Table of Contents
MySQL Server (mysqld) is the main program that does most of the work in a MySQL installation. This chapter provides an overview of MySQL Server and covers general server administration:
Server configuration
The data directory, particularly the mysql
system database
The server log files
Management of multiple servers on a single machine
For additional information on administrative topics, see also:
mysqld is the MySQL server. The following discussion covers these MySQL server configuration topics:
Startup options that the server supports. You can specify these options on the command line, through configuration files, or both.
Server system variables. These variables reflect the current state and values of the startup options, some of which can be modified while the server is running.
Server status variables. These variables contain counters and statistics about runtime operation.
How to set the server SQL mode. This setting modifies certain aspects of SQL syntax and semantics, for example for compatibility with code from other database systems, or to control the error handling for particular situations.
Configuring and using IPv6 support.
Configuring and using time zone support.
Server-side help capabilities.
The server shutdown process. There are performance and reliability considerations depending on the type of table (transactional or nontransactional) and whether you use replication.
For listings of MySQL server variables and options that have been added, deprecated, or removed in MySQL 5.7, see Section 1.5, “Server and Status Variables and Options Added, Deprecated, or Removed in MySQL 5.7”.
Not all storage engines are supported by all MySQL server binaries and configurations. To find out how to determine which storage engines your MySQL server installation supports, see Section 13.7.5.16, “SHOW ENGINES Statement”.
The MySQL server, mysqld, has many command options and system variables that can be set at startup to configure its operation. To determine the default command option and system variable values used by the server, execute this command:
shell> mysqld --verbose --help
The command produces a list of all mysqld options and configurable system variables. Its output includes the default option and variable values and looks something like this:
abort-slave-event-count 0 allow-suspicious-udfs FALSE archive ON auto-increment-increment 1 auto-increment-offset 1 autocommit TRUE automatic-sp-privileges TRUE avoid-temporal-upgrade FALSE back-log 80 basedir /home/jon/bin/mysql-5.7/ ... tmpdir /tmp transaction-alloc-block-size 8192 transaction-isolation REPEATABLE-READ transaction-prealloc-size 4096 transaction-read-only FALSE transaction-write-set-extraction OFF updatable-views-with-limit YES validate-user-plugins TRUE verbose TRUE wait-timeout 28800
To see the current system variable values actually used by the server as it runs, connect to it and execute this statement:
mysql> SHOW VARIABLES;
To see some statistical and status indicators for a running server, execute this statement:
mysql> SHOW STATUS;
System variable and status information also is available using the mysqladmin command:
shell>mysqladmin variablesshell>mysqladmin extended-status
For a full description of all command options, system variables, and status variables, see these sections:
More detailed monitoring information is available from the
Performance Schema; see Chapter 25, MySQL Performance Schema. In
addition, the MySQL sys schema is a set of
objects that provides convenient access to data collected by the
Performance Schema; see Chapter 26, MySQL sys Schema.
MySQL uses algorithms that are very scalable, so you can usually run with very little memory. However, normally better performance results from giving MySQL more memory.
When tuning a MySQL server, the two most important variables to
configure are key_buffer_size and
table_open_cache. You should
first feel confident that you have these set appropriately before
trying to change any other variables.
The following examples indicate some typical variable values for different runtime configurations.
If you have at least 1-2GB of memory and many tables and want maximum performance with a moderate number of clients, use something like this:
shell>mysqld_safe --key_buffer_size=384M --table_open_cache=4000 \--sort_buffer_size=4M --read_buffer_size=1M &
If you have only 256MB of memory and only a few tables, but you still do a lot of sorting, you can use something like this:
shell> mysqld_safe --key_buffer_size=64M --sort_buffer_size=1M
If there are very many simultaneous connections, swapping problems may occur unless mysqld has been configured to use very little memory for each connection. mysqld performs better if you have enough memory for all connections.
With little memory and lots of connections, use something like this:
shell>mysqld_safe --key_buffer_size=512K --sort_buffer_size=100K \--read_buffer_size=100K &
Or even this:
shell>mysqld_safe --key_buffer_size=512K --sort_buffer_size=16K \--table_open_cache=32 --read_buffer_size=8K \--net_buffer_length=1K &
If you are performing GROUP BY or
ORDER BY operations on tables that are much
larger than your available memory, increase the value of
read_rnd_buffer_size to speed up
the reading of rows following sorting operations.
If you specify an option on the command line for mysqld or mysqld_safe, it remains in effect only for that invocation of the server. To use the option every time the server runs, put it in an option file. See Section 4.2.2.2, “Using Option Files”.
The MySQL server has many operating parameters, which you can change at server startup using command-line options or configuration files (option files). It is also possible to change many parameters at runtime. For general instructions on setting parameters at startup or runtime, see Section 5.1.6, “Server Command Options”, and Section 5.1.7, “Server System Variables”.
On Windows, MySQL Installer interacts with the user and creates a
file named my.ini in the base installation
directory as the default option file. If you install on Windows
from a Zip archive, you can copy the
my-default.ini template file in the base
installation directory to my.ini and use the
latter as the default option file.
As of MySQL 5.7.18, my-default.ini is no
longer included in or installed by distribution packages.
On Windows, the .ini or
.cnf option file extension might not be
displayed.
After completing the installation process, you can edit the
default option file at any time to modify the parameters used by
the server. For example, to use a parameter setting in the file
that is commented with a # character at the
beginning of the line, remove the #, and modify
the parameter value if necessary. To disable a setting, either add
a # to the beginning of the line or remove it.
For non-Windows platforms, no default option file is created during either the server installation or the data directory initialization process. Create your option file by following the instructions given in Section 4.2.2.2, “Using Option Files”. Without an option file, the server just starts with its default settings—see Section 5.1.2, “Server Configuration Defaults” on how to check those settings.
For additional information about option file format and syntax, see Section 4.2.2.2, “Using Option Files”.
The following table lists all command-line options, system
variables, and status variables applicable within
mysqld.
The table lists command-line options (Cmd-line), options valid in configuration files (Option file), server system variables (System Var), and status variables (Status var) in one unified list, with an indication of where each option or variable is valid. If a server option set on the command line or in an option file differs from the name of the corresponding system variable, the variable name is noted immediately below the corresponding option. For system and status variables, the scope of the variable (Var Scope) is Global, Session, or both. Please see the corresponding item descriptions for details on setting and using the options and variables. Where appropriate, direct links to further information about the items are provided.
For a version of this table that is specific to NDB Cluster, see Section 21.3.2.5, “NDB Cluster mysqld Option and Variable Reference”.
Table 5.1 Command-Line Option, System Variable, and Status Variable Summary
Notes:
1. This option is dynamic, but only the server should set this information. You should not set the value of this variable manually.
The following table lists all system variables applicable within
mysqld.
The table lists command-line options (Cmd-line), options valid in configuration files (Option file), server system variables (System Var), and status variables (Status var) in one unified list, with an indication of where each option or variable is valid. If a server option set on the command line or in an option file differs from the name of the corresponding system variable, the variable name is noted immediately below the corresponding option. The scope of the variable (Var Scope) is Global, Session, or both. Please see the corresponding item descriptions for details on setting and using the variables. Where appropriate, direct links to further information about the items are provided.
Table 5.2 System Variable Summary
Notes:
1. This option is dynamic, but only the server should set this information. You should not set the value of this variable manually.
The following table lists all status variables applicable within
mysqld.
The table lists each variable's data type and scope. The last column indicates whether the scope for each variable is Global, Session, or both. Please see the corresponding item descriptions for details on setting and using the variables. Where appropriate, direct links to further information about the items are provided.
Table 5.3 Status Variable Summary
When you start the mysqld server, you can specify program options using any of the methods described in Section 4.2.2, “Specifying Program Options”. The most common methods are to provide options in an option file or on the command line. However, in most cases it is desirable to make sure that the server uses the same options each time it runs. The best way to ensure this is to list them in an option file. See Section 4.2.2.2, “Using Option Files”. That section also describes option file format and syntax.
mysqld reads options from the
[mysqld] and [server]
groups. mysqld_safe reads options from the
[mysqld], [server],
[mysqld_safe], and
[safe_mysqld] groups.
mysql.server reads options from the
[mysqld] and [mysql.server]
groups.
An embedded MySQL server usually reads options from the
[server], [embedded], and
[
groups, where xxxxx_SERVER]xxxxx is the name of the
application into which the server is embedded.
mysqld accepts many command options. For a brief summary, execute this command:
mysqld --help
To see the full list, use this command:
mysqld --verbose --help
Some of the items in the list are actually system variables that
can be set at server startup. These can be displayed at runtime
using the SHOW VARIABLES statement.
Some items displayed by the preceding mysqld
command do not appear in SHOW
VARIABLES output; this is because they are options only
and not system variables.
The following list shows some of the most common server options. Additional options are described in other sections:
Options that affect security: See Section 6.1.4, “Security-Related mysqld Options and Variables”.
SSL-related options: See Command Options for Encrypted Connections.
Binary log control options: See Section 5.4.4, “The Binary Log”.
Replication-related options: See Section 16.1.6, “Replication and Binary Logging Options and Variables”.
Options for loading plugins such as pluggable storage engines: See Section 5.5.1, “Installing and Uninstalling Plugins”.
Options specific to particular storage engines: See Section 14.15, “InnoDB Startup Options and System Variables” and Section 15.2.1, “MyISAM Startup Options”.
Some options control the size of buffers or caches. For a given buffer, the server might need to allocate internal data structures. These structures typically are allocated from the total memory allocated to the buffer, and the amount of space required might be platform dependent. This means that when you assign a value to an option that controls a buffer size, the amount of space actually available might differ from the value assigned. In some cases, the amount might be less than the value assigned. It is also possible that the server will adjust a value upward. For example, if you assign a value of 0 to an option for which the minimal value is 1024, the server will set the value to 1024.
Values for buffer sizes, lengths, and stack sizes are given in bytes unless otherwise specified.
Some options take file name values. Unless otherwise specified,
the default file location is the data directory if the value is a
relative path name. To specify the location explicitly, use an
absolute path name. Suppose that the data directory is
/var/mysql/data. If a file-valued option is
given as a relative path name, it will be located under
/var/mysql/data. If the value is an absolute
path name, its location is as given by the path name.
You can also set the values of server system variables at server
startup by using variable names as options. To assign a value to a
server system variable, use an option of the form
--.
For example,
var_name=value--sort_buffer_size=384M sets the
sort_buffer_size variable to a
value of 384MB.
When you assign a value to a variable, MySQL might automatically correct the value to stay within a given range, or adjust the value to the closest permissible value if only certain values are permitted.
To restrict the maximum value to which a system variable can be
set at runtime with the
SET
statement, specify this maximum by using an option of the form
--maximum-
at server startup.
var_name=value
You can change the values of most system variables at runtime with
the SET
statement. See Section 13.7.4.1, “SET Syntax for Variable Assignment”.
Section 5.1.7, “Server System Variables”, provides a full description for all variables, and additional information for setting them at server startup and runtime. For information on changing system variables, see Section 5.1.1, “Configuring the Server”.
--help, -?
| Property | Value |
|---|---|
| Command-Line Format | --help |
Display a short help message and exit. Use both the
--verbose and
--help options to see the full
message.
| Property | Value |
|---|---|
| Command-Line Format | --allow-suspicious-udfs[={OFF|ON}] |
| Type | Boolean |
| Default Value | OFF |
This option controls whether user-defined functions that have
only an xxx symbol for the main function
can be loaded. By default, the option is off and only UDFs
that have at least one auxiliary symbol can be loaded; this
prevents attempts at loading functions from shared object
files other than those containing legitimate UDFs. See
UDF Security Precautions.
| Property | Value |
|---|---|
| Command-Line Format | --ansi |
Use standard (ANSI) SQL syntax instead of MySQL syntax. For
more precise control over the server SQL mode, use the
--sql-mode option instead. See
Section 1.8, “MySQL Standards Compliance”, and
Section 5.1.10, “Server SQL Modes”.
--basedir=,
dir_name-b
dir_name
| Property | Value |
|---|---|
| Command-Line Format | --basedir=dir_name |
| System Variable | basedir |
| Scope | Global |
| Dynamic | No |
| Type | Directory name |
| Default Value | configuration-dependent default |
The path to the MySQL installation directory. This option sets
the basedir system variable.
| Property | Value |
|---|---|
| Command-Line Format | --bootstrap |
| Deprecated | Yes |
This option is used by the mysql_install_db program to create the MySQL privilege tables without having to start a full MySQL server.
mysql_install_db is deprecated because
its functionality has been integrated into
mysqld, the MySQL server. Consequently,
the --bootstrap server option
that mysql_install_db passes to
mysqld is also deprecated. To initialize
a MySQL installation, invoke mysqld with
the --initialize or
--initialize-insecure option.
For more information, see
Section 2.10.1, “Initializing the Data Directory”.
mysql_install_db and the
--bootstrap server option
will be removed in a future MySQL release.
--bootstrap is mutually
exclusive with --daemonize,
--initialize, and
--initialize-insecure.
Global transaction identifiers (GTIDs) are not disabled when
--bootstrap is used.
--bootstrap was used (Bug
#20980271). See Section 16.1.3, “Replication with Global Transaction Identifiers”.
When the server operates in bootstap mode, some functionality
is unavailable that limits the statements permitted in any
file named by the init_file
system variable. For more information, see the description of
that variable. In addition, the
disabled_storage_engines
system variable has no effect.
--character-set-client-handshake
| Property | Value |
|---|---|
| Command-Line Format | --character-set-client-handshake[={OFF|ON}] |
| Type | Boolean |
| Default Value | ON |
Do not ignore character set information sent by the client. To
ignore client information and use the default server character
set, use
--skip-character-set-client-handshake;
this makes MySQL behave like MySQL 4.0.
--chroot=,
dir_name-r
dir_name
| Property | Value |
|---|---|
| Command-Line Format | --chroot=dir_name |
| Type | Directory name |
Put the mysqld server in a closed
environment during startup by using the
chroot() system call. This is a recommended
security measure. Use of this option somewhat limits
LOAD DATA and
SELECT ... INTO
OUTFILE.
| Property | Value |
|---|---|
| Command-Line Format | --console |
| Platform Specific | Windows |
(Windows only.) Write the error log to
stderr and stdout (the
console). mysqld does not close the console
window if this option is used.
--console takes precedence over
--log-error if both are given.
(In MySQL 5.5 and 5.6, this is reversed:
--log-error takes precedence
over --console if both are
given.)
| Property | Value |
|---|---|
| Command-Line Format | --core-file[={OFF|ON}] |
| Type | Boolean |
| Default Value | OFF |
Write a core file if mysqld dies. The name
and location of the core file is system dependent. On Linux, a
core file named
core. is
written to the current working directory of the process, which
for mysqld is the data directory.
pidpid represents the process ID of
the server process. On macOS, a core file named
core. is
written to the pid/cores directory. On
Solaris, use the coreadm command to specify
where to write the core file and how to name it.
For some systems, to get a core file you must also specify the
--core-file-size option to
mysqld_safe. See
Section 4.3.2, “mysqld_safe — MySQL Server Startup Script”. On some systems, such as
Solaris, you do not get a core file if you are also using the
--user option. There might be
additional restrictions or limitations. For example, it might
be necessary to execute ulimit -c unlimited
before starting the server. Consult your system documentation.
| Property | Value |
|---|---|
| Command-Line Format | --daemonize[={OFF|ON}] |
| Type | Boolean |
| Default Value | OFF |
This option causes the server to run as a traditional, forking daemon, permitting it to work with operating systems that use systemd for process control. For more information, see Section 2.5.10, “Managing MySQL Server with systemd”.
--daemonize is mutually
exclusive with --bootstrap,
--initialize, and
--initialize-insecure.
--datadir=,
dir_name-h
dir_name
| Property | Value |
|---|---|
| Command-Line Format | --datadir=dir_name |
| System Variable | datadir |
| Scope | Global |
| Dynamic | No |
| Type | Directory name |
The path to the MySQL server data directory. This option sets
the datadir system variable.
See the description of that variable.
--debug[=,
debug_options]-# [
debug_options]
| Property | Value |
|---|---|
| Command-Line Format | --debug[=debug_options] |
| System Variable | debug |
| Scope | Global, Session |
| Dynamic | Yes |
| Type | String |
| Default Value (Windows) | d:t:i:O,\mysqld.trace |
| Default Value (Unix) | d:t:i:o,/tmp/mysqld.trace |
If MySQL is configured with the
-DWITH_DEBUG=1
CMake option, you can use this option to
get a trace file of what mysqld is doing. A
typical debug_options string is
d:t:o,.
The default is file_named:t:i:o,/tmp/mysqld.trace on
Unix and d:t:i:O,\mysqld.trace on Windows.
