Table of Contents
Access denied ErrorsMySQL Server (mysqld) is the main program that does most of the work in a MySQL installation. This section provides an overview of MySQL Server and covers topics that deal with administering a MySQL installation:
Configuring the server
The server log files
Managing user accounts
mysqld is the MySQL server. The following discussion covers these MySQL server configuration topics:
Startup options that the server supports
Server system variables
Server status variables
How to set the server SQL mode
The server shutdown process
Not all storage engines are supported by all MySQL server
binaries and configurations. To find out how to determine which
storage engines are supported by your MySQL server installation,
see Section 12.5.4.10, “SHOW ENGINES Syntax”.
The following table provides a list of all the command line
options, server and status variables applicable within
mysqld.
The table lists command line options (Cmd-line), options valid in configuration files (Option file), server system variables (Server Var), and status variables (Status var) in one unified list, with notification of where each option/variable is valid. If a server option set on the command line or in an option file differs from the name of the corresponding server system or status variable, the variable name is noted immediately below the corresponding option. For status variables, the scope of the variable is shown (Scope) as either global, session, or both. Please see the corresponding sections for details on setting and using the options and variables. Where appropriate, a direct link to further information on the item as available.
This table is part of an ongoing process to expand and simplify the information provided on these elements. Further improvements to the table, and corresponding descriptions will be applied over the coming months.
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”.
MySQL Enterprise. For expert advice on setting command options, subscribe to the MySQL Enterprise Monitor. For more information see http://www.mysql.com/products/enterprise/advisors.html.
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 mysqld --help. To see the full list, use mysqld --verbose --help.
The following list shows some of the most common server options. Additional options are described in other sections:
Options that affect security: See Section 5.3.3, “Security-Related mysqld Options”.
SSL-related options: See Section 5.5.7.3, “SSL Command Options”.
Binary log control options: See Section 5.2.3, “The Binary Log”.
Replication-related options: See Section 15.1.2, “Replication Startup Options and Variables”.
Options specific to particular storage engines: See
Section 13.1.1, “MyISAM Startup Options”, Section 13.5.3, “BDB Startup Options”,
Section 13.2.4, “InnoDB Startup Options and System Variables”, and
Section 16.4.2, “MySQL Cluster-Related Command Options for mysqld”.
You can also set the values of server system variables by using variable names as options, as described at the end of this section.
Display a short help message and exit. Use both the
--verbose and --help
options to see the full message.
| Value Set |
|
This option is used internally by the MySQL test suite for replication testing and debugging.
| Version Introduced | 5.0.3 | ||||
| Value Set |
|
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. This option was added in version 5.0.3. See
Section 26.2.4.6, “User-Defined Function Security Precautions”.
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 1.8.3, “Running MySQL in ANSI Mode”, and
Section 5.1.6, “SQL Modes”.
| Option Sets Variable | Yes, basedir | ||
| Variable Name | basedir | ||
| Variable Scope | Global | ||
| Dynamic Variable | no | ||
| Value Set |
|
The path to the MySQL installation directory. All paths are usually resolved relative to this directory.
| Option Sets Variable | Yes, big_tables | ||
| Variable Name | big-tables | ||
| Variable Scope | Session | ||
| Dynamic Variable | yes | ||
| Value Set |
|
Allow large result sets by saving all temporary sets in files. This option prevents most “table full” errors, but also slows down queries for which in-memory tables would suffice. Since MySQL 3.23.2, the server is able to handle large result sets automatically by using memory for small temporary tables and switching to disk tables where necessary.
| Value Set |
|
The IP address to bind to. Only one address can be selected. If this option is specified multiple times, the last address given is used.
This option is used by the mysql_install_db script to create the MySQL privilege tables without having to start a full MySQL server.
This option is unavailable if MySQL was configured with the
--disable-grant-options option. See
Section 2.4.15.2, “Typical configure Options”.
| Option Sets Variable | Yes, character_sets_dir | ||
| Variable Name | character-sets-dir | ||
| Variable Scope | Global | ||
| Dynamic Variable | no | ||
| Value Set |
|
The directory where character sets are installed. See Section 9.2, “The Character Set Used for Data and Sorting”.
--character-set-client-handshake
| Value Set |
|
Don't 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.
--character-set-filesystem=
charset_name
| Version Introduced | 5.0.19 | ||
| Option Sets Variable | Yes, character_set_filesystem | ||
| Variable Name | character_set_filesystem | ||
| Variable Scope | Both | ||
| Dynamic Variable | yes | ||
| Value Set |
|
The filesystem character set. This option sets the
character_set_filesystem system variable.
It was added in MySQL 5.0.19.
--character-set-server=,
charset_name-C
charset_name
| Option Sets Variable | Yes, character_set_server | ||
| Variable Name | character_set_server | ||
| Variable Scope | Both | ||
| Dynamic Variable | yes | ||
| Value Set |
|
Use charset_name as the default
server character set. See
Section 9.2, “The Character Set Used for Data and Sorting”. If you use this
option to specify a non-default character set, you should
also use --collation-server to specify the
collation.
| Value Set |
|
Put the mysqld server in a closed
environment during startup by using the
chroot() system call. This is a
recommended security measure. Note that use of this option
somewhat limits LOAD DATA INFILE and
SELECT ... INTO OUTFILE.
--collation-server=
collation_name
| Option Sets Variable | Yes, collation_server | ||
| Variable Name | collation_server | ||
| Variable Scope | Both | ||
| Dynamic Variable | yes | ||
| Value Set |
|
Use collation_name as the default
server collation. See
Section 9.2, “The Character Set Used for Data and Sorting”.
| Option Sets Variable | Yes, console |
| Platform Specific | windows |
(Windows only.) Write error log messages to
stderr and stdout even
if --log-error is specified.
mysqld does not close the console window
if this option is used.
| Value Set |
|
Write a core file if mysqld dies. For
some systems, you must also specify the
--core-file-size option to
mysqld_safe. See
Section 4.3.2, “mysqld_safe — MySQL Server Startup Script”. Note that on some systems,
such as Solaris, you do not get a core file if you are also
using the --user option.
| Option Sets Variable | Yes, datadir | ||
| Variable Name | datadir | ||
| Variable Scope | Global | ||
| Dynamic Variable | no | ||
| Value Set |
|
The path to the data directory.
--debug[=,
debug_options]-#
[
debug_options]
| Value Set |
|
If MySQL is configured with --with-debug,
you can use this option to get a trace file of what
mysqld is doing. The
debug_options string often is
'd:t:o,.
The default is file_name''d:t:i:o,mysqld.trace'.
See
MySQL
Internals: Porting.
As of MySQL 5.0.25, using --with-debug 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.
--default-character-set=
(DEPRECATED)
charset_name
| Deprecated | 5.0 | ||
| Value Set |
|
Use charset_name as the default
character set. This option is deprecated in favor of
--character-set-server. See
Section 9.2, “The Character Set Used for Data and Sorting”.
--default-collation=
collation_name
| Variable Name | default-collation | ||
| Variable Scope | |||
| Dynamic Variable | no | ||
| Deprecated | 4.1.3 | ||
| Value Set |
|
Use collation_name as the default
collation. This option is deprecated in favor of
--collation-server. See
Section 9.2, “The Character Set Used for Data and Sorting”.
Set the default storage engine (table type) for tables. See Chapter 13, Storage Engines.
| Deprecated | 5.0, by default-storage-engine | ||
| Value Set |
|
This option is a synonym for
--default-storage-engine.
| Value Set |
|
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.
--delay-key-write[={OFF|ON|ALL}]
| Option Sets Variable | Yes, delay_key_write | ||||||
| Variable Name | delay-key-write | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
Specify how to use delayed key writes. Delayed key writing
causes key buffers not to be flushed between writes for
MyISAM tables. OFF
disables delayed key writes. ON enables
delayed key writes for those tables that were created with
the DELAY_KEY_WRITE option.
ALL delays key writes for all
MyISAM tables. See
Section 7.5.2, “Tuning Server Parameters”, and
Section 13.1.1, “MyISAM Startup Options”.
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.
Read the default DES keys from this file. These keys are
used by the DES_ENCRYPT()
and DES_DECRYPT() functions.
--disconnect-slave-event-count
| Value Set |
|
This option is used internally by the MySQL test suite for replication testing and debugging.
| Platform Specific | windows |
Enable support for named pipes. This option can be used only with the mysqld-nt and mysqld-debug servers that support named-pipe connections.
| Value Set |
|
Print a symbolic stack trace on failure.
--exit-info[=,
flags]-T [
flags]
| Value Set |
|
This is a bit mask of different flags that you can use for debugging the mysqld server. Do not use this option unless you know exactly what it does!
| Option Sets Variable | Yes, external_locking | ||||
| Disabled By | skip-external-locking | ||||
| Value Set |
|
Enable external locking (system locking), which is disabled
by default as of MySQL 4.0. Note that 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. This option
previously was named --enable-locking.
For more information about external locking, including conditions under which it can and cannot be used, see Section 7.3.4, “External Locking”.
| Variable Name | flush | ||||
| Variable Scope | Global | ||||
| Dynamic Variable | yes | ||||
| Value Set |
|
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.1.4.2, “What to Do If MySQL Keeps Crashing”.
| Value Set |
|
Install an interrupt handler for SIGINT
(needed to stop mysqld with
^C to set breakpoints) and disable stack
tracing and core file handling. See
MySQL
Internals: Porting.
| Option Sets Variable | Yes, init_file | ||
| Variable Name | init_file | ||
| Variable Scope | Global | ||
| Dynamic Variable | no | ||
| Value Set |
|
Read SQL statements from this file at startup. Each statement must be on a single line and should not include comments.
This option is unavailable if MySQL was configured with the
--disable-grant-options option. See
Section 2.4.15.2, “Typical configure Options”.
| Version Introduced | 5.0.1 | ||
| Deprecated | 5.0.3 | ||
| Value Set |
|
Adds consistency guarantees between the content of
InnoDB tables and the binary log. See
Section 5.2.3, “The Binary Log”. This option was removed in
MySQL 5.0.3, having been made obsolete by the introduction
of XA transaction support.
--innodb-
xxx
The InnoDB options are listed in
Section 13.2.4, “InnoDB Startup Options and System Variables”.
--language=
lang_name, -L
lang_name
| Option Sets Variable | Yes, language | ||||
| Variable Name | language | ||||
| Variable Scope | Global | ||||
| Dynamic Variable | no | ||||
| Value Set |
|
Return client error messages in the given language.
lang_name can be given as the
language name or as the full pathname to the directory where
the language files are installed. See
Section 9.3, “Setting the Error Message Language”.
| Version Introduced | 5.0.3 | ||||||
| Option Sets Variable | Yes, large_pages | ||||||
| Variable Name | large_pages | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | no | ||||||
| Platform Specific | linux | ||||||
| Value Set |
|
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 OS. Applications that perform a lot of memory accesses may obtain performance improvements by using large pages due to reduced Translation Lookaside Buffer (TLB) misses.
Currently, MySQL supports only the Linux implementation of large pages support (which is called HugeTLB in Linux). We have plans to extend this support to FreeBSD, Solaris and possibly other platforms.
Before large pages can be used on Linux, it is necessary to
configure the HugeTLB memory pool. For reference, consult
the hugetlbpage.txt file in the Linux
kernel source.
This option is disabled by default. It was added in MySQL 5.0.3.
--log[=,
file_name]-l [
file_name]
| Option Sets Variable | Yes, log | ||||
| Variable Name | log | ||||
| Variable Scope | Global | ||||
| Dynamic Variable | yes | ||||
| Value Set |
|
Log connections and SQL statements received from clients to
this file. See Section 5.2.2, “The General Query Log”. If you omit the
filename, MySQL uses
host_name.log
| Value Set |
|
Enable binary logging. The server logs all statements that change data to the binary log, which is used for backup and replication. See Section 5.2.3, “The Binary Log”.
The option value, if given, is the basename for the log
sequence. The server creates binary log files in sequence by
adding a numeric suffix to the basename. It is recommended
that you specify a basename (see
Section B.1.8.1, “Open Issues in MySQL”, for the reason). Otherwise,
MySQL uses
host_name-bin
| Value Set |
|
The index file for binary log filenames. See
Section 5.2.3, “The Binary Log”. If you omit the filename, and
if you didn't specify one with --log-bin,
MySQL uses
host_name-bin.index
--log-bin-trust-function-creators[={0|1}]
| Version Introduced | 5.0.16 | ||||
| Option Sets Variable | Yes, log_bin_trust_function_creators | ||||
| Variable Name | log_bin_trust_function_creators | ||||
| Variable Scope | Global | ||||
| Dynamic Variable | yes | ||||
| Value Set |
|
With no argument or an argument of 1, this option sets the
log_bin_trust_function_creators system
variable to 1. With an argument of 0, this option sets the
system variable to 0.
log_bin_trust_function_creators affects
how MySQL enforces restrictions on stored function creation.
See Section 18.5, “Binary Logging of Stored Routines and Triggers”.
This option was added in MySQL 5.0.16.
--log-bin-trust-routine-creators[={0|1}]
| Version Introduced | 5.0.6 | ||||
| Option Sets Variable | Yes, log_bin_trust_routine_creators | ||||
| Variable Name | log-bin-trust-routine-creators | ||||
| Variable Scope | Global | ||||
| Dynamic Variable | yes | ||||
| Deprecated | 5.0.16, by log-bin-trust-function-creators | ||||
| Value Set |
|
This is the old name for
--log-bin-trust-function-creators. Before
MySQL 5.0.16, it also applies to stored procedures, not just
stored functions and sets the
log_bin_trust_routine_creators system
variable. As of 5.0.16, this option is deprecated. It is
recognized for backward compatibility but its use results in
a warning.
This option was added in MySQL 5.0.6.
| Option Sets Variable | Yes, log_error | ||
| Variable Name | log_error | ||
| Variable Scope | Global | ||
| Dynamic Variable | no | ||
| Value Set |
|
Log errors and startup messages to this file. See
Section 5.2.1, “The Error Log”. If you omit the filename, MySQL
uses
host_name.err.err.
| Value Set |
|
Log all MyISAM changes to this file (used
only when debugging MyISAM).
--log-long-format
(DEPRECATED)
| Deprecated | 4.1 |
Log extra information to the update log, binary update log,
and slow query log, if they have been activated. For
example, the username and timestamp are logged for all
queries. This option is deprecated, as it now represents the
default logging behavior. (See the description for
--log-short-format.) The
--log-queries-not-using-indexes option is
available for the purpose of logging queries that do not use
indexes to the slow query log.
--log-queries-not-using-indexes
| Version Introduced | 5.0.23 | ||
| Option Sets Variable | Yes, log_queries_not_using_indexes | ||
| Variable Name | log_queries_not_using_indexes | ||
| Variable Scope | Global | ||
| Dynamic Variable | no | ||
| Value Set |
|
If you are using this option with
--log-slow-queries, queries that do not use
indexes are logged to the slow query log. See
Section 5.2.4, “The Slow Query Log”.
| Value Set |
|
Log less information to the update log, binary update log, and slow query log, if they have been activated. For example, the username and timestamp are not logged for queries.
| Value Set |
|
Log slow administrative statements such as OPTIMIZE
TABLE, ANALYZE TABLE, and
ALTER TABLE to the slow query log.
--log-slow-queries[=
file_name]
| Option Sets Variable | Yes, log_slow_queries | ||
| Variable Name | log_slow_queries | ||
| Variable Scope | Global | ||
| Dynamic Variable | yes | ||
| Value Set |
|
Log all queries that have taken more than
long_query_time seconds to execute to
this file. See Section 5.2.4, “The Slow Query Log”. See the
descriptions of the --log-long-format and
--log-short-format options for details.
| Version Introduced | 5.0.3 | ||||
| Value Set |
|
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 pathname.
Currently, this option is unused. Added in MySQL 5.0.3.
| Version Introduced | 5.0.3 | ||||||
| Value Set |
|
The size in bytes of the memory-mapped transaction coordinator log. The default size is 24KB. Added in MySQL 5.0.3.
--log-warnings[=,
level]-W [
level]
| Option Sets Variable | Yes, log-warnings | ||||
| Variable Name | log_warnings | ||||
| Variable Scope | Both | ||||
| Dynamic Variable | yes | ||||
| Disabled By | skip-log-warnings | ||||
| Value Set |
|
Print out warnings such as Aborted
connection... to the error log. Enabling this
option is recommended, for example, if you use replication
(you get more information about what is happening, such as
messages about network failures and reconnections). This
option is enabled (1) by default, and the default
level value if omitted is 1. To
disable this option, use --log-warnings=0.
If the value is greater than 1, aborted connections are
written to the error log. See
Section B.1.2.11, “Communication Errors and Aborted Connections”.
| Option Sets Variable | Yes, low_priority_updates | ||||
| Variable Name | low_priority_updates | ||||
| Variable Scope | Both | ||||
| Dynamic Variable | yes | ||||
| Value Set |
|
Give table-modifying operations (INSERT,
REPLACE, DELETE,
UPDATE) lower priority than selects. This
can also be done via {INSERT | REPLACE | DELETE |
UPDATE} LOW_PRIORITY ... to lower the priority of
only one query, or by SET
LOW_PRIORITY_UPDATES=1 to change the priority in
one thread. This affects only storage engines that use only
table-level locking (MyISAM,
MEMORY, MERGE). See
Section 7.3.2, “Table Locking Issues”.
| Value Set |
|
This option is used internally by the MySQL test suite for replication testing and debugging.
| Variable Name | locked_in_memory | ||||
| Variable Scope | Global | ||||
| Dynamic Variable | no | ||||
| Value Set |
|
Lock the mysqld process in memory. This
works on systems such as Solaris that support the
mlockall() system call. This might help
if you have a problem where the operating system is causing
mysqld to swap on disk. Note that use of
this option requires that you run the server as
root, which is normally not a good idea
for security reasons. See
Section 5.3.5, “How to Run MySQL as a Normal User”.
--myisam-recover[=
option[,option]...]]
| Value Set |
|
Set the MyISAM storage engine recovery
mode. The option value is any combination of the values of
DEFAULT, BACKUP,
FORCE, or QUICK. If
you specify multiple values, separate them by commas.
Specifying the option with no argument is the same as
specifying DEFAULT, and specifying with
an explicit value of "" disables recovery
(same as not giving the option). If recovery is enabled,
each time mysqld opens a
MyISAM table, it checks whether the table
is marked as crashed or wasn't closed properly. (The last
option works only if you are running with external locking
disabled.) If this is the case, mysqld
runs a check on the table. If the table was corrupted,
mysqld attempts to repair it.
