Skip_Counter
field is based on event
counts, not GTIDs, and is not preserved.
These error fields are aliases for
Last_SQL_Errno
and
Last_SQL_Error
, so they are not
preserved:
Last_Errno Last_Error
In the Performance Schema, this error information is
available in the LAST_ERROR_NUMBER
and
LAST_ERROR_MESSAGE
columns of the
replication_applier_status_by_coordinator
table (and
replication_applier_status_by_worker
if the slave is multithreaded). Those tables provide more
specific per-thread error information than is available from
Last_Errno
and
Last_Error
.
Fields that provide information about command-line filtering options is not preserved:
Replicate_Do_DB Replicate_Ignore_DB Replicate_Do_Table Replicate_Ignore_Table Replicate_Wild_Do_Table Replicate_Wild_Ignore_Table
The Slave_IO_State
and
Slave_SQL_Running_State
fields are not
preserved. If needed, these values can be obtained from the
process list by using the THREAD_ID
column of the appropriate replication table and joining it
with the ID
column in the
INFORMATION_SCHEMA
PROCESSLIST
table to select the
STATE
column of the latter table.
The Executed_Gtid_Set
field can show a
large set with a great deal of text. Instead, the
Performance Schema tables show GTIDs of transactions that
are currently being applied by the slave. Alternatively, the
set of executed GTIDs can be obtained from the value of the
gtid_executed
system
variable.
The Seconds_Behind_Master
and
Relay_Log_Space
fields are in
to-be-decided status and are not preserved.
As of MySQL version 5.7.5, the following status variables
(previously monitored using SHOW
STATUS
) were moved to the Perfomance Schema
replication tables:
These status variables are now only relevant when a single replication channel is being used because they only report the status of the default replication channel. When multiple replication channels exist, use the Performance Schema replication tables described in this section, which report these variables for each existing replication channel.
The first column of the replication Performance Schema tables is
CHANNEL_NAME
. This enables the tables to be
viewed per replication channel. In a non-multisource replication
setup there is a single default replication channel. When you
are using multiple replication channels on a slave, you can
filter the tables per replication channel to monitor a specific
replication channel. See Section 16.2.3, “Replication Channels”
and Section 16.1.4.8, “Multi-Source Replication Monitoring” for
more information.
This table shows the configuration parameters used by the
slave server for connecting to the master server. Parameters
stored in the table can be changed at runtime with the
CHANGE MASTER TO
statement, as
indicated in the column descriptions.
Compared to the
replication_connection_status
table,
replication_connection_configuration
changes less frequently. It contains values that define how
the slave connects to the master and that remain constant
during the connection, whereas
replication_connection_status
contains values that change during the connection.
The
replication_connection_configuration
table has the following columns. The column descriptions
indicate the corresponding CHANGE MASTER TO
options from which the column values are taken, and the table
given later in this section shows the correspondence between
replication_connection_configuration
columns and SHOW SLAVE STATUS
columns.
CHANNEL_NAME
The replication channel which this row is displaying.
There is always a default replication channel, and more
replication channels can be added. See
Section 16.2.3, “Replication Channels” for more
information. (CHANGE MASTER TO
option:
FOR CHANNEL
)
HOST
The master host that the slave is connected to.
(CHANGE MASTER TO
option:
MASTER_HOST
)
PORT
The port used to connect to the master. (CHANGE
MASTER TO
option:
MASTER_PORT
)
USER
The user name of the account used to connect to the
master. (CHANGE MASTER TO
option:
MASTER_USER
)
NETWORK_INTERFACE
The network interface that the slave is bound to, if any.
(CHANGE MASTER TO
option:
MASTER_BIND
)
AUTO_POSITION
1 if autopositioning is in use; otherwise 0.
(CHANGE MASTER TO
option:
MASTER_AUTO_POSITION
)
SSL_ALLOWED
,
SSL_CA_FILE
,
SSL_CA_PATH
,
SSL_CERTIFICATE
,
SSL_CIPHER
, SSL_KEY
,
SSL_VERIFY_SERVER_CERTIFICATE
,
SSL_CRL_FILE
,
SSL_CRL_PATH
These columns show the SSL parameters used by the slave to connect to the master, if any.
SSL_ALLOWED
has these values:
Yes
if an SSL connection to the
master is permitted
No
if an SSL connection to the
master is not permitted
Ignored
if an SSL connection is
permitted but the slave server does not have SSL
support enabled
CHANGE MASTER TO
options for the other
SSL columns: MASTER_SSL_CA
,
MASTER_SSL_CAPATH
,
MASTER_SSL_CERT
,
MASTER_SSL_CIPHER
,
MASTER_SSL_CRL
,
MASTER_SSL_CRLPATH
,
MASTER_SSL_KEY
,
MASTER_SSL_VERIFY_SERVER_CERT
.
CONNECTION_RETRY_INTERVAL
The number of seconds between connect retries.
(CHANGE MASTER TO
option:
MASTER_CONNECT_RETRY
)
CONNECTION_RETRY_COUNT
The number of times the slave can attempt to reconnect to
the master in the event of a lost connection.
(CHANGE MASTER TO
option:
MASTER_RETRY_COUNT
)
HEARTBEAT_INTERVAL
The replication heartbeat interval on a slave, measured in
seconds. (CHANGE MASTER TO
option:
MASTER_HEARTBEAT_PERIOD
)
TLS_VERSION
The TLS version used on the master. For TLS version
information, see
Section 6.3.2, “Encrypted Connection TLS Protocols and Ciphers”.
(CHANGE MASTER TO
option:
MASTER_TLS_VERSION
)
This column was added in MySQL 5.7.10.
TRUNCATE TABLE
is not permitted
for the
replication_connection_configuration
table.
The following table shows the correspondence between
replication_connection_configuration
columns and SHOW SLAVE STATUS
columns.
replication_connection_configuration Column |
SHOW SLAVE STATUS Column |
---|---|
CHANNEL_NAME |
Channel_name |
HOST |
Master_Host |
PORT |
Master_Port |
USER |
Master_User |
NETWORK_INTERFACE |
Master_Bind |
AUTO_POSITION |
Auto_Position |
SSL_ALLOWED |
Master_SSL_Allowed |
SSL_CA_FILE |
Master_SSL_CA_File |
SSL_CA_PATH |
Master_SSL_CA_Path |
SSL_CERTIFICATE |
Master_SSL_Cert |
SSL_CIPHER |
Master_SSL_Cipher |
SSL_KEY |
Master_SSL_Key |
SSL_VERIFY_SERVER_CERTIFICATE |
Master_SSL_Verify_Server_Cert |
SSL_CRL_FILE |
Master_SSL_Crl |
SSL_CRL_PATH |
Master_SSL_Crlpath |
CONNECTION_RETRY_INTERVAL |
Connect_Retry |
CONNECTION_RETRY_COUNT |
Master_Retry_Count |
HEARTBEAT_INTERVAL |
None |
TLS_VERSION |
Master_TLS_Version |
This table shows the current status of the I/O thread that handles the slave server connection to the master server.
Compared to the
replication_connection_configuration
table,
replication_connection_status
changes more frequently. It contains values that change during
the connection, whereas
replication_connection_configuration
contains values which define how the slave connects to the
master and that remain constant during the connection.
The replication_connection_status
table has these columns:
CHANNEL_NAME
The replication channel which this row is displaying. There is always a default replication channel, and more replication channels can be added. See Section 16.2.3, “Replication Channels” for more information.
GROUP_NAME
If this server is a member of a group, shows the name of the group the server belongs to.
SOURCE_UUID
The server_uuid
value
from the master.
THREAD_ID
The I/O thread ID.
SERVICE_STATE
ON
(thread exists and is active or
idle), OFF
(thread no longer exists),
or CONNECTING
(thread exists and is
connecting to the master).
RECEIVED_TRANSACTION_SET
The set of global transaction IDs (GTIDs) corresponding to all transactions received by this slave. Empty if GTIDs are not in use. See GTID Sets for more information.
LAST_ERROR_NUMBER
,
LAST_ERROR_MESSAGE
The error number and error message of the most recent
error that caused the I/O thread to stop. An error number
of 0 and message of the empty string mean “no
error.” If the
LAST_ERROR_MESSAGE
value is not empty,
the error values also appear in the slave's error log.
Issuing RESET MASTER
or
RESET SLAVE
resets the
values shown in these columns.
LAST_ERROR_TIMESTAMP
A timestamp in YYMMDD hh:mm:ss
format that shows when the most recent I/O error took
place.
LAST_HEARTBEAT_TIMESTAMP
A timestamp in YYMMDD hh:mm:ss
format that shows when the most recent heartbeat signal
was received by a replication slave.
COUNT_RECEIVED_HEARTBEATS
The total number of heartbeat signals that a replication
slave received since the last time it was restarted or
reset, or a CHANGE MASTER TO
statement
was issued.
TRUNCATE TABLE
is not permitted
for the
replication_connection_status
table.
The following table shows the correspondence between
replication_connection_status
columns and SHOW SLAVE STATUS
columns.
replication_connection_status Column |
SHOW SLAVE STATUS Column |
---|---|
SOURCE_UUID |
Master_UUID |
THREAD_ID |
None |
SERVICE_STATE |
Slave_IO_Running |
RECEIVED_TRANSACTION_SET |
Retrieved_Gtid_Set |
LAST_ERROR_NUMBER |
Last_IO_Errno |
LAST_ERROR_MESSAGE |
Last_IO_Error |
LAST_ERROR_TIMESTAMP |
Last_IO_Error_Timestamp |
This table shows the configuration parameters that affect
transactions applied by the slave server. Parameters stored in
the table can be changed at runtime with the
CHANGE MASTER TO
statement, as
indicated in the column descriptions.
The
replication_applier_configuration
table has these columns:
CHANNEL_NAME
The replication channel which this row is displaying. There is always a default replication channel, and more replication channels can be added. See Section 16.2.3, “Replication Channels” for more information.
DESIRED_DELAY
The number of seconds that the slave must lag the master.
(CHANGE MASTER TO
option:
MASTER_DELAY
)
TRUNCATE TABLE
is not permitted
for the
replication_applier_configuration
table.
The following table shows the correspondence between
replication_applier_configuration
columns and SHOW SLAVE
STATUS
columns.
replication_applier_configuration Column |
SHOW SLAVE STATUS Column |
---|---|
DESIRED_DELAY |
SQL_Delay |
This table shows the current general transaction execution
status on the slave server. The table provides information
about general aspects of transaction applier status that are
not specific to any thread involved. Thread-specific status
information is available in the
replication_applier_status_by_coordinator
table (and
replication_applier_status_by_worker
if the slave is multithreaded).
The replication_applier_status
table has these columns:
CHANNEL_NAME
The replication channel which this row is displaying. There is always a default replication channel, and more replication channels can be added. See Section 16.2.3, “Replication Channels” for more information.
SERVICE_STATE
Shows ON
when the replication channel's
applier threads are active or idle, OFF
means that the applier threads are not active.
REMAINING_DELAY
If the slave is waiting for
DESIRED_DELAY
seconds to pass since the
master applied an event, this field contains the number of
delay seconds remaining. At other times, this field is
NULL
. (The
DESIRED_DELAY
value is stored in the
replication_applier_configuration
table.)
COUNT_TRANSACTIONS_RETRIES
Shows the number of retries that were made because the
slave SQL thread failed to apply a transaction. The
maximum number of retries for a given transaction is set
by the
slave_transaction_retries
system variable.
TRUNCATE TABLE
is not permitted
for the
replication_applier_status
table.
The following table shows the correspondence between
replication_applier_status
columns and SHOW SLAVE STATUS
columns.
replication_applier_status Column |
SHOW SLAVE STATUS Column |
---|---|
SERVICE_STATE |
None |
REMAINING_DELAY |
SQL_Remaining_Delay |
For a multithreaded slave, the slave uses multiple worker
threads and a coordinator thread to manage them, and this
table shows the status of the coordinator thread. For a
single-threaded slave, this table is empty. For a
multithreaded slave, the
replication_applier_status_by_worker
table shows the status of the worker threads.
The
replication_applier_status_by_coordinator
table has these columns:
CHANNEL_NAME
The replication channel which this row is displaying. There is always a default replication channel, and more replication channels can be added. See Section 16.2.3, “Replication Channels” for more information.
THREAD_ID
The SQL/coordinator thread ID.
SERVICE_STATE
ON
(thread exists and is active or
idle) or OFF
(thread no longer exists).
LAST_ERROR_NUMBER
,
LAST_ERROR_MESSAGE
The error number and error message of the most recent
error that caused the SQL/coordinator thread to stop. An
error number of 0 and message which is an empty string
means “no error”. If the
LAST_ERROR_MESSAGE
value is not empty,
the error values also appear in the slave's error log.
Issuing RESET MASTER
or
RESET SLAVE
resets the
values shown in these columns.
All error codes and messages displayed in the
LAST_ERROR_NUMBER
and
LAST_ERROR_MESSAGE
columns correspond
to error values listed in
Section B.3.1, “Server Error Message Reference”.
LAST_ERROR_TIMESTAMP
A timestamp in YYMMDD hh:mm:ss
format that shows when the most recent SQL/coordinator
error occurred.
TRUNCATE TABLE
is not permitted
for the
replication_applier_status_by_coordinator
table.
The following table shows the correspondence between
replication_applier_status_by_coordinator
columns and SHOW SLAVE STATUS
columns.
replication_applier_status_by_coordinator Column |
SHOW SLAVE STATUS Column |
---|---|
THREAD_ID |
None |
SERVICE_STATE |
Slave_SQL_Running |
LAST_ERROR_NUMBER |
Last_SQL_Errno |
LAST_ERROR_MESSAGE |
Last_SQL_Error |
LAST_ERROR_TIMESTAMP |
Last_SQL_Error_Timestamp |
If the slave is not multithreaded, this table shows the status
of the applier thread. Otherwise, the slave uses multiple
worker threads and a coordinator thread to manage them, and
this table shows the status of the worker threads. For a
multithreaded slave, the
replication_applier_status_by_coordinator
table shows the status of the coordinator thread.
The replication_applier_status_by_worker
table has these columns:
CHANNEL_NAME
The replication channel which this row is displaying. There is always a default replication channel, and more replication channels can be added. See Section 16.2.3, “Replication Channels” for more information.
WORKER_ID
The worker identifier (same value as the
id
column in the
mysql.slave_worker_info
table). After
STOP SLAVE
, the
THREAD_ID
column becomes
NULL
, but the
WORKER_ID
value is preserved.
THREAD_ID
The worker thread identifier.
SERVICE_STATE
ON
(thread exists and is active or
idle) or OFF
(thread no longer exists).
LAST_SEEN_TRANSACTION
The transaction that the worker has last seen. The worker has not necessarily applied this transaction because it could still be in the process of doing so.
If the gtid_mode
system
variable value is OFF
, this column is
ANONYMOUS
, indicating that transactions
do not have global transaction identifiers (GTIDs) and are
identified by file and position only.
If gtid_mode
is
ON
, the column value is defined as
follows:
If no transaction has executed, the column is empty.
When a transaction has executed, the column is set
from gtid_next
as
soon as gtid_next
is
set. From this moment, the column always shows a GTID.
The GTID is preserved until the next transaction is executed. If an error occurs, the column value is the GTID of the transaction being executed by the worker when the error occurred. The following statement shows whether or not that transaction has been committed:
SELECT GTID_SUBSET(LAST_SEEN_TRANSACTION, @@GLOBAL.GTID_EXECUTED) FROM performance_schema.replication_applier_status_by_worker;
If the statement returns zero, the transaction has not yet been committed, either because it is still being processed, or because the worker thread was stopped while it was being processed. If the statement returns nonzero, the transaction has been committed.
LAST_ERROR_NUMBER
,
LAST_ERROR_MESSAGE
The error number and error message of the most recent
error that caused the worker thread to stop. An error
number of 0 and message of the empty string mean “no
error”. If the
LAST_ERROR_MESSAGE
value is not empty,
the error values also appear in the slave's error log.
Issuing RESET MASTER
or
RESET SLAVE
resets the
values shown in these columns.
All error codes and messages displayed in the
LAST_ERROR_NUMBER
and
LAST_ERROR_MESSAGE
columns correspond
to error values listed in
Section B.3.1, “Server Error Message Reference”.
LAST_ERROR_TIMESTAMP
A timestamp in YYMMDD hh:mm:ss
format that shows when the most recent worker error
occurred.
TRUNCATE TABLE
is not permitted
for the
replication_applier_status_by_worker
table.
The following table shows the correspondence between
replication_applier_status_by_worker
columns and SHOW SLAVE STATUS
columns.
replication_applier_status_by_worker Column |
SHOW SLAVE STATUS Column |
---|---|
WORKER_ID |
None |
THREAD_ID |
None |
SERVICE_STATE |
None |
LAST_SEEN_TRANSACTION |
None |
LAST_ERROR_NUMBER |
Last_SQL_Errno |
LAST_ERROR_MESSAGE |
Last_SQL_Error |
LAST_ERROR_TIMESTAMP |
Last_SQL_Error_Timestamp |
This table shows network and status information for
replication group members. The network addresses shown are the
addresses used to connect clients to the group, and should not
be confused with the member's internal group communication
address specified by
group_replication_local_address
.