Using -DWITH_DEBUG=1 to
configure MySQL with debugging support enables you to use the
--debug="d,parser_debug" option
when you start the server. This causes the Bison parser that
is used to process SQL statements to dump a parser trace to
the server's standard error output. Typically, this output is
written to the error log.
This option may be given multiple times. Values that begin
with + or - are added to
or subtracted from the previous value. For example,
--debug=T
--debug=+P sets the value to
P:T.
For more information, see Section 28.5.3, “The DBUG Package”.
| Property | Value |
|---|---|
| Command-Line Format | --debug-sync-timeout[=#] |
| Type | Integer |
Controls whether the Debug Sync facility for testing and
debugging is enabled. Use of Debug Sync requires that MySQL be
configured with the
-DENABLE_DEBUG_SYNC=1
CMake option (see
Section 2.9.7, “MySQL Source-Configuration Options”). If Debug Sync
is not compiled in, this option is not available. The option
value is a timeout in seconds. The default value is 0, which
disables Debug Sync. To enable it, specify a value greater
than 0; this value also becomes the default timeout for
individual synchronization points. If the option is given
without a value, the timeout is set to 300 seconds.
For a description of the Debug Sync facility and how to use synchronization points, see MySQL Internals: Test Synchronization.
| Property | Value |
|---|---|
| Command-Line Format | --default-time-zone=name |
| Type | String |
Set the default server time zone. This option sets the global
time_zone system variable. If
this option is not given, the default time zone is the same as
the system time zone (given by the value of the
system_time_zone system
variable.
--defaults-extra-file=
file_name
Read this option file after the global option file but (on
Unix) before the user option file. If the file does not exist
or is otherwise inaccessible, an error occurs.
file_name is interpreted relative
to the current directory if given as a relative path name
rather than a full path name. This must be the first option on
the command line if it is used.
For additional information about this and other option-file options, see Section 4.2.2.3, “Command-Line Options that Affect Option-File Handling”.
Read only the given option file. If the file does not exist or
is otherwise inaccessible, an error occurs.
file_name is interpreted relative
to the current directory if given as a relative path name
rather than a full path name.
This must be the first option on the command line if it is
used, except that if the server is started with the
--defaults-file and
--install (or
--install-manual) options,
--install (or
--install-manual) must be
first.
For additional information about this and other option-file options, see Section 4.2.2.3, “Command-Line Options that Affect Option-File Handling”.
Read not only the usual option groups, but also groups with
the usual names and a suffix of
str. For example,
mysqld normally reads the
[mysqld] group. If the
--defaults-group-suffix=_other
option is given, mysqld also reads the
[mysqld_other] group.
For additional information about this and other option-file options, see Section 4.2.2.3, “Command-Line Options that Affect Option-File Handling”.
| Property | Value |
|---|---|
| Command-Line Format | --des-key-file=file_name |
| Deprecated | Yes |
Read the default DES keys from this file. These keys are used
by the DES_ENCRYPT() and
DES_DECRYPT() functions.
The DES_ENCRYPT() and
DES_DECRYPT() functions are
deprecated in MySQL 5.7, will be removed in a
future MySQL release, and should no longer be used.
Consequently, --des-key-file
also is deprecated and will be removed.
--disable-partition-engine-check
| Property | Value |
|---|---|
| Command-Line Format | --disable-partition-engine-check[={OFF|ON}] |
| Introduced | 5.7.17 |
| Deprecated | 5.7.17 |
| Type | Boolean |
| Default Value (>= 5.7.21) | ON |
| Default Value (>= 5.7.17, <= 5.7.20) | OFF |
Whether to disable the startup check for tables with nonnative partitioning.
As of MySQL 5.7.17, the generic partitioning handler in the
MySQL server is deprecated, and is removed in MySQL
8.0, when the storage engine used for a given table
is expected to provide its own (“native”)
partitioning handler. Currently, only the
InnoDB and
NDB storage engines do this.
Use of tables with nonnative partitioning results in an
ER_WARN_DEPRECATED_SYNTAX
warning. In MySQL 5.7.17 through 5.7.20, the server
automatically performs a check at startup to identify tables
that use nonnative partitioning; for any that are found, the
server writes a message to its error log. To disable this
check, use the
--disable-partition-engine-check
option. In MySQL 5.7.21 and later, this check is
not performed; in these versions, you
must start the server with
--disable-partition-engine-check=false,
if you wish for the server to check for tables using the
generic partitioning handler (Bug #85830, Bug #25846957).
Use of tables with nonnative partitioning results in an
ER_WARN_DEPRECATED_SYNTAX
warning. Also, the server performs a check at startup to
identify tables that use nonnative partitioning; for any
found, the server writes a message to its error log. To
disable this check, use the
--disable-partition-engine-check
option.
To prepare for migration to MySQL 8.0, any table
with nonnative partitioning should be changed to use an engine
that provides native partitioning, or be made nonpartitioned.
For example, to change a table to InnoDB,
execute this statement:
ALTER TABLE table_name ENGINE = INNODB;
--early-plugin-load=
plugin_list
| Property | Value |
|---|---|
| Command-Line Format | --early-plugin-load=plugin_list |
| Introduced | 5.7.11 |
| Type | String |
| Default Value (>= 5.7.12) | empty string |
| Default Value (5.7.11) | keyring_file plugin library file name |
This option tells the server which plugins to load before
loading mandatory built-in plugins and before storage engine
initialization. If multiple
--early-plugin-load options are
given, only the last one is used.
The option value is a semicolon-separated list of
name=plugin_library
and plugin_library values. Each
name is the name of a plugin to
load, and plugin_library is the
name of the library file that contains the plugin code. If a
plugin library is named without any preceding plugin name, the
server loads all plugins in the library. The server looks for
plugin library files in the directory named by the
plugin_dir system variable.
For example, if plugins named myplug1 and
myplug2 have library files
myplug1.so and
myplug2.so, use this option to perform an
early plugin load:
shell> mysqld --early-plugin-load="myplug1=myplug1.so;myplug2=myplug2.so"
Quotes are used around the argument value because otherwise a
semicolon (;) is interpreted as a special
character by some command interpreters. (Unix shells treat it
as a command terminator, for example.)
Each named plugin is loaded early for a single invocation of
mysqld only. After a restart, the plugin is
not loaded early unless
--early-plugin-load is used
again.
If the server is started using
--initialize or
--initialize-insecure, plugins
specified by
--early-plugin-load are not
loaded.
If the server is run with
--help, plugins specified by
--early-plugin-load are loaded
but not initialized. This behavior ensures that plugin options
are displayed in the help message.
As of MySQL 5.7.12, the default
--early-plugin-load value is
empty. To load your chosen keyring plugin, you must use an
explicit --early-plugin-load
option with a nonempty value.
In MySQL 5.7.11, the default
--early-plugin-load value was
the name of the keyring_file plugin
library file, so that plugin was loaded by default.
InnoDB tablespace encryption requires the
keyring_file plugin to be loaded prior to
InnoDB initialization, so this change of
default --early-plugin-load
value introduces an incompatibility for upgrades from 5.7.11
to 5.7.12 or higher. Administrators who have encrypted
InnoDB tablespaces must take explicit
action to ensure continued loading of the
keyring_file plugin: Start the server
with an --early-plugin-load
option that names the plugin library file. For additional
information, see Section 6.4.4.1, “Keyring Plugin Installation”.
The InnoDB tablespace encryption feature
relies on the keyring_file plugin for
encryption key management, and the
keyring_file plugin must be loaded prior to
storage engine initialization to facilitate
InnoDB recovery for encrypted tables. In
MySQL 5.7.11, if you do not want to load the
keyring_file plugin at server startup,
specify an empty string
(--early-plugin-load="").
For information about InnoDB tablespace
encryption, see Section 14.14, “InnoDB Data-at-Rest Encryption”. For
general information about plugin loading, see
Section 5.5.1, “Installing and Uninstalling Plugins”.
--exit-info[=,
flags]-T [
flags]
| Property | Value |
|---|---|
| Command-Line Format | --exit-info[=flags] |
| Type | Integer |
This is a bitmask of different flags that you can use for debugging the mysqld server. Do not use this option unless you know exactly what it does!
| Property | Value |
|---|---|
| Command-Line Format | --external-locking[={OFF|ON}] |
| Type | Boolean |
| Default Value | OFF |
Enable external locking (system locking), which is disabled by
default. If you use this option on a system on which
lockd does not fully work (such as Linux),
it is easy for mysqld to deadlock.
To disable external locking explicitly, use
--skip-external-locking.
External locking affects only
MyISAM table access. For more
information, including conditions under which it can and
cannot be used, see Section 8.11.5, “External Locking”.
| Property | Value |
|---|---|
| Command-Line Format | --flush[={OFF|ON}] |
| System Variable | flush |
| Scope | Global |
| Dynamic | Yes |
| Type | Boolean |
| Default Value | OFF |
Flush (synchronize) all changes to disk after each SQL statement. Normally, MySQL does a write of all changes to disk only after each SQL statement and lets the operating system handle the synchronizing to disk. See Section B.4.3.3, “What to Do If MySQL Keeps Crashing”.
If --flush is specified, the
value of flush_time does
not matter and changes to
flush_time have no effect
on flush behavior.
| Property | Value |
|---|---|
| Command-Line Format | --gdb[={OFF|ON}] |
| Type | Boolean |
| Default Value | OFF |
Install an interrupt handler for SIGINT
(needed to stop mysqld with
^C to set breakpoints) and disable stack
tracing and core file handling. See
Section 28.5.1.4, “Debugging mysqld under gdb”.
| Property | Value |
|---|---|
| Command-Line Format | --ignore-db-dir=dir_name |
| Deprecated | 5.7.16 |
| Type | Directory name |
This option tells the server to ignore the given directory
name for purposes of the SHOW
DATABASES statement or
INFORMATION_SCHEMA tables. For example, if
a MySQL configuration locates the data directory at the root
of a file system on Unix, the system might create a
lost+found directory there that the
server should ignore. Starting the server with
--ignore-db-dir=lost+found
causes that name not to be listed as a database.
To specify more than one name, use this option multiple times,
once for each name. Specifying the option with an empty value
(that is, as --ignore-db-dir=)
resets the directory list to the empty list.
Instances of this option given at server startup are used to
set the ignore_db_dirs system
variable.
This option is deprecated in MySQL 5.7. With the introduction of the data dictionary in MySQL 8.0, it became superfluous and was removed in that version.
| Property | Value |
|---|---|
| Command-Line Format | --initialize[={OFF|ON}] |
| Type | Boolean |
| Default Value | OFF |
This option is used to initialize a MySQL installation by
creating the data directory and populating the tables in the
mysql system database. For more
information, see
Section 2.10.1, “Initializing the Data Directory”.
When the server is started with
--initialize, some
functionality is unavailable that limits the statements
permitted in any file named by the
init_file system variable.
For more information, see the description of that variable. In
addition, the
disabled_storage_engines
system variable has no effect.
In MySQL NDB Cluster 7.5.4 and later, the
--ndbcluster option is ignored
when used together with --initialize. (Bug
#81689, Bug #23518923)
--initialize is mutually
exclusive with --bootstrap and
--daemonize.
| Property | Value |
|---|---|
| Command-Line Format | --initialize-insecure[={OFF|ON}] |
| Type | Boolean |
| Default Value | OFF |
This option is used to initialize a MySQL installation by
creating the data directory and populating the tables in the
mysql system database. This option implies
--initialize. For more
information, see the description of that option, and
Section 2.10.1, “Initializing the Data Directory”.
--initialize-insecure is
mutually exclusive with
--bootstrap and
--daemonize.
--innodb-
xxx
Set an option for the InnoDB storage
engine. The InnoDB options are listed in
Section 14.15, “InnoDB Startup Options and System Variables”.
| Property | Value |
|---|---|
| Command-Line Format | --install [service_name] |
| Platform Specific | Windows |
(Windows only) Install the server as a Windows service that
starts automatically during Windows startup. The default
service name is MySQL if no
service_name value is given. For
more information, see Section 2.3.4.8, “Starting MySQL as a Windows Service”.
If the server is started with the
--defaults-file and
--install options,
--install must be first.
--install-manual
[
service_name]
| Property | Value |
|---|---|
| Command-Line Format | --install-manual [service_name] |
| Platform Specific | Windows |
(Windows only) Install the server as a Windows service that
must be started manually. It does not start automatically
during Windows startup. The default service name is
MySQL if no
service_name value is given. For
more information, see Section 2.3.4.8, “Starting MySQL as a Windows Service”.
If the server is started with the
--defaults-file and
--install-manual options,
--install-manual must be
first.
--language=
lang_name,
-L lang_name
| Property | Value |
|---|---|
| Command-Line Format | --language=name |
| Deprecated | Yes; use lc-messages-dir instead |
| System Variable | language |
| Scope | Global |
| Dynamic | No |
| Type | Directory name |
| Default Value | /usr/local/mysql/share/mysql/english/ |
The language to use for error messages.
lang_name can be given as the
language name or as the full path name to the directory where
the language files are installed. See
Section 10.12, “Setting the Error Message Language”.
--lc-messages-dir and
--lc-messages should be used
rather than --language, which
is deprecated (and handled as an alias for
--lc-messages-dir). The
--language option will be
removed in a future MySQL release.
| Property | Value |
|---|---|
| Command-Line Format | --large-pages[={OFF|ON}] |
| System Variable | large_pages |
| Scope | Global |
| Dynamic | No |
| Platform Specific | Linux |
| Type | Boolean |
| Default Value | OFF |
Some hardware/operating system architectures support memory pages greater than the default (usually 4KB). The actual implementation of this support depends on the underlying hardware and operating system. Applications that perform a lot of memory accesses may obtain performance improvements by using large pages due to reduced Translation Lookaside Buffer (TLB) misses.
MySQL supports the Linux implementation of large page support
(which is called HugeTLB in Linux). See
Section 8.12.4.2, “Enabling Large Page Support”. For Solaris support of
large pages, see the description of the
--super-large-pages option.
--large-pages is disabled by
default.
| Property | Value |
|---|---|
| Command-Line Format | --lc-messages=name |
| System Variable | lc_messages |
| Scope | Global, Session |
| Dynamic | Yes |
| Type | String |
| Default Value | en_US |
The locale to use for error messages. The default is
en_US. The server converts the argument to
a language name and combines it with the value of
--lc-messages-dir to produce
the location for the error message file. See
Section 10.12, “Setting the Error Message Language”.
| Property | Value |
|---|---|
| Command-Line Format | --lc-messages-dir=dir_name |
| System Variable | lc_messages_dir |
| Scope | Global |
| Dynamic | No |
| Type | Directory name |
The directory where error messages are located. The server
uses the value together with the value of
--lc-messages to produce the
location for the error message file. See
Section 10.12, “Setting the Error Message Language”.
| Property | Value |
|---|---|
| Command-Line Format | --local-service |
(Windows only) A --local-service option
following the service name causes the server to run using the
LocalService Windows account that has
limited system privileges. If both
--defaults-file and
--local-service are given following the
service name, they can be in any order. See
Section 2.3.4.8, “Starting MySQL as a Windows Service”.
| Property | Value |
|---|---|
| Command-Line Format | --log-error[=file_name] |
| System Variable | log_error |
| Scope | Global |
| Dynamic | No |
| Type | File name |
Write the error log and startup messages to this file. See Section 5.4.2, “The Error Log”.
If the option names no file, the error log file name on Unix
and Unix-like systems is
host_name.err--pid-file option is
specified. In that case, the file name is the PID file base
name with a suffix of .err in the data
directory.
If the option names a file, the error log file has that name
(with an .err suffix added if the name
has no suffix), located under the data directory unless an
absolute path name is given to specify a different location.
On Windows, --console takes
precedence over --log-error if
both are given. In this case, the server writes the error log
to the console rather than to a file. (In MySQL 5.5 and 5.6,
this is reversed: --log-error
takes precedence over --console
if both are given.)
| Property | Value |
|---|---|
| Command-Line Format | --log-isam[=file_name] |
| Type | File name |
Log all MyISAM changes to this file (used
only when debugging MyISAM).
| Property | Value |
|---|---|
| Command-Line Format | --log-raw[={OFF|ON}] |
| Type | Boolean |
| Default Value | OFF |
Passwords in certain statements written to the general query
log, slow query log, and binary log are rewritten by the
server not to occur literally in plain text. Password
rewriting can be suppressed for the general query log by
starting the server with the
--log-raw option. This option
may be useful for diagnostic purposes, to see the exact text
of statements as received by the server, but for security
reasons is not recommended for production use.