The following options affect how the repair works:
| Option | Description |
DEFAULT | Recovery without backup, forcing, or quick checking. |
BACKUP | If the data file was changed during recovery, save a backup of the
|
FORCE | Run recovery even if we would lose more than one row from the
.MYD file. |
QUICK | Don't check the rows in the table if there aren't any delete blocks. |
Before the server automatically repairs a table, it writes a
note about the repair to the error log. If you want to be
able to recover from most problems without user
intervention, you should use the options
BACKUP,FORCE. This forces a repair of a
table even if some rows would be deleted, but it keeps the
old data file as a backup so that you can later examine what
happened.
| Option Sets Variable | Yes, old_passwords | ||||
| Variable Name | old_passwords | ||||
| Variable Scope | Both | ||||
| Dynamic Variable | yes | ||||
| Value Set |
|
Force the server to generate short (pre-4.1) password hashes for new passwords. This is useful for compatibility when the server must support older client programs. See Section 5.4.9, “Password Hashing as of MySQL 4.1”.
| Version Introduced | 5.0.3 | ||||
| Value Set |
|
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 5.5.4, “Limiting Account Resources”. This option was added in
MySQL 5.0.3.
Only use one thread (for debugging under Linux). This option is available only if the server is built with debugging enabled. See MySQL Internals: Porting.
| Option Sets Variable | Yes, open_files_limit | ||||||
| Variable Name | open_files_limit | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | no | ||||||
| Value Set |
|
Change the number of file descriptors available to
mysqld. If this option is not set or is
set to 0, mysqld uses the value to
reserve file descriptors with
setrlimit(). If the value is 0,
mysqld reserves
max_connections×5 or
max_connections +
table_open_cache×2 files (whichever is
larger). You should try increasing this value if
mysqld gives you the error Too
many open files.
| Option Sets Variable | Yes, pid_file | ||
| Variable Name | pid_file | ||
| Variable Scope | Global | ||
| Dynamic Variable | no | ||
| Value Set |
|
The pathname of the process ID file. This file is used by other programs such as mysqld_safe to determine the server's process ID.
| Option Sets Variable | Yes, port | ||||
| Variable Name | port | ||||
| Variable Scope | Global | ||||
| Dynamic Variable | no | ||||
| Value Set |
|
The port number to use when listening for TCP/IP
connections. The port number must be 1024 or higher unless
the server is started by the root system
user.
| Version Introduced | 5.0.19 | ||||
| Value Set |
|
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. This option was added in MySQL 5.0.19.
| Deprecated | 5.0 |
Skip some optimization stages.
--safe-show-database
(DEPRECATED)
| Option Sets Variable | Yes, safe_show_database | ||
| Variable Name | safe_show_database | ||
| Variable Scope | Global | ||
| Dynamic Variable | yes | ||
| Deprecated | 4.0.2 | ||
| Value Set |
|
| Option Sets Variable | Yes, safe-user-create | ||||
| Value Set |
|
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 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.
| Option Sets Variable | Yes, secure_auth | ||||
| Variable Name | secure_auth | ||||
| Variable Scope | Global | ||||
| Dynamic Variable | yes | ||||
| Value Set |
|
Disallow authentication by clients that attempt to use accounts that have old (pre-4.1) passwords.
| Version Introduced | 5.0.38 | ||
| Option Sets Variable | Yes, secure_file_priv | ||
| Variable Name | secure_file_priv | ||
| Variable Scope | Global | ||
| Dynamic Variable | no | ||
| Value Set |
|
This option limits the effect of the
LOAD_FILE() function and the
LOAD DATA and SELECT ... INTO
OUTFILE statements to work only with files in the
specified directory.
This option was added in MySQL 5.0.38.
Enable shared-memory connections by local clients. This option is available only on Windows.
--shared-memory-base-name=
name
The name of shared memory to use for shared-memory
connections. This option is available only on Windows. The
default name is MYSQL. The name is case
sensitive.
Disable the BDB storage engine. This
saves memory and might speed up some operations. Do not use
this option if you require BDB tables.
Turn off the ability to select and insert at the same time
on MyISAM tables. (This is to be used
only if you think you have found a bug in this feature.) See
Section 7.3.3, “Concurrent Inserts”.
Do not use external locking (system locking). For more information about external locking, including conditions under which it can and cannot be used, see Section 7.3.4, “External Locking”.
External locking has been disabled by default since MySQL 4.0.
This option causes the server not to use the privilege
system at all, which gives anyone with access to the server
unrestricted access to all databases.
You can cause a running server to start using the grant
tables again by executing mysqladmin
flush-privileges or mysqladmin
reload command from a system shell, or by issuing
a MySQL FLUSH PRIVILEGES statement after
connecting to the server. This option also suppresses
loading of user-defined functions (UDFs).
This option is unavailable if MySQL was configured with the
--disable-grant-options option. See
Section 2.4.15.2, “Typical configure Options”.
Do not use the internal hostname cache for faster name-to-IP resolution. Instead, query the DNS server every time a client connects. See Section 7.5.10, “How MySQL Uses DNS”.
Disable the InnoDB storage engine. This
saves memory and disk space and might speed up some
operations. Do not use this option if you require
InnoDB tables.
Disable the MERGE storage engine. This
option was added in MySQL 5.0.24. It can be used if the
following behavior is undesirable: If a user has access to
MyISAM table
t, that user can create a
MERGE table m
that accesses t. However, if the
user's privileges on t are
subsequently revoked, the user can continue to access
t by doing so through
m.
Do not resolve hostnames when checking client connections.
Use only IP numbers. If you use this option, all
Host column values in the grant tables
must be IP numbers or localhost. See
Section 7.5.10, “How MySQL Uses DNS”.
Don't listen for TCP/IP connections at all. All interaction with mysqld must be made via named pipes or shared memory (on Windows) or Unix socket files (on Unix). This option is highly recommended for systems where only local clients are allowed. See Section 7.5.10, “How MySQL Uses DNS”.
| Value Set |
|
This option is used internally by the MySQL test suite for replication testing and debugging.
Options that begin with --ssl specify
whether to allow clients to connect via SSL and indicate
where to find SSL keys and certificates. See
Section 5.5.7.3, “SSL Command Options”.
| Platform Specific | windows |
Instructs the MySQL server not to run as a service.
--symbolic-links,
--skip-symbolic-links
Enable or disable symbolic link support. This option has different effects on Windows and Unix:
On Windows, enabling symbolic links allows you to
establish a symbolic link to a database directory by
creating a
db_name.sym
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
options 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 7.6.1.2, “Using Symbolic Links for Tables on Unix”.
If MySQL is configured with
--with-debug=full, all MySQL programs check
for memory overruns during each memory allocation and memory
freeing operation. This checking is very slow, so for the
server you can avoid it when you don't need it by using the
--skip-safemalloc option.
| Option Sets Variable | Yes, skip_show_database |
| Variable Name | skip_show_database |
| Variable Scope | Global |
| Dynamic Variable | no |
With this option, the SHOW DATABASES
statement is allowed only to users who have the
SHOW DATABASES privilege, and the
statement displays all database names. Without this option,
SHOW DATABASES is allowed to all users,
but displays each database name only if the user has the
SHOW DATABASES privilege or some
privilege for the database. Note that
any global privilege is considered a
privilege for the database.
Don't 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 MySQL Internals: Porting.
Disable using thread priorities for faster response time.
| Option Sets Variable | Yes, socket | ||||||
| Variable Name | socket | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | no | ||||||
| Value Set |
| ||||||
| Value Set |
| ||||||
| Value Set |
| ||||||
| Value Set |
|
On Unix, this option specifies the Unix socket file to use
when listening for local connections. The default value is
/tmp/mysql.sock. 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...]]
| Option Sets Variable | Yes, sql_mode | ||||||
| Variable Name | sql_mode | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
Set the SQL mode. See Section 5.1.6, “SQL Modes”.
| Version Introduced | 5.0.20 | ||||
| Value Set |
|
As of MySQL 5.0.13,
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 11.6, “Date and Time Functions” and for
SET TIMESTAMP in
Section 12.5.3, “SET Syntax”.
This option was added in MySQL 5.0.20.
--tc-heuristic-recover={COMMIT|ROLLBACK}
| Version Introduced | 5.0.3 | ||||
| Value Set |
|
The type of decision to use in the heuristic recovery process. Currently, this option is unused. Added in MySQL 5.0.3.
| Value Set |
|
This option 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.
| Value Set |
|
Sets the default transaction isolation level. The
level value can be
READ-UNCOMMITTED,
READ-COMMITTED,
REPEATABLE-READ, or
SERIALIZABLE. See
Section 12.4.6, “SET TRANSACTION Syntax”.
| Option Sets Variable | Yes, tmpdir | ||
| Variable Name | tmpdir | ||
| Variable Scope | Global | ||
| Dynamic Variable | no | ||
| Value Set |
|
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,
NetWare, and OS/2. If the MySQL server is acting as a
replication slave, you should not set
--tmpdir to point to a directory on a
memory-based filesystem or to a directory that is cleared
when the server host restarts. For more information about
the storage location of temporary files, see
Section B.1.4.4, “Where MySQL Stores Temporary Files”. A replication slave needs
some of its temporary files to survive a machine restart so
that it can replicate temporary tables or LOAD DATA
INFILE operations. If files in the temporary file
directory are lost when the server restarts, replication
fails.
--user={,
user_name|user_id}-u
{
user_name|user_id}
| Value Set |
|
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 5.3.1, “General 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.
| Variable Name | version |
| Variable Scope | Global |
| Dynamic Variable | no |
Display version information and exit.
You can assign a value to a server system variable by using an
option of the form
--.
For example, var_name=value--key_buffer_size=32M sets the
key_buffer_size variable to a value of 32MB.
Note that 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 allowable value if only certain values are allowed.
If you want to restrict the maximum value to which a variable
can be set at runtime with SET, you can
define this by using the
--maximum-
command-line option.
var_name=value
It is also possible to set variables by using
--set-variable=
or var_name=value-O
syntax. This syntax is deprecated.
var_name=value
You can change the values of most system variables for a running
server with the SET statement. See
Section 12.5.3, “SET Syntax”.
Section 5.1.3, “System Variables”, provides a full description for all variables, and additional information for setting them at server startup and runtime. Section 7.5.2, “Tuning Server Parameters”, includes information on optimizing the server by tuning system variables.
The MySQL server maintains many system variables that indicate
how it is configured. 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 while the server is running by means of the
SET statement, which enables you to modify
operation of the server without having to stop and restart it.
You can refer to system variable values in expressions.
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 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.
This section provides a description of each system variable. Variables with no version indicated are present in all MySQL 5.0 releases. For historical information concerning their implementation, please see http://dev.mysql.com/doc/refman/4.1/en/.
The following table lists all available system variables:
For additional system variable information, see these sections:
Section 5.1.4, “Using System Variables”, discusses the syntax for setting and displaying system variable values.
Section 5.1.4.2, “Dynamic System Variables”, lists the variables that can be set at runtime.
Information on tuning system variables can be found in Section 7.5.2, “Tuning Server Parameters”.
Section 13.2.4, “InnoDB Startup Options and System Variables”, lists
InnoDB system 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. However, to set such a variable on the
command line or in an option file, you must set it to
1 or 0; setting it to
ON or OFF will not work.
For example, on the command line,
--delay_key_write=1 works but
--delay_key_write=ON does not.
Values for buffer sizes, lengths, and stack sizes are given in bytes unless otherwise specified.
| Version Introduced | 5.0.2 | ||||||
| Option Sets Variable | Yes, auto_increment_increment | ||||||
| Variable Name | auto_increment_increment | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
auto_increment_increment and
auto_increment_offset are intended for
use with master-to-master replication, and can be used to
control the operation of AUTO_INCREMENT
columns. Both variables can be set globally or locally, and
each can assume an integer value between 1 and 65,535
inclusive. Setting the value of either of these two
variables to 0 causes its value to be set to 1 instead.
Attempting to set the value of either of these two variables
to an integer greater than 65,535 or less than 0 causes its
value to be set to 65,535 instead. Attempting to set the
value of auto_increment_increment or
auto_increment_offset to a non-integer
value gives rise to an error, and the actual value of the
variable remains unchanged.
These two variables affect AUTO_INCREMENT
column behavior as follows:
auto_increment_increment controls the
interval between successive column values. For example:
mysql>SHOW VARIABLES LIKE 'auto_inc%';+--------------------------+-------+ | Variable_name | Value | +--------------------------+-------+ | auto_increment_increment | 1 | | auto_increment_offset | 1 | +--------------------------+-------+ 2 rows in set (0.00 sec) mysql>CREATE TABLE autoinc1->(col INT NOT NULL AUTO_INCREMENT PRIMARY KEY);Query OK, 0 rows affected (0.04 sec) mysql>SET @@auto_increment_increment=10;Query OK, 0 rows affected (0.00 sec) mysql>SHOW VARIABLES LIKE 'auto_inc%';+--------------------------+-------+ | Variable_name | Value | +--------------------------+-------+ | auto_increment_increment | 10 | | auto_increment_offset | 1 | +--------------------------+-------+ 2 rows in set (0.01 sec) mysql>INSERT INTO autoinc1 VALUES (NULL), (NULL), (NULL), (NULL);Query OK, 4 rows affected (0.00 sec) Records: 4 Duplicates: 0 Warnings: 0 mysql>SELECT col FROM autoinc1;+-----+ | col | +-----+ | 1 | | 11 | | 21 | | 31 | +-----+ 4 rows in set (0.00 sec)
(Note how SHOW VARIABLES is used here
to obtain the current values for these variables.)
auto_increment_offset determines the
starting point for the AUTO_INCREMENT
column value. Consider the following, assuming that
these statements are executed during the same session as
the example given in the description for
auto_increment_increment:
mysql>SET @@auto_increment_offset=5;Query OK, 0 rows affected (0.00 sec) mysql>SHOW VARIABLES LIKE 'auto_inc%';+--------------------------+-------+ | Variable_name | Value | +--------------------------+-------+ | auto_increment_increment | 10 | | auto_increment_offset | 5 | +--------------------------+-------+ 2 rows in set (0.00 sec) mysql>CREATE TABLE autoinc2->(col INT NOT NULL AUTO_INCREMENT PRIMARY KEY);Query OK, 0 rows affected (0.06 sec) mysql>INSERT INTO autoinc2 VALUES (NULL), (NULL), (NULL), (NULL);Query OK, 4 rows affected (0.00 sec) Records: 4 Duplicates: 0 Warnings: 0 mysql>SELECT col FROM autoinc2;+-----+ | col | +-----+ | 5 | | 15 | | 25 | | 35 | +-----+ 4 rows in set (0.02 sec)
If the value of auto_increment_offset
is greater than that of
auto_increment_increment, the value
of auto_increment_offset is ignored.
Should one or both of these variables be changed and then
new rows inserted into a table containing an
AUTO_INCREMENT column, the results may
seem counterintuitive because the series of
AUTO_INCREMENT values is calculated
without regard to any values already present in the column,
and the next value inserted is the least value in the series
that is greater than the maximum existing value in the
AUTO_INCREMENT column. In other words,
the series is calculated like so:
auto_increment_offset +
N ×
auto_increment_increment
where N is a positive integer
value in the series [1, 2, 3, ...]. For example:
mysql>SHOW VARIABLES LIKE 'auto_inc%';+--------------------------+-------+ | Variable_name | Value | +--------------------------+-------+ | auto_increment_increment | 10 | | auto_increment_offset | 5 | +--------------------------+-------+ 2 rows in set (0.00 sec) mysql>SELECT col FROM autoinc1;+-----+ | col | +-----+ | 1 | | 11 | | 21 | | 31 | +-----+ 4 rows in set (0.00 sec) mysql>INSERT INTO autoinc1 VALUES (NULL), (NULL), (NULL), (NULL);Query OK, 4 rows affected (0.00 sec) Records: 4 Duplicates: 0 Warnings: 0 mysql>SELECT col FROM autoinc1;+-----+ | col | +-----+ | 1 | | 11 | | 21 | | 31 | | 35 | | 45 | | 55 | | 65 | +-----+ 8 rows in set (0.00 sec)
The values shown for
auto_increment_increment and
auto_increment_offset generate the series
5 + N × 10, that is, [5,
15, 25, 35, 45, ...]. The greatest value present in the
col column prior to the
INSERT is 31, and the next available
value in the AUTO_INCREMENT series is 35,
so the inserted values for col begin at
that point and the results are as shown for the
SELECT query.
It is important to remember that it is not possible to
confine the effects of these two variables to a single
table, and thus they do not take the place of the sequences
offered by some other database management systems; these
variables control the behavior of all
AUTO_INCREMENT columns in
all tables on the MySQL server. If one
of these variables is set globally, its effects persist
until the global value is changed or overridden by setting
them locally, or until mysqld is
restarted. If set locally, the new value affects
AUTO_INCREMENT columns for all tables
into which new rows are inserted by the current user for the
duration of the session, unless the values are changed
during that session.