The replication_group_members
table has the
following columns:
CHANNEL_NAME
Name of the Group Replication channel.
MEMBER_ID
Identifier for this member; the same as the server UUID.
MEMBER_HOST
Network address of this member (host name or IP address).
Retrieved from the member's
hostname
variable.
MEMBER_PORT
Port on which the server is listening. Retrieved from the
member's port
variable.
MEMBER_STATE
Current state of this member; can be any one of the following:
OFFLINE
: The Group Replication
plugin is installed but has not been started.
RECOVERING
: The server has joined a
group from which it is retrieving data.
ONLINE
: The member is in a fully
functioning state.
ERROR
: The member has encountered
an error, either during applying transactions or
during the recovery phase, and is not participating in
the group's transactions.
UNREACHABLE
: The failure detection
process suspects that this member cannot be contacted,
because the group messages have timed out.
TRUNCATE TABLE
is not permitted
for the replication_group_members
table.
This table shows statistical information for MySQL Group Replication members. It is populated only when Group Replication is running.
The replication_group_member_stats
table
has the following columns:
CHANNEL_NAME
Name of the Group Replication channel.
VIEW_ID
Current view identifier for this group.
MEMBER_ID
The member server UUID. This has a different value for each member in the group. This also serves as a key because it is unique to each member.
COUNT_TRANSACTIONS_IN_QUEUE
The number of transactions in the queue pending conflict detection checks. Once the transactions have been checked for conflicts, if they pass the check, they are queued to be applied as well.
COUNT_TRANSACTIONS_CHECKED
The number of transactions that have been checked for conflicts.
COUNT_CONFLICTS_DETECTED
The number of transactions that have not passed the conflict detection check.
COUNT_TRANSACTIONS_ROWS_VALIDATING
Number of transaction rows which can be used for certification, but have not been garbage collected. Can be thought of as the current size of the conflict detection database against which each transaction is certified.
TRANSACTIONS_COMMITTED_ALL_MEMBERS
The transactions that have been successfully committed on all members of the replication group, shown as GTID Sets. This is updated at a fixed time interval.
LAST_CONFLICT_FREE_TRANSACTION
The transaction identifier of the last conflict free transaction which was checked.
TRUNCATE TABLE
is not permitted
for the
replication_group_member_stats
table.
The Performance Schema exposes lock information through these tables:
metadata_locks
: Metadata locks
held and requested
table_handles
: Table locks held
and requested
The following sections describe these tables in more detail.
MySQL uses metadata locking to manage concurrent access to
database objects and to ensure data consistency; see
Section 8.11.4, “Metadata Locking”. Metadata locking applies
not just to tables, but also to schemas, stored programs
(procedures, functions, triggers, scheduled events),
tablespaces, user locks acquired with the
GET_LOCK()
function (see
Section 12.14, “Locking Functions”), and locks acquired with
the locking service described in
Section 28.3.1, “The Locking Service”.
The Performance Schema exposes metadata lock information
through the metadata_locks
table:
Locks that have been granted (shows which sessions own which current metadata locks).
Locks that have been requested but not yet granted (shows which sessions are waiting for which metadata locks).
Lock requests that have been killed by the deadlock detector.
Lock requests that have timed out and are waiting for the requesting session's lock request to be discarded.
This information enables you to understand metadata lock dependencies between sessions. You can see not only which lock a session is waiting for, but which session currently holds that lock.
The metadata_locks
table is read
only and cannot be updated. It is autosized by default; to
configure the table size, set the
performance_schema_max_metadata_locks
system variable at server startup.
Metadata lock instrumentation uses the
wait/lock/metadata/sql/mdl
instrument,
which is disabled by default.
To control metadata lock instrumentation state at server
startup, use lines like these in your
my.cnf
file:
Enable:
[mysqld] performance-schema-instrument='wait/lock/metadata/sql/mdl=ON'
Disable:
[mysqld] performance-schema-instrument='wait/lock/metadata/sql/mdl=OFF'
To control metadata lock instrumentation state at runtime,
update the setup_instruments
table:
Enable:
UPDATE performance_schema.setup_instruments SET ENABLED = 'YES', TIMED = 'YES' WHERE NAME = 'wait/lock/metadata/sql/mdl';
Disable:
UPDATE performance_schema.setup_instruments SET ENABLED = 'NO', TIMED = 'NO' WHERE NAME = 'wait/lock/metadata/sql/mdl';
The Performance Schema maintains
metadata_locks
table content as
follows, using the LOCK_STATUS
column to
indicate the status of each lock:
When a metadata lock is requested and obtained
immediately, a row with a status of
GRANTED
is inserted.
When a metadata lock is requested and not obtained
immediately, a row with a status of
PENDING
is inserted.
When a metadata lock previously requested is granted, its
row status is updated to GRANTED
.
When a metadata lock is released, its row is deleted.
When a pending lock request is canceled by the deadlock
detector to break a deadlock
(ER_LOCK_DEADLOCK
), its
row status is updated from PENDING
to
VICTIM
.
When a pending lock request times out
(ER_LOCK_WAIT_TIMEOUT
),
its row status is updated from PENDING
to TIMEOUT
.
When granted lock or pending lock request is killed, its
row status is updated from GRANTED
or
PENDING
to KILLED
.
The VICTIM
, TIMEOUT
,
and KILLED
status values are brief and
signify that the lock row is about to be deleted.
The PRE_ACQUIRE_NOTIFY
and
POST_RELEASE_NOTIFY
status values are
brief and signify that the metadata locking subsubsystem
is notifying interested storage engines while entering
lock acquisition operations or leaving lock release
operations. These status values were added in MySQL
5.7.11.
The metadata_locks
table has
these columns:
OBJECT_TYPE
The type of lock used in the metadata lock subsystem. The
value is one of GLOBAL
,
SCHEMA
, TABLE
,
FUNCTION
, PROCEDURE
,
TRIGGER
(currently unused),
EVENT
, COMMIT
,
USER LEVEL LOCK
,
TABLESPACE
, or LOCKING
SERVICE
.
A value of USER LEVEL LOCK
indicates a
lock acquired with
GET_LOCK()
. A value of
LOCKING SERVICE
indicates a lock
acquired with the locking service described in
Section 28.3.1, “The Locking Service”.
OBJECT_SCHEMA
The schema that contains the object.
OBJECT_NAME
The name of the instrumented object.
OBJECT_INSTANCE_BEGIN
The address in memory of the instrumented object.
LOCK_TYPE
The lock type from the metadata lock subsystem. The value
is one of INTENTION_EXCLUSIVE
,
SHARED
,
SHARED_HIGH_PRIO
,
SHARED_READ
,
SHARED_WRITE
,
SHARED_UPGRADABLE
,
SHARED_NO_WRITE
,
SHARED_NO_READ_WRITE
, or
EXCLUSIVE
.
LOCK_DURATION
The lock duration from the metadata lock subsystem. The
value is one of STATEMENT
,
TRANSACTION
, or
EXPLICIT
. The
STATEMENT
and
TRANSACTION
values signify locks that
are released implicitly at statement or transaction end,
respectively. The EXPLICIT
value
signifies locks that survive statement or transaction end
and are released by explicit action, such as global locks
acquired with FLUSH TABLES WITH READ
LOCK
.
LOCK_STATUS
The lock status from the metadata lock subsystem. The
value is one of PENDING
,
GRANTED
, VICTIM
,
TIMEOUT
, KILLED
,
PRE_ACQUIRE_NOTIFY
, or
POST_RELEASE_NOTIFY
. The Performance
Schema assigns these values as described previously.
SOURCE
The name of the source file containing the instrumented code that produced the event and the line number in the file at which the instrumentation occurs. This enables you to check the source to determine exactly what code is involved.
OWNER_THREAD_ID
The thread requesting a metadata lock.
OWNER_EVENT_ID
The event requesting a metadata lock.
TRUNCATE TABLE
is not permitted
for the metadata_locks
table.
The Performance Schema exposes table lock information through
the table_handles
table to show
the table locks currently in effect for each opened table
handle. table_handles
reports
what is recorded by the table lock instrumentation. This
information shows which table handles the server has open, how
they are locked, and by which sessions.
The table_handles
table is read
only and cannot be updated. It is autosized by default; to
configure the table size, set the
performance_schema_max_table_handles
system variable at server startup.
Table lock instrumentation uses the
wait/lock/table/sql/handler
instrument,
which is enabled by default.
To control table lock instrumentation state at server startup,
use lines like these in your my.cnf
file:
Enable:
[mysqld] performance-schema-instrument='wait/lock/table/sql/handler=ON'
Disable:
[mysqld] performance-schema-instrument='wait/lock/table/sql/handler=OFF'
To control table lock instrumentation state at runtime, update
the setup_instruments
table:
Enable:
UPDATE performance_schema.setup_instruments SET ENABLED = 'YES', TIMED = 'YES' WHERE NAME = 'wait/lock/table/sql/handler';
Disable:
UPDATE performance_schema.setup_instruments SET ENABLED = 'NO', TIMED = 'NO' WHERE NAME = 'wait/lock/table/sql/handler';
The table_handles
table has these
columns:
OBJECT_TYPE
The table opened by a table handle.
OBJECT_SCHEMA
The schema that contains the object.
OBJECT_NAME
The name of the instrumented object.
OBJECT_INSTANCE_BEGIN
The table handle address in memory.
OWNER_THREAD_ID
The thread owning the table handle.
OWNER_EVENT_ID
The event which caused the table handle to be opened.
INTERNAL_LOCK
The table lock used at the SQL level. The value is one of
READ
, READ WITH SHARED
LOCKS
, READ HIGH PRIORITY
,
READ NO INSERT
, WRITE ALLOW
WRITE
, WRITE CONCURRENT
INSERT
, WRITE LOW PRIORITY
,
or WRITE
. For information about these
lock types, see the
include/thr_lock.h
source file.
EXTERNAL_LOCK
The table lock used at the storage engine level. The value
is one of READ EXTERNAL
or
WRITE EXTERNAL
.
TRUNCATE TABLE
is not permitted
for the table_handles
table.
The value of the
show_compatibility_56
system
variable affects the information available from the tables
described here. For details, see the description of that
variable in Section 5.1.7, “Server System Variables”.
The MySQL server maintains many system variables that indicate how it is configured (see Section 5.1.7, “Server System Variables”). System variable information is available in these Performance Schema tables:
global_variables
: Global system
variables. An application that wants only global values
should use this table.
session_variables
: System
variables for the current session. An application that wants
all system variable values for its own session should use
this table. It includes the session variables for its
session, as well as the values of global variables that have
no session counterpart.
variables_by_thread
: Session
system variables for each active session. An application
that wants to know the session variable values for specific
sessions should use this table. It includes session
variables only, identified by thread ID.
The session variable tables
(session_variables
,
variables_by_thread
) contain
information only for active sessions, not terminated sessions.
TRUNCATE TABLE
is not supported
for Performance Schema system variable tables.
The global_variables
and
session_variables
tables have these
columns:
VARIABLE_NAME
The system variable name.
VARIABLE_VALUE
The system variable value. For
global_variables
, this column
contains the global value. For
session_variables
, this column
contains the variable value in effect for the current
session.
The variables_by_thread
table has
these columns:
THREAD_ID
The thread identifier of the session in which the system variable is defined.
VARIABLE_NAME
The system variable name.
VARIABLE_VALUE
The session variable value for the session named by the
THREAD_ID
column.
The variables_by_thread
table
contains system variable information only about foreground
threads. If not all threads are instrumented by the Performance
Schema, this table will miss some rows. In this case, the
Performance_schema_thread_instances_lost
status variable will be greater than zero.
The value of the
show_compatibility_56
system
variable affects the information available from the tables
described here. For details, see the description of that
variable in Section 5.1.7, “Server System Variables”.
The MySQL server maintains many status variables that provide information about its operation (see Section 5.1.9, “Server Status Variables”). Status variable information is available in these Performance Schema tables:
global_status
: Global status
variables. An application that wants only global values
should use this table.
session_status
: Status
variables for the current session. An application that wants
all status variable values for its own session should use
this table. It includes the session variables for its
session, as well as the values of global variables that have
no session counterpart.
status_by_thread
: Session
status variables for each active session. An application
that wants to know the session variable values for specific
sessions should use this table. It includes session
variables only, identified by thread ID.
There are also summary tables that provide status variable information aggregated by account, host name, and user name. See Section 25.12.15.10, “Status Variable Summary Tables”.
The session variable tables
(session_status
,
status_by_thread
) contain
information only for active sessions, not terminated sessions.
The Performance Schema collects statistics for global status
variables only for threads for which the
INSTRUMENTED
value is YES
in the threads
table. Statistics
for session status variables are always collected, regardless of
the INSTRUMENTED
value.
The Performance Schema does not collect statistics for
Com_
status
variables in the status variable tables. To obtain global and
per-session statement execution counts, use the
xxx
events_statements_summary_global_by_event_name
and
events_statements_summary_by_thread_by_event_name
tables, respectively. For example:
SELECT EVENT_NAME, COUNT_STAR FROM performance_schema.events_statements_summary_global_by_event_name WHERE EVENT_NAME LIKE 'statement/sql/%';
The global_status
and
session_status
tables have these
columns:
VARIABLE_NAME
The status variable name.
VARIABLE_VALUE
The status variable value. For
global_status
, this column
contains the global value. For
session_status
, this column
contains the variable value for the current session.
The status_by_thread
table contains
the status of each active thread. It has these columns:
THREAD_ID
The thread identifier of the session in which the status variable is defined.
VARIABLE_NAME
The status variable name.
VARIABLE_VALUE
The session variable value for the session named by the
THREAD_ID
column.
The status_by_thread
table contains
status variable information only about foreground threads. If
the
performance_schema_max_thread_instances
system variable is not autoscaled (signified by a value of
−1) and the maximum permitted number of instrumented
thread objects is not greater than the number of background
threads, the table will be empty.
The Performance Schema supports TRUNCATE
TABLE
for status variable tables as follows:
global_status
: Resets thread,
account, host, and user status. Resets global status
variables except those that the server never resets.
session_status
: Not supported.
status_by_thread
: Aggregates
status for all threads to the global status and account
status, then resets thread status. If account statistics are
not collected, the session status is added to host and user
status, if host and user status are collected.
Account, host, and user statistics are not collected if the
performance_schema_accounts_size
,
performance_schema_hosts_size
,
and
performance_schema_users_size
system variables, respectively, are set to 0.
FLUSH STATUS
adds the session
status from all active sessions to the global status variables,
resets the status of all active sessions, and resets account,
host, and user status values aggregated from disconnected
sessions.
Summary tables provide aggregated information for terminated events over time. The tables in this group summarize event data in different ways.
events_waits_summary_by_account_by_event_name
:
Wait events per account and event name
events_waits_summary_by_host_by_event_name
:
Wait events per host name and event name
events_waits_summary_by_instance
:
Wait events per instance
events_waits_summary_by_thread_by_event_name
:
Wait events per thread and event name
events_waits_summary_by_user_by_event_name
:
Wait events per user name and event name
events_waits_summary_global_by_event_name
:
Wait events per event name
events_stages_summary_by_account_by_event_name
:
Stage events per account and event name
events_stages_summary_by_host_by_event_name
:
Stage events per host name and event name
events_stages_summary_by_thread_by_event_name
:
Stage waits per thread and event name
events_stages_summary_by_user_by_event_name
:
Stage events per user name and event name
events_stages_summary_global_by_event_name
:
Stage waits per event name
events_statements_summary_by_account_by_event_name
:
Statement events per account and event name
events_statements_summary_by_digest
:
Statement events per schema and digest value
events_statements_summary_by_host_by_event_name
:
Statement events per host name and event name
events_statements_summary_by_program
:
Statement events per stored program (stored procedures and
functions, triggers, and events)
events_statements_summary_by_thread_by_event_name
:
Statement events per thread and event name
events_statements_summary_by_user_by_event_name
:
Statement events per user name and event name
events_statements_summary_global_by_event_name
:
Statement events per event name
prepared_statements_instances
:
Prepared statement instances and statistics
events_transactions_summary_by_account_by_event_name
:
Transaction events per account and event name
events_transactions_summary_by_host_by_event_name
:
Transaction events per host name and event name
events_transactions_summary_by_thread_by_event_name
:
Transaction events per thread and event name
events_transactions_summary_by_user_by_event_name
:
Transaction events per user name and event name
events_transactions_summary_global_by_event_name
:
Transaction events per event name
objects_summary_global_by_type
:
Object summaries
file_summary_by_event_name
:
File events per event name
file_summary_by_instance
: File
events per file instance
table_io_waits_summary_by_index_usage
:
Table I/O waits per index
table_io_waits_summary_by_table
:
Table I/O waits per table
table_lock_waits_summary_by_table
:
Table lock waits per table
socket_summary_by_instance
:
Socket waits and I/O per instance
socket_summary_by_event_name
:
Socket waits and I/O per event name
memory_summary_by_account_by_event_name
:
Memory operations per account and event name
memory_summary_by_host_by_event_name
:
Memory operations per host and event name
memory_summary_by_thread_by_event_name
:
Memory operations per thread and event name
memory_summary_by_user_by_event_name
:
Memory operations per user and event name
memory_summary_global_by_event_name
:
Memory operations globally per event name
status_by_account
: Status
variables per account
status_by_host
: Status
variables per host name
status_by_user
: Status
variables per user name
Each summary table has grouping columns that determine how to group the data to be aggregated, and summary columns that contain the aggregated values. Tables that summarize events in similar ways often have similar sets of summary columns and differ only in the grouping columns used to determine how events are aggregated.