If a query rewrite plugin is installed, the
--log-raw option affects
statement logging as follows:
For more information, see Section 6.1.2.3, “Passwords and Logging”.
| Property | Value |
|---|---|
| Command-Line Format | --log-short-format[={OFF|ON}] |
| Type | Boolean |
| Default Value | OFF |
Log less information to the slow query log, if it has been activated.
| Property | Value |
|---|---|
| Command-Line Format | --log-tc=file_name |
| Type | File name |
| Default Value | tc.log |
The name of the memory-mapped transaction coordinator log file
(for XA transactions that affect multiple storage engines when
the binary log is disabled). The default name is
tc.log. The file is created under the
data directory if not given as a full path name. This option
is unused.
| Property | Value |
|---|---|
| Command-Line Format | --log-tc-size=# |
| Type | Integer |
| Default Value (64-bit platforms, >= 5.7.21) | 6 * page size |
| Default Value (64-bit platforms, <= 5.7.20) | 24576 |
| Default Value (32-bit platforms, >= 5.7.21) | 6 * page size |
| Default Value (32-bit platforms, <= 5.7.20) | 24576 |
| Minimum Value | 6 * page size |
| Maximum Value (64-bit platforms) | 18446744073709551615 |
| Maximum Value (32-bit platforms) | 4294967295 |
The size in bytes of the memory-mapped transaction coordinator log. The default and minimum values are 6 times the page size, and the value must be a multiple of the page size. (Before MySQL 5.7.21, the default size is 24KB.)
--log-warnings[=,
level]-W [
level]
| Property | Value |
|---|---|
| Command-Line Format | --log-warnings[=#] |
| Deprecated | Yes |
| System Variable | log_warnings |
| Scope | Global |
| Dynamic | Yes |
| Type | Integer |
| Default Value | 2 |
| Minimum Value | 0 |
| Maximum Value (64-bit platforms) | 18446744073709551615 |
| Maximum Value (32-bit platforms) | 4294967295 |
The log_error_verbosity
system variable is preferred over, and should be used
instead of, the
--log-warnings option or
log_warnings system
variable. For more information, see the descriptions of
log_error_verbosity and
log_warnings. The
--log-warnings command-line
option and log_warnings
system variable are deprecated and will be removed in a
future MySQL release.
Whether to produce additional warning messages to the error
log. This option is enabled by default. To disable it, use
--log-warnings=0. Specifying
the option without a level value
increments the current value by 1. The server logs messages
about statements that are unsafe for statement-based logging
if the value is greater than 0. Aborted connections and
access-denied errors for new connection attempts are logged if
the value is greater than 1. See
Section B.4.2.10, “Communication Errors and Aborted Connections”.
| Property | Value |
|---|---|
| Command-Line Format | --memlock[={OFF|ON}] |
| Type | Boolean |
| Default Value | OFF |
Lock the mysqld process in memory. This option might help if you have a problem where the operating system is causing mysqld to swap to disk.
--memlock works on systems that
support the mlockall() system call; this
includes Solaris, most Linux distributions that use a 2.4 or
higher kernel, and perhaps other Unix systems. On Linux
systems, you can tell whether or not
mlockall() (and thus this option) is
supported by checking to see whether or not it is defined in
the system mman.h file, like this:
shell> grep mlockall /usr/include/sys/mman.h
If mlockall() is supported, you should see
in the output of the previous command something like the
following:
extern int mlockall (int __flags) __THROW;
Use of this option may require you to run the server as
root, which, for reasons of security, is
normally not a good idea. See
Section 6.1.5, “How to Run MySQL as a Normal User”.
On Linux and perhaps other systems, you can avoid the need
to run the server as root by changing the
limits.conf file. See the notes
regarding the memlock limit in
Section 8.12.4.2, “Enabling Large Page Support”.
You must not try to use this option on a system that does
not support the mlockall() system call;
if you do so, mysqld will very likely
crash as soon as you try to start it.
| Property | Value |
|---|---|
| Command-Line Format | --myisam-block-size=# |
| Type | Integer |
| Default Value | 1024 |
| Minimum Value | 1024 |
| Maximum Value | 16384 |
The block size to be used for MyISAM index
pages.
Do not read any option files. If program startup fails due to
reading unknown options from an option file,
--no-defaults can be used to
prevent them from being read. This must be the first option on
the command line if it is used.
For additional information about this and other option-file options, see Section 4.2.2.3, “Command-Line Options that Affect Option-File Handling”.
| Property | Value |
|---|---|
| Command-Line Format | --old-style-user-limits[={OFF|ON}] |
| Type | Boolean |
| Default Value | OFF |
Enable old-style user limits. (Before MySQL 5.0.3, account
resource limits were counted separately for each host from
which a user connected rather than per account row in the
user table.) See
Section 6.2.16, “Setting Account Resource Limits”.
| Property | Value |
|---|---|
| Command-Line Format | --partition[={OFF|ON}] |
| Deprecated | 5.7.16 |
| Disabled by | skip-partition |
| Type | Boolean |
| Default Value | ON |
Enables or disables user-defined partitioning support in the MySQL Server.
This option is deprecated in MySQL 5.7.16, and is removed from MySQL 8.0 because in MySQL 8.0, the partitioning engine is replaced by native partitioning, which cannot be disabled.
--performance-schema-xxx
Configure a Performance Schema option. For details, see Section 25.14, “Performance Schema Command Options”.
| Property | Value |
|---|---|
| Command-Line Format | --plugin-load=plugin_list |
| System Variable | plugin_load |
| Scope | Global |
| Dynamic | No |
| Type | String |
This option tells the server to load the named plugins at
startup. If multiple
--plugin-load options are
given, only the last one is used. Additional plugins to load
may be specified using
--plugin-load-add options.
The option value is a semicolon-separated list of
name=plugin_library
and plugin_library values. Each
name is the name of a plugin to
load, and plugin_library is the
name of the library file that contains the plugin code. If a
plugin library is named without any preceding plugin name, the
server loads all plugins in the library. The server looks for
plugin library files in the directory named by the
plugin_dir system variable.
For example, if plugins named myplug1 and
myplug2 have library files
myplug1.so and
myplug2.so, use this option to perform an
early plugin load:
shell> mysqld --plugin-load="myplug1=myplug1.so;myplug2=myplug2.so"
Quotes are used around the argument value here because
otherwise semicolon (;) is interpreted as a
special character by some command interpreters. (Unix shells
treat it as a command terminator, for example.)
Each named plugin is loaded for a single invocation of
mysqld only. After a restart, the plugin is
not loaded unless --plugin-load
is used again. This is in contrast to
INSTALL PLUGIN, which adds an
entry to the mysql.plugins table to cause
the plugin to be loaded for every normal server startup.
Under normal startup, the server determines which plugins to
load by reading the mysql.plugins system
table. If the server is started with the
--skip-grant-tables option, it
does not consult the mysql.plugins table
and does not load plugins listed there.
--plugin-load enables plugins
to be loaded even when
--skip-grant-tables is given.
--plugin-load also enables
plugins to be loaded at startup that cannot be loaded at
runtime.
For additional information about plugin loading, see Section 5.5.1, “Installing and Uninstalling Plugins”.
| Property | Value |
|---|---|
| Command-Line Format | --plugin-load-add=plugin_list |
| System Variable | plugin_load_add |
| Scope | Global |
| Dynamic | No |
| Type | String |
This option complements the
--plugin-load option.
--plugin-load-add adds a plugin
or plugins to the set of plugins to be loaded at startup. The
argument format is the same as for
--plugin-load.
--plugin-load-add can be used
to avoid specifying a large set of plugins as a single long
unwieldy --plugin-load
argument.
--plugin-load-add can be given
in the absence of
--plugin-load, but any instance
of --plugin-load-add that
appears before --plugin-load.
has no effect because
--plugin-load resets the set of
plugins to load. In other words, these options:
--plugin-load=x --plugin-load-add=y
are equivalent to this option:
--plugin-load="x;y"
But these options:
--plugin-load-add=y --plugin-load=x
are equivalent to this option:
--plugin-load=x
For additional information about plugin loading, see Section 5.5.1, “Installing and Uninstalling Plugins”.
Specifies an option that pertains to a server plugin. For
example, many storage engines can be built as plugins, and for
such engines, options for them can be specified with a
--plugin prefix. Thus, the
--innodb-file-per-table option
for InnoDB can be specified as
--plugin-innodb-file-per-table.
For boolean options that can be enabled or disabled, the
--skip prefix and other alternative formats
are supported as well (see
Section 4.2.2.4, “Program Option Modifiers”). For example,
--skip-plugin-innodb-file-per-table
disables innodb-file-per-table.
The rationale for the --plugin prefix is that
it enables plugin options to be specified unambiguously if
there is a name conflict with a built-in server option. For
example, were a plugin writer to name a plugin
“sql” and implement a “mode” option,
the option name might be
--sql-mode, which would
conflict with the built-in option of the same name. In such
cases, references to the conflicting name are resolved in
favor of the built-in option. To avoid the ambiguity, users
can specify the plugin option as
--plugin-sql-mode. Use of the
--plugin prefix for plugin options is
recommended to avoid any question of ambiguity.
--port=,
port_num-P
port_num
| Property | Value |
|---|---|
| Command-Line Format | --port=port_num |
| System Variable | port |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | 3306 |
| Minimum Value | 0 |
| Maximum Value | 65535 |
The port number to use when listening for TCP/IP connections.
On Unix and Unix-like systems, the port number must be 1024 or
higher unless the server is started by the
root operating system user. Setting this
option to 0 causes the default value to be used.
| Property | Value |
|---|---|
| Command-Line Format | --port-open-timeout=# |
| Type | Integer |
| Default Value | 0 |
On some systems, when the server is stopped, the TCP/IP port might not become available immediately. If the server is restarted quickly afterward, its attempt to reopen the port can fail. This option indicates how many seconds the server should wait for the TCP/IP port to become free if it cannot be opened. The default is not to wait.
Print the program name and all options that it gets from
option files. Password values are masked. This must be the
first option on the command line if it is used, except that it
may be used immediately after
--defaults-file or
--defaults-extra-file.
For additional information about this and other option-file options, see Section 4.2.2.3, “Command-Line Options that Affect Option-File Handling”.
| Property | Value |
|---|---|
| Command-Line Format | --remove [service_name] |
| Platform Specific | Windows |
(Windows only) Remove a MySQL Windows service. The default
service name is MySQL if no
service_name value is given. For
more information, see Section 2.3.4.8, “Starting MySQL as a Windows Service”.
| Property | Value |
|---|---|
| Command-Line Format | --safe-user-create[={OFF|ON}] |
| Type | Boolean |
| Default Value | OFF |
If this option is enabled, a user cannot create new MySQL
users by using the GRANT
statement unless the user has the
INSERT privilege for the
mysql.user system table or any column in
the table. If you want a user to have the ability to create
new users that have those privileges that the user has the
right to grant, you should grant the user the following
privilege:
GRANT INSERT(user) ON mysql.user TO 'user_name'@'host_name';
This ensures that the user cannot change any privilege columns
directly, but has to use the
GRANT statement to give
privileges to other users.
| Property | Value |
|---|---|
| Command-Line Format | --skip-grant-tables[={OFF|ON}] |
| Type | Boolean |
| Default Value | OFF |
This option affects the server startup sequence:
--skip-grant-tables causes
the server not to read the grant tables in the
mysql system database, and thus to
start without using the privilege system at all. This
gives anyone with access to the server
unrestricted access to all databases.
To cause a server started with
--skip-grant-tables to load
the grant tables at runtime, perform a privilege-flushing
operation, which can be done in these ways:
Issue a MySQL FLUSH
PRIVILEGES statement after connecting to the
server.
Execute a mysqladmin flush-privileges or mysqladmin reload command from the command line.
Privilege flushing might also occur implicitly as a result of other actions performed after startup, thus causing the server to start using the grant tables. For example, mysql_upgrade flushes the privileges during the upgrade procedure.
In addition to causing the startup sequence not to load
the grant tables,
--skip-grant-tables causes
the server not to load certain other objects stored in the
mysql system database: plugins that
were installed with the INSTALL
PLUGIN statement, scheduled events, and
user-defined functions (UDFs). To cause plugins to be
loaded anyway, use the
--plugin-load or
--plugin-load-add option.
--skip-grant-tables causes
the
disabled_storage_engines
system variable to have no effect.
| Property | Value |
|---|---|
| Command-Line Format | --skip-host-cache |
Disable use of the internal host cache for faster name-to-IP resolution. With the cache disabled, the server performs a DNS lookup every time a client connects.
Use of --skip-host-cache is
similar to setting the
host_cache_size system
variable to 0, but
host_cache_size is more
flexible because it can also be used to resize, enable, or
disable the host cache at runtime, not just at server startup.
If you start the server with
--skip-host-cache, that does
not prevent changes to the value of
host_cache_size, but such
changes have no effect and the cache is not re-enabled even if
host_cache_size is set larger
than 0.
For more information about how the host cache works, see Section 8.12.5.2, “DNS Lookup Optimization and the Host Cache”.
Disable the InnoDB storage engine. In this
case, because the default storage engine is
InnoDB, the server will not start
unless you also use
--default-storage-engine and
--default-tmp-storage-engine to
set the default to some other engine for both permanent and
TEMPORARY tables.
The InnoDB storage engine cannot be
disabled, and the
--skip-innodb
option is deprecated and has no effect. Its use results in a
warning. This option will be removed in a future MySQL
release.
| Property | Value |
|---|---|
| Command-Line Format | --skip-new |
This option disables (what used to be considered) new,
possibly unsafe behaviors. It results in these settings:
delay_key_write=OFF,
concurrent_insert=NEVER,
automatic_sp_privileges=OFF.
It also causes OPTIMIZE TABLE
to be mapped to ALTER TABLE for
storage engines for which OPTIMIZE
TABLE is not supported.
| Property | Value |
|---|---|
| Command-Line Format |
|
| Deprecated | 5.7.16 |
Disables user-defined partitioning. Partitioned tables can be
seen using SHOW TABLES or by
querying the
INFORMATION_SCHEMA.TABLES table,
but cannot be created or modified, nor can data in such tables
be accessed. All partition-specific columns in the
INFORMATION_SCHEMA.PARTITIONS
table display NULL.
Since DROP TABLE removes table
definition (.frm) files, this statement
works on partitioned tables even when partitioning is disabled
using the option. The statement, however, does not remove
partition definitions associated with partitioned tables in
such cases. For this reason, you should avoid dropping
partitioned tables with partitioning disabled, or take action
to remove orphaned .par files manually
(if present).
In MySQL 5.7, partition definition
(.par) files are no longer created for
partitioned InnoDB tables. Instead,
partition definitions are stored in the
InnoDB internal data dictionary.
Partition definition (.par) files
continue to be used for partitioned
MyISAM tables.
This option is deprecated in MySQL 5.7.16, and is removed from MySQL 8.0 because in MySQL 8.0, the partitioning engine is replaced by native partitioning, which cannot be disabled.
| Property | Value |
|---|---|
| Command-Line Format | --skip-show-database |
| System Variable | skip_show_database |
| Scope | Global |
| Dynamic | No |
This option sets the
skip_show_database system
variable that controls who is permitted to use the
SHOW DATABASES statement. See
Section 5.1.7, “Server System Variables”.
| Property | Value |
|---|---|
| Command-Line Format | --skip-stack-trace |
Do not write stack traces. This option is useful when you are running mysqld under a debugger. On some systems, you also must use this option to get a core file. See Section 28.5, “Debugging and Porting MySQL”.
| Property | Value |
|---|---|
| Command-Line Format | --slow-start-timeout=# |
| Type | Integer |
| Default Value | 15000 |
This option controls the Windows service control manager's service start timeout. The value is the maximum number of milliseconds that the service control manager waits before trying to kill the windows service during startup. The default value is 15000 (15 seconds). If the MySQL service takes too long to start, you may need to increase this value. A value of 0 means there is no timeout.
| Property | Value |
|---|---|
| Command-Line Format | --socket={file_name|pipe_name} |
| System Variable | socket |
| Scope | Global |
| Dynamic | No |
| Type | String |
| Default Value (Other) | /tmp/mysql.sock |
| Default Value (Windows) | MySQL |
On Unix, this option specifies the Unix socket file to use
when listening for local connections. The default value is
/tmp/mysql.sock. If this option is given,
the server creates the file in the data directory unless an
absolute path name is given to specify a different directory.
On Windows, the option specifies the pipe name to use when
listening for local connections that use a named pipe. The
default value is MySQL (not
case-sensitive).
--sql-mode=
value[,value[,value...]]
| Property | Value |
|---|---|
| Command-Line Format | --sql-mode=name |
| System Variable | sql_mode |
| Scope | Global, Session |
| Dynamic | Yes |
| Type | Set |
| Default Value | ONLY_FULL_GROUP_BY STRICT_TRANS_TABLES NO_ZERO_IN_DATE NO_ZERO_DATE ERROR_FOR_DIVISION_BY_ZERO NO_AUTO_CREATE_USER NO_ENGINE_SUBSTITUTION |
| Valid Values |
|
Set the SQL mode. See Section 5.1.10, “Server SQL Modes”.