The auto_increment_increment variable was
added in MySQL 5.0.2. Its default value is 1. See
Auto-Increment in Multiple-Master Replication.
auto_increment_increment is supported for
use with NDB tables beginning with MySQL
5.0.46. Previously, setting it when using MySQL Cluster
tables produced unpredictable results.
| Version Introduced | 5.0.2 | ||||||
| Option Sets Variable | Yes, auto_increment_offset | ||||||
| Variable Name | auto_increment_offset | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
This variable was introduced in MySQL 5.0.2. Its default
value is 1. For particulars, see the description for
auto_increment_increment.
auto_increment_offset is supported for
use with NDB tables beginning with MySQL
5.0.46. Previously, setting it when using MySQL Cluster
tables produced unpredictable results.
| Version Introduced | 5.0.3 | ||||
| Variable Name | automatic_sp_privileges | ||||
| Variable Scope | Global | ||||
| Dynamic Variable | yes | ||||
| Disabled By | skip-automatic_sp_privileges | ||||
| Value Set |
|
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 privileges is required to drop the
routine.) The server also automatically drops those
privileges when the creator drops the routine. If
automatic_sp_privileges is 0, the server
does not automatically add and drop these privileges. This
variable was added in MySQL 5.0.3.
| Option Sets Variable | Yes, back_log | ||||||
| Variable Name | back_log | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | no | ||||||
| Value Set |
|
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.
basedir
| Option Sets Variable | Yes, basedir | ||
| Variable Name | basedir | ||
| Variable Scope | Global | ||
| Dynamic Variable | no | ||
| Value Set |
|
The MySQL installation base directory. This variable can be
set with the --basedir option.
| Command Line Format | --bdb_cache_size=# | ||||
| Config File Format | bdb_cache_size | ||||
| Option Sets Variable | Yes, bdb_cache_size | ||||
| Variable Name | bdb_cache_size | ||||
| Variable Scope | Global | ||||
| Dynamic Variable | no | ||||
| Value Set |
|
The size of the buffer that is allocated for caching indexes
and rows for BDB tables. If you don't use
BDB tables, you should start
mysqld with --skip-bdb
to not allocate memory for this cache.
| Command Line Format | --bdb-home=name | ||
| Variable Name | bdb_home | ||
| Variable Scope | Global | ||
| Dynamic Variable | no | ||
| Value Set |
|
The base directory for BDB tables. This
should be assigned the same value as the
datadir variable.
| Command Line Format | --bdb_log_buffer_size=# | ||||
| Config File Format | bdb_log_buffer_size | ||||
| Option Sets Variable | Yes, bdb_log_buffer_size | ||||
| Variable Name | bdb_log_buffer_size | ||||
| Variable Scope | Global | ||||
| Dynamic Variable | no | ||||
| Value Set |
|
The size of the buffer that is allocated for caching indexes
and rows for BDB tables. If you don't use
BDB tables, you should set this to 0 or
start mysqld with
--skip-bdb to not allocate memory for this
cache.
| Command Line Format | --bdb-logdir=file_name | ||
| Variable Name | bdb_logdir | ||
| Variable Scope | Global | ||
| Dynamic Variable | no | ||
| Value Set |
|
The directory where the BDB storage
engine writes its log files. This variable can be set with
the --bdb-logdir option.
| Command Line Format | --bdb_max_lock=# | ||||
| Config File Format | bdb_max_lock | ||||
| Option Sets Variable | Yes, bdb_max_lock | ||||
| Variable Name | bdb_max_lock | ||||
| Variable Scope | Global | ||||
| Dynamic Variable | no | ||||
| Value Set |
|
The maximum number of locks that can be active for a
BDB table (10,000 by default). You should
increase this value if errors such as the following occur
when you perform long transactions or when
mysqld has to examine many rows to
calculate a query:
bdb: Lock table is out of available locks Got error 12 from ...
| Command Line Format | --bdb-shared-data |
| Option Sets Variable | Yes, bdb_shared_data |
| Variable Name | bdb_shared_data |
| Variable Scope | Global |
| Dynamic Variable | no |
This is ON if you are using
--bdb-shared-data to start Berkeley DB in
multi-process mode. (Do not use
DB_PRIVATE when initializing Berkeley
DB.)
| Command Line Format | --bdb-tmpdir=name | ||
| Config File Format | bdb-tmpdir | ||
| Variable Name | bdb_tmpdir | ||
| Variable Scope | Global | ||
| Dynamic Variable | no | ||
| Value Set |
|
The BDB temporary file directory.
| Option Sets Variable | Yes, binlog_cache_size | ||||||
| Variable Name | binlog_cache_size | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
The size of the cache to hold the SQL statements for the
binary log during a transaction. A binary log cache is
allocated for each client if the server supports any
transactional storage engines and if the server has the
binary log enabled (--log-bin option). If
you often use large, multiple-statement transactions, you
can increase this cache size to get more performance. The
Binlog_cache_use and
Binlog_cache_disk_use status variables
can be useful for tuning the size of this variable. See
Section 5.2.3, “The Binary Log”.
MySQL Enterprise.
For recommendations on the optimum setting for
binlog_cache_size subscribe to the
MySQL Enterprise Monitor. For more information see
http://www.mysql.com/products/enterprise/advisors.html.
| Option Sets Variable | Yes, bulk_insert_buffer_size | ||||||
| Variable Name | bulk_insert_buffer_size | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
MyISAM uses a special tree-like cache to
make bulk inserts faster for INSERT ...
SELECT, INSERT ... VALUES (...), (...),
..., and LOAD DATA INFILE when
adding data to non-empty 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.
| Variable Name | character_set_client | ||
| Variable Scope | Both | ||
| Dynamic Variable | yes | ||
| Value Set |
|
The character set for statements that arrive from the client.
| Variable Name | character_set_connection | ||
| Variable Scope | Both | ||
| Dynamic Variable | yes | ||
| Value Set |
|
The character set used for literals that do not have a character set introducer and for number-to-string conversion.
| Variable Name | character_set_database | ||
| Variable Scope | Both | ||
| Dynamic Variable | yes | ||
| Value Set |
|
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.
| Version Introduced | 5.0.19 | ||
| Option Sets Variable | Yes, character_set_filesystem | ||
| Variable Name | character_set_filesystem | ||
| Variable Scope | Both | ||
| Dynamic Variable | yes | ||
| Value Set |
|
The filesystem character set. This variable is used to
interpret string literals that refer to filenames, such as
in the LOAD DATA INFILE and
SELECT ... INTO OUTFILE statements and
the LOAD_FILE() function.
Such filenames 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 multi-byte filenames are
allowed, a different value may be more appropriate. For
example, if the system represents filenames using UTF-8, set
character_set_filesystem to
'utf8'. This variable was added in MySQL
5.0.19.
| Variable Name | character_set_results | ||
| Variable Scope | Both | ||
| Dynamic Variable | yes | ||
| Value Set |
|
The character set used for returning query results to the client.
| Option Sets Variable | Yes, character_set_server | ||
| Variable Name | character_set_server | ||
| Variable Scope | Both | ||
| Dynamic Variable | yes | ||
| Value Set |
|
The server's default character set.
| Variable Name | character_set_system | ||
| Variable Scope | Global | ||
| Dynamic Variable | no | ||
| Value Set |
|
The character set used by the server for storing
identifiers. The value is always utf8.
| Option Sets Variable | Yes, character_sets_dir | ||
| Variable Name | character-sets-dir | ||
| Variable Scope | Global | ||
| Dynamic Variable | no | ||
| Value Set |
|
The directory where character sets are installed.
| Variable Name | collation_connection | ||
| Variable Scope | Both | ||
| Dynamic Variable | yes | ||
| Value Set |
|
The collation of the connection character set.
| Variable Name | collation_database | ||
| Variable Scope | Both | ||
| Dynamic Variable | yes | ||
| Value Set |
|
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.
| Option Sets Variable | Yes, collation_server | ||
| Variable Name | collation_server | ||
| Variable Scope | Both | ||
| Dynamic Variable | yes | ||
| Value Set |
|
The server's default collation.
| Version Introduced | 5.0.3 | ||||||
| Option Sets Variable | Yes, completion_type | ||||||
| Variable Name | competion_type | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
The transaction completion type:
If the value is 0 (the default),
COMMIT and
ROLLBACK are unaffected.
If the value is 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.)
If the value is 2, COMMIT and
ROLLBACK are equivalent to
COMMIT RELEASE and ROLLBACK
RELEASE, respectively. (The server disconnects
after terminating the transaction.)
This variable was added in MySQL 5.0.3
| Option Sets Variable | Yes, concurrent_insert | ||||||
| Variable Name | concurrent_insert | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
| ||||||
| Value Set |
|
If 1 (the default), MySQL allows INSERT
and SELECT statements to run concurrently
for MyISAM tables that have no free
blocks in the middle of the data file. You can turn this
option off by starting mysqld with
--safe or --skip-new.
In MySQL 5.0.6, this variable was changed to take three integer values:
| Value | Description |
| 0 | Off |
| 1 | (Default) Enables concurrent insert for MyISAM tables
that don't have holes |
| 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. |
See also Section 7.3.3, “Concurrent Inserts”.
| Option Sets Variable | Yes, connect_timeout | ||||||
| Variable Name | connect_timeout | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
| ||||||
| Value Set |
| ||||||
| Value Set |
| ||||||
| Value Set |
|
The number of seconds that the mysqld
server waits for a connect packet before responding with
Bad handshake. The default value is 10
seconds as of MySQL 5.0.52 and 5 seconds before that.
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
datadir
| Option Sets Variable | Yes, datadir | ||
| Variable Name | datadir | ||
| Variable Scope | Global | ||
| Dynamic Variable | no | ||
| Value Set |
|
The MySQL data directory. This variable can be set with the
--datadir option.
This variable is not implemented.
This variable is not implemented.
| Option Sets Variable | Yes, default_week_format | ||||||
| Variable Name | default_week_format | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
The default mode value to use for the
WEEK() function. See
Section 11.6, “Date and Time Functions”.
| Option Sets Variable | Yes, delay_key_write | ||||||
| Variable Name | delay-key-write | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
This option applies only to MyISAM
tables. It 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 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 option (for example,
--myisam-recover=BACKUP,FORCE). See
Section 5.1.2, “Command Options”, and
Section 13.1.1, “MyISAM Startup Options”.
Note that if you enable external locking with
--external-locking, there is no protection
against index corruption for tables that use delayed key
writes.
| Option Sets Variable | Yes, delayed_insert_limit | ||||||
| Variable Name | delayed_insert_limit | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
After inserting delayed_insert_limit
delayed rows, the INSERT DELAYED handler
thread checks whether there are any
SELECT statements pending. If so, it
allows them to execute before continuing to insert delayed
rows.
| Option Sets Variable | Yes, delayed_insert_timeout | ||||
| Variable Name | delayed_insert_timeout | ||||
| Variable Scope | Global | ||||
| Dynamic Variable | yes | ||||
| Value Set |
|
How many seconds an INSERT DELAYED
handler thread should wait for INSERT
statements before terminating.
| Option Sets Variable | Yes, delayed_queue_size | ||||||
| Variable Name | delayed_queue_size | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
This is a per-table limit on the number of rows to queue
when handling INSERT DELAYED statements.
If the queue becomes full, any client that issues an
INSERT DELAYED statement waits until
there is room in the queue again.
| Version Introduced | 5.0.6 | ||||||
| Option Sets Variable | Yes, div_precision_increment | ||||||
| Variable Name | div_precision_increment | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
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 | +----------------+
This variable was added in MySQL 5.0.6.
| Option Sets Variable | Yes, expire_logs_days | ||||||
| Variable Name | expire_logs_days | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
The number of days for automatic binary log removal. The default is 0, which means “no automatic removal.” Possible removals happen at startup and at binary log rotation.
flush
| Variable Name | flush | ||||
| Variable Scope | Global | ||||
| Dynamic Variable | yes | ||||
| Value Set |
|
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.1.4.2, “What to Do If MySQL Keeps Crashing”. This
variable is set to ON if you start
mysqld with the --flush
option.
| Option Sets Variable | Yes, flush_time | |||||||||
| Variable Name | flush_time | |||||||||
| Variable Scope | Global | |||||||||
| Dynamic Variable | yes | |||||||||
| Value Set |
| |||||||||
| Value Set |
| |||||||||
| Value Set |
| |||||||||
| Value Set |
| |||||||||
| Value Set |
| |||||||||
| Value Set |
|
If this is set to a non-zero value, all tables are closed
every flush_time seconds to free up
resources and synchronize unflushed data to disk. We
recommend that this option be used only on systems with
minimal resources.
| Variable Name | ft_boolean_syntax | ||||
| Variable Scope | Global | ||||
| Dynamic Variable | yes | ||||
| Value Set |
|
The list of operators supported by boolean full-text
searches performed using IN BOOLEAN MODE.
See Section 11.8.2, “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 non-alphanumeric character.
Either the first or second character must be a space.
No duplicates are allowed 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.
| Option Sets Variable | Yes, ft_max_word_len | ||||
| Variable Name | ft_max_word_len | ||||
| Variable Scope | Global | ||||
| Dynamic Variable | no | ||||
| Value Set |
|
The maximum length of the word to be included in a
FULLTEXT index.
FULLTEXT indexes must be rebuilt after
changing this variable. Use REPAIR TABLE
.
tbl_name QUICK
| Option Sets Variable | Yes, ft_min_word_len | ||||||
| Variable Name | ft_min_word_len | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | no | ||||||
| Value Set |
|
The minimum length of the word to be included in a
FULLTEXT index.
FULLTEXT indexes must be rebuilt after
changing this variable. Use REPAIR TABLE
.
tbl_name QUICK
| Option Sets Variable | Yes, ft_query_expansion_limit | ||||||
| Variable Name | ft_query_expansion_limit | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | no | ||||||
| Value Set |
|
The number of top matches to use for full-text searches
performed using WITH QUERY EXPANSION.
| Option Sets Variable | Yes, ft_stopword_file | ||
| Variable Name | ft_stopword_file | ||
| Variable Scope | Global | ||
| Dynamic Variable | no | ||
| Value Set |
|
The file from which to read the list of stopwords for
full-text searches. 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
myisam/ft_static.c file). Setting this
variable to the empty string ('')
disables stopword filtering.
FULLTEXT indexes must be rebuilt after
changing this variable or the contents of the stopword
file. Use REPAIR TABLE
.
tbl_name QUICK
| Option Sets Variable | Yes, group_concat_max_len | ||||||
| Variable Name | group_concat_max_len | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
The maximum allowed result length for the
GROUP_CONCAT() function. The
default is 1024.
YES if mysqld supports
ARCHIVE tables, NO if
not.
YES if mysqld supports
BDB tables. DISABLED
if --skip-bdb is used.
YES if mysqld supports
BLACKHOLE tables, NO
if not.
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.
YES if mysqld supports
CSV tables, NO if not.
YES if mysqld supports
EXAMPLE tables, NO if
not.
YES if mysqld supports
FEDERATED tables, NO
if not. This variable was added in MySQL 5.0.3.
YES if the server supports spatial data
types, NO if not.
YES if mysqld supports
InnoDB tables.
DISABLED if
--skip-innodb is used.
In MySQL 5.0, this variable appears only for
reasons of backward compatibility. It is always
NO because ISAM tables
are no longer supported.
YES if mysqld supports
MERGE tables. DISABLED
if --skip-merge is used. This variable was
added in MySQL 5.0.24.
YES if mysqld supports
SSL connections, NO if not. As of MySQL
5.0.38, this variable is an alias for
have_ssl.
YES if mysqld supports
the query cache, NO if not.
In MySQL 5.0, this variable appears only for
reasons of backward compatibility. It is always
NO because RAID tables
are no longer supported.
YES if RTREE indexes
are available, NO if not. (These are used
for spatial indexes in MyISAM tables.)
YES if mysqld supports
SSL connections, NO if not. This variable
was added in MySQL 5.0.38. Before that, use
have_openssl.
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, and on
Windows for support of data directory symlinks.
| Version Introduced | 5.0.38 | ||
| Variable Name | hostname | ||
| Variable Scope | Global | ||
| Dynamic Variable | no | ||
| Value Set |
|
The server sets this variable to the server hostname at startup. This variable was added in MySQL 5.0.38.
| Option Sets Variable | Yes, init_connect | ||
| Variable Name | init_connect | ||
| Variable Scope | Global | ||
| Dynamic Variable | yes | ||
| Value Set |
|
A string to be executed by the server for each client that
connects. The string consists of one or more SQL statements.
To specify multiple statements, separate them by semicolon
characters. For example, each client begins by default with
autocommit mode enabled. There is no global system variable
to specify that autocommit should be disabled by default,
but init_connect can be used to achieve
the same effect:
SET GLOBAL init_connect='SET AUTOCOMMIT=0';
This variable can also be set on the command line or in an option file. To set the variable as just shown using an option file, include these lines:
[mysqld] init_connect='SET AUTOCOMMIT=0'
Note that the content of init_connect is
not executed for users that have the
SUPER privilege. 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.
| Option Sets Variable | Yes, init_file | ||
| Variable Name | init_file | ||
| Variable Scope | Global | ||
| Dynamic Variable | no | ||
| Value Set |
|
The name of the file specified with the
--init-file option when you start the
server. This should be a file containing SQL statements that
you want the server to execute when it starts. Each
statement must be on a single line and should not include
comments.
Note that the --init-file option is
unavailable if MySQL was configured with the
--disable-grant-options option. See
Section 2.4.15.2, “Typical configure Options”.
| Option Sets Variable | Yes, init_slave | ||
| Variable Name | init_slave | ||
| Variable Scope | Global | ||
| Dynamic Variable | yes | ||
| Value Set |
|
This variable is similar to init_connect,
but is a string to be executed by a slave server each time
the SQL thread starts. The format of the string is the same
as for the init_connect variable.
innodb_
xxx
InnoDB system variables are listed in
Section 13.2.4, “InnoDB Startup Options and System Variables”.
| Option Sets Variable | Yes, interactive_timeout | ||||||
| Variable Name | interactive_timeout | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
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.
| Option Sets Variable | Yes, join_buffer_size | ||||||
| Variable Name | join_buffer_size | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
The size of the buffer that is used for 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.
The maximum allowable setting for
join_buffer_size is 4GB.
| Version Introduced | 5.0.48 | ||||
| Option Sets Variable | Yes, keep_files_on_create | ||||
| Variable Name | keep_files_on_create | ||||
| Variable Scope | Both | ||||
| Dynamic Variable | yes | ||||
| Value Set |
|
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.
This variable was added in MySQL 5.0.48.
| Option Sets Variable | Yes, key_buffer_size | ||||||
| Variable Name | key_buffer_size | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
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 allowable setting for
key_buffer_size is 4GB on 32-bit
platforms. As of MySQL 5.0.52, values larger than 4GB are
allowed for 64-bit platforms (except 64-bit Windows, for
which large values are truncated to 4GB with a warning). 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.
Increase the value to get better index handling (for all reads and multiple writes) to as much as you can afford. Using a value that is 25% of total memory on a machine that mainly runs MySQL is quite common. However, if you make the value too large (for example, more than 50% of your total memory) your system might start to page and become extremely slow. MySQL relies on the operating system to perform filesystem caching for data reads, so you must leave some room for the filesystem cache. Consider also the memory requirements of other storage engines.
For even more speed when writing many rows at the same time,
use LOCK TABLES. See
Section 7.2.17, “Speed of 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 12.5.4, “SHOW Syntax”.) 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 may be allocated internally for administrative structures.