Summary tables can be truncated with
TRUNCATE TABLE
. Generally, the
effect is to reset the summary columns to 0 or
NULL
, not to remove rows. This enables you to
clear collected values and restart aggregation. That might be
useful, for example, after you have made a runtime configuration
change. Exceptions to this truncation behavior are noted in
individual summary table sections.
The Performance Schema maintains tables for collecting current and recent wait events, and aggregates that information in summary tables. Section 25.12.4, “Performance Schema Wait Event Tables” describes the events on which wait summaries are based. See that discussion for information about the content of wait events, the current and recent wait event tables, and how to control wait event collection, which is disabled by default.
Example wait event summary information:
mysql>SELECT *
FROM performance_schema.events_waits_summary_global_by_event_name\G
... *************************** 6. row *************************** EVENT_NAME: wait/synch/mutex/sql/BINARY_LOG::LOCK_index COUNT_STAR: 8 SUM_TIMER_WAIT: 2119302 MIN_TIMER_WAIT: 196092 AVG_TIMER_WAIT: 264912 MAX_TIMER_WAIT: 569421 ... *************************** 9. row *************************** EVENT_NAME: wait/synch/mutex/sql/hash_filo::lock COUNT_STAR: 69 SUM_TIMER_WAIT: 16848828 MIN_TIMER_WAIT: 0 AVG_TIMER_WAIT: 244185 MAX_TIMER_WAIT: 735345 ...
Each wait event summary table has one or more grouping columns
to indicate how the table aggregates events. Event names refer
to names of event instruments in the
setup_instruments
table:
events_waits_summary_by_account_by_event_name
has EVENT_NAME
,
USER
, and HOST
columns. Each row summarizes events for a given account
(user and host combination) and event name.
events_waits_summary_by_host_by_event_name
has EVENT_NAME
and
HOST
columns. Each row summarizes
events for a given host and event name.
events_waits_summary_by_instance
has EVENT_NAME
and
OBJECT_INSTANCE_BEGIN
columns. Each row
summarizes events for a given event name and object. If an
instrument is used to create multiple instances, each
instance has a unique
OBJECT_INSTANCE_BEGIN
value and is
summarized separately in this table.
events_waits_summary_by_thread_by_event_name
has THREAD_ID
and
EVENT_NAME
columns. Each row summarizes
events for a given thread and event name.
events_waits_summary_by_user_by_event_name
has EVENT_NAME
and
USER
columns. Each row summarizes
events for a given user and event name.
events_waits_summary_global_by_event_name
has an EVENT_NAME
column. Each row
summarizes events for a given event name. An instrument
might be used to create multiple instances of the
instrumented object. For example, if there is an
instrument for a mutex that is created for each
connection, there are as many instances as there are
connections. The summary row for the instrument summarizes
over all these instances.
Each wait event summary table has these summary columns containing aggregated values:
COUNT_STAR
The number of summarized events. This value includes all events, whether timed or nontimed.
SUM_TIMER_WAIT
The total wait time of the summarized timed events. This
value is calculated only for timed events because nontimed
events have a wait time of NULL
. The
same is true for the other
values.
xxx
_TIMER_WAIT
MIN_TIMER_WAIT
The minimum wait time of the summarized timed events.
AVG_TIMER_WAIT
The average wait time of the summarized timed events.
MAX_TIMER_WAIT
The maximum wait time of the summarized timed events.
TRUNCATE TABLE
is permitted for
wait summary tables. It has these effects:
For summary tables not aggregated by account, host, or user, truncation resets the summary columns to zero rather than removing rows.
For summary tables aggregated by account, host, or user, truncation removes rows for accounts, hosts, or users with no connections, and resets the summary columns to zero for the remaining rows.
In addition, each wait summary table that is aggregated by
account, host, user, or thread is implicitly truncated by
truncation of the connection table on which it depends, or
truncation of
events_waits_summary_global_by_event_name
.
For details, see
Section 25.12.8, “Performance Schema Connection Tables”.
The Performance Schema maintains tables for collecting current and recent stage events, and aggregates that information in summary tables. Section 25.12.5, “Performance Schema Stage Event Tables” describes the events on which stage summaries are based. See that discussion for information about the content of stage events, the current and historical stage event tables, and how to control stage event collection, which is disabled by default.
Example stage event summary information:
mysql>SELECT *
FROM performance_schema.events_stages_summary_global_by_event_name\G
... *************************** 5. row *************************** EVENT_NAME: stage/sql/checking permissions COUNT_STAR: 57 SUM_TIMER_WAIT: 26501888880 MIN_TIMER_WAIT: 7317456 AVG_TIMER_WAIT: 464945295 MAX_TIMER_WAIT: 12858936792 ... *************************** 9. row *************************** EVENT_NAME: stage/sql/closing tables COUNT_STAR: 37 SUM_TIMER_WAIT: 662606568 MIN_TIMER_WAIT: 1593864 AVG_TIMER_WAIT: 17907891 MAX_TIMER_WAIT: 437977248 ...
Each stage summary table has one or more grouping columns to
indicate how the table aggregates events. Event names refer to
names of event instruments in the
setup_instruments
table:
events_stages_summary_by_account_by_event_name
has EVENT_NAME
,
USER
, and HOST
columns. Each row summarizes events for a given account
(user and host combination) and event name.
events_stages_summary_by_host_by_event_name
has EVENT_NAME
and
HOST
columns. Each row summarizes
events for a given host and event name.
events_stages_summary_by_thread_by_event_name
has THREAD_ID
and
EVENT_NAME
columns. Each row summarizes
events for a given thread and event name.
events_stages_summary_by_user_by_event_name
has EVENT_NAME
and
USER
columns. Each row summarizes
events for a given user and event name.
events_stages_summary_global_by_event_name
has an EVENT_NAME
column. Each row
summarizes events for a given event name.
Each stage summary table has these summary columns containing
aggregated values: COUNT_STAR
,
SUM_TIMER_WAIT
,
MIN_TIMER_WAIT
,
AVG_TIMER_WAIT
, and
MAX_TIMER_WAIT
. These columns are analogous
to the columns of the same names in the wait event summary
tables (see Section 25.12.15.1, “Wait Event Summary Tables”), except
that the stage summary tables aggregate events from
events_stages_current
rather than
events_waits_current
.
TRUNCATE TABLE
is permitted for
stage summary tables. It has these effects:
For summary tables not aggregated by account, host, or user, truncation resets the summary columns to zero rather than removing rows.
For summary tables aggregated by account, host, or user, truncation removes rows for accounts, hosts, or users with no connections, and resets the summary columns to zero for the remaining rows.
In addition, each stage summary table that is aggregated by
account, host, user, or thread is implicitly truncated by
truncation of the connection table on which it depends, or
truncation of
events_stages_summary_global_by_event_name
.
For details, see
Section 25.12.8, “Performance Schema Connection Tables”.
The Performance Schema maintains tables for collecting current and recent statement events, and aggregates that information in summary tables. Section 25.12.6, “Performance Schema Statement Event Tables” describes the events on which statement summaries are based. See that discussion for information about the content of statement events, the current and historical statement event tables, and how to control statement event collection, which is partially disabled by default.
Example statement event summary information:
mysql>SELECT *
FROM performance_schema.events_statements_summary_global_by_event_name\G
*************************** 1. row *************************** EVENT_NAME: statement/sql/select COUNT_STAR: 25 SUM_TIMER_WAIT: 1535983999000 MIN_TIMER_WAIT: 209823000 AVG_TIMER_WAIT: 61439359000 MAX_TIMER_WAIT: 1363397650000 SUM_LOCK_TIME: 20186000000 SUM_ERRORS: 0 SUM_WARNINGS: 0 SUM_ROWS_AFFECTED: 0 SUM_ROWS_SENT: 388 SUM_ROWS_EXAMINED: 370 SUM_CREATED_TMP_DISK_TABLES: 0 SUM_CREATED_TMP_TABLES: 0 SUM_SELECT_FULL_JOIN: 0 SUM_SELECT_FULL_RANGE_JOIN: 0 SUM_SELECT_RANGE: 0 SUM_SELECT_RANGE_CHECK: 0 SUM_SELECT_SCAN: 6 SUM_SORT_MERGE_PASSES: 0 SUM_SORT_RANGE: 0 SUM_SORT_ROWS: 0 SUM_SORT_SCAN: 0 SUM_NO_INDEX_USED: 6 SUM_NO_GOOD_INDEX_USED: 0 ...
Each statement summary table has one or more grouping columns
to indicate how the table aggregates events. Event names refer
to names of event instruments in the
setup_instruments
table:
events_statements_summary_by_account_by_event_name
has EVENT_NAME
,
USER
, and HOST
columns. Each row summarizes events for a given account
(user and host combination) and event name.
events_statements_summary_by_digest
has SCHEMA_NAME
and
DIGEST
columns. Each row summarizes
events per schema and digest value. (The
DIGEST_TEXT
column contains the
corresponding normalized statement digest text, but is
neither a grouping nor a summary column.)
The maximum number of rows in the table is autosized at
server startup. To set this maximum explicitly, set the
performance_schema_digests_size
system variable at server startup.
events_statements_summary_by_host_by_event_name
has EVENT_NAME
and
HOST
columns. Each row summarizes
events for a given host and event name.
events_statements_summary_by_program
has OBJECT_TYPE
,
OBJECT_SCHEMA
, and
OBJECT_NAME
columns. Each row
summarizes events for a given stored program (stored
procedure or function, trigger, or event).
events_statements_summary_by_thread_by_event_name
has THREAD_ID
and
EVENT_NAME
columns. Each row summarizes
events for a given thread and event name.
events_statements_summary_by_user_by_event_name
has EVENT_NAME
and
USER
columns. Each row summarizes
events for a given user and event name.
events_statements_summary_global_by_event_name
has an EVENT_NAME
column. Each row
summarizes events for a given event name.
prepared_statements_instances
has an OBJECT_INSTANCE_BEGIN
column.
Each row summarizes events for a given prepared statement.
Each statement summary table has these summary columns containing aggregated values (with exceptions as noted):
COUNT_STAR
,
SUM_TIMER_WAIT
,
MIN_TIMER_WAIT
,
AVG_TIMER_WAIT
,
MAX_TIMER_WAIT
These columns are analogous to the columns of the same
names in the wait event summary tables (see
Section 25.12.15.1, “Wait Event Summary Tables”), except that the
statement summary tables aggregate events from
events_statements_current
rather than
events_waits_current
.
The
prepared_statements_instances
table does not have these columns.
SUM_
xxx
The aggregate of the corresponding
xxx
column in the
events_statements_current
table. For example, the SUM_LOCK_TIME
and SUM_ERRORS
columns in statement
summary tables are the aggregates of the
LOCK_TIME
and ERRORS
columns in
events_statements_current
table.
The
events_statements_summary_by_digest
table has these additional summary columns:
FIRST_SEEN
,
LAST_SEEN
Timestamps indicating when statements with the given digest value were first seen and most recently seen.
The
events_statements_summary_by_program
table has these additional summary columns:
COUNT_STATEMENTS
,
SUM_STATEMENTS_WAIT
,
MIN_STATEMENTS_WAIT
,
AVG_STATEMENTS_WAIT
,
MAX_STATEMENTS_WAIT
Statistics about nested statements invoked during stored program execution.
The prepared_statements_instances
table has these additional summary columns:
COUNT_EXECUTE
,
SUM_TIMER_EXECUTE
,
MIN_TIMER_EXECUTE
,
AVG_TIMER_EXECUTE
,
MAX_TIMER_EXECUTE
Aggregated statistics for executions of the prepared statement.
TRUNCATE TABLE
is permitted for
statement summary tables. It has these effects:
For
events_statements_summary_by_digest
,
it removes the rows.
For other summary tables not aggregated by account, host, or user, truncation resets the summary columns to zero rather than removing rows.
For other summary tables aggregated by account, host, or user, truncation removes rows for accounts, hosts, or users with no connections, and resets the summary columns to zero for the remaining rows.
In addition, each statement summary table that is aggregated
by account, host, user, or thread is implicitly truncated by
truncation of the connection table on which it depends, or
truncation of
events_statements_summary_global_by_event_name
.
For details, see
Section 25.12.8, “Performance Schema Connection Tables”.
If the statements_digest
consumer is
enabled, aggregation into
events_statements_summary_by_digest
occurs as follows when a statement completes. Aggregation is
based on the DIGEST
value computed for
the statement.
If a
events_statements_summary_by_digest
row already exists with the digest value for the
statement that just completed, statistics for the
statement are aggregated to that row. The
LAST_SEEN
column is updated to the
current time.
If no row has the digest value for the statement that
just completed, and the table is not full, a new row is
created for the statement. The
FIRST_SEEN
and
LAST_SEEN
columns are initialized
with the current time.
If no row has the statement digest value for the
statement that just completed, and the table is full,
the statistics for the statement that just completed are
added to a special “catch-all” row with
DIGEST
= NULL
,
which is created if necessary. If the row is created,
the FIRST_SEEN
and
LAST_SEEN
columns are initialized
with the current time. Otherwise, the
LAST_SEEN
column is updated with the
current time.
The row with DIGEST
=
NULL
is maintained because Performance
Schema tables have a maximum size due to memory constraints.
The DIGEST
= NULL
row
permits digests that do not match other rows to be counted
even if the summary table is full, using a common
“other” bucket. This row helps you estimate
whether the digest summary is representative:
A DIGEST
= NULL
row that has a COUNT_STAR
value that
represents 5% of all digests shows that the digest
summary table is very representative; the other rows
cover 95% of the statements seen.
A DIGEST
= NULL
row that has a COUNT_STAR
value that
represents 50% of all digests shows that the digest
summary table is not very representative; the other rows
cover only half the statements seen. Most likely the DBA
should increase the maximum table size so that more of
the rows counted in the DIGEST
=
NULL
row would be counted using more
specific rows instead. To do this, set the
performance_schema_digests_size
system variable to a larger value at server startup. The
default size is 200.
For stored program types for which instrumentation is
enabled in the setup_objects
table,
events_statements_summary_by_program
maintains statistics for stored programs as follows:
A row is added for an object when it is first used in the server.
The row for an object is removed when the object is dropped.
Statistics are aggregated in the row for an object as it executes.
See also Section 25.4.3, “Event Pre-Filtering”.
The Performance Schema maintains tables for collecting current and recent transaction events, and aggregates that information in summary tables. Section 25.12.7, “Performance Schema Transaction Tables” describes the events on which transaction summaries are based. See that discussion for information about the content of transaction events, the current and historical transaction event tables, and how to control transaction event collection, which is disabled by default.
Example transaction event summary information:
mysql>SELECT *
FROM performance_schema.events_transactions_summary_global_by_event_name
LIMIT 1\G
*************************** 1. row *************************** EVENT_NAME: transaction COUNT_STAR: 5 SUM_TIMER_WAIT: 19550092000 MIN_TIMER_WAIT: 2954148000 AVG_TIMER_WAIT: 3910018000 MAX_TIMER_WAIT: 5486275000 COUNT_READ_WRITE: 5 SUM_TIMER_READ_WRITE: 19550092000 MIN_TIMER_READ_WRITE: 2954148000 AVG_TIMER_READ_WRITE: 3910018000 MAX_TIMER_READ_WRITE: 5486275000 COUNT_READ_ONLY: 0 SUM_TIMER_READ_ONLY: 0 MIN_TIMER_READ_ONLY: 0 AVG_TIMER_READ_ONLY: 0 MAX_TIMER_READ_ONLY: 0
Each transaction summary table has one or more grouping
columns to indicate how the table aggregates events. Event
names refer to names of event instruments in the
setup_instruments
table:
events_transactions_summary_by_account_by_event_name
has USER
, HOST
, and
EVENT_NAME
columns. Each row summarizes
events for a given account (user and host combination) and
event name.
events_transactions_summary_by_host_by_event_name
has HOST
and
EVENT_NAME
columns. Each row summarizes
events for a given host and event name.
events_transactions_summary_by_thread_by_event_name
has THREAD_ID
and
EVENT_NAME
columns. Each row summarizes
events for a given thread and event name.
events_transactions_summary_by_user_by_event_name
has USER
and
EVENT_NAME
columns. Each row summarizes
events for a given user and event name.
events_transactions_summary_global_by_event_name
has an EVENT_NAME
column. Each row
summarizes events for a given event name.