MySQL installation programs may configure the SQL mode during the installation process. If the SQL mode differs from the default or from what you expect, check for a setting in an option file that the server reads at startup.
Options that begin with --ssl
specify whether to permit clients to connect using SSL and
indicate where to find SSL keys and certificates. See
Command Options for Encrypted Connections.
| Property | Value |
|---|---|
| Command-Line Format | --standalone |
| Platform Specific | Windows |
Available on Windows only; instructs the MySQL server not to run as a service.
| Property | Value |
|---|---|
| Command-Line Format | --super-large-pages[={OFF|ON}] |
| Platform Specific | Solaris |
| Type | Boolean |
| Default Value | OFF |
Standard use of large pages in MySQL attempts to use the
largest size supported, up to 4MB. Under Solaris, a
“super large pages” feature enables uses of pages
up to 256MB. This feature is available for recent SPARC
platforms. It can be enabled or disabled by using the
--super-large-pages or
--skip-super-large-pages
option.
--symbolic-links,
--skip-symbolic-links
| Property | Value |
|---|---|
| Command-Line Format | --symbolic-links[={OFF|ON}] |
| Type | Boolean |
| Default Value | ON |
Enable or disable symbolic link support. On Unix, enabling
symbolic links means that you can link a
MyISAM index file or data file to another
directory with the INDEX DIRECTORY or
DATA DIRECTORY option of the
CREATE TABLE statement. If you
delete or rename the table, the files that its symbolic links
point to also are deleted or renamed. See
Section 8.12.3.2, “Using Symbolic Links for MyISAM Tables on Unix”.
This option has no meaning on Windows.
| Property | Value |
|---|---|
| Command-Line Format | --sysdate-is-now[={OFF|ON}] |
| Type | Boolean |
| Default Value | OFF |
SYSDATE() by default returns
the time at which it executes, not the time at which the
statement in which it occurs begins executing. This differs
from the behavior of NOW().
This option causes SYSDATE() to
be an alias for NOW(). For
information about the implications for binary logging and
replication, see the description for
SYSDATE() in
Section 12.6, “Date and Time Functions” and for SET
TIMESTAMP in
Section 5.1.7, “Server System Variables”.
--tc-heuristic-recover={COMMIT|ROLLBACK}
| Property | Value |
|---|---|
| Command-Line Format | --tc-heuristic-recover=name |
| Type | Enumeration |
| Default Value | COMMIT |
| Valid Values |
|
The type of decision to use in the heuristic recovery process. To use this option, two or more storage engines that support XA transactions must be installed.
| Property | Value |
|---|---|
| Command-Line Format | --temp-pool[={OFF|ON}] |
| Deprecated | 5.7.18 |
| Type | Boolean |
| Default Value (Other) | OFF |
| Default Value (Linux) | ON |
This option is ignored except on Linux. On Linux, it causes most temporary files created by the server to use a small set of names, rather than a unique name for each new file. This works around a problem in the Linux kernel dealing with creating many new files with different names. With the old behavior, Linux seems to “leak” memory, because it is being allocated to the directory entry cache rather than to the disk cache.
As of MySQL 5.7.18, this option is deprecated and is removed in MySQL 8.0.
| Property | Value |
|---|---|
| Command-Line Format | --transaction-isolation=name |
| System Variable (>= 5.7.20) | transaction_isolation |
| Scope (>= 5.7.20) | Global, Session |
| Dynamic (>= 5.7.20) | Yes |
| Type | Enumeration |
| Default Value | REPEATABLE-READ |
| Valid Values |
|
Sets the default transaction isolation level. The
level value can be
READ-UNCOMMITTED,
READ-COMMITTED,
REPEATABLE-READ, or
SERIALIZABLE. See
Section 13.3.6, “SET TRANSACTION Statement”.
The default transaction isolation level can also be set at
runtime using the SET
TRANSACTION statement or by setting the
tx_isolation (or, as of MySQL
5.7.20,
transaction_isolation) system
variable.
| Property | Value |
|---|---|
| Command-Line Format | --transaction-read-only[={OFF|ON}] |
| System Variable (>= 5.7.20) | transaction_read_only |
| Scope (>= 5.7.20) | Global, Session |
| Dynamic (>= 5.7.20) | Yes |
| Type | Boolean |
| Default Value | OFF |
Sets the default transaction access mode. By default, read-only mode is disabled, so the mode is read/write.
To set the default transaction access mode at runtime, use the
SET TRANSACTION statement or
set the tx_read_only (or, as
of MySQL 5.7.20,
transaction_read_only) system
variable. See Section 13.3.6, “SET TRANSACTION Statement”.
--tmpdir=,
dir_name-t
dir_name
| Property | Value |
|---|---|
| Command-Line Format | --tmpdir=dir_name |
| System Variable | tmpdir |
| Scope | Global |
| Dynamic | No |
| Type | Directory name |
The path of the directory to use for creating temporary files.
It might be useful if your default /tmp
directory resides on a partition that is too small to hold
temporary tables. This option accepts several paths that are
used in round-robin fashion. Paths should be separated by
colon characters (:) on Unix and semicolon
characters (;) on Windows.
--tmpdir can be a non-permanent
location, such as a directory on a memory-based file system or
a directory that is cleared when the server host restarts. If
the MySQL server is acting as a replication slave, and you are
using a non-permanent location for
--tmpdir, consider setting a
different temporary directory for the slave using the
slave_load_tmpdir system
variable. For a replication slave, the temporary files used to
replicate LOAD DATA statements
are stored in this directory, so with a permanent location
they can survive machine restarts, although replication can
now continue after a restart if the temporary files have been
removed.
For more information about the storage location of temporary files, see Section B.4.3.5, “Where MySQL Stores Temporary Files”.
--user={,
user_name|user_id}-u
{
user_name|user_id}
| Property | Value |
|---|---|
| Command-Line Format | --user=name |
| Type | String |
Run the mysqld server as the user having
the name user_name or the numeric
user ID user_id.
(“User” in this context refers to a system login
account, not a MySQL user listed in the grant tables.)
This option is mandatory when starting
mysqld as root. The
server changes its user ID during its startup sequence,
causing it to run as that particular user rather than as
root. See
Section 6.1.1, “Security Guidelines”.
To avoid a possible security hole where a user adds a
--user=root option to a
my.cnf file (thus causing the server to
run as root), mysqld
uses only the first --user
option specified and produces a warning if there are multiple
--user options. Options in
/etc/my.cnf and
$MYSQL_HOME/my.cnf are processed before
command-line options, so it is recommended that you put a
--user option in
/etc/my.cnf and specify a value other
than root. The option in
/etc/my.cnf is found before any other
--user options, which ensures
that the server runs as a user other than
root, and that a warning results if any
other --user option is found.
Use this option with the --help
option for detailed help.
--version, -V
Display version information and exit.
The MySQL server maintains many system variables that configure
its operation. Each system variable has a default value. System
variables can be set at server startup using options on the
command line or in an option file. Most of them can be changed
dynamically at runtime using the
SET
statement, which enables you to modify operation of the server
without having to stop and restart it. You can also use system
variable values in expressions.
At runtime, setting a global system variable value requires the
SUPER privilege. Setting a session
system variable value normally requires no special privileges and
can be done by any user, although there are exceptions. For more
information, see Section 5.1.8.1, “System Variable Privileges”
There are several ways to see the names and values of system variables:
To see the values that a server will use based on its compiled-in defaults and any option files that it reads, use this command:
mysqld --verbose --help
To see the values that a server will use based only on its compiled-in defaults, ignoring the settings in any option files, use this command:
mysqld --no-defaults --verbose --help
To see the current values used by a running server, use the
SHOW VARIABLES statement or the
Performance Schema system variable tables. See
Section 25.12.13, “Performance Schema System Variable Tables”.
This section provides a description of each system variable. For a system variable summary table, see Section 5.1.4, “Server System Variable Reference”. For more information about manipulation of system variables, see Section 5.1.8, “Using System Variables”.
For additional system variable information, see these sections:
Section 5.1.8, “Using System Variables”, discusses the syntax for setting and displaying system variable values.
Section 5.1.8.2, “Dynamic System Variables”, lists the variables that can be set at runtime.
Information on tuning system variables can be found in Section 5.1.1, “Configuring the Server”.
Section 14.15, “InnoDB Startup Options and System Variables”, lists
InnoDB system variables.
Section 21.3.3.9.2, “NDB Cluster System Variables”, lists system variables which are specific to NDB Cluster.
For information on server system variables specific to replication, see Section 16.1.6, “Replication and Binary Logging Options and Variables”.
Some of the following variable descriptions refer to
“enabling” or “disabling” a variable.
These variables can be enabled with the
SET
statement by setting them to ON or
1, or disabled by setting them to
OFF or 0. Boolean
variables can be set at startup to the values
ON, TRUE,
OFF, and FALSE (not
case-sensitive), as well as 1 and
0. See Section 4.2.2.4, “Program Option Modifiers”.
Some system variables control the size of buffers or caches. For a given buffer, the server might need to allocate internal data structures. These structures typically are allocated from the total memory allocated to the buffer, and the amount of space required might be platform dependent. This means that when you assign a value to a system variable that controls a buffer size, the amount of space actually available might differ from the value assigned. In some cases, the amount might be less than the value assigned. It is also possible that the server will adjust a value upward. For example, if you assign a value of 0 to a variable for which the minimal value is 1024, the server will set the value to 1024.
Values for buffer sizes, lengths, and stack sizes are given in bytes unless otherwise specified.
Some system variables take file name values. Unless otherwise
specified, the default file location is the data directory if the
value is a relative path name. To specify the location explicitly,
use an absolute path name. Suppose that the data directory is
/var/mysql/data. If a file-valued variable is
given as a relative path name, it will be located under
/var/mysql/data. If the value is an absolute
path name, its location is as given by the path name.
authentication_windows_log_level
| Property | Value |
|---|---|
| Command-Line Format | --authentication-windows-log-level=# |
| System Variable | authentication_windows_log_level |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | 2 |
| Minimum Value | 0 |
| Maximum Value | 4 |
This variable is available only if the
authentication_windows Windows
authentication plugin is enabled and debugging code is
enabled. See
Section 6.4.1.8, “Windows Pluggable Authentication”.
This variable sets the logging level for the Windows authentication plugin. The following table shows the permitted values.
| Value | Description |
|---|---|
| 0 | No logging |
| 1 | Log only error messages |
| 2 | Log level 1 messages and warning messages |
| 3 | Log level 2 messages and information notes |
| 4 | Log level 3 messages and debug messages |
authentication_windows_use_principal_name
| Property | Value |
|---|---|
| Command-Line Format | --authentication-windows-use-principal-name[={OFF|ON}] |
| System Variable | authentication_windows_use_principal_name |
| Scope | Global |
| Dynamic | No |
| Type | Boolean |
| Default Value | ON |
This variable is available only if the
authentication_windows Windows
authentication plugin is enabled. See
Section 6.4.1.8, “Windows Pluggable Authentication”.
A client that authenticates using the
InitSecurityContext() function should
provide a string identifying the service to which it connects
(targetName). MySQL uses the
principal name (UPN) of the account under which the server is
running. The UPN has the form
user_id@computer_name
This variable controls whether the server sends the UPN in the
initial challenge. By default, the variable is enabled. For
security reasons, it can be disabled to avoid sending the
server's account name to a client as cleartext. If the
variable is disabled, the server always sends a
0x00 byte in the first challenge, the
client does not specify targetName,
and as a result, NTLM authentication is used.
If the server fails to obtain its UPN (which will happen primarily in environments that do not support Kerberos authentication), the UPN is not sent by the server and NTLM authentication is used.
| Property | Value |
|---|---|
| Command-Line Format | --autocommit[={OFF|ON}] |
| System Variable | autocommit |
| Scope | Global, Session |
| Dynamic | Yes |
| Type | Boolean |
| Default Value | ON |
The autocommit mode. If set to 1, all changes to a table take
effect immediately. If set to 0, you must use
COMMIT to accept a transaction
or ROLLBACK
to cancel it. If autocommit
is 0 and you change it to 1, MySQL performs an automatic
COMMIT of any open transaction.
Another way to begin a transaction is to use a
START
TRANSACTION or
BEGIN
statement. See Section 13.3.1, “START TRANSACTION, COMMIT, and ROLLBACK Statements”.
By default, client connections begin with
autocommit set to 1. To cause
clients to begin with a default of 0, set the global
autocommit value by starting
the server with the
--autocommit=0 option. To set
the variable using an option file, include these lines:
[mysqld] autocommit=0
| Property | Value |
|---|---|
| Command-Line Format | --automatic-sp-privileges[={OFF|ON}] |
| System Variable | automatic_sp_privileges |
| Scope | Global |
| Dynamic | Yes |
| Type | Boolean |
| Default Value | ON |
When this variable has a value of 1 (the default), the server
automatically grants the
EXECUTE and
ALTER ROUTINE privileges to the
creator of a stored routine, if the user cannot already
execute and alter or drop the routine. (The
ALTER ROUTINE privilege is
required to drop the routine.) The server also automatically
drops those privileges from the creator when the routine is
dropped. If
automatic_sp_privileges is 0,
the server does not automatically add or drop these
privileges.
The creator of a routine is the account used to execute the
CREATE statement for it. This might not be
the same as the account named as the
DEFINER in the routine definition.
If you start mysqld with
--skip-new,
automatic_sp_privileges is
set to OFF.
See also Section 23.2.2, “Stored Routines and MySQL Privileges”.
| Property | Value |
|---|---|
| Command-Line Format | --auto-generate-certs[={OFF|ON}] |
| System Variable | auto_generate_certs |
| Scope | Global |
| Dynamic | No |
| Type | Boolean |
| Default Value | ON |
This variable is available if the server was compiled using OpenSSL (see Section 6.3.4, “SSL Library-Dependent Capabilities”). It controls whether the server autogenerates SSL key and certificate files in the data directory, if they do not already exist.
At startup, the server automatically generates server-side and
client-side SSL certificate and key files in the data
directory if the
auto_generate_certs system
variable is enabled, no SSL options other than
--ssl are specified, and the
server-side SSL files are missing from the data directory.
These files enable secure client connections using SSL; see
Section 6.3.1, “Configuring MySQL to Use Encrypted Connections”.
For more information about SSL file autogeneration, including file names and characteristics, see Section 6.3.3.1, “Creating SSL and RSA Certificates and Keys using MySQL”
The
sha256_password_auto_generate_rsa_keys
system variable is related but controls autogeneration of RSA
key-pair files needed for secure password exchange using RSA
over unencypted connections.
| Property | Value |
|---|---|
| Command-Line Format | --avoid-temporal-upgrade[={OFF|ON}] |
| Deprecated | Yes |
| System Variable | avoid_temporal_upgrade |
| Scope | Global |
| Dynamic | Yes |
| Type | Boolean |
| Default Value | OFF |
This variable controls whether ALTER
TABLE implicitly upgrades temporal columns found to
be in pre-5.6.4 format (TIME,
DATETIME, and
TIMESTAMP columns without
support for fractional seconds precision). Upgrading such
columns requires a table rebuild, which prevents any use of
fast alterations that might otherwise apply to the operation
to be performed.
This variable is disabled by default. Enabling it causes
ALTER TABLE not to rebuild
temporal columns and thereby be able to take advantage of
possible fast alterations.
This variable is deprecated and will be removed in a future MySQL release.
| Property | Value |
|---|---|
| Command-Line Format | --back-log=# |
| System Variable | back_log |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | -1 (signifies autosizing; do not assign this literal value) |
| Minimum Value | 1 |
| Maximum Value | 65535 |
The number of outstanding connection requests MySQL can have.
This comes into play when the main MySQL thread gets very many
connection requests in a very short time. It then takes some
time (although very little) for the main thread to check the
connection and start a new thread. The
back_log value indicates how
many requests can be stacked during this short time before
MySQL momentarily stops answering new requests. You need to
increase this only if you expect a large number of connections
in a short period of time.
In other words, this value is the size of the listen queue for
incoming TCP/IP connections. Your operating system has its own
limit on the size of this queue. The manual page for the Unix
listen() system call should have more
details. Check your OS documentation for the maximum value for
this variable. back_log
cannot be set higher than your operating system limit.
The default value is based on the following formula, capped to a limit of 900:
50 + (max_connections / 5)
| Property | Value |
|---|---|
| Command-Line Format | --basedir=dir_name |
| System Variable | basedir |
| Scope | Global |
| Dynamic | No |
| Type | Directory name |
| Default Value | configuration-dependent default |
The path to the MySQL installation base directory.
| Property | Value |
|---|---|
| Command-Line Format | --big-tables[={OFF|ON}] |
| System Variable | big_tables |
| Scope | Global, Session |
| Dynamic | Yes |
| Type | Boolean |
| Default Value | OFF |
If enabled, the server stores all temporary tables on disk
rather than in memory. This prevents most The table
errors
for tbl_name is fullSELECT operations that
require a large temporary table, but also slows down queries
for which in-memory tables would suffice.