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 7.4.6, “The MyISAM Key Cache”.
| Option Sets Variable | Yes, key_cache_age_threshold | ||||||
| Variable Name | key_cache_age_threshold | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
This value controls the demotion of buffers from the hot
sub-chain of a key cache to the warm sub-chain. Lower values
cause demotion to happen more quickly. The minimum value is
100. The default value is 300. See
Section 7.4.6, “The MyISAM Key Cache”.
| Option Sets Variable | Yes, key_cache_block_size | ||||||
| Variable Name | key_cache_block_size | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
The size in bytes of blocks in the key cache. The default
value is 1024. See Section 7.4.6, “The MyISAM Key Cache”.
| Option Sets Variable | Yes, key_cache_division_limit | ||||||
| Variable Name | key_cache_division_limit | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
The division point between the hot and warm sub-chains of
the key cache buffer chain. The value is the percentage of
the buffer chain to use for the warm sub-chain. Allowable
values range from 1 to 100. The default value is 100. See
Section 7.4.6, “The MyISAM Key Cache”.
language
| Option Sets Variable | Yes, language | ||||
| Variable Name | language | ||||
| Variable Scope | Global | ||||
| Dynamic Variable | no | ||||
| Value Set |
|
The language used for error messages.
| Variable Name | large_files_support |
| Variable Scope | Global |
| Dynamic Variable | no |
Whether mysqld was compiled with options for large file support.
| Version Introduced | 5.0.3 | ||||||
| Option Sets Variable | Yes, large_pages | ||||||
| Variable Name | large_pages | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | no | ||||||
| Platform Specific | linux | ||||||
| Value Set |
|
Whether large page support is enabled. This variable was added in MySQL 5.0.3.
For more information, see
the entry for the
--large-pages server option.
| Version Introduced | 5.0.3 | ||||||
| Variable Name | large_page_size | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | no | ||||||
| Value Set |
|
If large page support is enabled, this shows the size of memory pages. Currently, large memory pages are supported only on Linux; on other platforms, the value of this variable is always 0. This variable was added in MySQL 5.0.3.
For more information, see
the entry for the
--large-pages server option.
| Version Introduced | 5.0.25 | ||
| Variable Name | lc_time_names | ||
| Variable Scope | Both | ||
| Dynamic Variable | yes | ||
| Value Set |
|
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 9.7, “MySQL Server Locale Support”. This variable was
added in MySQL 5.0.25.
| Variable Name | license | ||||
| Variable Scope | Global | ||||
| Dynamic Variable | no | ||||
| Value Set |
|
The type of license the server has.
| Variable Name | local_infile |
| Variable Scope | Global |
| Dynamic Variable | yes |
Whether LOCAL is supported for
LOAD DATA INFILE statements. See
Section 5.3.4, “Security Issues with LOAD DATA LOCAL”.
| Variable Name | locked_in_memory |
| Variable Scope | Global |
| Dynamic Variable | no |
Whether mysqld was locked in memory with
--memlock.
Whether logging of all statements to the general query log is enabled. See Section 5.2.2, “The General Query Log”.
| Variable Name | log_bin |
| Variable Scope | Global |
| Dynamic Variable | no |
Whether the binary log is enabled. See Section 5.2.3, “The Binary Log”.
log_bin_trust_function_creators
| Version Introduced | 5.0.16 | ||||
| Option Sets Variable | Yes, log_bin_trust_function_creators | ||||
| Variable Name | log_bin_trust_function_creators | ||||
| Variable Scope | Global | ||||
| Dynamic Variable | yes | ||||
| Value Set |
|
This variable applies when binary logging is enabled. It
controls whether stored function creators can be trusted not
to create stored functions that will cause unsafe events to
be written to the binary log. If set to 0 (the default),
users are not allowed to create or alter stored functions
unless they have the SUPER privilege in
addition to the CREATE ROUTINE or
ALTER ROUTINE privilege. A setting of 0
also enforces the restriction that a function must be
declared with the DETERMINISTIC
characteristic, or with the READS SQL
DATA or NO SQL characteristic.
If the variable is set to 1, MySQL does not enforce these
restrictions on stored function creation. See
Section 18.5, “Binary Logging of Stored Routines and Triggers”.
This variable was added in MySQL 5.0.16.
log_bin_trust_routine_creators
This is the old name for
log_bin_trust_function_creators. Before
MySQL 5.0.16, it also applies to stored procedures, not just
stored functions. As of 5.0.16, this variable is deprecated.
It is recognized for backward compatibility but its use
results in a warning.
This variable was added in MySQL 5.0.6.
| Option Sets Variable | Yes, log_error | ||
| Variable Name | log_error | ||
| Variable Scope | Global | ||
| Dynamic Variable | no | ||
| Value Set |
|
The location of the error log.
| Version Introduced | 5.0.23 | ||
| Option Sets Variable | Yes, log_queries_not_using_indexes | ||
| Variable Name | log_queries_not_using_indexes | ||
| Variable Scope | Global | ||
| Dynamic Variable | no | ||
| Value Set |
|
Whether queries that do not use indexes are logged to the slow query log. See Section 5.2.4, “The Slow Query Log”. This variable was added in MySQL 5.0.23.
Whether updates received by a slave server from a master server should be logged to the slave's own binary log. Binary logging must be enabled on the slave for this variable to have any effect. See Section 15.1.2, “Replication Startup Options and Variables”.
| Option Sets Variable | Yes, log_slow_queries | ||
| Variable Name | log_slow_queries | ||
| Variable Scope | Global | ||
| Dynamic Variable | yes | ||
| Value Set |
|
Whether slow queries should be logged. “Slow”
is determined by the value of the
long_query_time variable. See
Section 5.2.4, “The Slow Query Log”.
| Option Sets Variable | Yes, log-warnings | ||||
| Variable Name | log_warnings | ||||
| Variable Scope | Both | ||||
| Dynamic Variable | yes | ||||
| Disabled By | skip-log-warnings | ||||
| Value Set |
|
Whether to produce additional warning messages. It is enabled (1) by default and can be disabled by setting it to 0. Aborted connections are not logged to the error log unless the value is greater than 1.
| Option Sets Variable | Yes, long_query_time | ||||||
| Variable Name | long_query_time | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
| ||||||
| Value Set |
| ||||||
| Value Set |
| ||||||
| Value Set |
|
If a query takes longer than this many seconds, the server
increments the Slow_queries status
variable. If you are using the
--log-slow-queries option, the query is
logged to the slow query log file. This value is measured in
real time, not CPU time, so a query that is under the
threshold on a lightly loaded system might be above the
threshold on a heavily loaded one. The minimum value is 1.
The default is 10. See Section 5.2.4, “The Slow Query Log”.
| Option Sets Variable | Yes, low_priority_updates | ||||
| Variable Name | low_priority_updates | ||||
| Variable Scope | Both | ||||
| Dynamic Variable | yes | ||||
| Value Set |
|
If set to 1, all
INSERT, UPDATE,
DELETE, and LOCK TABLE
WRITE statements wait until there is no pending
SELECT or LOCK TABLE
READ on the affected table. This affects only
storage engines that use only table-level locking
(MyISAM, MEMORY,
MERGE). This variable previously was
named sql_low_priority_updates.
| Option Sets Variable | Yes, lower_case_file_system | ||
| Variable Name | lower_case_file_system | ||
| Variable Scope | Global | ||
| Dynamic Variable | no | ||
| Value Set |
|
This variable describes the case sensitivity of filenames on
the filesystem where the data directory is located.
OFF means filenames are case sensitive,
ON means they are not case sensitive.
| Option Sets Variable | Yes, lower_case_table_names | ||||||
| Variable Name | lower_case_table_names | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | no | ||||||
| Value Set |
|
If set to 1, table names are stored in lowercase on disk and table name comparisons are not case sensitive. If set to 2 table names are stored as given but compared in lowercase. This option also applies to database names and table aliases. See Section 8.2.2, “Identifier Case Sensitivity”.
If you are using InnoDB tables, you
should set this variable to 1 on all platforms to force
names to be converted to lowercase.
You should not set this variable to 0
if you are running MySQL on a system that does not have
case-sensitive filenames (such as Windows or Mac OS X). If
this variable is not set at startup and the filesystem on
which the data directory is located does not have
case-sensitive filenames, MySQL automatically sets
lower_case_table_names to 2.
| Option Sets Variable | Yes, max_allowed_packet | ||||||
| Variable Name | max_allowed_packet | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
The maximum size of one packet or any generated/intermediate string.
The packet message buffer is initialized to
net_buffer_length bytes, but can grow up
to max_allowed_packet bytes when needed.
This value by default is small, to catch large (possibly
incorrect) packets.
You must increase this value if you are using large
BLOB columns or long strings. It should
be as big as the largest BLOB you want to
use. The protocol limit for
max_allowed_packet is 1GB.
| Option Sets Variable | Yes, max_binlog_cache_size | ||||||
| Variable Name | max_binlog_cache_size | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
If a multiple-statement transaction requires more than this
many bytes of memory, the server generates a
Multi-statement transaction required more than
'max_binlog_cache_size' bytes of storage error.
The minimum value is 4096, the maximum and default values
are 4GB.
| Option Sets Variable | Yes, max_binlog_size | ||||||
| Variable Name | max_binlog_size | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
If a write to the binary log causes the current log file size to exceed the value of this variable, the server rotates the binary logs (closes the current file and opens the next one). You cannot set this variable to more than 1GB or to less than 4096 bytes. The default value is 1GB.
A transaction is written in one chunk to the binary log, so
it is never split between several binary logs. Therefore, if
you have big transactions, you might see binary logs larger
than max_binlog_size.
If max_relay_log_size is 0, the value of
max_binlog_size applies to relay logs as
well.
| Option Sets Variable | Yes, max_connect_errors | ||||||
| Variable Name | max_connect_errors | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
If there are more than this number of interrupted
connections from a host, that host is blocked from further
connections. You can unblock blocked hosts with the
FLUSH HOSTS statement.
| Option Sets Variable | Yes, max_connections | ||||||
| Variable Name | max_connections | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
| ||||||
| Value Set |
| ||||||
| Value Set |
|
The number of simultaneous client connections allowed. By
default, this is 100. See
Section B.1.2.7, “Too many connections”, for more
information.
MySQL Enterprise.
For notification that the maximum number of connections is
getting dangerously high and for advice on setting the
optimum value for max_connections
subscribe to the MySQL Enterprise Monitor. For more
information see
http://www.mysql.com/products/enterprise/advisors.html.
Increasing this value increases the number of file descriptors that mysqld requires. See Section 7.4.8, “How MySQL Opens and Closes Tables”, for comments on file descriptor limits.
| Option Sets Variable | Yes, max_delayed_threads | ||||||
| Variable Name | max_delayed_threads | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
Do not start more than this number of threads to handle
INSERT DELAYED statements. If you try to
insert data into a new table after all INSERT
DELAYED threads are in use, the row is inserted as
if the DELAYED attribute wasn't
specified. If you set this to 0, MySQL never creates a
thread to handle DELAYED rows; in effect,
this disables DELAYED entirely.
| Option Sets Variable | Yes, max_error_count | ||||||
| Variable Name | max_error_count | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
The maximum number of error, warning, and note messages to
be stored for display by the SHOW ERRORS
and SHOW WARNINGS statements.
| Option Sets Variable | Yes, max_heap_table_size | ||||||
| Variable Name | max_heap_table_size | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
This variable sets the maximum size to which
MEMORY tables are allowed to grow. The
value of the variable is used to calculate
MEMORY table MAX_ROWS
values. Setting this variable has no effect on any existing
MEMORY table, unless the table is
re-created with a statement such as CREATE
TABLE or altered with ALTER
TABLE or TRUNCATE TABLE.
MySQL Enterprise.
Subscribers to the MySQL Enterprise Monitor receive
recommendations for the optimum setting for
max_heap_table_size. For more
information see
http://www.mysql.com/products/enterprise/advisors.html.
| Variable Name | max_insert_delayed_threads | ||
| Variable Scope | Both | ||
| Dynamic Variable | yes | ||
| Value Set |
|
This variable is a synonym for
max_delayed_threads.
| Option Sets Variable | Yes, max_join_size | ||||||
| Variable Name | max_join_size | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
Do not allow SELECT statements that
probably need to examine more than
max_join_size rows (for single-table
statements) or row combinations (for multiple-table
statements) or that are likely to do more than
max_join_size disk seeks. By setting this
value, you can catch SELECT statements
where keys are not used properly and that would probably
take a long time. Set it if your users tend to perform joins
that lack a WHERE clause, that take a
long time, or that return millions of rows.
Setting this variable to a value other than
DEFAULT resets the value of
SQL_BIG_SELECTS to 0.
If you set the SQL_BIG_SELECTS value
again, the max_join_size variable is
ignored.
If a query result is in the query cache, no result size check is performed, because the result has previously been computed and it does not burden the server to send it to the client.
This variable previously was named
sql_max_join_size.
| Option Sets Variable | Yes, max_length_for_sort_data | ||||||
| Variable Name | max_length_for_sort_data | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
The cutoff on the size of index values that determines which
filesort algorithm to use. See
Section 7.2.11, “ORDER BY Optimization”.
| Version Introduced | 5.0.21 | ||||||
| Command Line Format | --max_prepared_stmt_count=# | ||||||
| Config File Format | max_prepared_stmt_count | ||||||
| Option Sets Variable | Yes, max_prepared_stmt_count | ||||||
| Variable Name | max_prepared_stmt_count | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
This variable limits the total number of prepared statements in the server. It can be used in environments where there is the potential for denial-of-service attacks based on running the server out of memory by preparing huge numbers of statements. The default value is 16,382. The allowable range of values is from 0 to 1 million. If the value is set lower than the current number of prepared statements, existing statements are not affected and can be used, but no new statements can be prepared until the current number drops below the limit. This variable was added in MySQL 5.0.21.
| Option Sets Variable | Yes, max_relay_log_size | ||||||
| Variable Name | max_relay_log_size | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
If a write by a replication slave to its relay log causes
the current log file size to exceed the value of this
variable, the slave rotates the relay logs (closes the
current file and opens the next one). If
max_relay_log_size is 0, the server uses
max_binlog_size for both the binary log
and the relay log. If max_relay_log_size
is greater than 0, it constrains the size of the relay log,
which enables you to have different sizes for the two logs.
You must set max_relay_log_size to
between 4096 bytes and 1GB (inclusive), or to 0. The default
value is 0. See
Section 15.4.1, “Replication Implementation Details”.
| Option Sets Variable | Yes, max_seeks_for_key | ||||||
| Variable Name | max_seeks_for_key | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
Limit the assumed maximum number of seeks when looking up
rows based on a key. The MySQL optimizer assumes that no
more than this number of key seeks are required when
searching for matching rows in a table by scanning an index,
regardless of the actual cardinality of the index (see
Section 12.5.4.13, “SHOW INDEX Syntax”). By setting this to a low
value (say, 100), you can force MySQL to prefer indexes
instead of table scans.
| Option Sets Variable | Yes, max_sort_length | ||||||
| Variable Name | max_sort_length | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
The number of bytes to use when sorting
BLOB or TEXT values.
Only the first max_sort_length bytes of
each value are used; the rest are ignored.
| Version Introduced | 5.0.17 | ||||||
| Option Sets Variable | Yes, max_sp_recursion_depth | ||||||
| Variable Name | max_sp_recursion_depth | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
The number of times that any given stored procedure may be called recursively. The default value for this option is 0, which completely disallows recursion in stored procedures. The maximum value is 255.
Stored procedure recursion increases the demand on thread
stack space. If you increase the value of
max_sp_recursion_depth, it may be
necessary to increase thread stack size by increasing the
value of thread_stack at server startup.
This variable was added in MySQL 5.0.17.
| Option Sets Variable | Yes, max_tmp_tables | ||||||
| Variable Name | max_tmp_tables | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
The maximum number of temporary tables a client can keep open at the same time. (This option does not yet do anything.)
| Option Sets Variable | Yes, max_user_connections | ||||
| Variable Name | max_user_connections | ||||
| Variable Scope | Both | ||||
| Dynamic Variable | yes | ||||
| Value Set |
|
The maximum number of simultaneous connections allowed to any given MySQL account. A value of 0 means “no limit.”
Before MySQL 5.0.3, this variable has only global scope.
Beginning with MySQL 5.0.3, it also has a read-only session
scope. The session variable has the same value as the global
variable unless the current account has a non-zero
MAX_USER_CONNECTIONS resource limit. In
that case, the session value reflects the account limit.
| Option Sets Variable | Yes, max_write_lock_count | ||||||
| Variable Name | max_write_lock_count | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
After this many write locks, allow some pending read lock requests to be processed in between.
| Option Sets Variable | Yes, myisam_block_size | ||||||
| Variable Name | myisam_block_size | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
The block size to be used for MyISAM
index pages.
| Option Sets Variable | Yes, myisam_data_pointer_size | ||||||
| Variable Name | myisam_data_pointer_size | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
| ||||||
| Value Set |
|
The default pointer size in bytes, to be used by
CREATE TABLE for
MyISAM tables when no
MAX_ROWS option is specified. This
variable cannot be less than 2 or larger than 7. The default
value is 6 (4 before MySQL 5.0.6). See
Section B.1.2.12, “The table is full”.
myisam_max_extra_sort_file_size
(DEPRECATED)
This variable is not used. It was removed in MySQL 5.0.6.
| Option Sets Variable | Yes, myisam_max_sort_file_size | ||||
| Variable Name | myisam_max_sort_file_size | ||||
| Variable Scope | Global | ||||
| Dynamic Variable | yes | ||||
| Value Set |
|
The maximum size of the temporary file that MySQL is allowed
to use while re-creating a MyISAM index
(during REPAIR TABLE, ALTER
TABLE, or LOAD DATA INFILE). If
the file size would be larger than this value, the index is
created using the key cache instead, which is slower. The
value is given in bytes.
The default value is 2GB. If MyISAM index
files exceed this size and disk space is available,
increasing the value may help performance.
| Variable Name | myisam_recover_options |
| Variable Scope | Global |
| Dynamic Variable | no |
The value of the --myisam-recover option.
See Section 5.1.2, “Command Options”.
| Option Sets Variable | Yes, myisam_repair_threads | ||||||
| Variable Name | myisam_repair_threads | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
If this value is greater than 1, MyISAM
table indexes are created in parallel (each index in its own
thread) during the Repair by sorting
process. The default value is 1.
Multi-threaded repair is still beta-quality code.
| Option Sets Variable | Yes, myisam_sort_buffer_size | ||||||
| Variable Name | myisam_sort_buffer_size | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
The size of the buffer that is allocated when sorting
MyISAM indexes during a REPAIR
TABLE or when creating indexes with
CREATE INDEX or ALTER
TABLE.
The maximum allowable setting for
myisam_sort_buffer_size is 4GB.
| Version Introduced | 5.0.14 | ||||
| Option Sets Variable | Yes, myisam_stats_method | ||||
| Variable Name | myisam_stats_method | ||||
| Variable Scope | Both | ||||
| Dynamic Variable | yes | ||||
| Value Set |
| ||||
| Value Set |
|
How the server treats NULL values when
collecting statistics about the distribution of index values
for MyISAM tables. This variable has two
possible values, nulls_equal and
nulls_unequal. For
nulls_equal, all NULL
index values are considered equal and form a single value
group that has a size equal to the number of
NULL values. For
nulls_unequal, NULL
values are considered unequal, and each
NULL forms a distinct value group of size
1.