Each transaction summary table has these summary columns containing aggregated values:
COUNT_STAR
,
SUM_TIMER_WAIT
,
MIN_TIMER_WAIT
,
AVG_TIMER_WAIT
,
MAX_TIMER_WAIT
These columns are analogous to the columns of the same
names in the wait event summary tables (see
Section 25.12.15.1, “Wait Event Summary Tables”), except that the
transaction summary tables aggregate events from
events_transactions_current
rather than
events_waits_current
. These
columns summarize read-write and read-only transactions.
COUNT_READ_WRITE
,
SUM_TIMER_READ_WRITE
,
MIN_TIMER_READ_WRITE
,
AVG_TIMER_READ_WRITE
,
MAX_TIMER_READ_WRITE
These are similar to the COUNT_STAR
and
columns, but summarize read-write transactions only. The
transaction access mode specifies whether transactions
operate in read/write or read-only mode.
xxx
_TIMER_WAIT
COUNT_READ_ONLY
,
SUM_TIMER_READ_ONLY
,
MIN_TIMER_READ_ONLY
,
AVG_TIMER_READ_ONLY
,
MAX_TIMER_READ_ONLY
These are similar to the COUNT_STAR
and
columns, but summarize read-only transactions only. The
transaction access mode specifies whether transactions
operate in read/write or read-only mode.
xxx
_TIMER_WAIT
TRUNCATE TABLE
is permitted for
transaction summary tables. It has these effects:
For summary tables not aggregated by account, host, or user, truncation resets the summary columns to zero rather than removing rows.
For summary tables aggregated by account, host, or user, truncation removes rows for accounts, hosts, or users with no connections, and resets the summary columns to zero for the remaining rows.
In addition, each transaction summary table that is aggregated
by account, host, user, or thread is implicitly truncated by
truncation of the connection table on which it depends, or
truncation of
events_transactions_summary_global_by_event_name
.
For details, see
Section 25.12.8, “Performance Schema Connection Tables”.
Transaction event collection occurs without regard to isolation level, access mode, or autocommit mode.
Transaction event collection occurs for all non-aborted transactions initiated by the server, including empty transactions.
Read-write transactions are generally more resource intensive than read-only transactions, therefore transaction summary tables include separate aggregate columns for read-write and read-only transactions.
Resource requirements may also vary with transaction isolation level. However, presuming that only one isolation level would be used per server, aggregation by isolation level is not provided.
The Performance Schema maintains the
objects_summary_global_by_type
table for aggregating object wait events.
Example object wait event summary information:
mysql> SELECT * FROM performance_schema.objects_summary_global_by_type\G
...
*************************** 3. row ***************************
OBJECT_TYPE: TABLE
OBJECT_SCHEMA: test
OBJECT_NAME: t
COUNT_STAR: 3
SUM_TIMER_WAIT: 263126976
MIN_TIMER_WAIT: 1522272
AVG_TIMER_WAIT: 87708678
MAX_TIMER_WAIT: 258428280
...
*************************** 10. row ***************************
OBJECT_TYPE: TABLE
OBJECT_SCHEMA: mysql
OBJECT_NAME: user
COUNT_STAR: 14
SUM_TIMER_WAIT: 365567592
MIN_TIMER_WAIT: 1141704
AVG_TIMER_WAIT: 26111769
MAX_TIMER_WAIT: 334783032
...
The
objects_summary_global_by_type
table has these grouping columns to indicate how the table
aggregates events: OBJECT_TYPE
,
OBJECT_SCHEMA
, and
OBJECT_NAME
. Each row summarizes events for
the given object.
objects_summary_global_by_type
has the same summary columns as the
events_waits_summary_by_
tables. See Section 25.12.15.1, “Wait Event Summary Tables”.
xxx
TRUNCATE TABLE
is permitted for
the object summary table. It resets the summary columns to
zero rather than removing rows.
The Performance Schema maintains file I/O summary tables that aggregate information about I/O operations.
Example file I/O event summary information:
mysql>SELECT * FROM performance_schema.file_summary_by_event_name\G
... *************************** 2. row *************************** EVENT_NAME: wait/io/file/sql/binlog COUNT_STAR: 31 SUM_TIMER_WAIT: 8243784888 MIN_TIMER_WAIT: 0 AVG_TIMER_WAIT: 265928484 MAX_TIMER_WAIT: 6490658832 ... mysql>SELECT * FROM performance_schema.file_summary_by_instance\G
... *************************** 2. row *************************** FILE_NAME: /var/mysql/share/english/errmsg.sys EVENT_NAME: wait/io/file/sql/ERRMSG EVENT_NAME: wait/io/file/sql/ERRMSG OBJECT_INSTANCE_BEGIN: 4686193384 COUNT_STAR: 5 SUM_TIMER_WAIT: 13990154448 MIN_TIMER_WAIT: 26349624 AVG_TIMER_WAIT: 2798030607 MAX_TIMER_WAIT: 8150662536 ...
Each file I/O summary table has one or more grouping columns
to indicate how the table aggregates events. Event names refer
to names of event instruments in the
setup_instruments
table:
file_summary_by_event_name
has an EVENT_NAME
column. Each row
summarizes events for a given event name.
file_summary_by_instance
has
FILE_NAME
,
EVENT_NAME
, and
OBJECT_INSTANCE_BEGIN
columns. Each row
summarizes events for a given file and event name.
Each file I/O summary table has the following summary columns containing aggregated values. Some columns are more general and have values that are the same as the sum of the values of more fine-grained columns. In this way, aggregations at higher levels are available directly without the need for user-defined views that sum lower-level columns.
COUNT_STAR
,
SUM_TIMER_WAIT
,
MIN_TIMER_WAIT
,
AVG_TIMER_WAIT
,
MAX_TIMER_WAIT
These columns aggregate all I/O operations.
COUNT_READ
,
SUM_TIMER_READ
,
MIN_TIMER_READ
,
AVG_TIMER_READ
,
MAX_TIMER_READ
,
SUM_NUMBER_OF_BYTES_READ
These columns aggregate all read operations, including
FGETS
, FGETC
,
FREAD
, and READ
.
COUNT_WRITE
,
SUM_TIMER_WRITE
,
MIN_TIMER_WRITE
,
AVG_TIMER_WRITE
,
MAX_TIMER_WRITE
,
SUM_NUMBER_OF_BYTES_WRITE
These columns aggregate all write operations, including
FPUTS
, FPUTC
,
FPRINTF
, VFPRINTF
,
FWRITE
, and PWRITE
.
COUNT_MISC
,
SUM_TIMER_MISC
,
MIN_TIMER_MISC
,
AVG_TIMER_MISC
,
MAX_TIMER_MISC
These columns aggregate all other I/O operations,
including CREATE
,
DELETE
, OPEN
,
CLOSE
, STREAM_OPEN
,
STREAM_CLOSE
, SEEK
,
TELL
, FLUSH
,
STAT
, FSTAT
,
CHSIZE
, RENAME
, and
SYNC
. There are no byte counts for
these operations.
TRUNCATE TABLE
is permitted for
file I/O summary tables. It resets the summary columns to zero
rather than removing rows.
The MySQL server uses several techniques to avoid I/O operations by caching information read from files, so it is possible that statements you might expect to result in I/O events will not. You may be able to ensure that I/O does occur by flushing caches or restarting the server to reset its state.
The following sections describe the table I/O and lock wait summary tables:
table_io_waits_summary_by_index_usage
:
Table I/O waits per index
table_io_waits_summary_by_table
:
Table I/O waits per table
table_lock_waits_summary_by_table
:
Table lock waits per table
The
table_io_waits_summary_by_table
table aggregates all table I/O wait events, as generated by
the wait/io/table/sql/handler
instrument.
The grouping is by table.
The
table_io_waits_summary_by_table
table has these grouping columns to indicate how the table
aggregates events: OBJECT_TYPE
,
OBJECT_SCHEMA
, and
OBJECT_NAME
. These columns have the same
meaning as in the
events_waits_current
table.
They identify the table to which the row applies.
table_io_waits_summary_by_table
has the following summary columns containing aggregated
values. As indicated in the column descriptions, some
columns are more general and have values that are the same
as the sum of the values of more fine-grained columns. For
example, columns that aggregate all writes hold the sum of
the corresponding columns that aggregate inserts, updates,
and deletes. In this way, aggregations at higher levels are
available directly without the need for user-defined views
that sum lower-level columns.
COUNT_STAR
,
SUM_TIMER_WAIT
,
MIN_TIMER_WAIT
,
AVG_TIMER_WAIT
,
MAX_TIMER_WAIT
These columns aggregate all I/O operations. They are the
same as the sum of the corresponding
and
xxx
_READ
columns.
xxx
_WRITE
COUNT_READ
,
SUM_TIMER_READ
,
MIN_TIMER_READ
,
AVG_TIMER_READ
,
MAX_TIMER_READ
These columns aggregate all read operations. They are
the same as the sum of the corresponding
columns.
xxx
_FETCH
COUNT_WRITE
,
SUM_TIMER_WRITE
,
MIN_TIMER_WRITE
,
AVG_TIMER_WRITE
,
MAX_TIMER_WRITE
These columns aggregate all write operations. They are
the same as the sum of the corresponding
,
xxx
_INSERT
,
and
xxx
_UPDATE
columns.
xxx
_DELETE
COUNT_FETCH
,
SUM_TIMER_FETCH
,
MIN_TIMER_FETCH
,
AVG_TIMER_FETCH
,
MAX_TIMER_FETCH
These columns aggregate all fetch operations.
COUNT_INSERT
,
SUM_TIMER_INSERT
,
MIN_TIMER_INSERT
,
AVG_TIMER_INSERT
,
MAX_TIMER_INSERT
These columns aggregate all insert operations.
COUNT_UPDATE
,
SUM_TIMER_UPDATE
,
MIN_TIMER_UPDATE
,
AVG_TIMER_UPDATE
,
MAX_TIMER_UPDATE
These columns aggregate all update operations.
COUNT_DELETE
,
SUM_TIMER_DELETE
,
MIN_TIMER_DELETE
,
AVG_TIMER_DELETE
,
MAX_TIMER_DELETE
These columns aggregate all delete operations.
TRUNCATE TABLE
is permitted
for table I/O summary tables. It resets the summary columns
to zero rather than removing rows. Truncating this table
also truncates the
table_io_waits_summary_by_index_usage
table.
The
table_io_waits_summary_by_index_usage
table aggregates all table index I/O wait events, as
generated by the
wait/io/table/sql/handler
instrument. The
grouping is by table index.
The columns of
table_io_waits_summary_by_index_usage
are nearly identical to
table_io_waits_summary_by_table
.
The only difference is the additional group column,
INDEX_NAME
, which corresponds to the name
of the index that was used when the table I/O wait event was
recorded:
A value of PRIMARY
indicates that
table I/O used the primary index.
A value of NULL
means that table I/O
used no index.
Inserts are counted against INDEX_NAME =
NULL
.
TRUNCATE TABLE
is permitted
for table I/O summary tables. It resets the summary columns
to zero rather than removing rows. This table is also
truncated by truncation of the
table_io_waits_summary_by_table
table. A DDL operation that changes the index structure of a
table may cause the per-index statistics to be reset.
The
table_lock_waits_summary_by_table
table aggregates all table lock wait events, as generated by
the wait/lock/table/sql/handler
instrument. The grouping is by table.
This table contains information about internal and external locks:
An internal lock corresponds to a lock in the SQL layer.
This is currently implemented by a call to
thr_lock()
. In event rows, these
locks are distinguished by the
OPERATION
column, which has one of
these values:
read normal read with shared locks read high priority read no insert write allow write write concurrent insert write delayed write low priority write normal
An external lock corresponds to a lock in the storage
engine layer. This is currently implemented by a call to
handler::external_lock()
. In event
rows, these locks are distinguished by the
OPERATION
column, which has one of
these values:
read external write external
The
table_lock_waits_summary_by_table
table has these grouping columns to indicate how the table
aggregates events: OBJECT_TYPE
,
OBJECT_SCHEMA
, and
OBJECT_NAME
. These columns have the same
meaning as in the
events_waits_current
table.
They identify the table to which the row applies.
table_lock_waits_summary_by_table
has the following summary columns containing aggregated
values. As indicated in the column descriptions, some
columns are more general and have values that are the same
as the sum of the values of more fine-grained columns. For
example, columns that aggregate all locks hold the sum of
the corresponding columns that aggregate read and write
locks. In this way, aggregations at higher levels are
available directly without the need for user-defined views
that sum lower-level columns.
COUNT_STAR
,
SUM_TIMER_WAIT
,
MIN_TIMER_WAIT
,
AVG_TIMER_WAIT
,
MAX_TIMER_WAIT
These columns aggregate all lock operations. They are
the same as the sum of the corresponding
and
xxx
_READ
columns.
xxx
_WRITE
COUNT_READ
,
SUM_TIMER_READ
,
MIN_TIMER_READ
,
AVG_TIMER_READ
,
MAX_TIMER_READ
These columns aggregate all read-lock operations. They
are the same as the sum of the corresponding
,
xxx
_READ_NORMAL
,
xxx
_READ_WITH_SHARED_LOCKS
,
and
xxx
_READ_HIGH_PRIORITY
columns.
xxx
_READ_NO_INSERT
COUNT_WRITE
,
SUM_TIMER_WRITE
,
MIN_TIMER_WRITE
,
AVG_TIMER_WRITE
,
MAX_TIMER_WRITE
These columns aggregate all write-lock operations. They
are the same as the sum of the corresponding
,
xxx
_WRITE_ALLOW_WRITE
,
xxx
_WRITE_CONCURRENT_INSERT
,
and
xxx
_WRITE_LOW_PRIORITY
columns.
xxx
_WRITE_NORMAL
COUNT_READ_NORMAL
,
SUM_TIMER_READ_NORMAL
,
MIN_TIMER_READ_NORMAL
,
AVG_TIMER_READ_NORMAL
,
MAX_TIMER_READ_NORMAL
These columns aggregate internal read locks.
COUNT_READ_WITH_SHARED_LOCKS
,
SUM_TIMER_READ_WITH_SHARED_LOCKS
,
MIN_TIMER_READ_WITH_SHARED_LOCKS
,
AVG_TIMER_READ_WITH_SHARED_LOCKS
,
MAX_TIMER_READ_WITH_SHARED_LOCKS
These columns aggregate internal read locks.
COUNT_READ_HIGH_PRIORITY
,
SUM_TIMER_READ_HIGH_PRIORITY
,
MIN_TIMER_READ_HIGH_PRIORITY
,
AVG_TIMER_READ_HIGH_PRIORITY
,
MAX_TIMER_READ_HIGH_PRIORITY
These columns aggregate internal read locks.
COUNT_READ_NO_INSERT
,
SUM_TIMER_READ_NO_INSERT
,
MIN_TIMER_READ_NO_INSERT
,
AVG_TIMER_READ_NO_INSERT
,
MAX_TIMER_READ_NO_INSERT
These columns aggregate internal read locks.
COUNT_READ_EXTERNAL
,
SUM_TIMER_READ_EXTERNAL
,
MIN_TIMER_READ_EXTERNAL
,
AVG_TIMER_READ_EXTERNAL
,
MAX_TIMER_READ_EXTERNAL
These columns aggregate external read locks.
COUNT_WRITE_ALLOW_WRITE
,
SUM_TIMER_WRITE_ALLOW_WRITE
,
MIN_TIMER_WRITE_ALLOW_WRITE
,
AVG_TIMER_WRITE_ALLOW_WRITE
,
MAX_TIMER_WRITE_ALLOW_WRITE
These columns aggregate internal write locks.
COUNT_WRITE_CONCURRENT_INSERT
,
SUM_TIMER_WRITE_CONCURRENT_INSERT
,
MIN_TIMER_WRITE_CONCURRENT_INSERT
,
AVG_TIMER_WRITE_CONCURRENT_INSERT
,
MAX_TIMER_WRITE_CONCURRENT_INSERT
These columns aggregate internal write locks.
COUNT_WRITE_LOW_PRIORITY
,
SUM_TIMER_WRITE_LOW_PRIORITY
,
MIN_TIMER_WRITE_LOW_PRIORITY
,
AVG_TIMER_WRITE_LOW_PRIORITY
,
MAX_TIMER_WRITE_LOW_PRIORITY
These columns aggregate internal write locks.
COUNT_WRITE_NORMAL
,
SUM_TIMER_WRITE_NORMAL
,
MIN_TIMER_WRITE_NORMAL
,
AVG_TIMER_WRITE_NORMAL
,
MAX_TIMER_WRITE_NORMAL
These columns aggregate internal write locks.
COUNT_WRITE_EXTERNAL
,
SUM_TIMER_WRITE_EXTERNAL
,
MIN_TIMER_WRITE_EXTERNAL
,
AVG_TIMER_WRITE_EXTERNAL
,
MAX_TIMER_WRITE_EXTERNAL
These columns aggregate external write locks.