The default value for new connection is OFF
(use in-memory temporary tables). Normally, it should never be
necessary to enable this variable because the server is able
to handle large result sets automatically by using memory for
small temporary tables and switching to disk-based tables as
required.
| Property | Value |
|---|---|
| Command-Line Format | --bind-address=addr |
| System Variable | bind_address |
| Scope | Global |
| Dynamic | No |
| Type | String |
| Default Value | * |
The MySQL server listens on a single network socket for TCP/IP
connections. This socket is bound to a single address, but it
is possible for an address to map onto multiple network
interfaces. To specify an address, set
bind_address=
at server startup, where addraddr is an
IPv4 or IPv6 address or a host name. If
addr is a host name, the server
resolves the name to an IP address and binds to that address.
If a host name resolves to multiple IP addresses, the server
uses the first IPv4 address if there are any, or the first
IPv6 address otherwise.
The server treats different types of addresses as follows:
If the address is *, the server accepts
TCP/IP connections on all server host IPv4 interfaces,
and, if the server host supports IPv6, on all IPv6
interfaces. Use this address to permit both IPv4 and IPv6
connections on all server interfaces. This value is the
default.
If the address is 0.0.0.0, the server
accepts TCP/IP connections on all server host IPv4
interfaces.
If the address is ::, the server
accepts TCP/IP connections on all server host IPv4 and
IPv6 interfaces.
If the address is an IPv4-mapped address, the server
accepts TCP/IP connections for that address, in either
IPv4 or IPv6 format. For example, if the server is bound
to ::ffff:127.0.0.1, clients can
connect using --host=127.0.0.1 or
--host=::ffff:127.0.0.1.
If the address is a “regular” IPv4 or IPv6
address (such as 127.0.0.1 or
::1), the server accepts TCP/IP
connections only for that IPv4 or IPv6 address.
If binding to the address fails, the server produces an error and does not start.
If you intend to bind the server to a specific address, be
sure that the mysql.user system table
contains an account with administrative privileges that you
can use to connect to that address. Otherwise, you will not be
able to shut down the server. For example, if you bind the
server to *, you can connect to it using
all existing accounts. But if you bind the server to
::1, it accepts connections only on that
address. In that case, first make sure that the
'root'@'::1' account is present in the
mysql.user table so you can still connect
to the server to shut it down.
This variable has no effect for the embedded server
(libmysqld) and is not visible within the
embedded server.
| Property | Value |
|---|---|
| Command-Line Format | --block-encryption-mode=# |
| System Variable | block_encryption_mode |
| Scope | Global, Session |
| Dynamic | Yes |
| Type | String |
| Default Value | aes-128-ecb |
This variable controls the block encryption mode for
block-based algorithms such as AES. It affects encryption for
AES_ENCRYPT() and
AES_DECRYPT().
block_encryption_mode takes a
value in
aes-
format, where keylen-modekeylen is the key
length in bits and mode is the
encryption mode. The value is not case-sensitive. Permitted
keylen values are 128, 192, and
256. Permitted encryption modes depend on whether MySQL was
compiled using OpenSSL or yaSSL:
For OpenSSL, permitted mode
values are: ECB,
CBC, CFB1,
CFB8, CFB128,
OFB
For yaSSL, permitted mode
values are: ECB, CBC
For example, this statement causes the AES encryption functions to use a key length of 256 bits and the CBC mode:
SET block_encryption_mode = 'aes-256-cbc';
An error occurs for attempts to set
block_encryption_mode to a
value containing an unsupported key length or a mode that the
SSL library does not support.
| Property | Value |
|---|---|
| Command-Line Format | --bulk-insert-buffer-size=# |
| System Variable | bulk_insert_buffer_size |
| Scope | Global, Session |
| Dynamic | Yes |
| Type | Integer |
| Default Value | 8388608 |
| Minimum Value | 0 |
| Maximum Value (64-bit platforms) | 18446744073709551615 |
| Maximum Value (32-bit platforms) | 4294967295 |
MyISAM uses a special tree-like cache to
make bulk inserts faster for
INSERT ...
SELECT, INSERT ... VALUES (...), (...),
..., and LOAD DATA
when adding data to nonempty tables. This variable limits the
size of the cache tree in bytes per thread. Setting it to 0
disables this optimization. The default value is 8MB.
| Property | Value |
|---|---|
| System Variable | character_set_client |
| Scope | Global, Session |
| Dynamic | Yes |
| Type | String |
| Default Value | utf8 |
The character set for statements that arrive from the client.
The session value of this variable is set using the character
set requested by the client when the client connects to the
server. (Many clients support a
--default-character-set option to enable this
character set to be specified explicitly. See also
Section 10.4, “Connection Character Sets and Collations”.) The global value of the
variable is used to set the session value in cases when the
client-requested value is unknown or not available, or the
server is configured to ignore client requests:
The client requests a character set not known to the
server. For example, a Japanese-enabled client requests
sjis when connecting to a server not
configured with sjis support.
The client is from a version of MySQL older than MySQL 4.1, and thus does not request a character set.
mysqld was started with the
--skip-character-set-client-handshake
option, which causes it to ignore client character set
configuration. This reproduces MySQL 4.0 behavior and is
useful should you wish to upgrade the server without
upgrading all the clients.
Some character sets cannot be used as the client character
set. Attempting to use them as the
character_set_client value
produces an error. See
Impermissible Client Character Sets.
| Property | Value |
|---|---|
| System Variable | character_set_connection |
| Scope | Global, Session |
| Dynamic | Yes |
| Type | String |
| Default Value | utf8 |
The character set used for literals specified without a character set introducer and for number-to-string conversion. For information about introducers, see Section 10.3.8, “Character Set Introducers”.
| Property | Value |
|---|---|
| System Variable | character_set_database |
| Scope | Global, Session |
| Dynamic | Yes |
| Type | String |
| Default Value | latin1 |
| Footnote | This option is dynamic, but only the server should set this information. You should not set the value of this variable manually. |
The character set used by the default database. The server
sets this variable whenever the default database changes. If
there is no default database, the variable has the same value
as character_set_server.
The global
character_set_database and
collation_database system
variables are deprecated in MySQL 5.7 and will be
removed in a future version of MySQL.
Assigning a value to the session
character_set_database and
collation_database system
variables is deprecated in MySQL 5.7 and
assignments produce a warning. The session variables will
become read only in a future version of MySQL and assignments
will produce an error. It will remain possible to access the
session variables to determine the database character set and
collation for the default database.
| Property | Value |
|---|---|
| Command-Line Format | --character-set-filesystem=name |
| System Variable | character_set_filesystem |
| Scope | Global, Session |
| Dynamic | Yes |
| Type | String |
| Default Value | binary |
The file system character set. This variable is used to
interpret string literals that refer to file names, such as in
the LOAD DATA and
SELECT ... INTO
OUTFILE statements and the
LOAD_FILE() function. Such file
names are converted from
character_set_client to
character_set_filesystem
before the file opening attempt occurs. The default value is
binary, which means that no conversion
occurs. For systems on which multibyte file names are
permitted, a different value may be more appropriate. For
example, if the system represents file names using UTF-8, set
character_set_filesystem to
'utf8mb4'.
| Property | Value |
|---|---|
| System Variable | character_set_results |
| Scope | Global, Session |
| Dynamic | Yes |
| Type | String |
| Default Value | utf8 |
The character set used for returning query results to the client. This includes result data such as column values, result metadata such as column names, and error messages.
| Property | Value |
|---|---|
| Command-Line Format | --character-set-server=name |
| System Variable | character_set_server |
| Scope | Global, Session |
| Dynamic | Yes |
| Type | String |
| Default Value | latin1 |
The servers default character set. See
Section 10.15, “Character Set Configuration”. If you set this
variable, you should also set
collation_server to specify
the collation for the character set.
| Property | Value |
|---|---|
| System Variable | character_set_system |
| Scope | Global |
| Dynamic | No |
| Type | String |
| Default Value | utf8 |
The character set used by the server for storing identifiers.
The value is always utf8.
| Property | Value |
|---|---|
| Command-Line Format | --character-sets-dir=dir_name |
| System Variable | character_sets_dir |
| Scope | Global |
| Dynamic | No |
| Type | Directory name |
The directory where character sets are installed. See Section 10.15, “Character Set Configuration”.
| Property | Value |
|---|---|
| Command-Line Format | --check-proxy-users[={OFF|ON}] |
| System Variable | check_proxy_users |
| Scope | Global |
| Dynamic | Yes |
| Type | Boolean |
| Default Value | OFF |
Some authentication plugins implement proxy user mapping for
themselves (for example, the PAM and Windows authentication
plugins). Other authentication plugins do not support proxy
users by default. Of these, some can request that the MySQL
server itself map proxy users according to granted proxy
privileges: mysql_native_password,
sha256_password.
If the check_proxy_users
system variable is enabled, the server performs proxy user
mapping for any authentication plugins that make such a
request. However, it may also be necessary to enable
plugin-specific system variables to take advantage of server
proxy user mapping support:
For the mysql_native_password plugin,
enable
mysql_native_password_proxy_users.
For the sha256_password plugin, enable
sha256_password_proxy_users.
For information about user proxying, see Section 6.2.14, “Proxy Users”.
| Property | Value |
|---|---|
| System Variable | collation_connection |
| Scope | Global, Session |
| Dynamic | Yes |
| Type | String |
The collation of the connection character set.
collation_connection is
important for comparisons of literal strings. For comparisons
of strings with column values,
collation_connection does not
matter because columns have their own collation, which has a
higher collation precedence (see
Section 10.8.4, “Collation Coercibility in Expressions”).
| Property | Value |
|---|---|
| System Variable | collation_database |
| Scope | Global, Session |
| Dynamic | Yes |
| Type | String |
| Default Value | latin1_swedish_ci |
| Footnote | This option is dynamic, but only the server should set this information. You should not set the value of this variable manually. |
The collation used by the default database. The server sets
this variable whenever the default database changes. If there
is no default database, the variable has the same value as
collation_server.
The global
character_set_database and
collation_database system
variables are deprecated in MySQL 5.7 and will be
removed in a future version of MySQL.
Assigning a value to the session
character_set_database and
collation_database system
variables is deprecated in MySQL 5.7 and
assignments produce a warning. The session variables will
become read only in a future version of MySQL and assignments
will produce an error. It will remain possible to access the
session variables to determine the database character set and
collation for the default database.
| Property | Value |
|---|---|
| Command-Line Format | --collation-server=name |
| System Variable | collation_server |
| Scope | Global, Session |
| Dynamic | Yes |
| Type | String |
| Default Value | latin1_swedish_ci |
The server's default collation. See Section 10.15, “Character Set Configuration”.
| Property | Value |
|---|---|
| Command-Line Format | --completion-type=# |
| System Variable | completion_type |
| Scope | Global, Session |
| Dynamic | Yes |
| Type | Enumeration |
| Default Value | NO_CHAIN |
| Valid Values |
|
The transaction completion type. This variable can take the values shown in the following table. The variable can be assigned using either the name values or corresponding integer values.
| Value | Description |
|---|---|
NO_CHAIN (or 0) |
COMMIT and
ROLLBACK
are unaffected. This is the default value. |
CHAIN (or 1) |
COMMIT and
ROLLBACK
are equivalent to COMMIT AND CHAIN
and ROLLBACK AND CHAIN, respectively.
(A new transaction starts immediately with the same
isolation level as the just-terminated transaction.) |
RELEASE (or 2) |
COMMIT and
ROLLBACK
are equivalent to COMMIT RELEASE and
ROLLBACK RELEASE, respectively. (The
server disconnects after terminating the transaction.) |
completion_type affects
transactions that begin with
START
TRANSACTION or
BEGIN and
end with COMMIT or
ROLLBACK. It
does not apply to implicit commits resulting from execution of
the statements listed in Section 13.3.3, “Statements That Cause an Implicit Commit”. It
also does not apply for
XA
COMMIT,
XA
ROLLBACK, or when
autocommit=1.
| Property | Value |
|---|---|
| Command-Line Format | --concurrent-insert[=value] |
| System Variable | concurrent_insert |
| Scope | Global |
| Dynamic | Yes |
| Type | Enumeration |
| Default Value | AUTO |
| Valid Values |
|
If AUTO (the default), MySQL permits
INSERT and
SELECT statements to run
concurrently for MyISAM tables that have no
free blocks in the middle of the data file.
This variable can take the values shown in the following table. The variable can be assigned using either the name values or corresponding integer values.
| Value | Description |
|---|---|
NEVER (or 0) |
Disables concurrent inserts |
AUTO (or 1) |
(Default) Enables concurrent insert for MyISAM tables
that do not have holes |
ALWAYS (or 2) |
Enables concurrent inserts for all MyISAM tables,
even those that have holes. For a table with a hole, new
rows are inserted at the end of the table if it is in
use by another thread. Otherwise, MySQL acquires a
normal write lock and inserts the row into the hole. |
If you start mysqld with
--skip-new,
concurrent_insert is set to
NEVER.
See also Section 8.11.3, “Concurrent Inserts”.
| Property | Value |
|---|---|
| Command-Line Format | --connect-timeout=# |
| System Variable | connect_timeout |
| Scope | Global |
| Dynamic | Yes |
| Type | Integer |
| Default Value | 10 |
| Minimum Value | 2 |
| Maximum Value | 31536000 |
The number of seconds that the mysqld
server waits for a connect packet before responding with
Bad handshake. The default value is 10
seconds.
Increasing the
connect_timeout value might
help if clients frequently encounter errors of the form
Lost connection to MySQL server at
'.
XXX', system error:
errno
| Property | Value |
|---|---|
| System Variable | core_file |
| Scope | Global |
| Dynamic | No |
| Type | Boolean |
| Default Value | OFF |
Whether to write a core file if the server crashes. This
variable is set by the
--core-file option.
| Property | Value |
|---|---|
| Command-Line Format | --datadir=dir_name |
| System Variable | datadir |
| Scope | Global |
| Dynamic | No |
| Type | Directory name |
The path to the MySQL server data directory. Relative paths
are resolved with respect to the current directory. If the
server will be started automatically (that is, in contexts for
which you cannot assume what the current directory will be),
it is best to specify the
datadir value as an absolute
path.
This variable is unused. It is deprecated and is removed in MySQL 8.0.
This variable is unused. It is deprecated and is removed in MySQL 8.0.
| Property | Value |
|---|---|
| Command-Line Format | --debug[=debug_options] |
| System Variable | debug |
| Scope | Global, Session |
| Dynamic | Yes |
| Type | String |
| Default Value (Windows) | d:t:i:O,\mysqld.trace |
| Default Value (Unix) | d:t:i:o,/tmp/mysqld.trace |
This variable indicates the current debugging settings. It is
available only for servers built with debugging support. The
initial value comes from the value of instances of the
--debug option given at server
startup. The global and session values may be set at runtime.
Setting the session value of this system variable is a restricted operation. The session user must have privileges sufficient to set restricted session variables. See Section 5.1.8.1, “System Variable Privileges”.
Assigning a value that begins with + or
- cause the value to added to or subtracted
from the current value:
mysql>SET debug = 'T';mysql>SELECT @@debug;+---------+ | @@debug | +---------+ | T | +---------+ mysql>SET debug = '+P';mysql>SELECT @@debug;+---------+ | @@debug | +---------+ | P:T | +---------+ mysql>SET debug = '-P';mysql>SELECT @@debug;+---------+ | @@debug | +---------+ | T | +---------+
For more information, see Section 28.5.3, “The DBUG Package”.
| Property | Value |
|---|---|
| System Variable | debug_sync |
| Scope | Session |
| Dynamic | Yes |
| Type | String |
This variable is the user interface to the Debug Sync
facility. Use of Debug Sync requires that MySQL be configured
with the -DENABLE_DEBUG_SYNC=1
CMake option (see
Section 2.9.7, “MySQL Source-Configuration Options”). If Debug Sync
is not compiled in, this system variable is not available.
The global variable value is read only and indicates whether
the facility is enabled. By default, Debug Sync is disabled
and the value of debug_sync
is OFF. If the server is started with
--debug-sync-timeout=,
where NN is a timeout value greater
than 0, Debug Sync is enabled and the value of
debug_sync is ON -
current signal followed by the signal name. Also,
N becomes the default timeout for
individual synchronization points.
The session value can be read by any user and will have the same value as the global variable. The session value can be set to control synchronization points.
Setting the session value of this system variable is a restricted operation. The session user must have privileges sufficient to set restricted session variables. See Section 5.1.8.1, “System Variable Privileges”.