The method that is used for generating table statistics
influences how the optimizer chooses indexes for query
execution, as described in
Section 7.4.7, “MyISAM Index Statistics Collection”.
This variable was added in MySQL 5.0.14. For older versions,
the statistics collection method is equivalent to
nulls_equal.
| Variable Name | named_pipe |
| Variable Scope | Global |
| Dynamic Variable | no |
| Platform Specific | windows |
(Windows only.) Indicates whether the server supports connections over named pipes.
| Option Sets Variable | Yes, net_buffer_length | ||||||
| Variable Name | net_buffer_length | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
Each client thread is associated with a connection buffer
and result buffer. Both begin with a size given by
net_buffer_length but are dynamically
enlarged up to max_allowed_packet bytes
as needed. The result buffer shrinks to
net_buffer_length after each SQL
statement.
This variable should not normally be changed, but if you
have very little memory, you can set it to the expected
length of statements sent by clients. If statements exceed
this length, the connection buffer is automatically
enlarged. The maximum value to which
net_buffer_length can be set is 1MB.
| Option Sets Variable | Yes, net_read_timeout | ||||||
| Variable Name | net_read_timeout | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
The number of seconds to wait for more data from a
connection before aborting the read. This timeout applies
only to TCP/IP connections, not to connections made via Unix
socket files, named pipes, or shared memory. When the server
is reading from the client,
net_read_timeout is the timeout value
controlling when to abort. When the server is writing to the
client, net_write_timeout is the timeout
value controlling when to abort. See also
slave_net_timeout.
| Option Sets Variable | Yes, net_retry_count | ||||||
| Variable Name | net_retry_count | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
If a read on a communication port is interrupted, retry this many times before giving up. This value should be set quite high on FreeBSD because internal interrupts are sent to all threads.
| Option Sets Variable | Yes, net_write_timeout | ||||||
| Variable Name | net_write_timeout | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
The number of seconds to wait for a block to be written to a
connection before aborting the write. This timeout applies
only to TCP/IP connections, not to connections made via Unix
socket files, named pipes, or shared memory. See also
net_read_timeout.
| Option Sets Variable | Yes, new | ||||
| Variable Name | new | ||||
| Variable Scope | Both | ||||
| Dynamic Variable | yes | ||||
| Disabled By | skip-new | ||||
| Value Set |
|
This variable was used in MySQL 4.0 to turn on some 4.1
behaviors, and is retained for backward compatibility. In
MySQL 5.0, its value is always
OFF.
| Option Sets Variable | Yes, old_passwords | ||||
| Variable Name | old_passwords | ||||
| Variable Scope | Both | ||||
| Dynamic Variable | yes | ||||
| Value Set |
|
Whether the server should use pre-4.1-style passwords for
MySQL user accounts. See Section B.1.2.4, “Client does not support authentication protocol”.
This is not a variable, but it can be used when setting some
variables. It is described in Section 12.5.3, “SET Syntax”.
| Option Sets Variable | Yes, open_files_limit | ||||||
| Variable Name | open_files_limit | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | no | ||||||
| Value Set |
|
The number of files that the operating system allows
mysqld to open. This is the real value
allowed by the system and might be different from the value
you gave using the --open-files-limit
option to mysqld or
mysqld_safe. The value is 0 on systems
where MySQL can't change the number of open files.
| Version Introduced | 5.0.1 | ||||
| Option Sets Variable | Yes, optimizer_prune_level | ||||
| Variable Name | optimizer_prune_level | ||||
| Variable Scope | Both | ||||
| Dynamic Variable | yes | ||||
| Value Set |
|
Controls the heuristics applied during query optimization to prune less-promising partial plans from the optimizer search space. A value of 0 disables heuristics so that the optimizer performs an exhaustive search. A value of 1 causes the optimizer to prune plans based on the number of rows retrieved by intermediate plans. This variable was added in MySQL 5.0.1.
| Version Introduced | 5.0.1 | ||||
| Option Sets Variable | Yes, optimizer_search_depth | ||||
| Variable Name | optimizer_search_depth | ||||
| Variable Scope | Both | ||||
| Dynamic Variable | yes | ||||
| Value Set |
|
The maximum depth of search performed by the query optimizer. Values larger than the number of relations in a query result in better query plans, but take longer to generate an execution plan for a query. Values smaller than the number of relations in a query return an execution plan quicker, but the resulting plan may be far from being optimal. If set to 0, the system automatically picks a reasonable value. If set to the maximum number of tables used in a query plus 2, the optimizer switches to the algorithm used in MySQL 5.0.0 (and previous versions) for performing searches. This variable was added in MySQL 5.0.1.
| Option Sets Variable | Yes, pid_file | ||
| Variable Name | pid_file | ||
| Variable Scope | Global | ||
| Dynamic Variable | no | ||
| Value Set |
|
The pathname of the process ID (PID) file. This variable can
be set with the --pid-file option.
port
| Option Sets Variable | Yes, port | ||||
| Variable Name | port | ||||
| Variable Scope | Global | ||||
| Dynamic Variable | no | ||||
| Value Set |
|
The number of the port on which the server listens for
TCP/IP connections. This variable can be set with the
--port option.
| Option Sets Variable | Yes, preload_buffer_size | ||||||
| Variable Name | preload_buffer_size | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
The size of the buffer that is allocated when preloading indexes.
| Version Introduced | 5.0.21 | ||
| Variable Name | prepared_stmt_count | ||
| Variable Scope | Both | ||
| Dynamic Variable | no | ||
| Value Set |
|
The current number of prepared statements. (The maximum
number of statements is given by the
max_prepared_stmt_count system variable.)
This variable was added in MySQL 5.0.21. In MySQL 5.0.32, it
was converted to the global
Prepared_stmt_count status variable.
| Variable Name | protocol_version | ||
| Variable Scope | Global | ||
| Dynamic Variable | no | ||
| Value Set |
|
The version of the client/server protocol used by the MySQL server.
| Option Sets Variable | Yes, query_alloc_block_size | ||||||
| Variable Name | query_alloc_block_size | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
The allocation size of memory blocks that are allocated for objects created during statement parsing and execution. If you have problems with memory fragmentation, it might help to increase this a bit.
| Option Sets Variable | Yes, query_cache_limit | ||||||
| Variable Name | query_cache_limit | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
Don't cache results that are larger than this number of bytes. The default value is 1MB.
| Option Sets Variable | Yes, query_cache_min_res_unit | ||||||
| Variable Name | query_cache_min_res_unit | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
The minimum size (in bytes) for blocks allocated by the query cache. The default value is 4096 (4KB). Tuning information for this variable is given in Section 7.5.4.3, “Query Cache Configuration”.
| Option Sets Variable | Yes, query_cache_size | ||||
| Variable Name | query_cache_size | ||||
| Variable Scope | Global | ||||
| Dynamic Variable | yes | ||||
| Value Set |
|
The amount of memory allocated for caching query results.
The default value is 0, which disables the query cache. The
allowable values are multiples of 1024; other values are
rounded down to the nearest multiple. Note that
query_cache_size bytes of memory are
allocated even if query_cache_type is set
to 0. See Section 7.5.4.3, “Query Cache Configuration”, for
more information.
| Option Sets Variable | Yes, query_cache_type | ||||||
| Variable Name | query_cache_type | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
Set the query cache type. Setting the
GLOBAL value sets the type for all
clients that connect thereafter. Individual clients can set
the SESSION value to affect their own use
of the query cache. Possible values are shown in the
following table:
| Option | Description |
0 or OFF | Don't cache results in or retrieve results from the query cache. Note
that this does not deallocate the query cache
buffer. To do that, you should set
query_cache_size to 0. |
1 or ON | Cache all query results except for those that begin with SELECT
SQL_NO_CACHE. |
2 or DEMAND | Cache results only for queries that begin with SELECT
SQL_CACHE. |
This variable defaults to ON.
| Option Sets Variable | Yes, query_cache_wlock_invalidate | ||||
| Variable Name | query_cache_wlock_invalidate | ||||
| Variable Scope | Both | ||||
| Dynamic Variable | yes | ||||
| Value Set |
|
Normally, when one client acquires a
WRITE lock on a MyISAM
table, other clients are not blocked from issuing statements
that read from the table if the query results are present in
the query cache. Setting this variable to 1 causes
acquisition of a WRITE lock for a table
to invalidate any queries in the query cache that refer to
the table. This forces other clients that attempt to access
the table to wait while the lock is in effect.
| Option Sets Variable | Yes, query_prealloc_size | ||||||
| Variable Name | query_prealloc_size | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
The size of the persistent buffer used for statement parsing
and execution. This buffer is not freed between statements.
If you are running complex queries, a larger
query_prealloc_size value might be
helpful in improving performance, because it can reduce the
need for the server to perform memory allocation during
query execution operations.
| Option Sets Variable | Yes, range_alloc_block_size | ||||||
| Variable Name | range_alloc_block_size | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
| ||||||
| Value Set |
|
The size of blocks that are allocated when doing range optimization.
| Option Sets Variable | Yes, read_buffer_size | ||||||
| Variable Name | read_buffer_size | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
Each thread that does a sequential scan allocates a buffer of this size (in bytes) for each table it scans. If you do many sequential scans, you might want to increase this value, which defaults to 131072. The value of this variable should be a multiple of 4KB. If it is set to a value that is not a multiple of 4KB, its value will be rounded down to the nearest multiple of 4KB.
The maximum allowable setting for
read_buffer_size is 2GB.
read_buffer_size and
read_rnd_buffer_size are not specific to
any storage engine and apply in a general manner for
optimization. See Section 7.5.8, “How MySQL Uses Memory”, for example.
| Option Sets Variable | Yes, read_only | ||||
| Variable Name | read_only | ||||
| Variable Scope | Global | ||||
| Dynamic Variable | yes | ||||
| Value Set |
|
This variable is off by default. When it is enabled, the
server allows no updates except from users that have the
SUPER privilege or (on a slave server)
from updates performed by slave threads. On a slave server,
this can be useful to ensure that the slave accepts updates
only from its master server and not from clients. As of
MySQL 5.0.16, this variable does not apply to
TEMPORARY tables.
read_only exists only as a
GLOBAL variable, so changes to its value
require the SUPER privilege. Changes to
read_only on a master server are not
replicated to slave servers. The value can be set on a slave
server independent of the setting on the master.
| Option Sets Variable | Yes, read_rnd_buffer_size | ||||||
| Variable Name | read_rnd_buffer_size | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
When reading rows in sorted order following a key-sorting
operation, the rows are read through this buffer to avoid
disk seeks. See Section 7.2.11, “ORDER BY Optimization”.
Setting the variable to a large value can improve
ORDER BY performance by a lot. However,
this is a buffer allocated for each client, so you should
not set the global variable to a large value. Instead,
change the session variable only from within those clients
that need to run large queries.
The maximum allowable setting for
read_rnd_buffer_size is 2GB.
read_buffer_size and
read_rnd_buffer_size are not specific to
any storage engine and apply in a general manner for
optimization. See Section 7.5.8, “How MySQL Uses Memory”, for example.
| Option Sets Variable | Yes, relay_log_purge | ||||
| Variable Name | relay_log_purge | ||||
| Variable Scope | Global | ||||
| Dynamic Variable | yes | ||||
| Value Set |
|
Disables or enables automatic purging of relay log files as
soon as they are not needed any more. The default value is 1
(ON).
This variable is unused.
| Option Sets Variable | Yes, secure_auth | ||||
| Variable Name | secure_auth | ||||
| Variable Scope | Global | ||||
| Dynamic Variable | yes | ||||
| Value Set |
|
If the MySQL server has been started with the
--secure-auth option, it blocks connections
from all accounts that have passwords stored in the old
(pre-4.1) format. In that case, the value of this variable
is ON, otherwise it is
OFF.
You should enable this option if you want to prevent all use of passwords employing the old format (and hence insecure communication over the network).
Server startup fails with an error if this option is enabled
and the privilege tables are in pre-4.1 format. See
Section B.1.2.4, “Client does not support authentication protocol”.
| Version Introduced | 5.0.38 | ||
| Option Sets Variable | Yes, secure_file_priv | ||
| Variable Name | secure_file_priv | ||
| Variable Scope | Global | ||
| Dynamic Variable | no | ||
| Value Set |
|
By default, this variable is empty. If set to the name of a
directory, it limits the effect of the
LOAD_FILE() function and the
LOAD DATA and SELECT ... INTO
OUTFILE statements to work only with files in that
directory.
This variable was added in MySQL 5.0.38.
| Option Sets Variable | Yes, server_id | ||||
| Variable Name | server_id | ||||
| Variable Scope | Global | ||||
| Dynamic Variable | yes | ||||
| Value Set |
|
The server ID. This value is set by the
--server-id option. It is used for
replication to enable master and slave servers to identify
themselves uniquely.
| Variable Name | shared_memory |
| Variable Scope | Global |
| Dynamic Variable | no |
| Platform Specific | windows |
(Windows only.) Whether the server allows shared-memory connections.
| Variable Name | shared_memory_base_name |
| Variable Scope | Global |
| Dynamic Variable | no |
| Platform Specific | windows |
(Windows only.) The name of shared memory to use for
shared-memory connections. This is useful when running
multiple MySQL instances on a single physical machine. The
default name is MYSQL. The name is case
sensitive.
This is OFF if mysqld
uses external locking, ON if external
locking is disabled.
skip_networking
This is ON if the server allows only
local (non-TCP/IP) connections. On Unix, local connections
use a Unix socket file. On Windows, local connections use a
named pipe or shared memory. On NetWare, only TCP/IP
connections are supported, so do not set this variable to
ON. This variable can be set to
ON with the
--skip-networking option.
This prevents people from using the SHOW
DATABASES statement if they do not have the
SHOW DATABASES privilege. This can
improve security if you have concerns about users being able
to see databases belonging to other users. Its effect
depends on the SHOW DATABASES privilege:
If the variable value is ON, the
SHOW DATABASES statement is allowed only
to users who have the SHOW DATABASES
privilege, and the statement displays all database names. If
the value is OFF, SHOW
DATABASES is allowed to all users, but displays
the names of only those databases for which the user has the
SHOW DATABASES or other privilege.
| Option Sets Variable | Yes, slave_compressed_protocol | ||||
| Variable Name | slave_compressed_protocol | ||||
| Variable Scope | Global | ||||
| Dynamic Variable | yes | ||||
| Value Set |
|
Whether to use compression of the slave/master protocol if both the slave and the master support it.
| Option Sets Variable | Yes, slave_load_tmpdir | ||||
| Variable Name | slave_load_tmpdir | ||||
| Variable Scope | Global | ||||
| Dynamic Variable | no | ||||
| Value Set |
|
The name of the directory where the slave creates temporary
files for replicating LOAD DATA INFILE
statements.
| Option Sets Variable | Yes, slave_net_timeout | ||||||
| Variable Name | slave_net_timeout | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
The number of seconds to wait for more data from a master/slave connection before aborting the read. This timeout applies only to TCP/IP connections, not to connections made via Unix socket files, named pipes, or shared memory.
slave_skip_errors
| Option Sets Variable | Yes, slave_skip_errors |
| Variable Name | slave_skip_errors |
| Variable Scope | Global |
| Dynamic Variable | no |
Normally, replication stops when an error occurs on the slave. This gives you the opportunity to resolve the inconsistency in the data manually. This variable tells the slave SQL thread to continue replication when a statement returns any of the errors listed in the variable value.
| Version Introduced | 5.0.3 | ||||||
| Option Sets Variable | Yes, slave_transaction_retries | ||||||
| Variable Name | slave_transaction_retries | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
If a replication slave SQL thread fails to execute a
transaction because of an InnoDB deadlock
or exceeded InnoDB's
innodb_lock_wait_timeout or NDBCluster's
TransactionDeadlockDetectionTimeout or
TransactionInactiveTimeout, it
automatically retries
slave_transaction_retries times before
stopping with an error. The default prior to MySQL 4.0.3 is
0. You must explicitly set the value greater than 0 to
enable the “retry” behavior, which is probably
a good idea. In MySQL 5.0.3 or newer, the default is 10.
| Option Sets Variable | Yes, slow_launch_time | ||||
| Variable Name | slow_launch_time | ||||
| Variable Scope | Global | ||||
| Dynamic Variable | yes | ||||
| Value Set |
|
If creating a thread takes longer than this many seconds,
the server increments the
Slow_launch_threads status variable.
socket
| Option Sets Variable | Yes, socket | ||||||
| Variable Name | socket | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | no | ||||||
| Value Set |
| ||||||
| Value Set |
| ||||||
| Value Set |
| ||||||
| Value Set |
|
On Unix platforms, this variable is the name of the socket
file that is used for local client connections. The default
is /tmp/mysql.sock. (For some
distribution formats, the directory might be different, such
as /var/lib/mysql for RPMs.)
On Windows, this variable is the name of the named pipe that
is used for local client connections. The default value is
MySQL (not case sensitive).
| Option Sets Variable | Yes, sort_buffer_size | ||||||
| Variable Name | sort_buffer_size | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
Each thread that needs to do a sort allocates a buffer of
this size. Increase this value for faster ORDER
BY or GROUP BY operations. See
Section B.1.4.4, “Where MySQL Stores Temporary Files”.