TRUNCATE TABLE
is permitted
for table lock summary tables. It resets the summary columns
to zero rather than removing rows.
These socket summary tables aggregate timer and byte count information for socket operations:
socket_summary_by_event_name
:
Aggregate timer and byte count statistics generated by the
wait/io/socket/*
instruments for all
socket I/O operations, per socket instrument.
socket_summary_by_instance
:
Aggregate timer and byte count statistics generated by the
wait/io/socket/*
instruments for all
socket I/O operations, per socket instance. When a
connection terminates, the row in
socket_summary_by_instance
corresponding to it is deleted.
The socket summary tables do not aggregate waits generated by
idle
events while sockets are waiting for
the next request from the client. For idle
event aggregations, use the wait-event summary tables; see
Section 25.12.15.1, “Wait Event Summary Tables”.
Each socket summary table has one or more grouping columns to
indicate how the table aggregates events. Event names refer to
names of event instruments in the
setup_instruments
table:
socket_summary_by_event_name
has an EVENT_NAME
column. Each row
summarizes events for a given event name.
socket_summary_by_instance
has an OBJECT_INSTANCE_BEGIN
column.
Each row summarizes events for a given object.
Each socket summary table has these summary columns containing aggregated values:
COUNT_STAR
,
SUM_TIMER_WAIT
,
MIN_TIMER_WAIT
,
AVG_TIMER_WAIT
,
MAX_TIMER_WAIT
These columns aggregate all operations.
COUNT_READ
,
SUM_TIMER_READ
,
MIN_TIMER_READ
,
AVG_TIMER_READ
,
MAX_TIMER_READ
,
SUM_NUMBER_OF_BYTES_READ
These columns aggregate all receive operations
(RECV
, RECVFROM
, and
RECVMSG
).
COUNT_WRITE
,
SUM_TIMER_WRITE
,
MIN_TIMER_WRITE
,
AVG_TIMER_WRITE
,
MAX_TIMER_WRITE
,
SUM_NUMBER_OF_BYTES_WRITE
These columns aggregate all send operations
(SEND
, SENDTO
, and
SENDMSG
).
COUNT_MISC
,
SUM_TIMER_MISC
,
MIN_TIMER_MISC
,
AVG_TIMER_MISC
,
MAX_TIMER_MISC
These columns aggregate all other socket operations, such
as CONNECT
, LISTEN
,
ACCEPT
, CLOSE
, and
SHUTDOWN
. There are no byte counts for
these operations.
The socket_summary_by_instance
table also has an EVENT_NAME
column that
indicates the class of the socket:
client_connection
,
server_tcpip_socket
,
server_unix_socket
. This column can be
grouped on to isolate, for example, client activity from that
of the server listening sockets.
TRUNCATE TABLE
is permitted for
socket summary tables. Except for
events_statements_summary_by_digest
,
tt resets the summary columns to zero rather than removing
rows.
The Performance Schema instruments memory usage and aggregates memory usage statistics, detailed by these factors:
Type of memory used (various caches, internal buffers, and so forth)
Thread, account, user, host indirectly performing the memory operation
The Performance Schema instruments the following aspects of memory use
Memory sizes used
Operation counts
Low and high water marks
Memory sizes help to understand or tune the memory consumption of the server.
Operation counts help to understand or tune the overall pressure the server is putting on the memory allocator, which has an impact on performance. Allocating a single byte one million times is not the same as allocating one million bytes a single time; tracking both sizes and counts can expose the difference.
Low and high water marks are critical to detect workload spikes, overall workload stability, and possible memory leaks.
Memory summary tables do not contain timing information because memory events are not timed.
For information about collecting memory usage data, see Memory Instrumentation Behavior.
Example memory event summary information:
mysql>SELECT *
FROM performance_schema.memory_summary_global_by_event_name
WHERE EVENT_NAME = 'memory/sql/TABLE'\G
*************************** 1. row *************************** EVENT_NAME: memory/sql/TABLE COUNT_ALLOC: 1381 COUNT_FREE: 924 SUM_NUMBER_OF_BYTES_ALLOC: 2059873 SUM_NUMBER_OF_BYTES_FREE: 1407432 LOW_COUNT_USED: 0 CURRENT_COUNT_USED: 457 HIGH_COUNT_USED: 461 LOW_NUMBER_OF_BYTES_USED: 0 CURRENT_NUMBER_OF_BYTES_USED: 652441 HIGH_NUMBER_OF_BYTES_USED: 669269
Each memory summary table has one or more grouping columns to
indicate how the table aggregates events. Event names refer to
names of event instruments in the
setup_instruments
table:
memory_summary_by_account_by_event_name
has USER
, HOST
, and
EVENT_NAME
columns. Each row summarizes
events for a given account (user and host combination) and
event name.
memory_summary_by_host_by_event_name
has HOST
and
EVENT_NAME
columns. Each row summarizes
events for a given host and event name.
memory_summary_by_thread_by_event_name
has THREAD_ID
and
EVENT_NAME
columns. Each row summarizes
events for a given thread and event name.
memory_summary_by_user_by_event_name
has USER
and
EVENT_NAME
columns. Each row summarizes
events for a given user and event name.
memory_summary_global_by_event_name
has an EVENT_NAME
column. Each row
summarizes events for a given event name.
Each memory summary table has these summary columns containing aggregated values:
COUNT_ALLOC
,
COUNT_FREE
The aggregated numbers of calls to memory-allocation and memory-free functions.
SUM_NUMBER_OF_BYTES_ALLOC
,
SUM_NUMBER_OF_BYTES_FREE
The aggregated sizes of allocated and freed memory blocks.
CURRENT_COUNT_USED
The aggregated number of currently allocated blocks that
have not been freed yet. This is a convenience column,
equal to COUNT_ALLOC
−
COUNT_FREE
.
CURRENT_NUMBER_OF_BYTES_USED
The aggregated size of currently allocated memory blocks
that have not been freed yet. This is a convenience
column, equal to
SUM_NUMBER_OF_BYTES_ALLOC
−
SUM_NUMBER_OF_BYTES_FREE
.
LOW_COUNT_USED
,
HIGH_COUNT_USED
The low and high water marks corresponding to the
CURRENT_COUNT_USED
column.
LOW_NUMBER_OF_BYTES_USED
,
HIGH_NUMBER_OF_BYTES_USED
The low and high water marks corresponding to the
CURRENT_NUMBER_OF_BYTES_USED
column.
TRUNCATE TABLE
is permitted for
memory summary tables. It has these effects:
In general, truncation resets the baseline for statistics, but does not change the server state. That is, truncating a memory table does not free memory.
COUNT_ALLOC
and
COUNT_FREE
are reset to a new baseline,
by reducing each counter by the same value.
Likewise, SUM_NUMBER_OF_BYTES_ALLOC
and
SUM_NUMBER_OF_BYTES_FREE
are reset to a
new baseline.
LOW_COUNT_USED
and
HIGH_COUNT_USED
are reset to
CURRENT_COUNT_USED
.
LOW_NUMBER_OF_BYTES_USED
and
HIGH_NUMBER_OF_BYTES_USED
are reset to
CURRENT_NUMBER_OF_BYTES_USED
.
In addition, each memory summary table that is aggregated by
account, host, user, or thread is implicitly truncated by
truncation of the connection table on which it depends, or
truncation of
memory_summary_global_by_event_name
.
For details, see
Section 25.12.8, “Performance Schema Connection Tables”.
Memory instruments are listed in the
setup_instruments
table and
have names of the form
memory/
.
Most memory instrumentation is disabled by default.
code_area
/instrument_name
Instruments named with the prefix
memory/performance_schema/
expose how
much memory is allocated for internal buffers in the
Performance Schema itself. The
memory/performance_schema/
instruments
are built in, always enabled, and cannot be disabled at
startup or runtime. Built-in memory instruments are
displayed only in the
memory_summary_global_by_event_name
table.
To control memory instrumentation state at server startup,
use lines like these in your my.cnf
file:
Enable:
[mysqld] performance-schema-instrument='memory/%=ON'
Disable:
[mysqld] performance-schema-instrument='memory/%=OFF'
To control memory instrumentation state at runtime, update
the ENABLED
column of the relevant
instruments in the
setup_instruments
table:
Enable:
UPDATE performance_schema.setup_instruments SET ENABLED = 'YES' WHERE NAME LIKE 'memory/%';
Disable:
UPDATE performance_schema.setup_instruments SET ENABLED = 'NO' WHERE NAME LIKE 'memory/%';
For memory instruments, the TIMED
column
in setup_instruments
is ignored
because memory operations are not timed.
When a thread in the server executes a memory allocation that has been instrumented, these rules apply:
If the thread is not instrumented or the memory instrument is not enabled, the memory block allocated is not instrumented.
Otherwise (that is, both the thread and the instrument are enabled), the memory block allocated is instrumented.
For deallocation, these rules apply:
If a memory allocation operation was instrumented, the corresponding free operation is instrumented, regardless of the current instrument or thread enabled status.
If a memory allocation operation was not instrumented, the corresponding free operation is not instrumented, regardless of the current instrument or thread enabled status.
For the per-thread statistics, the following rules apply.
When an instrumented memory block of size
N
is allocated, the Performance
Schema makes these updates to memory summary table columns:
COUNT_ALLOC
: Increased by 1
CURRENT_COUNT_USED
: Increased by 1
HIGH_COUNT_USED
: Increased if
CURRENT_COUNT_USED
is a new maximum
SUM_NUMBER_OF_BYTES_ALLOC
: Increased
by N
CURRENT_NUMBER_OF_BYTES_USED
:
Increased by N
HIGH_NUMBER_OF_BYTES_USED
: Increased
if CURRENT_NUMBER_OF_BYTES_USED
is a
new maximum
When an instrumented memory block is deallocated, the Performance Schema makes these updates to memory summary table columns:
COUNT_FREE
: Increased by 1
CURRENT_COUNT_USED
: Decreased by 1
LOW_COUNT_USED
: Decreased if
CURRENT_COUNT_USED
is a new minimum
SUM_NUMBER_OF_BYTES_FREE
: Increased
by N
CURRENT_NUMBER_OF_BYTES_USED
:
Decreased by N
LOW_NUMBER_OF_BYTES_USED
: Decreased
if CURRENT_NUMBER_OF_BYTES_USED
is a
new minimum
For higher-level aggregates (global, by account, by user, by host), the same rules apply as expected for low and high water marks.
LOW_COUNT_USED
and
LOW_NUMBER_OF_BYTES_USED
are lower
estimates. The value reported by the Performance Schema
is guaranteed to be less than or equal to the lowest
count or size of memory effectively used at runtime.
HIGH_COUNT_USED
and
HIGH_NUMBER_OF_BYTES_USED
are higher
estimates. The value reported by the Performance Schema
is guaranteed to be greater than or equal to the highest
count or size of memory effectively used at runtime.
For lower estimates in summary tables other than
memory_summary_global_by_event_name
,
it is possible for values to go negative if memory ownership
is transferred between threads.
Here is an example of estimate computation; but note that estimate implementation is subject to change:
Thread 1 uses memory in the range from 1MB to 2MB during
execution, as reported by the
LOW_NUMBER_OF_BYTES_USED
and
HIGH_NUMBER_OF_BYTES_USED
columns of the
memory_summary_by_thread_by_event_name
table.
Thread 2 uses memory in the range from 10MB to 12MB during execution, as reported likewise.
When these two threads belong to the same user account, the
per-account summary estimates that this account used memory
in the range from 11MB to 14MB. That is, the
LOW_NUMBER_OF_BYTES_USED
for the higher
level aggregate is the sum of each
LOW_NUMBER_OF_BYTES_USED
(assuming the
worst case). Likewise, the
HIGH_NUMBER_OF_BYTES_USED
for the higher
level aggregate is the sum of each
HIGH_NUMBER_OF_BYTES_USED
(assuming the
worst case).
11MB is a lower estimate that can occur only if both threads hit the low usage mark at the same time.
14MB is a higher estimate that can occur only if both threads hit the high usage mark at the same time.
The real memory usage for this account could have been in the range from 11.5MB to 13.5MB.
For capacity planning, reporting the worst case is actually the desired behavior, as it shows what can potentially happen when sessions are uncorrelated, which is typically the case.
The value of the
show_compatibility_56
system variable affects the information available from the
tables described here. For details, see the description of
that variable in Section 5.1.7, “Server System Variables”.
The Performance Schema makes status variable information available in the tables described in Section 25.12.14, “Performance Schema Status Variable Tables”. It also makes aggregated status variable information available in summary tables, described here. Each status variable summary table has one or more grouping columns to indicate how the table aggregates status values:
status_by_account
has
USER
, HOST
, and
VARIABLE_NAME
columns to summarize
status variables by account.
status_by_host
has
HOST
and
VARIABLE_NAME
columns to summarize
status variables by the host from which clients connected.
status_by_user
has
USER
and
VARIABLE_NAME
columns to summarize
status variables by client user name.
Each status variable summary table has this summary column containing aggregated values:
VARIABLE_VALUE
The aggregated status variable value for active and terminated sessions.
The meaning of “account” in these tables is
similar to its meaning in the MySQL grant tables in the
mysql
system database, in the sense that
the term refers to a combination of user and host values. They
differ in that, for grant tables, the host part of an account
can be a pattern, whereas for Performance Schema tables, the
host value is always a specific nonpattern host name.
Account status is collected when sessions terminate. The session status counters are added to the global status counters and the corresponding account status counters. If account statistics are not collected, the session status is added to host and user status, if host and user status are collected.
Account, host, and user statistics are not collected if the
performance_schema_accounts_size
,
performance_schema_hosts_size
,
and
performance_schema_users_size
system variables, respectively, are set to 0.
The Performance Schema supports TRUNCATE
TABLE
for status variable summary tables as follows;
in all cases, status for active sessions is unaffected:
status_by_account
: Aggregates
account status from terminated sessions to user and host
status, then resets account status.
status_by_host
: Resets
aggregated host status from terminated sessions.
status_by_user
: Resets
aggregated user status from terminated sessions.
FLUSH STATUS
adds the session
status from all active sessions to the global status
variables, resets the status of all active sessions, and
resets account, host, and user status values aggregated from
disconnected sessions.
The following sections describe tables that do not fall into the table categories discussed in the preceding sections:
host_cache
: Information from
the internal host cache
performance_timers
: Which event
timers are available
threads
: Information about
server threads
The host_cache
table provides
access to the contents of the host cache, which contains
client host name and IP address information and is used to
avoid Domain Name System (DNS) lookups. The
host_cache_size
system
variable controls the size of the host cache, as well as the
size of the host_cache
table that
exposes the cache contents. For operational and configuration
information about the host cache, see
Section 8.12.5.2, “DNS Lookup Optimization and the Host Cache”.
Because the host_cache
table
exposes the contents of the host cache, it can be examined
using SELECT
statements. This
may help you diagnose the causes of connection problems. The
Performance Schema must be enabled or this table is empty.
The host_cache
table has these
columns:
IP
The IP address of the client that connected to the server, expressed as a string.
HOST
The resolved DNS host name for that client IP, or
NULL
if the name is unknown.
HOST_VALIDATED
Whether the IP-to-host name-to-IP DNS resolution was
performed successfully for the client IP. If
HOST_VALIDATED
is
YES
, the HOST
column
is used as the host name corresponding to the IP so that
additional calls to DNS can be avoided. While
HOST_VALIDATED
is
NO
, DNS resolution is attempted for
each connection attempt, until it eventually completes
with either a valid result or a permanent error. This
information enables the server to avoid caching bad or
missing host names during temporary DNS failures, which
would negatively affect clients forever.
SUM_CONNECT_ERRORS
The number of connection errors that are deemed
“blocking” (assessed against the
max_connect_errors
system
variable). Only protocol handshake errors are counted, and
only for hosts that passed validation
(HOST_VALIDATED = YES
).
Once SUM_CONNECT_ERRORS
for a given
host reaches the value of
max_connect_errors
, new
connections from that host are blocked. The
SUM_CONNECT_ERRORS
value can exceed the
max_connect_errors
value
because multiple connection attempts from a host can occur
simultaneously while the host is not blocked. Any or all
of them can fail, independently incrementing
SUM_CONNECT_ERRORS
, possibly beyond the
value of
max_connect_errors
.
Suppose that
max_connect_errors
is 200
and SUM_CONNECT_ERRORS
for a given host
is 199. If 10 clients attempt to connect from that host
simultaneously, none of them are blocked because
SUM_CONNECT_ERRORS
has not reached 200.
If blocking errors occur for five of the clients,
SUM_CONNECT_ERRORS
is increased by one
for each client, for a resulting
SUM_CONNECT_ERRORS
value of 204. The
other five clients succeed and are not blocked because the
value of SUM_CONNECT_ERRORS
when their
connection attempts began had not reached 200. New
connections from the host that begin after
SUM_CONNECT_ERRORS
reaches 200 are
blocked.