For a description of the Debug Sync facility and how to use synchronization points, see MySQL Internals: Test Synchronization.
| Property | Value |
|---|---|
| Command-Line Format | --default-authentication-plugin=plugin_name |
| System Variable | default_authentication_plugin |
| Scope | Global |
| Dynamic | No |
| Type | Enumeration |
| Default Value | mysql_native_password |
| Valid Values |
|
The default authentication plugin. These values are permitted:
mysql_native_password: Use MySQL native
passwords; see
Section 6.4.1.1, “Native Pluggable Authentication”.
sha256_password: Use SHA-256 passwords;
see Section 6.4.1.5, “SHA-256 Pluggable Authentication”.
If this variable has a value other than
mysql_native_password, clients older than
MySQL 5.5.7 cannot connect because, of the permitted default
authentication plugins, they understand only the
mysql_native_password authentication
protocol.
The
default_authentication_plugin
value affects these aspects of server operation:
It determines which authentication plugin the server
assigns to new accounts created by
CREATE USER and
GRANT statements that do
not explicitly specify an authentication plugin.
The old_passwords system
variable affects password hashing for accounts that use
the mysql_native_password or
sha256_password authentication plugin.
If the default authentication plugin is one of those
plugins, the server sets
old_passwords at startup
to the value required by the plugin password hashing
method.
For an account created with either of the following statements, the server associates the account with the default authentication plugin and assigns the account the given password, hashed as required by that plugin:
CREATE USER ... IDENTIFIED BY 'cleartext password'; GRANT ... IDENTIFIED BY 'cleartext password';
For an account created with either of the following statements, the server associates the account with the default authentication plugin and assigns the account the given password hash, if the password hash has the format required by the plugin:
CREATE USER ... IDENTIFIED BY PASSWORD 'encrypted password'; GRANT ... IDENTIFIED BY PASSWORD 'encrypted password';
If the password hash is not in the format required by the default authentication plugin, the statement fails.
| Property | Value |
|---|---|
| Command-Line Format | --default-password-lifetime=# |
| System Variable | default_password_lifetime |
| Scope | Global |
| Dynamic | Yes |
| Type | Integer |
| Default Value (>= 5.7.11) | 0 |
| Default Value (<= 5.7.10) | 360 |
| Minimum Value | 0 |
| Maximum Value | 65535 |
This variable defines the global automatic password expiration
policy. The default
default_password_lifetime
value is 0, which disables automatic password expiration. If
the value of
default_password_lifetime is
a positive integer N, it indicates
the permitted password lifetime; passwords must be changed
every N days.
The global password expiration policy can be overridden as
desired for individual accounts using the password expiration
options of the ALTER USER
statement. See Section 6.2.11, “Password Management”.
Prior to MySQL 5.7.11, the default
default_password_lifetime
value is 360 (passwords must be changed approximately once
per year). For those versions, be aware that, if you make no
changes to the
default_password_lifetime
variable or to individual user accounts, all user passwords
will expire after 360 days, and all user accounts will start
running in restricted mode when this happens. Clients (which
are effectively users) connecting to the server will then
get an error indicating that the password must be changed:
ERROR 1820 (HY000): You must reset your password
using ALTER USER statement before executing this
statement.
However, this is easy to miss for clients that automatically connect to the server, such as connections made from scripts. To avoid having such clients suddenly stop working due to a password expiring, make sure to change the password expiration settings for those clients, like this:
ALTER USER 'script'@'localhost' PASSWORD EXPIRE NEVER
Alternatively, set the
default_password_lifetime
variable to 0, thus disabling automatic
password expiration for all users.
| Property | Value |
|---|---|
| Command-Line Format | --default-storage-engine=name |
| System Variable | default_storage_engine |
| Scope | Global, Session |
| Dynamic | Yes |
| Type | Enumeration |
| Default Value | InnoDB |
The default storage engine for tables. See
Chapter 15, Alternative Storage Engines. This variable sets the
storage engine for permanent tables only. To set the storage
engine for TEMPORARY tables, set the
default_tmp_storage_engine
system variable.
To see which storage engines are available and enabled, use
the SHOW ENGINES statement or
query the INFORMATION_SCHEMA
ENGINES table.
If you disable the default storage engine at server startup,
you must set the default engine for both permanent and
TEMPORARY tables to a different engine or
the server will not start.
| Property | Value |
|---|---|
| Command-Line Format | --default-tmp-storage-engine=name |
| System Variable | default_tmp_storage_engine |
| Scope | Global, Session |
| Dynamic | Yes |
| Type | Enumeration |
| Default Value | InnoDB |
The default storage engine for TEMPORARY
tables (created with
CREATE TEMPORARY
TABLE). To set the storage engine for permanent
tables, set the
default_storage_engine system
variable. Also see the discussion of that variable regarding
possible values.
If you disable the default storage engine at server startup,
you must set the default engine for both permanent and
TEMPORARY tables to a different engine or
the server will not start.
| Property | Value |
|---|---|
| Command-Line Format | --default-week-format=# |
| System Variable | default_week_format |
| Scope | Global, Session |
| Dynamic | Yes |
| Type | Integer |
| Default Value | 0 |
| Minimum Value | 0 |
| Maximum Value | 7 |
The default mode value to use for the
WEEK() function. See
Section 12.6, “Date and Time Functions”.
| Property | Value |
|---|---|
| Command-Line Format | --delay-key-write[={OFF|ON|ALL}] |
| System Variable | delay_key_write |
| Scope | Global |
| Dynamic | Yes |
| Type | Enumeration |
| Default Value | ON |
| Valid Values |
|
This variable specifies how to use delayed key writes. It
applies only to MyISAM tables. Delayed key
writing causes key buffers not to be flushed between writes.
See also Section 15.2.1, “MyISAM Startup Options”.
This variable can have one of the following values to affect
handling of the DELAY_KEY_WRITE table
option that can be used in CREATE
TABLE statements.
| Option | Description |
|---|---|
OFF |
DELAY_KEY_WRITE is ignored. |
ON |
MySQL honors any DELAY_KEY_WRITE option specified in
CREATE TABLE statements.
This is the default value. |
ALL |
All new opened tables are treated as if they were created with the
DELAY_KEY_WRITE option enabled. |
If you set this variable to ALL, you
should not use MyISAM tables from within
another program (such as another MySQL server or
myisamchk) when the tables are in use.
Doing so leads to index corruption.
If DELAY_KEY_WRITE is enabled for a table,
the key buffer is not flushed for the table on every index
update, but only when the table is closed. This speeds up
writes on keys a lot, but if you use this feature, you should
add automatic checking of all MyISAM tables
by starting the server with the
myisam_recover_options system
variable set (for example,
myisam_recover_options='BACKUP,FORCE').
See Section 5.1.7, “Server System Variables”, and
Section 15.2.1, “MyISAM Startup Options”.
If you start mysqld with
--skip-new,
delay_key_write is set to
OFF.
If you enable external locking with
--external-locking, there is
no protection against index corruption for tables that use
delayed key writes.
| Property | Value |
|---|---|
| Command-Line Format | --delayed-insert-limit=# |
| Deprecated | Yes |
| System Variable | delayed_insert_limit |
| Scope | Global |
| Dynamic | Yes |
| Type | Integer |
| Default Value | 100 |
| Minimum Value | 1 |
| Maximum Value (64-bit platforms) | 18446744073709551615 |
| Maximum Value (32-bit platforms) | 4294967295 |
This system variable is deprecated (because
DELAYED inserts are not supported), and
will be removed in a future release.
| Property | Value |
|---|---|
| Command-Line Format | --delayed-insert-timeout=# |
| Deprecated | Yes |
| System Variable | delayed_insert_timeout |
| Scope | Global |
| Dynamic | Yes |
| Type | Integer |
| Default Value | 300 |
This system variable is deprecated (because
DELAYED inserts are not supported), and
will be removed in a future release.
| Property | Value |
|---|---|
| Command-Line Format | --delayed-queue-size=# |
| Deprecated | Yes |
| System Variable | delayed_queue_size |
| Scope | Global |
| Dynamic | Yes |
| Type | Integer |
| Default Value | 1000 |
| Minimum Value | 1 |
| Maximum Value (64-bit platforms) | 18446744073709551615 |
| Maximum Value (32-bit platforms) | 4294967295 |
This system variable is deprecated (because
DELAYED inserts are not supported), and
will be removed in a future release.
| Property | Value |
|---|---|
| Command-Line Format | --disabled-storage-engines=engine[,engine]... |
| System Variable | disabled_storage_engines |
| Scope | Global |
| Dynamic | No |
| Type | String |
| Default Value | empty string |
This variable indicates which storage engines cannot be used
to create tables or tablespaces. For example, to prevent new
MyISAM or FEDERATED
tables from being created, start the server with these lines
in the server option file:
[mysqld] disabled_storage_engines="MyISAM,FEDERATED"
By default,
disabled_storage_engines is
empty (no engines disabled), but it can be set to a
comma-separated list of one or more engines (not
case-sensitive). Any engine named in the value cannot be used
to create tables or tablespaces with
CREATE TABLE or
CREATE TABLESPACE, and cannot
be used with
ALTER TABLE ...
ENGINE or
ALTER
TABLESPACE ... ENGINE to change the storage engine
of existing tables or tablespaces. Attempts to do so result in
an ER_DISABLED_STORAGE_ENGINE
error.
disabled_storage_engines does
not restrict other DDL statements for existing tables, such as
CREATE INDEX,
TRUNCATE TABLE,
ANALYZE TABLE,
DROP TABLE, or
DROP TABLESPACE. This permits a
smooth transition so that existing tables or tablespaces that
use a disabled engine can be migrated to a permitted engine by
means such as
ALTER TABLE ...
ENGINE .
permitted_engine
It is permitted to set the
default_storage_engine or
default_tmp_storage_engine
system variable to a storage engine that is disabled. This
could cause applications to behave erratically or fail,
although that might be a useful technique in a development
environment for identifying applications that use disabled
engines, so that they can be modified.
disabled_storage_engines is
disabled and has no effect if the server is started with any
of these options: --bootstrap,
--initialize,
--initialize-insecure,
--skip-grant-tables.
Setting
disabled_storage_engines
might cause an issue with mysql_upgrade.
For details, see Section 4.4.7, “mysql_upgrade — Check and Upgrade MySQL Tables”.
disconnect_on_expired_password
| Property | Value |
|---|---|
| Command-Line Format | --disconnect-on-expired-password[={OFF|ON}] |
| System Variable | disconnect_on_expired_password |
| Scope | Global |
| Dynamic | No |
| Type | Boolean |
| Default Value | ON |
This variable controls how the server handles clients with expired passwords:
If the client indicates that it can handle expired
passwords, the value of
disconnect_on_expired_password
is irrelevant. The server permits the client to connect
but puts it in sandbox mode.
If the client does not indicate that it can handle expired
passwords, the server handles the client according to the
value of
disconnect_on_expired_password:
If
disconnect_on_expired_password:
is enabled, the server disconnects the client.
If
disconnect_on_expired_password:
is disabled, the server permits the client to connect
but puts it in sandbox mode.
For more information about the interaction of client and server settings relating to expired-password handling, see Section 6.2.12, “Server Handling of Expired Passwords”.
| Property | Value |
|---|---|
| Command-Line Format | --div-precision-increment=# |
| System Variable | div_precision_increment |
| Scope | Global, Session |
| Dynamic | Yes |
| Type | Integer |
| Default Value | 4 |
| Minimum Value | 0 |
| Maximum Value | 30 |
This variable indicates the number of digits by which to
increase the scale of the result of division operations
performed with the
/ operator.
The default value is 4. The minimum and maximum values are 0
and 30, respectively. The following example illustrates the
effect of increasing the default value.
mysql>SELECT 1/7;+--------+ | 1/7 | +--------+ | 0.1429 | +--------+ mysql>SET div_precision_increment = 12;mysql>SELECT 1/7;+----------------+ | 1/7 | +----------------+ | 0.142857142857 | +----------------+
| Property | Value |
|---|---|
| Command-Line Format | --end-markers-in-json[={OFF|ON}] |
| System Variable | end_markers_in_json |
| Scope | Global, Session |
| Dynamic | Yes |
| Type | Boolean |
| Default Value | OFF |
Whether optimizer JSON output should add end markers. See MySQL Internals: The end_markers_in_json System Variable.
| Property | Value |
|---|---|
| Command-Line Format | --eq-range-index-dive-limit=# |
| System Variable | eq_range_index_dive_limit |
| Scope | Global, Session |
| Dynamic | Yes |
| Type | Integer |
| Default Value | 200 |
| Minimum Value | 0 |
| Maximum Value | 4294967295 |
This variable indicates the number of equality ranges in an
equality comparison condition when the optimizer should switch
from using index dives to index statistics in estimating the
number of qualifying rows. It applies to evaluation of
expressions that have either of these equivalent forms, where
the optimizer uses a nonunique index to look up
col_name values:
col_nameIN(val1, ...,valN)col_name=val1OR ... ORcol_name=valN
In both cases, the expression contains
N equality ranges. The optimizer
can make row estimates using index dives or index statistics.
If eq_range_index_dive_limit
is greater than 0, the optimizer uses existing index
statistics instead of index dives if there are
eq_range_index_dive_limit or
more equality ranges. Thus, to permit use of index dives for
up to N equality ranges, set
eq_range_index_dive_limit to
N + 1. To disable use of index
statistics and always use index dives regardless of
N, set
eq_range_index_dive_limit to
0.
For more information, see Equality Range Optimization of Many-Valued Comparisons.
To update table index statistics for best estimates, use
ANALYZE TABLE.
The number of errors that resulted from the last statement that generated messages. This variable is read only. See Section 13.7.5.17, “SHOW ERRORS Statement”.
| Property | Value |
|---|---|
| Command-Line Format | --event-scheduler[=value] |
| System Variable | event_scheduler |
| Scope | Global |
| Dynamic | Yes |
| Type | Enumeration |
| Default Value | OFF |
| Valid Values |
|
This variable enables or disables, and starts or stops, the
Event Scheduler. The possible status values are
ON, OFF, and
DISABLED, with the default being
OFF. Turning the Event Scheduler
OFF is not the same as disabling the Event
Scheduler, which requires setting the status to
DISABLED. This variable and its effects on
the Event Scheduler's operation are discussed in greater
detail in Section 23.4.2, “Event Scheduler Configuration”
explicit_defaults_for_timestamp
| Property | Value |
|---|---|
| Command-Line Format | --explicit-defaults-for-timestamp[={OFF|ON}] |
| Deprecated | Yes |
| System Variable | explicit_defaults_for_timestamp |
| Scope | Global, Session |
| Dynamic | Yes |
| Type | Boolean |
| Default Value | OFF |
This system variable determines whether the server enables
certain nonstandard behaviors for default values and
NULL-value handling in
TIMESTAMP columns. By default,
explicit_defaults_for_timestamp
is disabled, which enables the nonstandard behaviors.
If
explicit_defaults_for_timestamp
is disabled, the server enables the nonstandard behaviors and
handles TIMESTAMP columns as
follows:
TIMESTAMP columns not
explicitly declared with the NULL
attribute are automatically declared with the NOT
NULL attribute. Assigning such a column a value
of NULL is permitted and sets the
column to the current timestamp.
The first TIMESTAMP column
in a table, if not explicitly declared with the
NULL attribute or an explicit
DEFAULT or ON UPDATE
attribute, is automatically declared with the
DEFAULT CURRENT_TIMESTAMP and
ON UPDATE CURRENT_TIMESTAMP attributes.
TIMESTAMP columns following
the first one, if not explicitly declared with the
NULL attribute or an explicit
DEFAULT attribute, are automatically
declared as DEFAULT '0000-00-00
00:00:00' (the “zero” timestamp).
For inserted rows that specify no explicit value for such
a column, the column is assigned '0000-00-00
00:00:00' and no warning occurs.
Depending on whether strict SQL mode or the
NO_ZERO_DATE SQL mode is
enabled, a default value of '0000-00-00
00:00:00' may be invalid. Be aware that the
TRADITIONAL SQL mode
includes strict mode and
NO_ZERO_DATE. See
Section 5.1.10, “Server SQL Modes”.
The nonstandard behaviors just described are deprecated and will be removed in a future MySQL release.
If
explicit_defaults_for_timestamp
is enabled, the server disables the nonstandard behaviors and
handles TIMESTAMP columns as
follows:
It is not possible to assign a
TIMESTAMP column a value of
NULL to set it to the current
timestamp. To assign the current timestamp, set the column
to CURRENT_TIMESTAMP or a
synonym such as NOW().
TIMESTAMP columns not
explicitly declared with the NOT NULL
attribute are automatically declared with the
NULL attribute and permit
NULL values. Assigning such a column a
value of NULL sets it to
NULL, not the current timestamp.