The maximum allowable setting for
sort_buffer_size is 4GB.
| Option Sets Variable | Yes, sql_mode | ||||||
| Variable Name | sql_mode | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
The current server SQL mode, which can be set dynamically. See Section 5.1.6, “SQL Modes”.
| Variable Name | sql_slave_skip_counter | ||
| Variable Scope | Global | ||
| Dynamic Variable | yes | ||
| Value Set |
|
The number of events from the master that a slave server
should skip. See
Section 12.6.2.6, “SET GLOBAL SQL_SLAVE_SKIP_COUNTER Syntax”.
| Version Introduced | 5.0.23 | ||
| Option Sets Variable | Yes, ssl_ca | ||
| Variable Name | ssl_ca | ||
| Variable Scope | Global | ||
| Dynamic Variable | no | ||
| Value Set |
|
The path to a file with a list of trusted SSL CAs. This variable was added in MySQL 5.0.23.
| Version Introduced | 5.0.23 | ||
| Option Sets Variable | Yes, ssl_capath | ||
| Variable Name | ssl_capath | ||
| Variable Scope | Global | ||
| Dynamic Variable | no | ||
| Value Set |
|
The path to a directory that contains trusted SSL CA certificates in PEM format. This variable was added in MySQL 5.0.23.
| Version Introduced | 5.0.23 | ||
| Option Sets Variable | Yes, ssl_cert | ||
| Variable Name | ssl_cert | ||
| Variable Scope | Global | ||
| Dynamic Variable | no | ||
| Value Set |
|
The name of the SSL certificate file to use for establishing a secure connection. This variable was added in MySQL 5.0.23.
| Version Introduced | 5.0.23 | ||
| Option Sets Variable | Yes, ssl_cipher | ||
| Variable Name | ssl_cipher | ||
| Variable Scope | Global | ||
| Dynamic Variable | no | ||
| Value Set |
|
A list of allowable ciphers to use for SSL encryption. This variable was added in MySQL 5.0.23.
| Version Introduced | 5.0.23 | ||
| Option Sets Variable | Yes, ssl_key | ||
| Variable Name | ssl_key | ||
| Variable Scope | Global | ||
| Dynamic Variable | no | ||
| Value Set |
|
The name of the SSL key file to use for establishing a secure connection. This variable was added in MySQL 5.0.23.
| Variable Name | storage_engine | ||
| Variable Scope | Both | ||
| Dynamic Variable | yes | ||
| Value Set |
|
The default storage engine (table type). To set the storage
engine at server startup, use the
--default-storage-engine option. See
Section 5.1.2, “Command Options”.
| Version Introduced | 5.0.1 | ||||||
| Option Sets Variable | Yes, sync_binlog | ||||||
| Variable Name | sync_binlog | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
If the value of this variable is positive, the MySQL server
synchronizes its binary log to disk (using
fdatasync()) after every
sync_binlog writes to the binary log.
Note that there is one write to the binary log per statement
if autocommit is enabled, and one write per transaction
otherwise. The default value is 0, which does no
synchronizing to disk. A value of 1 is the safest choice,
because in the event of a crash you lose at most one
statement or transaction from the binary log. However, it is
also the slowest choice (unless the disk has a
battery-backed cache, which makes synchronization very
fast).
If the value of sync_binlog is 0 (the
default), no extra flushing is done. The server relies on
the operating system to flush the file contents occasionally
as for any other file.
| Option Sets Variable | Yes, sync_frm | ||||
| Variable Name | sync_frm | ||||
| Variable Scope | Global | ||||
| Dynamic Variable | yes | ||||
| Value Set |
|
If this variable is set to 1, when any non-temporary table
is created its .frm file is
synchronized to disk (using fdatasync()).
This is slower but safer in case of a crash. The default is
1.
| Variable Name | system_time_zone | ||
| Variable Scope | Global | ||
| Dynamic Variable | no | ||
| Value Set |
|
The server system time zone. When the server begins
executing, it inherits a time zone setting from the machine
defaults, possibly modified by the environment of the
account used for running the server or the startup script.
The value is used to set
system_time_zone. Typically the time zone
is specified by the TZ environment
variable. It also can be specified using the
--timezone option of the
mysqld_safe script.
The system_time_zone variable differs
from time_zone. Although they might have
the same value, the latter variable is used to initialize
the time zone for each client that connects. See
Section 9.6, “MySQL Server Time Zone Support”.
| Option Sets Variable | Yes, table_cache | ||||||
| Variable Name | table_cache | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | yes | ||||||
| Deprecated | 5.1.3, by table_open_cache | ||||||
| Value Set |
|
The number of open tables for all threads. Increasing this
value increases the number of file descriptors that
mysqld requires. You can check whether
you need to increase the table cache by checking the
Opened_tables status variable. See
Section 5.1.5, “Status Variables”. If the value of
Opened_tables is large and you don't do
FLUSH TABLES often (which just forces all
tables to be closed and reopened), then you should increase
the value of the table_cache variable.
For more information about the table cache, see
Section 7.4.8, “How MySQL Opens and Closes Tables”.
| Version Introduced | 5.0.10 | ||||||
| Option Sets Variable | Yes, table_lock_wait_timeout | ||||||
| Variable Name | table_lock_wait_timeout | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
Specifies a wait timeout for table-level locks, in seconds.
The default timeout is 50 seconds. The timeout is active
only if the connection has open cursors. This variable can
also be set globally at runtime (you need the
SUPER privilege to do this). It's
available as of MySQL 5.0.10.
| Variable Name | table_type | ||
| Variable Scope | Both | ||
| Dynamic Variable | yes | ||
| Deprecated | 5.2.5, by storage_engine | ||
| Value Set |
|
This variable is a synonym for
storage_engine. In MySQL
5.0, storage_engine is the
preferred name.
| Option Sets Variable | Yes, thread_cache_size | ||||||
| Variable Name | thread_cache_size | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
How many threads the server should cache for reuse. When a
client disconnects, the client's threads are put in the
cache if there are fewer than
thread_cache_size threads there. Requests
for threads are satisfied by reusing threads taken from the
cache if possible, and only when the cache is empty is a new
thread created. This variable can be increased to improve
performance if you have a lot of new connections. (Normally,
this doesn't provide a notable performance improvement if
you have a good thread implementation.) By examining the
difference between the Connections and
Threads_created status variables, you can
see how efficient the thread cache is. For details, see
Section 5.1.5, “Status Variables”.
| Option Sets Variable | Yes, thread_concurrency | ||||||
| Variable Name | thread_concurrency | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | no | ||||||
| Value Set |
|
On Solaris, mysqld calls
thr_setconcurrency() with this value.
This function enables applications to give the threads
system a hint about the desired number of threads that
should be run at the same time.
| Option Sets Variable | Yes, thread_stack | ||||||
| Variable Name | thread_stack | ||||||
| Variable Scope | Global | ||||||
| Dynamic Variable | no | ||||||
| Value Set |
|
The stack size for each thread. Many of the limits detected
by the crash-me test are dependent on
this value. See Section 7.1.4, “The MySQL Benchmark Suite”. The
default (192KB) is large enough for normal operation. If the
thread stack size is too small, it limits the complexity of
the SQL statements that the server can handle, the recursion
depth of stored procedures, and other memory-consuming
actions.
This variable is not implemented.
| Variable Name | time_zone | ||
| Variable Scope | Both | ||
| Dynamic Variable | yes | ||
| Value Set |
|
The current time zone. This variable is used to initialize
the time zone for each client that connects. By default, the
initial value of this is 'SYSTEM' (which
means, “use the value of
system_time_zone”). The value can
be specified explicitly at server startup with the
--default-time-zone option. See
Section 9.6, “MySQL Server Time Zone Support”.
| Version Introduced | 5.0.3 | ||||
| Option Sets Variable | Yes, timed_mutexes | ||||
| Variable Name | timed_mutexes | ||||
| Variable Scope | Global | ||||
| Dynamic Variable | yes | ||||
| Value Set |
|
This variable controls whether InnoDB
mutexes are timed. If this variable is set to 0 or
OFF (the default), mutex timing is
disabled. If the variable is set to 1 or
ON, mutex timing is enabled. With timing
enabled, the os_wait_times value in the
output from SHOW ENGINE INNODB MUTEX
indicates the amount of time (in ms) spent in operating
system waits. Otherwise, the value is 0. This variable was
added in MySQL 5.0.3.
| Option Sets Variable | Yes, tmp_table_size | ||||||
| Variable Name | tmp_table_size | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
The maximum size of internal in-memory temporary tables.
(The actual limit is determined as the smaller of
max_heap_table_size and
tmp_table_size.) If an in-memory
temporary table exceeds the limit, MySQL automatically
converts it to an on-disk MyISAM table.
Increase the value of tmp_table_size (and
max_heap_table_size if necessary) if you
do many advanced GROUP BY queries and you
have lots of memory. This variable does not apply to
user-created MEMORY tables.
tmpdir
| Option Sets Variable | Yes, tmpdir | ||
| Variable Name | tmpdir | ||
| Variable Scope | Global | ||
| Dynamic Variable | no | ||
| Value Set |
|
The directory used for temporary files and temporary tables.
This variable can be set to a list of several paths that are
used in round-robin fashion. Paths should be separated by
colon characters (“:”) on
Unix and semicolon characters
(“;”) on Windows, NetWare,
and OS/2.
The multiple-directory feature can be used to spread the
load between several physical disks. If the MySQL server is
acting as a replication slave, you should not set
tmpdir to point to a directory on a
memory-based filesystem or to a directory that is cleared
when the server host restarts. A replication slave needs
some of its temporary files to survive a machine restart so
that it can replicate temporary tables or LOAD DATA
INFILE operations. If files in the temporary file
directory are lost when the server restarts, replication
fails. However, if you are using MySQL 4.0.0 or later, you
can set the slave's temporary directory using the
slave_load_tmpdir variable. In that case,
the slave won't use the general tmpdir
value and you can set tmpdir to a
non-permanent location.
| Option Sets Variable | Yes, transaction_alloc_block_size | ||||||
| Variable Name | transaction_alloc_block_size | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
The amount in bytes by which to increase a per-transaction
memory pool which needs memory. See the description of
transaction_prealloc_size.
| Option Sets Variable | Yes, transaction_prealloc_size | ||||
| Variable Name | transaction_prealloc_size | ||||
| Variable Scope | Both | ||||
| Dynamic Variable | yes | ||||
| Value Set |
|
There is a per-transaction memory pool from which various
transaction-related allocations take memory. The initial
size of the pool in bytes is
transaction_prealloc_size. For every
allocation that cannot be satisfied from the pool because it
has insufficient memory available, the pool is increased by
transaction_alloc_block_size bytes. When
the transaction ends, the pool is truncated to
transaction_prealloc_size bytes.
By making transaction_prealloc_size
sufficiently large to contain all statements within a single
transaction, you can avoid many malloc()
calls.
| Variable Name | tx_isolation | ||||||
| Variable Scope | Both | ||||||
| Dynamic Variable | yes | ||||||
| Value Set |
|
The default transaction isolation level. Defaults to
REPEATABLE-READ.
This variable is set by the SET TRANSACTION
ISOLATION LEVEL statement. See
Section 12.4.6, “SET TRANSACTION Syntax”. If you set
tx_isolation directly to an isolation
level name that contains a space, the name should be
enclosed within quotes, with the space replaced by a dash.
For example:
SET tx_isolation = 'READ-COMMITTED';
| Version Introduced | 5.0.2 | ||||
| Option Sets Variable | Yes, updatable_views_with_limit | ||||
| Variable Name | updatable_views_with_limit | ||||
| Variable Scope | Both | ||||
| Dynamic Variable | yes | ||||
| Value Set |
|
This variable controls whether updates to a view can be made
when the view does not contain all columns of the primary
key defined in the underlying table, if the update statement
contains a LIMIT clause. (Such updates
often are generated by GUI tools.) An update is an
UPDATE or DELETE
statement. Primary key here means a PRIMARY
KEY, or a UNIQUE index in which
no column can contain NULL.
The variable can have two values:
1 or YES: Issue a
warning only (not an error message). This is the default
value.
0 or NO: Prohibit
the update.
This variable was added in MySQL 5.0.2.
version
| Variable Name | version |
| Variable Scope | Global |
| Dynamic Variable | no |
The version number for the server.
| Variable Name | version |
| Variable Scope | Global |
| Dynamic Variable | no |
Starting with MySQL 5.0.24, the version number will also
indicate whether the server is a standard release
(Community) or Enterprise release (for example,
5.0.28-enterprise-gpl-nt).
The BDB storage engine version.
The configure script has a
--with-comment option that allows a comment
to be specified when building MySQL. This variable contains
the value of that comment.
For precompiled binaries, this variable will hold the server
version and license information. Starting with MySQL 5.0.24,
version_comment will include the full
server type and license. For community users this will
appear as MySQL Community Edition - Standard
(GPL). For Enterprise users, the version might be
displayed as MySQL Enterprise Server
(GPL). The corresponding license for your MySQL
binary is shown in parentheses. For server compiled from
source, the default value will be the same as that for
Community releases.
The type of machine or architecture on which MySQL was built.
| Variable Name | version_compile_os | ||
| Variable Scope | Global | ||
| Dynamic Variable | no | ||
| Value Set |
|
The type of operating system on which MySQL was built.
| Option Sets Variable | Yes, wait_timeout | ||||
| Variable Name | wait_timeout | ||||
| Variable Scope | Both | ||||
| Dynamic Variable | yes | ||||
| Value Set |
|
The number of seconds the server waits for activity on a non-interactive connection before closing it. This timeout applies only to TCP/IP and Unix socket file connections, not to connections made via named pipes, or shared memory.
On thread startup, the session
wait_timeout value is initialized from
the global wait_timeout value or from the
global interactive_timeout value,
depending on the type of client (as defined by the
CLIENT_INTERACTIVE connect option to
mysql_real_connect()). See
also interactive_timeout.
MySQL Enterprise. Expert use of server system variables is part of the service offered by the MySQL Enterprise Monitor. To subscribe see http://www.mysql.com/products/enterprise/advisors.html.
The MySQL server maintains many system variables that indicate
how it is configured. Section 5.1.3, “System Variables”,
describes the meaning of these variables. 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 while the server is
running by means of the SET statement, which
enables you to modify operation of the server without having to
stop and restart it. You can refer to system variable values in
expressions.
The server maintains two kinds of system variables. Global variables affect the overall operation of the server. Session variables affect its operation for individual client connections. A given system variable can have both a global and a session value. Global and session system variables are related as follows:
When the server starts, it initializes all global variables to their default values. These defaults can be changed by options specified on the command line or in an option file. (See Section 4.2.2, “Specifying Program Options”.)
The server also maintains a set of session variables for
each client that connects. The client's session variables
are initialized at connect time using the current values of
the corresponding global variables. For example, the
client's SQL mode is controlled by the session
sql_mode value, which is initialized when
the client connects to the value of the global
sql_mode value.
System variable values can be set globally at server startup by
using options on the command line or in an option file. When you
use a startup option to set a variable that takes a numeric
value, the value can be given with a suffix of
K, M, or
G (either uppercase or lowercase) to indicate
a multiplier of 1024, 10242 or
10243; that is, units of kilobytes,
megabytes, or gigabytes, respectively. Thus, the following
command starts the server with a query cache size of 16
megabytes and a maximum packet size of one gigabyte:
mysqld --query_cache_size=16M --max_allowed_packet=1G
Within an option file, those variables are set like this:
[mysqld] query_cache_size=16M max_allowed_packet=1G
The lettercase of suffix letters does not matter;
16M and 16m are
equivalent, as are 1G and
1g.
If you want to restrict the maximum value to which a system
variable can be set at runtime with the SET
statement, you can specify this maximum by using an option of
the form
--maximum-
at server startup. For example, to prevent the value of
var_name=valuequery_cache_size from being increased to more
than 32MB at runtime, use the option
--maximum-query_cache_size=32M.
Many system variables are dynamic and can be changed while the
server runs by using the SET statement. For a
list, see Section 5.1.4.2, “Dynamic System Variables”. To change
a system variable with SET, refer to it as
var_name, optionally preceded by a
modifier:
To indicate explicitly that a variable is a global variable,
precede its name by GLOBAL or
@@global.. The SUPER
privilege is required to set global variables.
To indicate explicitly that a variable is a session
variable, precede its name by SESSION,
@@session., or @@.
Setting a session variable requires no special privilege,
but a client can change only its own session variables, not
those of any other client.
LOCAL and @@local. are
synonyms for SESSION and
@@session..
If no modifier is present, SET changes
the session variable.
A SET statement can contain multiple variable
assignments, separated by commas. If you set several system
variables, the most recent GLOBAL or
SESSION modifier in the statement is used for
following variables that have no modifier specified.
Examples:
SET sort_buffer_size=10000; SET @@local.sort_buffer_size=10000; SET GLOBAL sort_buffer_size=1000000, SESSION sort_buffer_size=1000000; SET @@sort_buffer_size=1000000; SET @@global.sort_buffer_size=1000000, @@local.sort_buffer_size=1000000;
When you assign a value to a system variable with
SET, you cannot use suffix letters in the
value (as can be done with startup options). However, the value
can take the form of an expression:
SET sort_buffer_size = 10 * 1024 * 1024;
The @@
syntax for system variables is supported for compatibility with
some other database systems.
var_name
If you change a session system variable, the value remains in effect until your session ends or until you change the variable to a different value. The change is not visible to other clients.
If you change a global system variable, the value is remembered
and used for new connections until the server restarts. (To make
a global system variable setting permanent, you should set it in
an option file.) The change is visible to any client that
accesses that global variable. However, the change affects the
corresponding session variable only for clients that connect
after the change. The global variable change does not affect the
session variable for any client that is currently connected (not
even that of the client that issues the SET
GLOBAL statement).
To prevent incorrect usage, MySQL produces an error if you use
SET GLOBAL with a variable that can only be
used with SET SESSION or if you do not
specify GLOBAL (or
@@global.) when setting a global variable.
To set a SESSION variable to the
GLOBAL value or a GLOBAL
value to the compiled-in MySQL default value, use the
DEFAULT keyword. For example, the following
two statements are identical in setting the session value of
max_join_size to the global value:
SET max_join_size=DEFAULT; SET @@session.max_join_size=@@global.max_join_size;
Not all system variables can be set to
DEFAULT. In such cases, use of
DEFAULT results in an error.
You can refer to the values of specific global or sesson system
variables in expressions by using one of the
@@-modifiers. For example, you can retrieve
values in a SELECT statement like this:
SELECT @@global.sql_mode, @@session.sql_mode, @@sql_mode;
When you refer to a system variable in an expression as
@@ (that
is, when you do not specify var_name@@global. or
@@session.), MySQL returns the session value
if it exists and the global value otherwise. (This differs from
SET @@, which always refers
to the session value.)
var_name =
value
Some system variables can be enabled with the
SET statement by setting them to
ON or 1, or disabled by
setting them to OFF or
0. However, to set such a variable on the
command line or in an option file, you must set it to
1 or 0; setting it to
ON or OFF will not work.
For example, on the command line,
--delay_key_write=1 works but
--delay_key_write=ON does not.