COUNT_HOST_BLOCKED_ERRORS
The number of connections that were blocked because
SUM_CONNECT_ERRORS
exceeded the value
of the max_connect_errors
system variable.
COUNT_NAMEINFO_TRANSIENT_ERRORS
The number of transient errors during IP-to-host name DNS resolution.
COUNT_NAMEINFO_PERMANENT_ERRORS
The number of permanent errors during IP-to-host name DNS resolution.
COUNT_FORMAT_ERRORS
The number of host name format errors. MySQL does not
perform matching of Host
column values
in the mysql.user
system table against
host names for which one or more of the initial components
of the name are entirely numeric, such as
1.2.example.com
. The client IP address
is used instead. For the rationale why this type of
matching does not occur, see
Section 6.2.4, “Specifying Account Names”.
COUNT_ADDRINFO_TRANSIENT_ERRORS
The number of transient errors during host name-to-IP reverse DNS resolution.
COUNT_ADDRINFO_PERMANENT_ERRORS
The number of permanent errors during host name-to-IP reverse DNS resolution.
COUNT_FCRDNS_ERRORS
The number of forward-confirmed reverse DNS errors. These errors occur when IP-to-host name-to-IP DNS resolution produces an IP address that does not match the client originating IP address.
COUNT_HOST_ACL_ERRORS
The number of errors that occur because no users are
permitted to connect from the client host. In such cases,
the server returns
ER_HOST_NOT_PRIVILEGED
and
does not even ask for a user name or password.
COUNT_NO_AUTH_PLUGIN_ERRORS
The number of errors due to requests for an unavailable authentication plugin. A plugin can be unavailable if, for example, it was never loaded or a load attempt failed.
COUNT_AUTH_PLUGIN_ERRORS
The number of errors reported by authentication plugins.
An authentication plugin can report different error codes
to indicate the root cause of a failure. Depending on the
type of error, one of these columns is incremented:
COUNT_AUTHENTICATION_ERRORS
,
COUNT_AUTH_PLUGIN_ERRORS
,
COUNT_HANDSHAKE_ERRORS
. New return
codes are an optional extension to the existing plugin
API. Unknown or unexpected plugin errors are counted in
the COUNT_AUTH_PLUGIN_ERRORS
column.
COUNT_HANDSHAKE_ERRORS
The number of errors detected at the wire protocol level.
COUNT_PROXY_USER_ERRORS
The number of errors detected when proxy user A is proxied to another user B who does not exist.
COUNT_PROXY_USER_ACL_ERRORS
The number of errors detected when proxy user A is proxied
to another user B who does exist but for whom A does not
have the PROXY
privilege.
COUNT_AUTHENTICATION_ERRORS
The number of errors caused by failed authentication.
COUNT_SSL_ERRORS
The number of errors due to SSL problems.
COUNT_MAX_USER_CONNECTIONS_ERRORS
The number of errors caused by exceeding per-user connection quotas. See Section 6.2.16, “Setting Account Resource Limits”.
COUNT_MAX_USER_CONNECTIONS_PER_HOUR_ERRORS
The number of errors caused by exceeding per-user connections-per-hour quotas. See Section 6.2.16, “Setting Account Resource Limits”.
COUNT_DEFAULT_DATABASE_ERRORS
The number of errors related to the default database. For example, the database does not exist or the user has no privileges to access it.
COUNT_INIT_CONNECT_ERRORS
The number of errors caused by execution failures of
statements in the
init_connect
system
variable value.
COUNT_LOCAL_ERRORS
The number of errors local to the server implementation and not related to the network, authentication, or authorization. For example, out-of-memory conditions fall into this category.
COUNT_UNKNOWN_ERRORS
The number of other, unknown errors not accounted for by
other columns in this table. This column is reserved for
future use, in case new error conditions must be reported,
and if preserving the backward compatibility and structure
of the host_cache
table is
required.
FIRST_SEEN
The timestamp of the first connection attempt seen from
the client in the IP
column.
LAST_SEEN
The timestamp of the most recent connection attempt seen
from the client in the IP
column.
FIRST_ERROR_SEEN
The timestamp of the first error seen from the client in
the IP
column.
LAST_ERROR_SEEN
The timestamp of the most recent error seen from the
client in the IP
column.
The FLUSH HOSTS
statement,
TRUNCATE TABLE
host_cache
statement, and mysqladmin
flush-hosts command have the same effect: They clear
the host cache, remove all rows from the
host_cache
table that exposes the
cache contents, and unblock any blocked hosts (see
Section B.4.2.5, “Host 'host_name' is blocked”). FLUSH
HOSTS
and mysqladmin flush-hosts
require the RELOAD
privilege.
TRUNCATE TABLE
requires the
DROP
privilege for the
host_cache
table.
The performance_timers
table
shows which event timers are available:
mysql> SELECT * FROM performance_schema.performance_timers;
+-------------+-----------------+------------------+----------------+
| TIMER_NAME | TIMER_FREQUENCY | TIMER_RESOLUTION | TIMER_OVERHEAD |
+-------------+-----------------+------------------+----------------+
| CYCLE | 2389029850 | 1 | 72 |
| NANOSECOND | 1000000000 | 1 | 112 |
| MICROSECOND | 1000000 | 1 | 136 |
| MILLISECOND | 1036 | 1 | 168 |
| TICK | 105 | 1 | 2416 |
+-------------+-----------------+------------------+----------------+
If the values associated with a given timer name are
NULL
, that timer is not supported on your
platform. The rows that do not contain NULL
indicate which timers you can use in
setup_timers
. For an explanation
of how event timing occurs, see
Section 25.4.1, “Performance Schema Event Timing”.
As of MySQL 5.7.21, the Performance Schema
setup_timers
table is
deprecated and is removed in MySQL 8.0, as is the
TICKS
row in the
performance_timers
table.
The performance_timers
table has
these columns:
TIMER_NAME
The name by which to refer to the timer when configuring
the setup_timers
table.
TIMER_FREQUENCY
The number of timer units per second. For a cycle timer,
the frequency is generally related to the CPU speed. For
example, on a system with a 2.4GHz processor, the
CYCLE
may be close to 2400000000.
TIMER_RESOLUTION
Indicates the number of timer units by which timer values increase. If a timer has a resolution of 10, its value increases by 10 each time.
TIMER_OVERHEAD
The minimal number of cycles of overhead to obtain one timing with the given timer. The Performance Schema determines this value by invoking the timer 20 times during initialization and picking the smallest value. The total overhead really is twice this amount because the instrumentation invokes the timer at the start and end of each event. The timer code is called only for timed events, so this overhead does not apply for nontimed events.
TRUNCATE TABLE
is not permitted
for the performance_timers
table.
The threads
table contains a row
for each server thread. Each row contains information about a
thread and indicates whether monitoring and historical event
logging are enabled for it:
mysql> SELECT * FROM performance_schema.threads\G
*************************** 1. row ***************************
THREAD_ID: 1
NAME: thread/sql/main
TYPE: BACKGROUND
PROCESSLIST_ID: NULL
PROCESSLIST_USER: NULL
PROCESSLIST_HOST: NULL
PROCESSLIST_DB: NULL
PROCESSLIST_COMMAND: NULL
PROCESSLIST_TIME: 80284
PROCESSLIST_STATE: NULL
PROCESSLIST_INFO: NULL
PARENT_THREAD_ID: NULL
ROLE: NULL
INSTRUMENTED: YES
HISTORY: YES
CONNECTION_TYPE: NULL
THREAD_OS_ID: 489803
...
*************************** 4. row ***************************
THREAD_ID: 51
NAME: thread/sql/one_connection
TYPE: FOREGROUND
PROCESSLIST_ID: 34
PROCESSLIST_USER: isabella
PROCESSLIST_HOST: localhost
PROCESSLIST_DB: performance_schema
PROCESSLIST_COMMAND: Query
PROCESSLIST_TIME: 0
PROCESSLIST_STATE: Sending data
PROCESSLIST_INFO: SELECT * FROM performance_schema.threads
PARENT_THREAD_ID: 1
ROLE: NULL
INSTRUMENTED: YES
HISTORY: YES
CONNECTION_TYPE: SSL/TLS
THREAD_OS_ID: 755399
...
When the Performance Schema initializes, it populates the
threads
table based on the
threads in existence then. Thereafter, a new row is added each
time the server creates a thread.
The INSTRUMENTED
and
HISTORY
column values for new threads are
determined by the contents of the
setup_actors
table. For
information about how to use the
setup_actors
table to control
these columns, see
Section 25.4.6, “Pre-Filtering by Thread”.
Removal of rows from the threads
table occurs when threads end. For a thread associated with a
client session, removal occurs when the session ends. If a
client has auto-reconnect enabled and the session reconnects
after a disconnect, the session becomes associated with a new
row in the threads
table that has
a different PROCESSLIST_ID
value. The
initial INSTRUMENTED
and
HISTORY
values for the new thread may be
different from those of the original thread: The
setup_actors
table may have
changed in the meantime, and if the
INSTRUMENTED
or HISTORY
value for the original thread was changed after the row was
initialized, the change does not carry over to the new thread.
The threads
table columns with
names having a prefix of PROCESSLIST_
provide information similar to that available from the
INFORMATION_SCHEMA.PROCESSLIST
table or the SHOW PROCESSLIST
statement. Thus, all three sources provide thread-monitoring
information. Use of threads
differs from use of the other two sources in these ways:
Access to threads
does not
require a mutex and has minimal impact on server
performance.
INFORMATION_SCHEMA.PROCESSLIST
and SHOW PROCESSLIST
have
negative performance consequences because they require a
mutex.
threads
provides additional
information for each thread, such as whether it is a
foreground or background thread, and the location within
the server associated with the thread.
threads
provides information
about background threads, so it can be used to monitor
activity the other thread information sources cannot.
You can enable or disable thread monitoring (that is,
whether events executed by the thread are instrumented)
and historical event logging. To control the initial
INSTRUMENTED
and
HISTORY
values for new foreground
threads, use the setup_actors
table. To control these aspects of existing threads, set
the INSTRUMENTED
and
HISTORY
columns of
threads
table rows. (For more
information about the conditions under which thread
monitoring and historical event logging occur, see the
descriptions of the INSTRUMENTED
and
HISTORY
columns.)
For these reasons, DBAs who perform server monitoring using
INFORMATION_SCHEMA.PROCESSLIST
or
SHOW PROCESSLIST
may wish to
monitor using the threads
table
instead.
For
INFORMATION_SCHEMA.PROCESSLIST
and SHOW PROCESSLIST
,
information about threads for other users is shown only if
the current user has the
PROCESS
privilege. That is
not true of the threads
table;
all rows are shown to any user who has the
SELECT
privilege for the table. Users who
should not be able to see threads for other users should not
be given that privilege.
The threads
table has these
columns:
THREAD_ID
A unique thread identifier.
NAME
The name associated with the thread instrumentation code
in the server. For example,
thread/sql/one_connection
corresponds
to the thread function in the code responsible for
handling a user connection, and
thread/sql/main
stands for the
main()
function of the server.
TYPE
The thread type, either FOREGROUND
or
BACKGROUND
. User connection threads are
foreground threads. Threads associated with internal
server activity are background threads. Examples are
internal InnoDB
threads, “binlog
dump” threads sending information to slaves, and
slave I/O and SQL threads.
PROCESSLIST_ID
For threads that are displayed in the
INFORMATION_SCHEMA.PROCESSLIST
table, this is the same value displayed in the
ID
column of that table. It is also the
value displayed in the Id
column of
SHOW PROCESSLIST
output,
and the value that
CONNECTION_ID()
would
return within that thread.
For background threads (threads not associated with a user
connection), PROCESSLIST_ID
is
NULL
, so the values are not unique.
PROCESSLIST_USER
The user associated with a foreground thread,
NULL
for a background thread.
PROCESSLIST_HOST
The host name of the client associated with a foreground
thread, NULL
for a background thread.
Unlike the HOST
column of the
INFORMATION_SCHEMA
PROCESSLIST
table or the
Host
column of
SHOW PROCESSLIST
output,
the PROCESSLIST_HOST
column does not
include the port number for TCP/IP connections. To obtain
this information from the Performance Schema, enable the
socket instrumentation (which is not enabled by default)
and examine the
socket_instances
table:
mysql>SELECT * FROM performance_schema.setup_instruments
WHERE NAME LIKE 'wait/io/socket%';
+----------------------------------------+---------+-------+ | NAME | ENABLED | TIMED | +----------------------------------------+---------+-------+ | wait/io/socket/sql/server_tcpip_socket | NO | NO | | wait/io/socket/sql/server_unix_socket | NO | NO | | wait/io/socket/sql/client_connection | NO | NO | +----------------------------------------+---------+-------+ 3 rows in set (0.01 sec) mysql>UPDATE performance_schema.setup_instruments
SET ENABLED='YES'
WHERE NAME LIKE 'wait/io/socket%';
Query OK, 3 rows affected (0.00 sec) Rows matched: 3 Changed: 3 Warnings: 0 mysql>SELECT * FROM performance_schema.socket_instances\G
*************************** 1. row *************************** EVENT_NAME: wait/io/socket/sql/client_connection OBJECT_INSTANCE_BEGIN: 140612577298432 THREAD_ID: 31 SOCKET_ID: 53 IP: ::ffff:127.0.0.1 PORT: 55642 STATE: ACTIVE ...
PROCESSLIST_DB
The default database for the thread, or
NULL
if there is none.
PROCESSLIST_COMMAND
For foreground threads, the type of command the thread is
executing on behalf of the client, or
Sleep
if the session is idle. For
descriptions of thread commands, see
Section 8.14, “Examining Thread Information”. The value of this
column corresponds to the
COM_
commands of the client/server protocol and
xxx
Com_
status variables. See
Section 5.1.9, “Server Status Variables”
xxx
Background threads do not execute commands on behalf of
clients, so this column may be NULL
.
PROCESSLIST_TIME
The time in seconds that the thread has been in its current state.
PROCESSLIST_STATE
An action, event, or state that indicates what the thread
is doing. For descriptions of
PROCESSLIST_STATE
values, see
Section 8.14, “Examining Thread Information”. If the value if
NULL
, the thread may correspond to an
idle client session or the work it is doing is not
instrumented with stages.
Most states correspond to very quick operations. If a thread stays in a given state for many seconds, there might be a problem that bears investigation.
PROCESSLIST_INFO
The statement the thread is executing, or
NULL
if it is not executing any
statement. The statement might be the one sent to the
server, or an innermost statement if the statement
executes other statements. For example, if a
CALL
statement executes a stored
procedure that is executing a
SELECT
statement, the
PROCESSLIST_INFO
value shows the
SELECT
statement.
PARENT_THREAD_ID
If this thread is a subthread (spawned by another thread),
this is the THREAD_ID
value of the
spawning thread.
ROLE
Unused.
INSTRUMENTED
Whether events executed by the thread are instrumented.
The value is YES
or
NO
.
For foreground threads, the initial
INSTRUMENTED
value is determined by
whether the user account associated with the thread
matches any row in the
setup_actors
table.
Matching is based on the values of the
PROCESSLIST_USER
and
PROCESSLIST_HOST
columns.
If the thread spawns a subthread, matching occurs
again for the threads
table row created for the subthread.
For background threads,
INSTRUMENTED
is
YES
by default.
setup_actors
is not
consulted because there is no associated user for
background threads.
For any thread, its INSTRUMENTED
value can be changed during the lifetime of the
thread.
For monitoring of events executed by the thread to occur, these things must be true:
The thread_instrumentation
consumer
in the setup_consumers
table must be YES
.
The threads.INSTRUMENTED
column
must be YES
.
Monitoring occurs only for those thread events
produced from instruments that have the
ENABLED
column set to
YES
in the
setup_instruments
table.
HISTORY
Whether to log historical events for the thread. The value
is YES
or NO
.
For foreground threads, the initial
HISTORY
value is determined by
whether the user account associated with the thread
matches any row in the
setup_actors
table.
Matching is based on the values of the
PROCESSLIST_USER
and
PROCESSLIST_HOST
columns.
If the thread spawns a subthread, matching occurs
again for the threads
table row created for the subthread.
For background threads, HISTORY
is
YES
by default.
setup_actors
is not
consulted because there is no associated user for
background threads.
For any thread, its HISTORY
value
can be changed during the lifetime of the thread.
For historical event logging for the thread to occur, these things must be true:
The appropriate history-related consumers in the
setup_consumers
table
must be enabled. For example, wait event logging in
the events_waits_history
and
events_waits_history_long
tables requires the corresponding
events_waits_history
and
events_waits_history_long
consumers
to be YES
.
The threads.HISTORY
column must be
YES
.
Logging occurs only for those thread events produced
from instruments that have the
ENABLED
column set to
YES
in the
setup_instruments
table.
CONNECTION_TYPE
The protocol used to establish the connection, or
NULL
for background threads. Permitted
values are TCP/IP
(TCP/IP connection
established without encryption),
SSL/TLS
(TCP/IP connection established
with encryption), Socket
(Unix socket
file connection), Named Pipe
(Windows
named pipe connection), and Shared
Memory
(Windows shared memory connection).