TIMESTAMP columns declared
with the NOT NULL attribute do not
permit NULL values. For inserts that
specify NULL for such a column, the
result is either an error for a single-row insert or if
strict SQL mode is enabled, or '0000-00-00
00:00:00' is inserted for multiple-row inserts
with strict SQL mode disabled. In no case does assigning
the column a value of NULL set it to
the current timestamp.
TIMESTAMP columns
explicitly declared with the NOT NULL
attribute and without an explicit
DEFAULT attribute are treated as having
no default value. For inserted rows that specify no
explicit value for such a column, the result depends on
the SQL mode. If strict SQL mode is enabled, an error
occurs. If strict SQL mode is not enabled, the column is
declared with the implicit default of '0000-00-00
00:00:00' and a warning occurs. This is similar
to how MySQL treats other temporal types such as
DATETIME.
No TIMESTAMP column is
automatically declared with the DEFAULT
CURRENT_TIMESTAMP or ON UPDATE
CURRENT_TIMESTAMP attributes. Those attributes
must be explicitly specified.
The first TIMESTAMP column
in a table is not handled differently from
TIMESTAMP columns following
the first one.
If
explicit_defaults_for_timestamp
is disabled at server startup, this warning appears in the
error log:
[Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details).
As indicated by the warning, to disable the deprecated
nonstandard behaviors, enable the
explicit_defaults_for_timestamp
system variable at server startup.
explicit_defaults_for_timestamp
is itself deprecated because its only purpose is to permit
control over deprecated
TIMESTAMP behaviors that are
to be removed in a future MySQL release. When removal of
those behaviors occurs,
explicit_defaults_for_timestamp
will have no purpose and will be removed as well.
For additional information, see Section 11.2.6, “Automatic Initialization and Updating for TIMESTAMP and DATETIME”.
| Property | Value |
|---|---|
| System Variable | external_user |
| Scope | Session |
| Dynamic | No |
| Type | String |
The external user name used during the authentication process,
as set by the plugin used to authenticate the client. With
native (built-in) MySQL authentication, or if the plugin does
not set the value, this variable is NULL.
See Section 6.2.14, “Proxy Users”.
| Property | Value |
|---|---|
| Command-Line Format | --flush[={OFF|ON}] |
| System Variable | flush |
| Scope | Global |
| Dynamic | Yes |
| Type | Boolean |
| Default Value | OFF |
If ON, the server flushes (synchronizes)
all changes to disk after each SQL statement. Normally, MySQL
does a write of all changes to disk only after each SQL
statement and lets the operating system handle the
synchronizing to disk. See Section B.4.3.3, “What to Do If MySQL Keeps Crashing”. This
variable is set to ON if you start
mysqld with the
--flush option.
If flush is enabled, the
value of flush_time does
not matter and changes to
flush_time have no effect
on flush behavior.
| Property | Value |
|---|---|
| Command-Line Format | --flush-time=# |
| System Variable | flush_time |
| Scope | Global |
| Dynamic | Yes |
| Type | Integer |
| Default Value | 0 |
| Minimum Value | 0 |
If this is set to a nonzero value, all tables are closed every
flush_time seconds to free up
resources and synchronize unflushed data to disk. This option
is best used only on systems with minimal resources.
If flush is enabled, the
value of flush_time does
not matter and changes to
flush_time have no effect
on flush behavior.
| Property | Value |
|---|---|
| System Variable | foreign_key_checks |
| Scope | Global, Session |
| Dynamic | Yes |
| Type | Boolean |
| Default Value | ON |
If set to 1 (the default), foreign key constraints are
checked. If set to 0, foreign key constraints are ignored,
with a couple of exceptions. When re-creating a table that was
dropped, an error is returned if the table definition does not
conform to the foreign key constraints referencing the table.
Likewise, an ALTER TABLE
operation returns an error if a foreign key definition is
incorrectly formed. For more information, see
Section 13.1.18.6, “FOREIGN KEY Constraints”.
Setting this variable has the same effect on
NDB tables as it does for
InnoDB tables. Typically you leave this
setting enabled during normal operation, to enforce
referential
integrity. Disabling foreign key checking can be useful
for reloading InnoDB tables in an order
different from that required by their parent/child
relationships. See
Section 13.1.18.6, “FOREIGN KEY Constraints”.
Setting foreign_key_checks to 0 also
affects data definition statements:
DROP
SCHEMA drops a schema even if it contains tables
that have foreign keys that are referred to by tables outside
the schema, and DROP TABLE
drops tables that have foreign keys that are referred to by
other tables.
Setting foreign_key_checks to 1 does not
trigger a scan of the existing table data. Therefore, rows
added to the table while
foreign_key_checks=0 will
not be verified for consistency.
Dropping an index required by a foreign key constraint is
not permitted, even with
foreign_key_checks=0. The foreign key
constraint must be removed before dropping the index (Bug
#70260).
| Property | Value |
|---|---|
| Command-Line Format | --ft-boolean-syntax=name |
| System Variable | ft_boolean_syntax |
| Scope | Global |
| Dynamic | Yes |
| Type | String |
| Default Value | + -><()~*:""&| |
The list of operators supported by boolean full-text searches
performed using IN BOOLEAN MODE. See
Section 12.9.2, “Boolean Full-Text Searches”.
The default variable value is
'+ -><()~*:""&|'. The rules
for changing the value are as follows:
Operator function is determined by position within the string.
The replacement value must be 14 characters.
Each character must be an ASCII nonalphanumeric character.
Either the first or second character must be a space.
No duplicates are permitted except the phrase quoting operators in positions 11 and 12. These two characters are not required to be the same, but they are the only two that may be.
Positions 10, 13, and 14 (which by default are set to
:, &, and
|) are reserved for future extensions.
| Property | Value |
|---|---|
| Command-Line Format | --ft-max-word-len=# |
| System Variable | ft_max_word_len |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Minimum Value | 10 |
The maximum length of the word to be included in a
MyISAM FULLTEXT index.
FULLTEXT indexes on
MyISAM tables must be rebuilt after
changing this variable. Use REPAIR TABLE
.
tbl_name QUICK
| Property | Value |
|---|---|
| Command-Line Format | --ft-min-word-len=# |
| System Variable | ft_min_word_len |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | 4 |
| Minimum Value | 1 |
The minimum length of the word to be included in a
MyISAM FULLTEXT index.
FULLTEXT indexes on
MyISAM tables must be rebuilt after
changing this variable. Use REPAIR TABLE
.
tbl_name QUICK
| Property | Value |
|---|---|
| Command-Line Format | --ft-query-expansion-limit=# |
| System Variable | ft_query_expansion_limit |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | 20 |
| Minimum Value | 0 |
| Maximum Value | 1000 |
The number of top matches to use for full-text searches
performed using WITH QUERY EXPANSION.
| Property | Value |
|---|---|
| Command-Line Format | --ft-stopword-file=file_name |
| System Variable | ft_stopword_file |
| Scope | Global |
| Dynamic | No |
| Type | File name |
The file from which to read the list of stopwords for
full-text searches on MyISAM tables. The
server looks for the file in the data directory unless an
absolute path name is given to specify a different directory.
All the words from the file are used; comments are
not honored. By default, a built-in list
of stopwords is used (as defined in the
storage/myisam/ft_static.c file). Setting
this variable to the empty string ('')
disables stopword filtering. See also
Section 12.9.4, “Full-Text Stopwords”.
FULLTEXT indexes on
MyISAM tables must be rebuilt after
changing this variable or the contents of the stopword file.
Use REPAIR TABLE
.
tbl_name QUICK
| Property | Value |
|---|---|
| Command-Line Format | --general-log[={OFF|ON}] |
| System Variable | general_log |
| Scope | Global |
| Dynamic | Yes |
| Type | Boolean |
| Default Value | OFF |
Whether the general query log is enabled. The value can be 0
(or OFF) to disable the log or 1 (or
ON) to enable the log. The destination for
log output is controlled by the
log_output system variable;
if that value is NONE, no log entries are
written even if the log is enabled.
| Property | Value |
|---|---|
| Command-Line Format | --general-log-file=file_name |
| System Variable | general_log_file |
| Scope | Global |
| Dynamic | Yes |
| Type | File name |
| Default Value | host_name.log |
The name of the general query log file. The default value is
host_name.log--general_log_file option.
| Property | Value |
|---|---|
| Command-Line Format | --group-concat-max-len=# |
| System Variable | group_concat_max_len |
| Scope | Global, Session |
| Dynamic | Yes |
| Type | Integer |
| Default Value | 1024 |
| Minimum Value | 4 |
| Maximum Value (64-bit platforms) | 18446744073709551615 |
| Maximum Value (32-bit platforms) | 4294967295 |
The maximum permitted result length in bytes for the
GROUP_CONCAT() function. The
default is 1024.
YES if the zlib
compression library is available to the server,
NO if not. If not, the
COMPRESS() and
UNCOMPRESS() functions cannot
be used.
YES if the crypt()
system call is available to the server, NO
if not. If not, the ENCRYPT()
function cannot be used.
The ENCRYPT() function is
deprecated in MySQL 5.7, will be removed in a
future MySQL release, and should no longer be used. (For
one-way hashing, consider using
SHA2() instead.)
Consequently, have_crypt
also is deprecated and will be removed.
YES if mysqld supports
dynamic loading of plugins, NO if not. If
the value is NO, you cannot use options
such as --plugin-load to load
plugins at server startup, or the INSTALL
PLUGIN statement to load plugins at runtime.
YES if the server supports spatial data
types, NO if not.
This variable is an alias for
have_ssl.
YES if statement profiling capability is
present, NO if not. If present, the
profiling system variable controls whether
this capability is enabled or disabled. See
Section 13.7.5.31, “SHOW PROFILES Statement”.
This variable is deprecated and will be removed in a future MySQL release.
YES if mysqld supports
the query cache, NO if not.
The query cache is deprecated as of MySQL 5.7.20, and is
removed in MySQL 8.0. Deprecation includes
have_query_cache.
YES if RTREE indexes are
available, NO if not. (These are used for
spatial indexes in MyISAM tables.)
| Property | Value |
|---|---|
| System Variable | have_ssl |
| Scope | Global |
| Dynamic | No |
| Type | String |
| Valid Values |
|
YES if mysqld supports
SSL connections, DISABLED if the server was
compiled with SSL support, but was not started with the
appropriate
--ssl- options.
For more information, see
Section 2.9.6, “Configuring SSL Library Support”.
xxx
| Property | Value |
|---|---|
| System Variable | have_statement_timeout |
| Scope | Global |
| Dynamic | No |
| Type | Boolean |
Whether the statement execution timeout feature is available
(see Statement Execution Time Optimizer Hints). The
value can be NO if the background thread
used by this feature could not be initialized.
YES if symbolic link support is enabled,
NO if not. This is required on Unix for
support of the DATA DIRECTORY and
INDEX DIRECTORY table options. If the
server is started with the
--skip-symbolic-links
option, the value is DISABLED.
This variable has no meaning on Windows.
| Property | Value |
|---|---|
| Command-Line Format | --host-cache-size=# |
| System Variable | host_cache_size |
| Scope | Global |
| Dynamic | Yes |
| Type | Integer |
| Default Value | -1 (signifies autosizing; do not assign this literal value) |
| Minimum Value | 0 |
| Maximum Value | 65536 |
This variable controls the size of the host cache, as well as
the size of the Performance Schema
host_cache table that exposes the
cache contents. Setting the size to 0 disables the host cache.
Changing the cache size at runtime causes an implicit
FLUSH HOSTS operation that
clears the host cache, truncates the
host_cache table, and unblocks
any blocked hosts.
The default value is autosized to 128, plus 1 for a value of
max_connections up to 500,
plus 1 for every increment of 20 over 500 in the
max_connections value, capped
to a limit of 2000.
Using the --skip-host-cache
option is similar to setting the
host_cache_size system
variable to 0, but
host_cache_size is more
flexible because it can also be used to resize, enable, and
disable the host cache at runtime, not just at server startup.
Starting the server with
--skip-host-cache does not
prevent changes to the value of
host_cache_size, but such
changes have no effect and the cache is not re-enabled even if
host_cache_size is set larger
than 0 at runtime.
For more information about how the host cache works, see Section 8.12.5.2, “DNS Lookup Optimization and the Host Cache”.
| Property | Value |
|---|---|
| System Variable | hostname |
| Scope | Global |
| Dynamic | No |
| Type | String |
The server sets this variable to the server host name at startup.
This variable is a synonym for the
last_insert_id variable. It
exists for compatibility with other database systems. You can
read its value with SELECT @@identity, and
set it using SET identity.
| Property | Value |
|---|---|
| Deprecated | 5.7.16 |
| System Variable | ignore_db_dirs |
| Scope | Global |
| Dynamic | No |
| Type | String |
A comma-separated list of names that are not considered as
database directories in the data directory. The value is set
from any instances of
--ignore-db-dir given at server
startup.
As of MySQL 5.7.11,
--ignore-db-dir can be used at
data directory initialization time with mysqld
--initialize to specify directories that the server
should ignore for purposes of assessing whether an existing
data directory is considered empty. See
Section 2.10.1, “Initializing the Data Directory”.
This system variable is deprecated in MySQL 5.7. With the introduction of the data dictionary in MySQL 8.0, it became superfluous and was removed in that version.
| Property | Value |
|---|---|
| Command-Line Format | --init-connect=name |
| System Variable | init_connect |
| Scope | Global |
| Dynamic | Yes |
| Type | String |
A string to be executed by the server for each client that connects. The string consists of one or more SQL statements, separated by semicolon characters.
For users that have the SUPER
privilege, the content of
init_connect is not executed.
This is done so that an erroneous value for
init_connect does not prevent
all clients from connecting. For example, the value might
contain a statement that has a syntax error, thus causing
client connections to fail. Not executing
init_connect for users that
have the SUPER privilege
enables them to open a connection and fix the
init_connect value.
As of MySQL 5.7.22,
init_connect execution is
skipped for any client user with an expired password. This is
done because such a user cannot execute arbitrary statements,
and thus init_connect
execution will fail, leaving the client unable to connect.
Skipping init_connect
execution enables the user to connect and change password.
The server discards any result sets produced by statements in
the value of of init_connect.
| Property | Value |
|---|---|
| Command-Line Format | --init-file=file_name |
| System Variable | init_file |
| Scope | Global |
| Dynamic | No |
| Type | File name |
If specified, this variable names a file containing SQL statements to be read and executed during the startup process. Each statement must be on a single line and should not include comments.
If the server is started with any of the
--bootstrap,
--initialize, or
--initialize-insecure options,
it operates in bootstap mode and some functionality is
unavailable that limits the statements permitted in the file.
These include statements that relate to account management
(such as CREATE USER or
GRANT), replication, and global
transaction identifiers. See
Section 16.1.3, “Replication with Global Transaction Identifiers”.
innodb_
xxx
InnoDB system variables are
listed in Section 14.15, “InnoDB Startup Options and System Variables”. These variables
control many aspects of storage, memory use, and I/O patterns
for InnoDB tables, and are especially
important now that InnoDB is the default
storage engine.
The value to be used by the following
INSERT or
ALTER TABLE statement when
inserting an AUTO_INCREMENT value. This is
mainly used with the binary log.
| Property | Value |
|---|---|
| Command-Line Format | --interactive-timeout=# |
| System Variable | interactive_timeout |
| Scope | Global, Session |
| Dynamic | Yes |
| Type | Integer |
| Default Value | 28800 |
| Minimum Value | 1 |
The number of seconds the server waits for activity on an
interactive connection before closing it. An interactive
client is defined as a client that uses the
CLIENT_INTERACTIVE option to
mysql_real_connect(). See also
wait_timeout.
internal_tmp_disk_storage_engine
| Property | Value |
|---|---|
| Command-Line Format | --internal-tmp-disk-storage-engine=# |
| System Variable | internal_tmp_disk_storage_engine |
| Scope | Global |
| Dynamic | Yes |
| Type | Enumeration |
| Default Value | INNODB |
| Valid Values |
|
The storage engine for on-disk internal temporary tables (see
Section 8.4.4, “Internal Temporary Table Use in MySQL”). Permitted values
are MYISAM and INNODB
(the default).
The optimizer uses the
storage engine defined by
internal_tmp_disk_storage_engine
for on-disk internal temporary tables.
When using
internal_tmp_disk_storage_engine=INNODB
(the default), queries that generate on-disk internal
temporary tables that exceed
InnoDB row or
column limits will return Row size too
large or Too many columns
errors. The workaround is to set
internal_tmp_disk_storage_engine
to MYISAM.
| Property | Value |
|---|---|
| Command-Line Format | --join-buffer-size=# |
| System Variable | join_buffer_size |
| Scope | Global, Session |
| Dynamic | Yes |
| Type | Integer |
| Default Value | 262144 |
| Minimum Value | 128 |
| Maximum Value (Other, 64-bit platforms) | 18446744073709547520 |
| Maximum Value (Other, 32-bit platforms) | 4294967295 |
| Maximum Value (Windows) | 4294967295 |
The minimum size of the buffer that is used for plain index
scans, range index scans, and joins that do not use indexes
and thus perform full table scans. Normally, the best way to
get fast joins is to add indexes. Increase the value of
join_buffer_size to get a
faster full join when adding indexes is not possible. One join
buffer is allocated for each full join between two tables. For
a complex join between several tables for which indexes are
not used, multiple join buffers might be necessary.