To display system variable names and values, use the
SHOW VARIABLES statement:
mysql> SHOW VARIABLES;
+--------+--------------------------------------------------------------+
| Variable_name | Value |
+--------+--------------------------------------------------------------+
| auto_increment_increment | 1 |
| auto_increment_offset | 1 |
| automatic_sp_privileges | ON |
| back_log | 50 |
| basedir | / |
| bdb_cache_size | 8388600 |
| bdb_home | /var/lib/mysql/ |
| bdb_log_buffer_size | 32768 |
| bdb_logdir | |
| bdb_max_lock | 10000 |
| bdb_shared_data | OFF |
| bdb_tmpdir | /tmp/ |
| binlog_cache_size | 32768 |
| bulk_insert_buffer_size | 8388608 |
| character_set_client | latin1 |
| character_set_connection | latin1 |
| character_set_database | latin1 |
| character_set_results | latin1 |
| character_set_server | latin1 |
| character_set_system | utf8 |
| character_sets_dir | /usr/share/mysql/charsets/ |
| collation_connection | latin1_swedish_ci |
| collation_database | latin1_swedish_ci |
| collation_server | latin1_swedish_ci |
...
| innodb_additional_mem_pool_size | 1048576 |
| innodb_autoextend_increment | 8 |
| innodb_buffer_pool_awe_mem_mb | 0 |
| innodb_buffer_pool_size | 8388608 |
| innodb_checksums | ON |
| innodb_commit_concurrency | 0 |
| innodb_concurrency_tickets | 500 |
| innodb_data_file_path | ibdata1:10M:autoextend |
| innodb_data_home_dir | |
...
| version | 5.0.19 |
| version_comment | MySQL Community Edition - (GPL) |
| version_compile_machine | i686 |
| version_compile_os | pc-linux-gnu |
| wait_timeout | 28800 |
+--------+--------------------------------------------------------------+
With a LIKE clause, the
statement displays only those variables that match the pattern.
To obtain a specific variable name, use a
LIKE clause as shown:
SHOW VARIABLES LIKE 'max_join_size'; SHOW SESSION VARIABLES LIKE 'max_join_size';
To get a list of variables whose name match a pattern, use the
“%” wildcard character in a
LIKE clause:
SHOW VARIABLES LIKE '%size%'; SHOW GLOBAL VARIABLES LIKE '%size%';
Wildcard characters can be used in any position within the
pattern to be matched. Strictly speaking, because
“_” is a wildcard that matches
any single character, you should escape it as
“\_” to match it literally. In
practice, this is rarely necessary.
For SHOW VARIABLES, if you specify neither
GLOBAL nor SESSION, MySQL
returns SESSION values.
The reason for requiring the GLOBAL keyword
when setting GLOBAL-only variables but not
when retrieving them is to prevent problems in the future. If we
were to remove a SESSION variable that has
the same name as a GLOBAL variable, a client
with the SUPER privilege might accidentally
change the GLOBAL variable rather than just
the SESSION variable for its own connection.
If we add a SESSION variable with the same
name as a GLOBAL variable, a client that
intends to change the GLOBAL variable might
find only its own SESSION variable changed.
A structured variable differs from a regular system variable in two respects:
Its value is a structure with components that specify server parameters considered to be closely related.
There might be several instances of a given type of structured variable. Each one has a different name and refers to a different resource maintained by the server.
MySQL 5.0 supports one structured variable type, which specifies parameters governing the operation of key caches. A key cache structured variable has these components:
key_buffer_size
key_cache_block_size
key_cache_division_limit
key_cache_age_threshold
This section describes the syntax for referring to structured
variables. Key cache variables are used for syntax examples,
but specific details about how key caches operate are found
elsewhere, in Section 7.4.6, “The MyISAM Key Cache”.
To refer to a component of a structured variable instance, you
can use a compound name in
instance_name.component_name
format. Examples:
hot_cache.key_buffer_size hot_cache.key_cache_block_size cold_cache.key_cache_block_size
For each structured system variable, an instance with the name
of default is always predefined. If you
refer to a component of a structured variable without any
instance name, the default instance is
used. Thus, default.key_buffer_size and
key_buffer_size both refer to the same
system variable.
Structured variable instances and components follow these naming rules:
For a given type of structured variable, each instance
must have a name that is unique
within variables of that type.
However, instance names need not be unique
across structured variable types. For
example, each structured variable has an instance named
default, so default
is not unique across variable types.
The names of the components of each structured variable type must be unique across all system variable names. If this were not true (that is, if two different types of structured variables could share component member names), it would not be clear which default structured variable to use for references to member names that are not qualified by an instance name.
If a structured variable instance name is not legal as an
unquoted identifier, refer to it as a quoted identifier
using backticks. For example, hot-cache
is not legal, but `hot-cache` is.
global, session, and
local are not legal instance names.
This avoids a conflict with notation such as
@@global.
for referring to non-structured system variables.
var_name
Currently, the first two rules have no possibility of being violated because the only structured variable type is the one for key caches. These rules will assume greater significance if some other type of structured variable is created in the future.
With one exception, you can refer to structured variable components using compound names in any context where simple variable names can occur. For example, you can assign a value to a structured variable using a command-line option:
shell> mysqld --hot_cache.key_buffer_size=64K
In an option file, use this syntax:
[mysqld] hot_cache.key_buffer_size=64K
If you start the server with this option, it creates a key
cache named hot_cache with a size of 64KB
in addition to the default key cache that has a default size
of 8MB.
Suppose that you start the server as follows:
shell>mysqld --key_buffer_size=256K \--extra_cache.key_buffer_size=128K \--extra_cache.key_cache_block_size=2048
In this case, the server sets the size of the default key
cache to 256KB. (You could also have written
--default.key_buffer_size=256K.) In addition,
the server creates a second key cache named
extra_cache that has a size of 128KB, with
the size of block buffers for caching table index blocks set
to 2048 bytes.
The following example starts the server with three different key caches having sizes in a 3:1:1 ratio:
shell>mysqld --key_buffer_size=6M \--hot_cache.key_buffer_size=2M \--cold_cache.key_buffer_size=2M
Structured variable values may be set and retrieved at runtime
as well. For example, to set a key cache named
hot_cache to a size of 10MB, use either of
these statements:
mysql>SET GLOBAL hot_cache.key_buffer_size = 10*1024*1024;mysql>SET @@global.hot_cache.key_buffer_size = 10*1024*1024;
To retrieve the cache size, do this:
mysql> SELECT @@global.hot_cache.key_buffer_size;
However, the following statement does not work. The variable
is not interpreted as a compound name, but as a simple string
for a LIKE pattern-matching
operation:
mysql> SHOW GLOBAL VARIABLES LIKE 'hot_cache.key_buffer_size';
This is the exception to being able to use structured variable names anywhere a simple variable name may occur.
Many server system variables are dynamic and can be set at
runtime using SET GLOBAL or SET
SESSION. You can also obtain their values using
SELECT. See
Section 5.1.4, “Using System Variables”.
The following table shows the full list of all dynamic system
variables. The last column indicates for each variable whether
GLOBAL or SESSION (or
both) apply. The table also lists session options that can be
set with the SET statement.
Section 12.5.3, “SET Syntax”, discusses these options.
Variables that have a type of “string” take a
string value. Variables that have a type of
“numeric” take a numeric value. Variables that
have a type of “boolean” can be set to 0, 1,
ON or OFF. (If you set
them on the command line or in an option file, use the numeric
values.) Variables that are marked as
“enumeration” normally should be set to one of
the available values for the variable, but can also be set to
the number that corresponds to the desired enumeration value.
For enumerated system variables, the first enumeration value
corresponds to 0. This differs from ENUM
columns, for which the first enumeration value corresponds to
1.
| Variable Name | Variable Type | Variable Scope |
|---|---|---|
autocommit | boolean | SESSION |
auto_increment_increment | numeric | GLOBAL | SESSION |
auto_increment_offset | numeric | GLOBAL | SESSION |
automatic_sp_privileges | boolean | GLOBAL |
big_tables | boolean | SESSION |
binlog_cache_size | numeric | GLOBAL |
bulk_insert_buffer_size | numeric | GLOBAL | SESSION |
character_set_client | string | GLOBAL | SESSION |
character_set_connection | string | GLOBAL | SESSION |
character_set_database | string | GLOBAL | SESSION |
character_set_filesystem | string | GLOBAL | SESSION |
character_set_results | string | GLOBAL | SESSION |
character_set_server | string | GLOBAL | SESSION |
collation_connection | string | GLOBAL | SESSION |
collation_database | string | GLOBAL | SESSION |
collation_server | string | GLOBAL | SESSION |
completion_type | numeric | GLOBAL | SESSION |
concurrent_insert | boolean | GLOBAL |
connect_timeout | numeric | GLOBAL |
date_format | string | GLOBAL | SESSION |
datetime_format | string | GLOBAL | SESSION |
default_week_format | numeric | GLOBAL | SESSION |
delayed_insert_limit | numeric | GLOBAL |
delayed_insert_timeout | numeric | GLOBAL |
delayed_queue_size | numeric | GLOBAL |
delay_key_write | enumeration | GLOBAL |
div_precision_increment | numeric | GLOBAL | SESSION |
engine_condition_pushdown | boolean | GLOBAL | SESSION |
expire_logs_days | numeric | GLOBAL |
flush | boolean | GLOBAL |
flush_time | numeric | GLOBAL |
foreign_key_checks | boolean | SESSION |
ft_boolean_syntax | string | GLOBAL |
group_concat_max_len | numeric | GLOBAL | SESSION |
identity | numeric | SESSION |
init_connect | string | GLOBAL |
init_slave | string | GLOBAL |
innodb_autoextend_increment | numeric | GLOBAL |
innodb_commit_concurrency | numeric | GLOBAL |
innodb_concurrency_tickets | numeric | GLOBAL |
innodb_fast_shutdown | boolean | GLOBAL |
innodb_flush_log_at_trx_commit | numeric | GLOBAL |
innodb_max_dirty_pages_pct | numeric | GLOBAL |
innodb_max_purge_lag | numeric | GLOBAL |
innodb_support_xa | boolean | GLOBAL | SESSION |
innodb_sync_spin_loops | numeric | GLOBAL |
innodb_table_locks | boolean | GLOBAL | SESSION |
innodb_thread_concurrency | numeric | GLOBAL |
innodb_thread_sleep_delay | numeric | GLOBAL |
insert_id | numeric | SESSION |
interactive_timeout | numeric | GLOBAL | SESSION |
join_buffer_size | numeric | GLOBAL | SESSION |
keep_files_on_create | boolean | GLOBAL | SESSION |
key_buffer_size | numeric | GLOBAL |
key_cache_age_threshold | numeric | GLOBAL |
key_cache_block_size | numeric | GLOBAL |
key_cache_division_limit | numeric | GLOBAL |
last_insert_id | numeric | SESSION |
lc_time_names | string | GLOBAL | SESSION |
local_infile | GLOBAL | |
log | string | GLOBAL |
log_bin_trust_function_creators | boolean | GLOBAL |
log_bin_trust_routine_creators | boolean | GLOBAL |
log_slow_queries | boolean | GLOBAL |
log-warnings | numeric | GLOBAL | SESSION |
long_query_time | numeric | GLOBAL | SESSION |
low_priority_updates | boolean | GLOBAL | SESSION |
max_allowed_packet | numeric | GLOBAL | SESSION |
max_binlog_cache_size | numeric | GLOBAL |
max_binlog_size | numeric | GLOBAL |
max_connect_errors | numeric | GLOBAL |
max_connections | numeric | GLOBAL |
max_delayed_threads | numeric | GLOBAL | SESSION |
max_error_count | numeric | GLOBAL | SESSION |
max_heap_table_size | numeric | GLOBAL | SESSION |
max_insert_delayed_threads | numeric | GLOBAL | SESSION |
max_join_size | numeric | GLOBAL | SESSION |
max_length_for_sort_data | numeric | GLOBAL | SESSION |
max_prepared_stmt_count | numeric | GLOBAL |
max_relay_log_size | numeric | GLOBAL |
max_seeks_for_key | numeric | GLOBAL | SESSION |
max_sort_length | numeric | GLOBAL | SESSION |
max_sp_recursion_depth | numeric | GLOBAL | SESSION |
max_tmp_tables | numeric | GLOBAL | SESSION |
max_user_connections | numeric | GLOBAL | SESSION |
max_write_lock_count | numeric | GLOBAL |
multi_range_count | numeric | GLOBAL | SESSION |
myisam_block_size | numeric | GLOBAL | SESSION |
myisam_data_pointer_size | numeric | GLOBAL |
myisam_max_sort_file_size | numeric | GLOBAL |
myisam_repair_threads | numeric | GLOBAL | SESSION |
myisam_sort_buffer_size | numeric | GLOBAL | SESSION |
myisam_stats_method | enumeration | GLOBAL | SESSION |
ndb_autoincrement_prefetch_sz | numeric | GLOBAL | SESSION |
ndb_cache_check_time | numeric | GLOBAL |
ndbcluster | boolean | GLOBAL | SESSION |
ndb_force_send | boolean | GLOBAL | SESSION |
ndb_use_exact_count | boolean | GLOBAL | SESSION |
net_buffer_length | numeric | GLOBAL | SESSION |
net_read_timeout | numeric | GLOBAL | SESSION |
net_retry_count | numeric | GLOBAL | SESSION |
net_write_timeout | numeric | GLOBAL | SESSION |
new | boolean | GLOBAL | SESSION |
old_passwords | boolean | GLOBAL | SESSION |
optimizer_prune_level | boolean | GLOBAL | SESSION |
optimizer_search_depth | numeric | GLOBAL | SESSION |
preload_buffer_size | numeric | GLOBAL | SESSION |
profiling | boolean | SESSION |
profiling_history_size | numeric | GLOBAL | SESSION |
query_alloc_block_size | numeric | GLOBAL | SESSION |
query_cache_limit | numeric | GLOBAL |
query_cache_min_res_unit | numeric | GLOBAL |
query_cache_size | numeric | GLOBAL |
query_cache_type | enumeration | GLOBAL | SESSION |
query_cache_wlock_invalidate | boolean | GLOBAL | SESSION |
query_prealloc_size | numeric | GLOBAL | SESSION |
range_alloc_block_size | numeric | GLOBAL | SESSION |
read_buffer_size | numeric | GLOBAL | SESSION |
read_only | numeric | GLOBAL |
read_rnd_buffer_size | numeric | GLOBAL | SESSION |
relay_log_purge | boolean | GLOBAL |
rpl_recovery_rank | numeric | GLOBAL |
secure_auth | boolean | GLOBAL |
server_id | numeric | GLOBAL |
slave_compressed_protocol | boolean | GLOBAL |
slave_net_timeout | numeric | GLOBAL |
slave_transaction_retries | numeric | GLOBAL |
slow_launch_time | numeric | GLOBAL |
sort_buffer_size | numeric | GLOBAL | SESSION |
sql_big_selects | boolean | SESSION |
sql_big_tables | boolean | SESSION |
sql_buffer_result | boolean | SESSION |
sql_log_bin | boolean | SESSION |
sql_log_off | boolean | SESSION |
sql_log_update | boolean | SESSION |
sql_low_priority_updates | boolean | GLOBAL | SESSION |
sql_max_join_size | numeric | GLOBAL | SESSION |
sql_mode | enumeration | GLOBAL | SESSION |
sql_notes | boolean | SESSION |
sql_quote_show_create | boolean | SESSION |
sql_safe_updates | boolean | SESSION |
sql_select_limit | numeric | GLOBAL | SESSION |
sql_slave_skip_counter | numeric | GLOBAL |
sql_warnings | boolean | SESSION |
storage_engine | enumeration | GLOBAL | SESSION |
sync_binlog | numeric | GLOBAL |
sync_frm | boolean | GLOBAL |
table_cache | numeric | GLOBAL |
table_lock_wait_timeout | numeric | GLOBAL |
table_open_cache | numeric | GLOBAL |
table_type | enumeration | GLOBAL | SESSION |
thread_cache_size | numeric | GLOBAL |
timed_mutexes | boolean | GLOBAL |
time_format | string | GLOBAL | SESSION |
timestamp | string | SESSION |
time_zone | string | GLOBAL | SESSION |
tmp_table_size | numeric | GLOBAL | SESSION |
transaction_alloc_block_size | numeric | GLOBAL | SESSION |
transaction_prealloc_size | numeric | GLOBAL | SESSION |
tx_isolation | enumeration | GLOBAL | SESSION |
unique_checks | boolean | SESSION |
updatable_views_with_limit | boolean | GLOBAL | SESSION |
wait_timeout | numeric | GLOBAL | SESSION |
MySQL Enterprise. Improper configuration of system variables can adversely affect performance and security. The MySQL Enterprise Monitor continually monitors system variables and provides expert advice about appropriate settings. For more information see http://www.mysql.com/products/enterprise/advisors.html.