THREAD_OS_ID
The thread or task identifier as defined by the underlying operating system, if there is one:
When a MySQL thread is associated with the same
operating system thread for its lifetime,
THREAD_OS_ID
contains the operating
system thread ID.
When a MySQL thread is not associated with the same
operating system thread for its lifetime,
THREAD_OS_ID
contains
NULL
. This is typical for user
sessions when the thread pool plugin is used (see
Section 5.5.3, “MySQL Enterprise Thread Pool”).
For Windows, THREAD_OS_ID
corresponds
to the thread ID visible in Process Explorer
(https://technet.microsoft.com/en-us/sysinternals/bb896653.aspx).
For Linux, THREAD_OS_ID
corresponds to
the value of the gettid()
function.
This value is exposed, for example, using the
perf or ps -L
commands, or in the proc
file system
(/proc/
).
For more information, see the
[pid]
/task/[tid]
perf-stat(1)
, ps(1)
,
and proc(5)
man pages.
TRUNCATE TABLE
is not permitted
for the threads
table.
Table 25.3 Performance Schema Variable Reference
Performance Schema parameters can be specified at server startup on the command line or in option files to configure Performance Schema instruments and consumers. Runtime configuration is also possible in many cases (see Section 25.4, “Performance Schema Runtime Configuration”), but startup configuration must be used when runtime configuration is too late to affect instruments that have already been initialized during the startup process.
Performance Schema consumers and instruments can be configured at startup using the following syntax. For additional details, see Section 25.3, “Performance Schema Startup Configuration”.
--performance-schema-consumer-
consumer_name
=value
Configure a Performance Schema consumer. Consumer names in the
setup_consumers
table use
underscores, but for consumers set at startup, dashes and
underscores within the name are equivalent. Options for
configuring individual consumers are detailed later in this
section.
--performance-schema-instrument=
instrument_name
=value
Configure a Performance Schema instrument. The name may be given as a pattern to configure instruments that match the pattern.
The following items configure individual consumers:
--performance-schema-consumer-events-stages-current=
value
Configure the events-stages-current
consumer.
--performance-schema-consumer-events-stages-history=
value
Configure the events-stages-history
consumer.
--performance-schema-consumer-events-stages-history-long=
value
Configure the events-stages-history-long
consumer.
--performance-schema-consumer-events-statements-current=
value
Configure the events-statements-current
consumer.
--performance-schema-consumer-events-statements-history=
value
Configure the events-statements-history
consumer.
--performance-schema-consumer-events-statements-history-long=
value
Configure the
events-statements-history-long
consumer.
--performance-schema-consumer-events-transactions-current=
value
Configure the Performance Schema
events-transactions-current
consumer.
--performance-schema-consumer-events-transactions-history=
value
Configure the Performance Schema
events-transactions-history
consumer.
--performance-schema-consumer-events-transactions-history-long=
value
Configure the Performance Schema
events-transactions-history-long
consumer.
--performance-schema-consumer-events-waits-current=
value
Configure the events-waits-current
consumer.
--performance-schema-consumer-events-waits-history=
value
Configure the events-waits-history
consumer.
--performance-schema-consumer-events-waits-history-long=
value
Configure the events-waits-history-long
consumer.
--performance-schema-consumer-global-instrumentation=
value
Configure the global-instrumentation
consumer.
--performance-schema-consumer-statements-digest=
value
Configure the statements-digest
consumer.
--performance-schema-consumer-thread-instrumentation=
value
Configure the thread-instrumentation
consumer.
The Performance Schema implements several system variables that provide configuration information:
mysql> SHOW VARIABLES LIKE 'perf%';
+----------------------------------------------------------+-------+
| Variable_name | Value |
+----------------------------------------------------------+-------+
| performance_schema | ON |
| performance_schema_accounts_size | -1 |
| performance_schema_digests_size | 10000 |
| performance_schema_events_stages_history_long_size | 10000 |
| performance_schema_events_stages_history_size | 10 |
| performance_schema_events_statements_history_long_size | 10000 |
| performance_schema_events_statements_history_size | 10 |
| performance_schema_events_transactions_history_long_size | 10000 |
| performance_schema_events_transactions_history_size | 10 |
| performance_schema_events_waits_history_long_size | 10000 |
| performance_schema_events_waits_history_size | 10 |
| performance_schema_hosts_size | -1 |
| performance_schema_max_cond_classes | 80 |
| performance_schema_max_cond_instances | -1 |
| performance_schema_max_digest_length | 1024 |
| performance_schema_max_file_classes | 50 |
| performance_schema_max_file_handles | 32768 |
| performance_schema_max_file_instances | -1 |
| performance_schema_max_index_stat | -1 |
| performance_schema_max_memory_classes | 320 |
| performance_schema_max_metadata_locks | -1 |
| performance_schema_max_mutex_classes | 200 |
| performance_schema_max_mutex_instances | -1 |
| performance_schema_max_prepared_statements_instances | -1 |
| performance_schema_max_program_instances | -1 |
| performance_schema_max_rwlock_classes | 40 |
| performance_schema_max_rwlock_instances | -1 |
| performance_schema_max_socket_classes | 10 |
| performance_schema_max_socket_instances | -1 |
| performance_schema_max_sql_text_length | 1024 |
| performance_schema_max_stage_classes | 150 |
| performance_schema_max_statement_classes | 192 |
| performance_schema_max_statement_stack | 10 |
| performance_schema_max_table_handles | -1 |
| performance_schema_max_table_instances | -1 |
| performance_schema_max_table_lock_stat | -1 |
| performance_schema_max_thread_classes | 50 |
| performance_schema_max_thread_instances | -1 |
| performance_schema_session_connect_attrs_size | 512 |
| performance_schema_setup_actors_size | -1 |
| performance_schema_setup_objects_size | -1 |
| performance_schema_users_size | -1 |
+----------------------------------------------------------+-------+
Performance Schema system variables can be set at server startup on the command line or in option files, and many can be set at runtime. See Section 25.13, “Performance Schema Option and Variable Reference”.
The Performance Schema automatically sizes the values of several of its parameters at server startup if they are not set explicitly. For more information, see Section 25.3, “Performance Schema Startup Configuration”.
Performance Schema system variables have the following meanings:
Property | Value |
---|---|
Command-Line Format | --performance-schema[={OFF|ON}] |
System Variable | performance_schema |
Scope | Global |
Dynamic | No |
Type | Boolean |
Default Value | ON |
The value of this variable is ON
or
OFF
to indicate whether the Performance
Schema is enabled. By default, the value is
ON
. At server startup, you can specify this
variable with no value or a value of ON
or
1 to enable it, or with a value of OFF
or 0
to disable it.
Even when the Performance Schema is disabled, it continues to
populate the global_variables
,
session_variables
,
global_status
, and
session_status
tables. This
occurs as necessary to permit the results for the
SHOW VARIABLES
and
SHOW STATUS
statements to be
drawn from those tables, depending on the setting of the
show_compatibiliy_56
system variable.
performance_schema_accounts_size
Property | Value |
---|---|
Command-Line Format | --performance-schema-accounts-size=# |
System Variable | performance_schema_accounts_size |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | -1 (signifies autoscaling; do not assign this literal value) |
Minimum Value | -1 (signifies autoscaling; do not assign this literal value) |
Maximum Value | 1048576 |
The number of rows in the
accounts
table. If this variable
is 0, the Performance Schema does not maintain connection
statistics in the accounts
table
or status variable information in the
status_by_account
table.
performance_schema_digests_size
Property | Value |
---|---|
Command-Line Format | --performance-schema-digests-size=# |
System Variable | performance_schema_digests_size |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | -1 (signifies autosizing; do not assign this literal value) |
Minimum Value | -1 |
Maximum Value | 1048576 |
The maximum number of rows in the
events_statements_summary_by_digest
table. If this maximum is exceeded such that a digest cannot
be instrumented, the Performance Schema increments the
Performance_schema_digest_lost
status variable.
For more information about statement digesting, see Section 25.10, “Performance Schema Statement Digests”.
performance_schema_events_stages_history_long_size
Property | Value |
---|---|
Command-Line Format | --performance-schema-events-stages-history-long-size=# |
System Variable | performance_schema_events_stages_history_long_size |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | -1 (signifies autosizing; do not assign this literal value) |
The number of rows in the
events_stages_history_long
table.
performance_schema_events_stages_history_size
Property | Value |
---|---|
Command-Line Format | --performance-schema-events-stages-history-size=# |
System Variable | performance_schema_events_stages_history_size |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | -1 (signifies autosizing; do not assign this literal value) |
The number of rows per thread in the
events_stages_history
table.
performance_schema_events_statements_history_long_size
Property | Value |
---|---|
Command-Line Format | --performance-schema-events-statements-history-long-size=# |
System Variable | performance_schema_events_statements_history_long_size |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | -1 (signifies autosizing; do not assign this literal value) |
The number of rows in the
events_statements_history_long
table.
performance_schema_events_statements_history_size
Property | Value |
---|---|
Command-Line Format | --performance-schema-events-statements-history-size=# |
System Variable | performance_schema_events_statements_history_size |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | -1 (signifies autosizing; do not assign this literal value) |
The number of rows per thread in the
events_statements_history
table.
performance_schema_events_transactions_history_long_size
Property | Value |
---|---|
Command-Line Format | --performance-schema-events-transactions-history-long-size=# |
System Variable | performance_schema_events_transactions_history_long_size |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | -1 (signifies autosizing; do not assign this literal value) |
The number of rows in the
events_transactions_history_long
table.
performance_schema_events_transactions_history_size
Property | Value |
---|---|
Command-Line Format | --performance-schema-events-transactions-history-size=# |
System Variable | performance_schema_events_transactions_history_size |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | -1 (signifies autosizing; do not assign this literal value) |
The number of rows per thread in the
events_transactions_history
table.
performance_schema_events_waits_history_long_size
Property | Value |
---|---|
Command-Line Format | --performance-schema-events-waits-history-long-size=# |
System Variable | performance_schema_events_waits_history_long_size |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | -1 (signifies autosizing; do not assign this literal value) |
The number of rows in the
events_waits_history_long
table.
performance_schema_events_waits_history_size
Property | Value |
---|---|
Command-Line Format | --performance-schema-events-waits-history-size=# |
System Variable | performance_schema_events_waits_history_size |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | -1 (signifies autosizing; do not assign this literal value) |
The number of rows per thread in the
events_waits_history
table.
Property | Value |
---|---|
Command-Line Format | --performance-schema-hosts-size=# |
System Variable | performance_schema_hosts_size |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | -1 (signifies autoscaling; do not assign this literal value) |
Minimum Value | -1 (signifies autoscaling; do not assign this literal value) |
Maximum Value | 1048576 |
The number of rows in the hosts
table. If this variable is 0, the Performance Schema does not
maintain connection statistics in the
hosts
table or status variable
information in the status_by_host
table.
performance_schema_max_cond_classes
Property | Value |
---|---|
Command-Line Format | --performance-schema-max-cond-classes=# |
System Variable | performance_schema_max_cond_classes |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | 80 |
Minimum Value | 0 |
Maximum Value | 256 |
The maximum number of condition instruments. For information about how to set and use this variable, see Section 25.7, “Performance Schema Status Monitoring”.
performance_schema_max_cond_instances
Property | Value |
---|---|
Command-Line Format | --performance-schema-max-cond-instances=# |
System Variable | performance_schema_max_cond_instances |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | -1 (signifies autoscaling; do not assign this literal value) |
The maximum number of instrumented condition objects. For information about how to set and use this variable, see Section 25.7, “Performance Schema Status Monitoring”.
performance_schema_max_digest_length
Property | Value |
---|---|
Command-Line Format | --performance-schema-max-digest-length=# |
System Variable | performance_schema_max_digest_length |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | 1024 |
Minimum Value | 0 |
Maximum Value | 1048576 |
The maximum number of bytes of memory reserved per statement
for computation of normalized statement digest values in the
Performance Schema. This variable is related to
max_digest_length
; see the
description of that variable in
Section 5.1.7, “Server System Variables”.
For more information about statement digesting, including considerations regarding memory use, see Section 25.10, “Performance Schema Statement Digests”.
performance_schema_max_file_classes
Property | Value |
---|---|
Command-Line Format | --performance-schema-max-file-classes=# |
System Variable | performance_schema_max_file_classes |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | 80 |
Minimum Value | 0 |
Maximum Value | 256 |
The maximum number of file instruments. For information about how to set and use this variable, see Section 25.7, “Performance Schema Status Monitoring”.
performance_schema_max_file_handles
Property | Value |
---|---|
Command-Line Format | --performance-schema-max-file-handles=# |
System Variable | performance_schema_max_file_handles |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | 32768 |
The maximum number of opened file objects. For information about how to set and use this variable, see Section 25.7, “Performance Schema Status Monitoring”.
The value of
performance_schema_max_file_handles
should be greater than the value of
open_files_limit
:
open_files_limit
affects the
maximum number of open file handles the server can support and
performance_schema_max_file_handles
affects how many of these file handles can be instrumented.
performance_schema_max_file_instances
Property | Value |
---|---|
Command-Line Format | --performance-schema-max-file-instances=# |
System Variable | performance_schema_max_file_instances |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | -1 (signifies autoscaling; do not assign this literal value) |
The maximum number of instrumented file objects. For information about how to set and use this variable, see Section 25.7, “Performance Schema Status Monitoring”.
performance_schema_max_index_stat
Property | Value |
---|---|
Command-Line Format | --performance-schema-max-index-stat=# |
System Variable | performance_schema_max_index_stat |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | -1 (signifies autosizing; do not assign this literal value) |
The maximum number of indexes for which the Performance Schema
maintains statistics. If this maximum is exceeded such that
index statistics are lost, the Performance Schema increments
the
Performance_schema_index_stat_lost
status variable. The default value is autosized using the
value of
performance_schema_max_table_instances
.
performance_schema_max_memory_classes
Property | Value |
---|---|
Command-Line Format | --performance-schema-max-memory-classes=# |
System Variable | performance_schema_max_memory_classes |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | 320 |
The maximum number of memory instruments. For information about how to set and use this variable, see Section 25.7, “Performance Schema Status Monitoring”.
performance_schema_max_metadata_locks
Property | Value |
---|---|
Command-Line Format | --performance-schema-max-metadata-locks=# |
System Variable | performance_schema_max_metadata_locks |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | -1 (signifies autoscaling; do not assign this literal value) |
The maximum number of metadata lock instruments. This value
controls the size of the
metadata_locks
table. If this
maximum is exceeded such that a metadata lock cannot be
instrumented, the Performance Schema increments the
Performance_schema_metadata_lock_lost
status variable.
performance_schema_max_mutex_classes
Property | Value |
---|---|
Command-Line Format | --performance-schema-max-mutex-classes=# |
System Variable | performance_schema_max_mutex_classes |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | 200 |
Minimum Value | 0 |
Maximum Value | 256 |
The maximum number of mutex instruments. For information about how to set and use this variable, see Section 25.7, “Performance Schema Status Monitoring”.
performance_schema_max_mutex_instances
Property | Value |
---|---|
Command-Line Format | --performance-schema-max-mutex-instances=# |
System Variable | performance_schema_max_mutex_instances |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | -1 (signifies autoscaling; do not assign this literal value) |
The maximum number of instrumented mutex objects. For information about how to set and use this variable, see Section 25.7, “Performance Schema Status Monitoring”.
performance_schema_max_prepared_statements_instances
Property | Value |
---|---|
Command-Line Format | --performance-schema-max-prepared-statements-instances=# |
System Variable | performance_schema_max_prepared_statements_instances |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | -1 (signifies autoscaling; do not assign this literal value) |
The maximum number of rows in the
prepared_statements_instances
table. If this maximum is exceeded such that a prepared
statement cannot be instrumented, the Performance Schema
increments the
Performance_schema_prepared_statements_lost
status variable. For information about how to set and use this
variable, see
Section 25.7, “Performance Schema Status Monitoring”.