Unless a Block Nested-Loop or Batched Key Access algorithm is used, there is no gain from setting the buffer larger than required to hold each matching row, and all joins allocate at least the minimum size, so use caution in setting this variable to a large value globally. It is better to keep the global setting small and change the session setting to a larger value only in sessions that are doing large joins. Memory allocation time can cause substantial performance drops if the global size is larger than needed by most queries that use it.
When Block Nested-Loop is used, a larger join buffer can be beneficial up to the point where all required columns from all rows in the first table are stored in the join buffer. This depends on the query; the optimal size may be smaller than holding all rows from the first tables.
When Batched Key Access is used, the value of
join_buffer_size defines how
large the batch of keys is in each request to the storage
engine. The larger the buffer, the more sequential access will
be to the right hand table of a join operation, which can
significantly improve performance.
The default is 256KB. The maximum permissible setting for
join_buffer_size is
4GB−1. Larger values are permitted for 64-bit platforms
(except 64-bit Windows, for which large values are truncated
to 4GB−1 with a warning).
For additional information about join buffering, see Section 8.2.1.6, “Nested-Loop Join Algorithms”. For information about Batched Key Access, see Section 8.2.1.11, “Block Nested-Loop and Batched Key Access Joins”.
| Property | Value |
|---|---|
| Command-Line Format | --keep-files-on-create[={OFF|ON}] |
| System Variable | keep_files_on_create |
| Scope | Global, Session |
| Dynamic | Yes |
| Type | Boolean |
| Default Value | OFF |
If a MyISAM table is created with no
DATA DIRECTORY option, the
.MYD file is created in the database
directory. By default, if MyISAM finds an
existing .MYD file in this case, it
overwrites it. The same applies to .MYI
files for tables created with no INDEX
DIRECTORY option. To suppress this behavior, set the
keep_files_on_create variable
to ON (1), in which case
MyISAM will not overwrite existing files
and returns an error instead. The default value is
OFF (0).
If a MyISAM table is created with a
DATA DIRECTORY or INDEX
DIRECTORY option and an existing
.MYD or .MYI file is
found, MyISAM always returns an error. It will not overwrite a
file in the specified directory.
| Property | Value |
|---|---|
| Command-Line Format | --key-buffer-size=# |
| System Variable | key_buffer_size |
| Scope | Global |
| Dynamic | Yes |
| Type | Integer |
| Default Value | 8388608 |
| Minimum Value | 8 |
| Maximum Value (64-bit platforms) | OS_PER_PROCESS_LIMIT |
| Maximum Value (32-bit platforms) | 4294967295 |
Index blocks for MyISAM tables are buffered
and are shared by all threads.
key_buffer_size is the size
of the buffer used for index blocks. The key buffer is also
known as the key cache.
The maximum permissible setting for
key_buffer_size is
4GB−1 on 32-bit platforms. Larger values are permitted
for 64-bit platforms. The effective maximum size might be
less, depending on your available physical RAM and per-process
RAM limits imposed by your operating system or hardware
platform. The value of this variable indicates the amount of
memory requested. Internally, the server allocates as much
memory as possible up to this amount, but the actual
allocation might be less.
You can increase the value to get better index handling for
all reads and multiple writes; on a system whose primary
function is to run MySQL using the
MyISAM storage engine, 25% of the
machine's total memory is an acceptable value for this
variable. However, you should be aware that, if you make the
value too large (for example, more than 50% of the
machine's total memory), your system might start to page
and become extremely slow. This is because MySQL relies on the
operating system to perform file system caching for data
reads, so you must leave some room for the file system cache.
You should also consider the memory requirements of any other
storage engines that you may be using in addition to
MyISAM.
For even more speed when writing many rows at the same time,
use LOCK TABLES. See
Section 8.2.4.1, “Optimizing INSERT Statements”.
You can check the performance of the key buffer by issuing a
SHOW STATUS statement and
examining the
Key_read_requests,
Key_reads,
Key_write_requests, and
Key_writes status variables.
(See Section 13.7.5, “SHOW Statements”.) The
Key_reads/Key_read_requests ratio should
normally be less than 0.01. The
Key_writes/Key_write_requests ratio is
usually near 1 if you are using mostly updates and deletes,
but might be much smaller if you tend to do updates that
affect many rows at the same time or if you are using the
DELAY_KEY_WRITE table option.
The fraction of the key buffer in use can be determined using
key_buffer_size in
conjunction with the
Key_blocks_unused status
variable and the buffer block size, which is available from
the key_cache_block_size
system variable:
1 - ((Key_blocks_unused * key_cache_block_size) / key_buffer_size)
This value is an approximation because some space in the key buffer is allocated internally for administrative structures. Factors that influence the amount of overhead for these structures include block size and pointer size. As block size increases, the percentage of the key buffer lost to overhead tends to decrease. Larger blocks results in a smaller number of read operations (because more keys are obtained per read), but conversely an increase in reads of keys that are not examined (if not all keys in a block are relevant to a query).
It is possible to create multiple MyISAM
key caches. The size limit of 4GB applies to each cache
individually, not as a group. See
Section 8.10.2, “The MyISAM Key Cache”.
| Property | Value |
|---|---|
| Command-Line Format | --key-cache-age-threshold=# |
| System Variable | key_cache_age_threshold |
| Scope | Global |
| Dynamic | Yes |
| Type | Integer |
| Default Value | 300 |
| Minimum Value | 100 |
| Maximum Value (64-bit platforms) | 18446744073709551615 |
| Maximum Value (32-bit platforms) | 4294967295 |
This value controls the demotion of buffers from the hot sublist of a key cache to the warm sublist. Lower values cause demotion to happen more quickly. The minimum value is 100. The default value is 300. See Section 8.10.2, “The MyISAM Key Cache”.
| Property | Value |
|---|---|
| Command-Line Format | --key-cache-block-size=# |
| System Variable | key_cache_block_size |
| Scope | Global |
| Dynamic | Yes |
| Type | Integer |
| Default Value | 1024 |
| Minimum Value | 512 |
| Maximum Value | 16384 |
The size in bytes of blocks in the key cache. The default value is 1024. See Section 8.10.2, “The MyISAM Key Cache”.
| Property | Value |
|---|---|
| Command-Line Format | --key-cache-division-limit=# |
| System Variable | key_cache_division_limit |
| Scope | Global |
| Dynamic | Yes |
| Type | Integer |
| Default Value | 100 |
| Minimum Value | 1 |
| Maximum Value | 100 |
The division point between the hot and warm sublists of the key cache buffer list. The value is the percentage of the buffer list to use for the warm sublist. Permissible values range from 1 to 100. The default value is 100. See Section 8.10.2, “The MyISAM Key Cache”.
| Property | Value |
|---|---|
| System Variable | large_files_support |
| Scope | Global |
| Dynamic | No |
Whether mysqld was compiled with options for large file support.
| Property | Value |
|---|---|
| Command-Line Format | --large-pages[={OFF|ON}] |
| System Variable | large_pages |
| Scope | Global |
| Dynamic | No |
| Platform Specific | Linux |
| Type | Boolean |
| Default Value | OFF |
Whether large page support is enabled (via the
--large-pages option). See
Section 8.12.4.2, “Enabling Large Page Support”.
| Property | Value |
|---|---|
| System Variable | large_page_size |
| Scope | Global |
| Dynamic | No |
| Type | Integer |
| Default Value | 0 |
If large page support is enabled, this shows the size of memory pages. Large memory pages are supported only on Linux; on other platforms, the value of this variable is always 0. See Section 8.12.4.2, “Enabling Large Page Support”.
The value to be returned from
LAST_INSERT_ID(). This is
stored in the binary log when you use
LAST_INSERT_ID() in a statement
that updates a table. Setting this variable does not update
the value returned by the
mysql_insert_id() C API
function.
| Property | Value |
|---|---|
| Command-Line Format | --lc-messages=name |
| System Variable | lc_messages |
| Scope | Global, Session |
| Dynamic | Yes |
| Type | String |
| Default Value | en_US |
The locale to use for error messages. The default is
en_US. The server converts the argument to
a language name and combines it with the value of
lc_messages_dir to produce
the location for the error message file. See
Section 10.12, “Setting the Error Message Language”.
| Property | Value |
|---|---|
| Command-Line Format | --lc-messages-dir=dir_name |
| System Variable | lc_messages_dir |
| Scope | Global |
| Dynamic | No |
| Type | Directory name |
The directory where error messages are located. The server
uses the value together with the value of
lc_messages to produce the
location for the error message file. See
Section 10.12, “Setting the Error Message Language”.
| Property | Value |
|---|---|
| Command-Line Format | --lc-time-names=value |
| System Variable | lc_time_names |
| Scope | Global, Session |
| Dynamic | Yes |
| Type | String |
This variable specifies the locale that controls the language
used to display day and month names and abbreviations. This
variable affects the output from the
DATE_FORMAT(),
DAYNAME() and
MONTHNAME() functions. Locale
names are POSIX-style values such as
'ja_JP' or 'pt_BR'. The
default value is 'en_US' regardless of your
system's locale setting. For further information, see
Section 10.16, “MySQL Server Locale Support”.
| Property | Value |
|---|---|
| System Variable | license |
| Scope | Global |
| Dynamic | No |
| Type | String |
| Default Value | GPL |
The type of license the server has.
| Property | Value |
|---|---|
| Command-Line Format | --local-infile[={OFF|ON}] |
| System Variable | local_infile |
| Scope | Global |
| Dynamic | Yes |
| Type | Boolean |
| Default Value | ON |
This variable controls server-side LOCAL
capability for LOAD DATA
statements. Depending on the
local_infile setting, the
server refuses or permits local data loading by clients that
have LOCAL enabled on the client side.
To explicitly cause the server to refuse or permit
LOAD DATA
LOCAL statements (regardless of how client programs
and libraries are configured at build time or runtime), start
mysqld with
local_infile disabled or
enabled, respectively.
local_infile can also be set
at runtime. For more information, see
Section 6.1.6, “Security Issues with LOAD DATA LOCAL”.
| Property | Value |
|---|---|
| Command-Line Format | --lock-wait-timeout=# |
| System Variable | lock_wait_timeout |
| Scope | Global, Session |
| Dynamic | Yes |
| Type | Integer |
| Default Value | 31536000 |
| Minimum Value | 1 |
| Maximum Value | 31536000 |
This variable specifies the timeout in seconds for attempts to acquire metadata locks. The permissible values range from 1 to 31536000 (1 year). The default is 31536000.
This timeout applies to all statements that use metadata
locks. These include DML and DDL operations on tables, views,
stored procedures, and stored functions, as well as
LOCK TABLES,
FLUSH TABLES WITH READ LOCK,
and HANDLER statements.
This timeout does not apply to implicit accesses to system
tables in the mysql database, such as grant
tables modified by GRANT or
REVOKE statements or table
logging statements. The timeout does apply to system tables
accessed directly, such as with
SELECT or
UPDATE.
The timeout value applies separately for each metadata lock
attempt. A given statement can require more than one lock, so
it is possible for the statement to block for longer than the
lock_wait_timeout value
before reporting a timeout error. When lock timeout occurs,
ER_LOCK_WAIT_TIMEOUT is
reported.
lock_wait_timeout does not
apply to delayed inserts, which always execute with a timeout
of 1 year. This is done to avoid unnecessary timeouts because
a session that issues a delayed insert receives no
notification of delayed insert timeouts.
| Property | Value |
|---|---|
| System Variable | locked_in_memory |
| Scope | Global |
| Dynamic | No |
| Property | Value |
|---|---|
| Command-Line Format | --log-error[=file_name] |
| System Variable | log_error |
| Scope | Global |
| Dynamic | No |
| Type | File name |
The error log output destination. If the destination is the
console, the value is stderr. Otherwise,
the destination is a file and the
log_error value is the file
name. See Section 5.4.2, “The Error Log”.
| Property | Value |
|---|---|
| Command-Line Format | --log-error-verbosity=# |
| System Variable | log_error_verbosity |
| Scope | Global |
| Dynamic | Yes |
| Type | Integer |
| Default Value | 3 |
| Minimum Value | 1 |
| Maximum Value | 3 |
The verbosity of the server in writing error, warning, and note messages to the error log. The following table shows the permitted values. The default is 3.
| Desired Log Filtering | log_error_verbosity Value |
|---|---|
| Error messages | 1 |
| Error and warning messages | 2 |
| Error, warning, and information messages | 3 |
log_error_verbosity was added
in MySQL 5.7.2. It is preferred over, and should be used
instead of, the older
log_warnings system variable.
See the description of
log_warnings for information
about how that variable relates to
log_error_verbosity. In
particular, assigning a value to
log_warnings assigns a value
to log_error_verbosity and
vice versa.
| Property | Value |
|---|---|
| Command-Line Format | --log-output=name |
| System Variable | log_output |
| Scope | Global |
| Dynamic | Yes |
| Type | Set |
| Default Value | FILE |
| Valid Values |
|
The destination or destinations for general query log and slow
query log output. The value is a list one or more
comma-separated words chosen from TABLE,
FILE, and NONE.
TABLE selects logging to the
general_log and
slow_log tables in the
mysql system database.
FILE selects logging to log files.
NONE disables logging. If
NONE is present in the value, it takes
precedence over any other words that are present.
TABLE and FILE can both
be given to select both log output destinations.
This variable selects log output destinations, but does not
enable log output. To do that, enable the
general_log and
slow_query_log system
variables. For FILE logging, the
general_log_file and
slow_query_log_file system
variables determine the log file locations. For more
information, see Section 5.4.1, “Selecting General Query Log and Slow Query Log Output Destinations”.
| Property | Value |
|---|---|
| Command-Line Format | --log-queries-not-using-indexes[={OFF|ON}] |
| System Variable | log_queries_not_using_indexes |
| Scope | Global |
| Dynamic | Yes |
| Type | Boolean |
| Default Value | OFF |
If you enable this variable with the slow query log enabled, queries that are expected to retrieve all rows are logged. See Section 5.4.5, “The Slow Query Log”. This option does not necessarily mean that no index is used. For example, a query that uses a full index scan uses an index but would be logged because the index would not limit the number of rows.
| Property | Value |
|---|---|
| Command-Line Format | --log-slow-admin-statements[={OFF|ON}] |
| System Variable | log_slow_admin_statements |
| Scope | Global |
| Dynamic | Yes |
| Type | Boolean |
| Default Value | OFF |
Include slow administrative statements in the statements
written to the slow query log. Administrative statements
include ALTER TABLE,
ANALYZE TABLE,
CHECK TABLE,
CREATE INDEX,
DROP INDEX,
OPTIMIZE TABLE, and
REPAIR TABLE.
| Property | Value |
|---|---|
| Command-Line Format | --log-syslog[={OFF|ON}] |
| System Variable | log_syslog |
| Scope | Global |
| Dynamic | Yes |
| Type | Boolean |
| Default Value (Windows) | ON |
| Default Value (Unix) | OFF |
Whether to write error log output to the system log. This is
the Event Log on Windows, and syslog on
Unix and Unix-like systems. The default value is platform
specific:
On Windows, Event Log output is enabled by default.
On Unix and Unix-like systems, syslog
output is disabled by default.
Regardless of the default,
log_syslog can be set
explicitly to control output on any supported platform.
System log output control is distinct from sending error output to a file or the console. Error output can be directed to a file or the console in addition to or instead of the system log as desired. See Section 5.4.2, “The Error Log”.
| Property | Value |
|---|---|
| Command-Line Format | --log-syslog-facility=value |
| System Variable | log_syslog_facility |
| Scope | Global |
| Dynamic | Yes |
| Type | String |
| Default Value | daemon |
The facility for error log output written to
syslog (what type of program is sending the
message). This variable has no effect unless the
log_syslog system variable is
enabled. See Section 5.4.2.3, “Error Logging to the System Log”.
The permitted values can vary per operating system; consult
your system syslog documentation.
This variable does not exist on Windows.
| Property | Value |
|---|---|
| Command-Line Format | --log-syslog-include-pid[={OFF|ON}] |
| System Variable | log_syslog_include_pid |
| Scope | Global |
| Dynamic | Yes |
| Type | Boolean |
| Default Value | ON |
Whether to include the server process ID in each line of error
log output written to syslog. This variable
has no effect unless the
log_syslog system variable is
enabled. See