The default value of this variable is autosized based on the
value of the
max_prepared_stmt_count
system variable.
performance_schema_max_rwlock_classes
Property | Value |
---|---|
Command-Line Format | --performance-schema-max-rwlock-classes=# |
System Variable | performance_schema_max_rwlock_classes |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | 40 |
Minimum Value | 0 |
Maximum Value | 256 |
The maximum number of rwlock instruments. For information about how to set and use this variable, see Section 25.7, “Performance Schema Status Monitoring”.
performance_schema_max_program_instances
Property | Value |
---|---|
Command-Line Format | --performance-schema-max-program-instances=# |
System Variable | performance_schema_max_program_instances |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | -1 (signifies autoscaling; do not assign this literal value) |
The maximum number of stored programs for which the
Performance Schema maintains statistics. If this maximum is
exceeded, the Performance Schema increments the
Performance_schema_program_lost
status variable. For information about how to set and use this
variable, see
Section 25.7, “Performance Schema Status Monitoring”.
performance_schema_max_rwlock_instances
Property | Value |
---|---|
Command-Line Format | --performance-schema-max-rwlock-instances=# |
System Variable | performance_schema_max_rwlock_instances |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | -1 (signifies autoscaling; do not assign this literal value) |
The maximum number of instrumented rwlock objects. For information about how to set and use this variable, see Section 25.7, “Performance Schema Status Monitoring”.
performance_schema_max_socket_classes
Property | Value |
---|---|
Command-Line Format | --performance-schema-max-socket-classes=# |
System Variable | performance_schema_max_socket_classes |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | 10 |
Minimum Value | 0 |
Maximum Value | 256 |
The maximum number of socket instruments. For information about how to set and use this variable, see Section 25.7, “Performance Schema Status Monitoring”.
performance_schema_max_socket_instances
Property | Value |
---|---|
Command-Line Format | --performance-schema-max-socket-instances=# |
System Variable | performance_schema_max_socket_instances |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | -1 (signifies autoscaling; do not assign this literal value) |
The maximum number of instrumented socket objects. For information about how to set and use this variable, see Section 25.7, “Performance Schema Status Monitoring”.
performance_schema_max_sql_text_length
Property | Value |
---|---|
Command-Line Format | --performance-schema-max-sql-text-length=# |
System Variable | performance_schema_max_sql_text_length |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | 1024 |
Minimum Value | 0 |
Maximum Value | 1048576 |
The maximum number of bytes used to store SQL statements in
the SQL_TEXT
column of the
events_statements_current
,
events_statements_history
, and
events_statements_history_long
statement event tables. Any bytes in excess of
performance_schema_max_sql_text_length
are discarded and do not appear in the
SQL_TEXT
column. Statements differing only
after that many initial bytes are indistinguishable in this
column.
Decreasing the
performance_schema_max_sql_text_length
value reduces memory use but causes more statements to become
indistinguishable if they differ only at the end. Increasing
the value increases memory use but permits longer statements
to be distinguished.
performance_schema_max_stage_classes
Property | Value |
---|---|
Command-Line Format | --performance-schema-max-stage-classes=# |
System Variable | performance_schema_max_stage_classes |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | 150 |
Minimum Value | 0 |
Maximum Value | 256 |
The maximum number of stage instruments. For information about how to set and use this variable, see Section 25.7, “Performance Schema Status Monitoring”.
performance_schema_max_statement_classes
Property | Value |
---|---|
Command-Line Format | --performance-schema-max-statement-classes=# |
System Variable | performance_schema_max_statement_classes |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | -1 (signifies autosizing; do not assign this literal value) |
The maximum number of statement instruments. For information about how to set and use this variable, see Section 25.7, “Performance Schema Status Monitoring”.
The default value is calculated at server build time based on the number of commands in the client/server protocol and the number of SQL statement types supported by the server.
This variable should not be changed, unless to set it to 0 to disable all statement instrumentation and save all memory associated with it. Setting the variable to nonzero values other than the default has no benefit; in particular, values larger than the default cause more memory to be allocated then is needed.
performance_schema_max_statement_stack
Property | Value |
---|---|
Command-Line Format | --performance-schema-max-statement-stack=# |
System Variable | performance_schema_max_statement_stack |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | 10 |
The maximum depth of nested stored program calls for which the
Performance Schema maintains statistics. When this maximum is
exceeded, the Performance Schema increments the
Performance_schema_nested_statement_lost
status variable for each stored program statement executed.
performance_schema_max_table_handles
Property | Value |
---|---|
Command-Line Format | --performance-schema-max-table-handles=# |
System Variable | performance_schema_max_table_handles |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | -1 (signifies autoscaling; do not assign this literal value) |
The maximum number of opened table objects. This value
controls the size of the
table_handles
table. If this
maximum is exceeded such that a table handle cannot be
instrumented, the Performance Schema increments the
Performance_schema_table_handles_lost
status variable. For information about how to set and use this
variable, see
Section 25.7, “Performance Schema Status Monitoring”.
performance_schema_max_table_instances
Property | Value |
---|---|
Command-Line Format | --performance-schema-max-table-instances=# |
System Variable | performance_schema_max_table_instances |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | -1 (signifies autoscaling; do not assign this literal value) |
The maximum number of instrumented table objects. For information about how to set and use this variable, see Section 25.7, “Performance Schema Status Monitoring”.
performance_schema_max_table_lock_stat
Property | Value |
---|---|
Command-Line Format | --performance-schema-max-table-lock-stat=# |
System Variable | performance_schema_max_table_lock_stat |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | -1 (signifies autosizing; do not assign this literal value) |
The maximum number of tables for which the Performance Schema
maintains lock statistics. If this maximum is exceeded such
that table lock statistics are lost, the Performance Schema
increments the
Performance_schema_table_lock_stat_lost
status variable.
performance_schema_max_thread_classes
Property | Value |
---|---|
Command-Line Format | --performance-schema-max-thread-classes=# |
System Variable | performance_schema_max_thread_classes |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | 50 |
Minimum Value | 0 |
Maximum Value | 256 |
The maximum number of thread instruments. For information about how to set and use this variable, see Section 25.7, “Performance Schema Status Monitoring”.
performance_schema_max_thread_instances
Property | Value |
---|---|
Command-Line Format | --performance-schema-max-thread-instances=# |
System Variable | performance_schema_max_thread_instances |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | -1 (signifies autoscaling; do not assign this literal value) |
The maximum number of instrumented thread objects. The value
controls the size of the threads
table. If this maximum is exceeded such that a thread cannot
be instrumented, the Performance Schema increments the
Performance_schema_thread_instances_lost
status variable. For information about how to set and use this
variable, see
Section 25.7, “Performance Schema Status Monitoring”.
The max_connections
system
variable affects how many threads can run in the server.
performance_schema_max_thread_instances
affects how many of these running threads can be instrumented.
The variables_by_thread
and
status_by_thread
tables contain
system and status variable information only about foreground
threads. If not all threads are instrumented by the
Performance Schema, this table will miss some rows. In this
case, the
Performance_schema_thread_instances_lost
status variable will be greater than zero.
performance_schema_session_connect_attrs_size
Property | Value |
---|---|
Command-Line Format | --performance-schema-session-connect-attrs-size=# |
System Variable | performance_schema_session_connect_attrs_size |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | -1 (signifies autosizing; do not assign this literal value) |
Minimum Value | -1 |
Maximum Value | 1048576 |
The amount of preallocated memory per thread reserved to hold
connection attribute key-value pairs. If the aggregate size of
connection attribute data sent by a client is larger than this
amount, the Performance Schema truncates the attribute data,
increments the
Performance_schema_session_connect_attrs_lost
status variable, and writes a message to the error log
indicating that truncation occurred if the
log_error_verbosity
system
variable value is greater than 1.
The default value of
performance_schema_session_connect_attrs_size
is autosized at server startup. This value may be small, so if
truncation occurs
(Performance_schema_session_connect_attrs_lost
becomes nonzero), you may wish to set
performance_schema_session_connect_attrs_size
explicitly to a larger value.
Although the maximum permitted
performance_schema_session_connect_attrs_size
value is 1MB, the effective maximum is 64KB because the server
imposes a limit of 64KB on the aggregate size of connection
attribute data it will accept. If a client attempts to send
more than 64KB of attribute data, the server rejects the
connection. For more information, see
Section 25.12.9, “Performance Schema Connection Attribute Tables”.
performance_schema_setup_actors_size
Property | Value |
---|---|
Command-Line Format | --performance-schema-setup-actors-size=# |
System Variable | performance_schema_setup_actors_size |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | -1 (signifies autoscaling; do not assign this literal value) |
The number of rows in the
setup_actors
table.
performance_schema_setup_objects_size
Property | Value |
---|---|
Command-Line Format | --performance-schema-setup-objects-size=# |
System Variable | performance_schema_setup_objects_size |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | -1 (signifies autoscaling; do not assign this literal value) |
The number of rows in the
setup_objects
table.
Property | Value |
---|---|
Command-Line Format | --performance-schema-users-size=# |
System Variable | performance_schema_users_size |
Scope | Global |
Dynamic | No |
Type | Integer |
Default Value | -1 (signifies autoscaling; do not assign this literal value) |
Minimum Value | -1 (signifies autoscaling; do not assign this literal value) |
Maximum Value | 1048576 |
The number of rows in the users
table. If this variable is 0, the Performance Schema does not
maintain connection statistics in the
users
table or status variable
information in the status_by_user
table.
The Performance Schema implements several status variables that provide information about instrumentation that could not be loaded or created due to memory constraints:
mysql> SHOW STATUS LIKE 'perf%';
+-------------------------------------------+-------+
| Variable_name | Value |
+-------------------------------------------+-------+
| Performance_schema_accounts_lost | 0 |
| Performance_schema_cond_classes_lost | 0 |
| Performance_schema_cond_instances_lost | 0 |
| Performance_schema_file_classes_lost | 0 |
| Performance_schema_file_handles_lost | 0 |
| Performance_schema_file_instances_lost | 0 |
| Performance_schema_hosts_lost | 0 |
| Performance_schema_locker_lost | 0 |
| Performance_schema_mutex_classes_lost | 0 |
| Performance_schema_mutex_instances_lost | 0 |
| Performance_schema_rwlock_classes_lost | 0 |
| Performance_schema_rwlock_instances_lost | 0 |
| Performance_schema_socket_classes_lost | 0 |
| Performance_schema_socket_instances_lost | 0 |
| Performance_schema_stage_classes_lost | 0 |
| Performance_schema_statement_classes_lost | 0 |
| Performance_schema_table_handles_lost | 0 |
| Performance_schema_table_instances_lost | 0 |
| Performance_schema_thread_classes_lost | 0 |
| Performance_schema_thread_instances_lost | 0 |
| Performance_schema_users_lost | 0 |
+-------------------------------------------+-------+
For information on using these variables to check Performance Schema status, see Section 25.7, “Performance Schema Status Monitoring”.
Performance Schema status variables have the following meanings:
Performance_schema_accounts_lost
The number of times a row could not be added to the
accounts
table because it was
full.
Performance_schema_cond_classes_lost
How many condition instruments could not be loaded.
Performance_schema_cond_instances_lost
How many condition instrument instances could not be created.
Performance_schema_digest_lost
The number of digest instances that could not be instrumented
in the
events_statements_summary_by_digest
table. This can be nonzero if the value of
performance_schema_digests_size
is too small.
Performance_schema_file_classes_lost
How many file instruments could not be loaded.
Performance_schema_file_handles_lost
How many file instrument instances could not be opened.
Performance_schema_file_instances_lost
How many file instrument instances could not be created.
The number of times a row could not be added to the
hosts
table because it was full.
Performance_schema_index_stat_lost
The number of indexes for which statistics were lost. This can
be nonzero if the value of
performance_schema_max_index_stat
is too small.
Performance_schema_locker_lost
How many events are “lost” or not recorded, due to the following conditions:
Events are recursive (for example, waiting for A caused a wait on B, which caused a wait on C).
The depth of the nested events stack is greater than the limit imposed by the implementation.
Events recorded by the Performance Schema are not recursive, so this variable should always be 0.
Performance_schema_memory_classes_lost
The number of times a memory instrument could not be loaded.
Performance_schema_metadata_lock_lost
The number of metadata locks that could not be instrumented in
the metadata_locks
table. This
can be nonzero if the value of
performance_schema_max_metadata_locks
is too small.
Performance_schema_mutex_classes_lost
How many mutex instruments could not be loaded.
Performance_schema_mutex_instances_lost
How many mutex instrument instances could not be created.
Performance_schema_nested_statement_lost
The number of stored program statements for which statistics
were lost. This can be nonzero if the value of
performance_schema_max_statement_stack
is too small.
Performance_schema_prepared_statements_lost
The number of prepared statements that could not be
instrumented in the
prepared_statements_instances
table. This can be nonzero if the value of
performance_schema_max_prepared_statements_instances
is too small.
Performance_schema_program_lost
The number of stored programs for which statistics were lost.
This can be nonzero if the value of
performance_schema_max_program_instances
is too small.
Performance_schema_rwlock_classes_lost
How many rwlock instruments could not be loaded.
Performance_schema_rwlock_instances_lost
How many rwlock instrument instances could not be created.
Performance_schema_session_connect_attrs_lost
The number of connections for which connection attribute
truncation has occurred. For a given connection, if the client
sends connection attribute key-value pairs for which the
aggregate size is larger than the reserved storage permitted
by the value of the
performance_schema_session_connect_attrs_size
system variable, the Performance Schema truncates the
attribute data and increments
Performance_schema_session_connect_attrs_lost
.
If this value is nonzero, you may wish to set
performance_schema_session_connect_attrs_size
to a larger value.
For more information about connection attributes, see Section 25.12.9, “Performance Schema Connection Attribute Tables”.
Performance_schema_socket_classes_lost
How many socket instruments could not be loaded.
Performance_schema_socket_instances_lost
How many socket instrument instances could not be created.
Performance_schema_stage_classes_lost
How many stage instruments could not be loaded.
Performance_schema_statement_classes_lost
How many statement instruments could not be loaded.
Performance_schema_table_handles_lost
How many table instrument instances could not be opened. This
can be nonzero if the value of
performance_schema_max_table_handles
is too small.
Performance_schema_table_instances_lost
How many table instrument instances could not be created.
Performance_schema_table_lock_stat_lost
The number of tables for which lock statistics were lost. This
can be nonzero if the value of
performance_schema_max_table_lock_stat
is too small.
Performance_schema_thread_classes_lost
How many thread instruments could not be loaded.
Performance_schema_thread_instances_lost
The number of thread instances that could not be instrumented
in the threads
table. This can be
nonzero if the value of
performance_schema_max_thread_instances
is too small.
The number of times a row could not be added to the
users
table because it was full.
The Performance Schema uses this memory allocation model:
May allocate memory at server startup
May allocate additional memory during server operation
Never free memory during server operation (although it might be recycled)
Free all memory used at shutdown
The result is to relax memory constraints so that the Performance Schema can be used with less configuration, and to decrease the memory footprint so that consumption scales with server load. Memory used depends on the load actually seen, not the load estimated or explicitly configured for.
Several Performance Schema sizing parameters are autoscaled and need not be configured explicitly unless you want to establish an explicit limit on memory allocation:
performance_schema_accounts_size performance_schema_hosts_size performance_schema_max_cond_instances performance_schema_max_file_instances performance_schema_max_index_stat performance_schema_max_metadata_locks performance_schema_max_mutex_instances performance_schema_max_prepared_statements_instances performance_schema_max_program_instances performance_schema_max_rwlock_instances performance_schema_max_socket_instances performance_schema_max_table_handles performance_schema_max_table_instances performance_schema_max_table_lock_stat performance_schema_max_thread_instances performance_schema_users_size
For an autoscaled parameter, configuration works like this:
With the value set to -1 (the default), the parameter is autoscaled:
The corresponding internal buffer is empty initially and no memory is allocated.
As the Performance Schema collects data, memory is allocated in the corresponding buffer. The buffer size is unbounded, and may grow with the load.
With the value set to 0:
The corresponding internal buffer is empty initially and no memory is allocated.
With the value set to N
> 0:
The corresponding internal buffer is empty initially and no memory is allocated.
As the Performance Schema collects data, memory is
allocated in the corresponding buffer, until the buffer
size reaches N
.
Once the buffer size reaches N
,
no more memory is allocated. Data collected by the
Performance Schema for this buffer is lost, and any
corresponding “lost instance” counters are
incremented.
To see how much memory the Performance Schema is using, check the
instruments designed for that purpose. The Performance Schema
allocates memory internally and associates each buffer with a
dedicated instrument so that memory consumption can be traced to
individual buffers. Instruments named with the prefix
memory/performance_schema/
expose how much
memory is allocated for these internal buffers. The buffers are
global to the server, so the instruments are displayed only in the
memory_summary_global_by_event_name
table, and not in other
memory_summary_by_
tables.
xxx
_by_event_name
This query shows the information associated with the memory instruments:
SELECT * FROM performance_schema.memory_summary_global_by_event_name WHERE EVENT_NAME LIKE 'memory/performance_schema/%';
Removing a plugin with UNINSTALL
PLUGIN
does not affect information already collected for
code in that plugin. Time spent executing the code while the
plugin was loaded was still spent even if the plugin is unloaded
later. The associated event information, including aggregate
information, remains readable in
performance_schema
database tables. For
additional information about the effect of plugin installation and
removal, see
Section 25.7, “Performance Schema Status Monitoring”.
A plugin implementor who instruments plugin code should document its instrumentation characteristics to enable those who load the plugin to account for its requirements. For example, a third-party storage engine should include in its documentation how much memory the engine needs for mutex and other instruments.
The Performance Schema is a tool to help a DBA do performance tuning by taking real measurements instead of “wild guesses.” This section demonstrates some ways to use the Performance Schema for this purpose. The discussion here relies on the use of event filtering, which is described in Se