The server maintains many status variables that provide
information about its operation. You can view these variables
and their values by using the SHOW [GLOBAL]
STATUS statement. The optional
GLOBAL keyword aggregates the values over all
connections.
mysql> SHOW GLOBAL STATUS;
+-----------------------------------+------------+
| Variable_name | Value |
+-----------------------------------+------------+
| Aborted_clients | 0 |
| Aborted_connects | 0 |
| Bytes_received | 155372598 |
| Bytes_sent | 1176560426 |
...
| Connections | 30023 |
| Created_tmp_disk_tables | 0 |
| Created_tmp_files | 3 |
| Created_tmp_tables | 2 |
...
| Threads_created | 217 |
| Threads_running | 88 |
| Uptime | 1389872 |
+-----------------------------------+------------+
The following table lists all available server status variables:
| Variable Name | Variable Type | Variable Scope |
|---|---|---|
Aborted_clients | numeric | GLOBAL | SESSION |
Aborted_connects | numeric | GLOBAL | SESSION |
Binlog_cache_disk_use | numeric | GLOBAL | SESSION |
Binlog_cache_use | numeric | GLOBAL | SESSION |
Bytes_received | numeric | GLOBAL | SESSION |
Bytes_sent | numeric | GLOBAL | SESSION |
Com_admin_commands | numeric | GLOBAL | SESSION |
Com_alter_db | numeric | GLOBAL | SESSION |
Com_alter_event | numeric | GLOBAL | SESSION |
Com_alter_table | numeric | GLOBAL | SESSION |
Com_analyze | numeric | GLOBAL | SESSION |
Com_backup_table | numeric | GLOBAL | SESSION |
Com_begin | numeric | GLOBAL | SESSION |
Com_call_procedure | numeric | GLOBAL | SESSION |
Com_change_db | numeric | GLOBAL | SESSION |
Com_change_master | numeric | GLOBAL | SESSION |
Com_check | numeric | GLOBAL | SESSION |
Com_checksum | numeric | GLOBAL | SESSION |
Com_commit | numeric | GLOBAL | SESSION |
Com_create_db | numeric | GLOBAL | SESSION |
Com_create_event | numeric | GLOBAL | SESSION |
Com_create_function | numeric | GLOBAL | SESSION |
Com_create_index | numeric | GLOBAL | SESSION |
Com_create_table | numeric | GLOBAL | SESSION |
Com_create_user | numeric | GLOBAL | SESSION |
Com_dealloc_sql | numeric | GLOBAL | SESSION |
Com_delete | numeric | GLOBAL | SESSION |
Com_delete_multi | numeric | GLOBAL | SESSION |
Com_do | numeric | GLOBAL | SESSION |
Com_drop_db | numeric | GLOBAL | SESSION |
Com_drop_event | numeric | GLOBAL | SESSION |
Com_drop_function | numeric | GLOBAL | SESSION |
Com_drop_index | numeric | GLOBAL | SESSION |
Com_drop_table | numeric | GLOBAL | SESSION |
Com_drop_user | numeric | GLOBAL | SESSION |
Com_execute_sql | numeric | GLOBAL | SESSION |
Com_flush | numeric | GLOBAL | SESSION |
Com_grant | numeric | GLOBAL | SESSION |
Com_ha_close | numeric | GLOBAL | SESSION |
Com_ha_open | numeric | GLOBAL | SESSION |
Com_ha_read | numeric | GLOBAL | SESSION |
Com_help | numeric | GLOBAL | SESSION |
Com_insert | numeric | GLOBAL | SESSION |
Com_insert_select | numeric | GLOBAL | SESSION |
Com_kill | numeric | GLOBAL | SESSION |
Com_load | numeric | GLOBAL | SESSION |
Com_lock_tables | numeric | GLOBAL | SESSION |
Com_optimize | numeric | GLOBAL | SESSION |
Com_preload_keys | numeric | GLOBAL | SESSION |
Com_prepare_sql | numeric | GLOBAL | SESSION |
Compression | numeric | GLOBAL | SESSION |
Com_purge | numeric | GLOBAL | SESSION |
Com_purge_before_date | numeric | GLOBAL | SESSION |
Com_rename_table | numeric | GLOBAL | SESSION |
Com_repair | numeric | GLOBAL | SESSION |
Com_replace | numeric | GLOBAL | SESSION |
Com_replace_select | numeric | GLOBAL | SESSION |
Com_reset | numeric | GLOBAL | SESSION |
Com_restore_table | numeric | GLOBAL | SESSION |
Com_revoke | numeric | GLOBAL | SESSION |
Com_revoke_all | numeric | GLOBAL | SESSION |
Com_rollback | numeric | GLOBAL | SESSION |
Com_savepoint | numeric | GLOBAL | SESSION |
Com_select | numeric | GLOBAL | SESSION |
Com_set_option | numeric | GLOBAL | SESSION |
Com_show_binlog_events | numeric | GLOBAL | SESSION |
Com_show_binlogs | numeric | GLOBAL | SESSION |
Com_show_charsets | numeric | GLOBAL | SESSION |
Com_show_collations | numeric | GLOBAL | SESSION |
Com_show_column_types | numeric | GLOBAL | SESSION |
Com_show_create_db | numeric | GLOBAL | SESSION |
Com_show_create_event | numeric | GLOBAL | SESSION |
Com_show_create_table | numeric | GLOBAL | SESSION |
Com_show_databases | numeric | GLOBAL | SESSION |
Com_show_engine_logs | numeric | GLOBAL | SESSION |
Com_show_engine_mutex | numeric | GLOBAL | SESSION |
Com_show_engine_status | numeric | GLOBAL | SESSION |
Com_show_errors | numeric | GLOBAL | SESSION |
Com_show_events | numeric | GLOBAL | SESSION |
Com_show_fields | numeric | GLOBAL | SESSION |
Com_show_grants | numeric | GLOBAL | SESSION |
Com_show_innodb_status | numeric | GLOBAL | SESSION |
Com_show_keys | numeric | GLOBAL | SESSION |
Com_show_logs | numeric | GLOBAL | SESSION |
Com_show_master_status | numeric | GLOBAL | SESSION |
Com_show_ndb_status | numeric | GLOBAL | SESSION |
Com_show_new_master | numeric | GLOBAL | SESSION |
Com_show_open_tables | numeric | GLOBAL | SESSION |
Com_show_plugins | numeric | GLOBAL | SESSION |
Com_show_privileges | numeric | GLOBAL | SESSION |
Com_show_processlist | numeric | GLOBAL | SESSION |
Com_show_slave_hosts | numeric | GLOBAL | SESSION |
Com_show_slave_status | numeric | GLOBAL | SESSION |
Com_show_status | numeric | GLOBAL | SESSION |
Com_show_storage_engines | numeric | GLOBAL | SESSION |
Com_show_tables | numeric | GLOBAL | SESSION |
Com_show_triggers | numeric | GLOBAL | SESSION |
Com_show_variables | numeric | GLOBAL | SESSION |
Com_show_warnings | numeric | GLOBAL | SESSION |
Com_slave_start | numeric | GLOBAL | SESSION |
Com_slave_stop | numeric | GLOBAL | SESSION |
Com_stmt_close | numeric | GLOBAL | SESSION |
Com_stmt_execute | numeric | GLOBAL | SESSION |
Com_stmt_fetch | numeric | GLOBAL | SESSION |
Com_stmt_prepare | numeric | GLOBAL | SESSION |
Com_stmt_reset | numeric | GLOBAL | SESSION |
Com_stmt_send_long_data | numeric | GLOBAL | SESSION |
Com_truncate | numeric | GLOBAL | SESSION |
Com_unlock_tables | numeric | GLOBAL | SESSION |
Com_update | numeric | GLOBAL | SESSION |
Com_update_multi | numeric | GLOBAL | SESSION |
Com_xa_commit | numeric | GLOBAL | SESSION |
Com_xa_end | numeric | GLOBAL | SESSION |
Com_xa_prepare | numeric | GLOBAL | SESSION |
Com_xa_recover | numeric | GLOBAL | SESSION |
Com_xa_rollback | numeric | GLOBAL | SESSION |
Com_xa_start | numeric | GLOBAL | SESSION |
Connections | numeric | GLOBAL | SESSION |
Created_tmp_disk_tables | numeric | GLOBAL | SESSION |
Created_tmp_files | numeric | GLOBAL | SESSION |
Created_tmp_tables | numeric | GLOBAL | SESSION |
Delayed_errors | numeric | GLOBAL | SESSION |
Delayed_insert_threads | numeric | GLOBAL | SESSION |
Delayed_writes | numeric | GLOBAL | SESSION |
Flush_commands | numeric | GLOBAL | SESSION |
Handler_commit | numeric | GLOBAL | SESSION |
Handler_delete | numeric | GLOBAL | SESSION |
Handler_discover | numeric | GLOBAL | SESSION |
Handler_prepare | numeric | GLOBAL | SESSION |
Handler_read_first | numeric | GLOBAL | SESSION |
Handler_read_key | numeric | GLOBAL | SESSION |
Handler_read_next | numeric | GLOBAL | SESSION |
Handler_read_prev | numeric | GLOBAL | SESSION |
Handler_read_rnd | numeric | GLOBAL | SESSION |
Handler_read_rnd_next | numeric | GLOBAL | SESSION |
Handler_rollback | numeric | GLOBAL | SESSION |
Handler_savepoint | numeric | GLOBAL | SESSION |
Handler_savepoint_rollback | numeric | GLOBAL | SESSION |
Handler_update | numeric | GLOBAL | SESSION |
Handler_write | numeric | GLOBAL | SESSION |
Innodb_buffer_pool_pages_data | numeric | GLOBAL | SESSION |
Innodb_buffer_pool_pages_dirty | numeric | GLOBAL | SESSION |
Innodb_buffer_pool_pages_flushed | numeric | GLOBAL | SESSION |
Innodb_buffer_pool_pages_free | numeric | GLOBAL | SESSION |
Innodb_buffer_pool_pages_latched | numeric | GLOBAL | SESSION |
Innodb_buffer_pool_pages_misc | numeric | GLOBAL | SESSION |
Innodb_buffer_pool_pages_total | numeric | GLOBAL | SESSION |
Innodb_buffer_pool_read_ahead_rnd | numeric | GLOBAL | SESSION |
Innodb_buffer_pool_read_ahead_seq | numeric | GLOBAL | SESSION |
Innodb_buffer_pool_read_requests | numeric | GLOBAL | SESSION |
Innodb_buffer_pool_reads | numeric | GLOBAL | SESSION |
Innodb_buffer_pool_wait_free | numeric | GLOBAL | SESSION |
Innodb_buffer_pool_write_requests | numeric | GLOBAL | SESSION |
Innodb_data_fsyncs | numeric | GLOBAL | SESSION |
Innodb_data_pending_fsyncs | numeric | GLOBAL | SESSION |
Innodb_data_pending_reads | numeric | GLOBAL | SESSION |
Innodb_data_pending_writes | numeric | GLOBAL | SESSION |
Innodb_data_read | numeric | GLOBAL | SESSION |
Innodb_data_reads | numeric | GLOBAL | SESSION |
Innodb_data_writes | numeric | GLOBAL | SESSION |
Innodb_data_written | numeric | GLOBAL | SESSION |
Innodb_dblwr_pages_written | numeric | GLOBAL | SESSION |
Innodb_dblwr_writes | numeric | GLOBAL | SESSION |
Innodb_log_waits | numeric | GLOBAL | SESSION |
Innodb_log_write_requests | numeric | GLOBAL | SESSION |
Innodb_log_writes | numeric | GLOBAL | SESSION |
Innodb_os_log_fsyncs | numeric | GLOBAL | SESSION |
Innodb_os_log_pending_fsyncs | numeric | GLOBAL | SESSION |
Innodb_os_log_pending_writes | numeric | GLOBAL | SESSION |
Innodb_os_log_written | numeric | GLOBAL | SESSION |
Innodb_pages_created | numeric | GLOBAL | SESSION |
Innodb_page_size | numeric | GLOBAL | SESSION |
Innodb_pages_read | numeric | GLOBAL | SESSION |
Innodb_pages_written | numeric | GLOBAL | SESSION |
Innodb_row_lock_current_waits | numeric | GLOBAL | SESSION |
Innodb_row_lock_time | numeric | GLOBAL | SESSION |
Innodb_row_lock_time_avg | numeric | GLOBAL | SESSION |
Innodb_row_lock_time_max | numeric | GLOBAL | SESSION |
Innodb_row_lock_waits | numeric | GLOBAL | SESSION |
Innodb_rows_deleted | numeric | GLOBAL | SESSION |
Innodb_rows_inserted | numeric | GLOBAL | SESSION |
Innodb_rows_read | numeric | GLOBAL | SESSION |
Innodb_rows_updated | numeric | GLOBAL | SESSION |
Key_blocks_not_flushed | numeric | GLOBAL | SESSION |
Key_blocks_unused | numeric | GLOBAL | SESSION |
Key_blocks_used | numeric | GLOBAL | SESSION |
Key_read_requests | numeric | GLOBAL | SESSION |
Key_reads | numeric | GLOBAL | SESSION |
Key_write_requests | numeric | GLOBAL | SESSION |
Key_writes | numeric | GLOBAL | SESSION |
Last_query_cost | numeric | GLOBAL | SESSION |
Max_used_connections | numeric | GLOBAL | SESSION |
Ndb_cluster_node_id | numeric | GLOBAL | SESSION |
Ndb_config_from_host | numeric | GLOBAL | SESSION |
Ndb_config_from_port | numeric | GLOBAL | SESSION |
Not_flushed_delayed_rows | numeric | GLOBAL | SESSION |
Opened_tables | numeric | GLOBAL | SESSION |
Open_files | numeric | GLOBAL | SESSION |
Open_streams | numeric | GLOBAL | SESSION |
Open_tables | numeric | GLOBAL | SESSION |
prepared_stmt_count | numeric | GLOBAL | SESSION |
Qcache_free_blocks | numeric | GLOBAL | SESSION |
Qcache_free_memory | numeric | GLOBAL | SESSION |
Qcache_hits | numeric | GLOBAL | SESSION |
Qcache_inserts | numeric | GLOBAL | SESSION |
Qcache_lowmem_prunes | numeric | GLOBAL | SESSION |
Qcache_not_cached | numeric | GLOBAL | SESSION |
Qcache_queries_in_cache | numeric | GLOBAL | SESSION |
Qcache_total_blocks | numeric | GLOBAL | SESSION |
Questions | numeric | GLOBAL | SESSION |
Rpl_status | string | GLOBAL | SESSION |
Select_full_join | numeric | GLOBAL | SESSION |
Select_full_range_join | numeric | GLOBAL | SESSION |
Select_range | numeric | GLOBAL | SESSION |
Select_range_check | numeric | GLOBAL | SESSION |
Select_scan | numeric | GLOBAL | SESSION |
Slave_open_temp_tables | numeric | GLOBAL | SESSION |
Slave_retried_transactions | numeric | GLOBAL | SESSION |
Slave_running | boolean | GLOBAL | SESSION |
Slow_launch_threads | numeric | GLOBAL | SESSION |
Slow_queries | numeric | GLOBAL | SESSION |
Sort_merge_passes | numeric | GLOBAL | SESSION |
Sort_range | numeric | GLOBAL | SESSION |
Sort_rows | numeric | GLOBAL | SESSION |
Sort_scan | numeric | GLOBAL | SESSION |
Table_locks_immediate | numeric | GLOBAL | SESSION |
Table_locks_waited | numeric | GLOBAL | SESSION |
Tc_log_max_pages_used | numeric | GLOBAL | SESSION |
Tc_log_page_size | numeric | GLOBAL | SESSION |
Tc_log_page_waits | numeric | GLOBAL | SESSION |
Threads_cached | numeric | GLOBAL | SESSION |
Threads_connected | numeric | GLOBAL | SESSION |
Threads_created | numeric | GLOBAL | SESSION |
Threads_running | numeric | GLOBAL | SESSION |
Uptime | numeric | GLOBAL | SESSION |
Uptime_since_flush_status | numeric | GLOBAL | SESSION |
Before MySQL 5.0.2, SHOW STATUS returned
global status values. Because the default as of 5.0.2 is to
return session values, this is incompatible with previous
versions. To issue a SHOW STATUS statement
that will retrieve global status values for all versions of
MySQL, write it like this:
SHOW /*!50002 GLOBAL */ STATUS;
Many status variables are reset to 0 by the FLUSH
STATUS statement.
MySQL Enterprise. For expert advice on using status variables, subscribe to the MySQL Enterprise Monitor. For more information see http://www.mysql.com/products/enterprise/advisors.html.
The status variables have the following meanings. Variables with no version indicated were already present prior to MySQL 5.0. For information regarding their implementation history, see MySQL 3.23, 4.0, 4.1 Reference Manual.
The number of connections that were aborted because the client died without closing the connection properly. See Section B.1.2.11, “Communication Errors and Aborted Connections”.
The number of failed attempts to connect to the MySQL server. See Section B.1.2.11, “Communication Errors and Aborted Connections”.
The number of transactions that used the temporary binary
log cache but that exceeded the value of
binlog_cache_size and used a temporary
file to store statements from the transaction.
The number of transactions that used the temporary binary log cache.
The number of bytes received from all clients.
The number of bytes sent to all clients.
The Com_
statement counter variables indicate the number of times
each xxxxxx statement has been
executed. There is one status variable for each type of
statement. For example, Com_delete and
Com_insert count
DELETE and INSERT
statements, respectively. However, if a query result is
returned from query cache, the server increments the
Qcache_hits status variable, not
Com_select. See
Section 7.5.4.4, “Query Cache Status and Maintenance”.
All of the
Com_stmt_
variables are increased even if a prepared statement
argument is unknown or an error occurred during execution.
In other words, their values correspond to the number of
requests issued, not to the number of requests successfully
completed.
xxx
The
Com_stmt_
status variables were added in 5.0.8:
xxx
Com_stmt_prepare
Com_stmt_execute
Com_stmt_fetch
Com_stmt_send_long_data
Com_stmt_reset
Com_stmt_close
Those variables stand for prepared statement commands. Their
names refer to the
COM_
command set used in the network layer. In other words, their
values increase whenever prepared statement API calls such
as mysql_stmt_prepare(),
mysql_stmt_execute(), and so forth are
executed. However, xxxCom_stmt_prepare,
Com_stmt_execute and
Com_stmt_close also increase for
PREPARE, EXECUTE, or
DEALLOCATE PREPARE, respectively.
Additionally, the values of the older (available since MySQL
4.1.3) statement counter variables
Com_prepare_sql,
Com_execute_sql, and
Com_dealloc_sql increase for the
PREPARE, EXECUTE, and
DEALLOCATE PREPARE statements.
Com_stmt_fetch stands for the total
number of network round-trips issued when fetching from
cursors.
Whether the client connection uses compression in the client/server protocol. Added in MySQL 5.0.16.
The number of connection attempts (successful or not) to the MySQL server.
The number of temporary tables on disk created automatically by the server while executing statements.
How many temporary files mysqld has created.
The number of in-memory temporary tables created
automatically by the server while executing statements. If
Created_tmp_disk_tables is large, you may
want to increase the tmp_table_size value
to cause temporary tables to be memory-based instead of
disk-based.
The number of rows written with INSERT
DELAYED for which some error occurred (probably
duplicate key).
The number of INSERT DELAYED handler
threads in use.
The number of INSERT DELAYED rows
written.
The number of executed FLUSH statements.
The number of internal COMMIT statements.
The number of times that rows have been deleted from tables.
A counter for the prepare phase of two-phase commit operations. Added in MySQL 5.0.3.
The number of times the first entry was read from an index.
If this value is high, it suggests that the server is doing
a lot of full index scans; for example, SELECT col1
FROM foo, assuming that col1 is
indexed.
The number of requests to read a row based on a key. If this value is high, it is a good indication that your tables are properly indexed for your queries.
The number of requests to read the next row in key order. This value is incremented if you are querying an index column with a range constraint or if you are doing an index scan.
The number of requests to read the previous row in key
order. This read method is mainly used to optimize
ORDER BY ... DESC.
The number of requests to read a row based on a fixed position. This value is high if you are doing a lot of queries that require sorting of the result. You probably have a lot of queries that require MySQL to scan entire tables or you have joins that don't use keys properly.
The number of requests to read the next row in the data file. This value is high if you are doing a lot of table scans. Generally this suggests that your tables are not properly indexed or that your queries are not written to take advantage of the indexes you have.
The number of requests for a storage engine to perform a rollback operation.
The number of requests for a storage engine to place a savepoint. Added in MySQL 5.0.3.
The number of requests for a storage engine to roll back to a savepoint. Added in MySQL 5.0.3.
The number of requests to update a row in a table.
The number of requests to insert a row in a table.
The number of pages containing data (dirty or clean). Added in MySQL 5.0.2.
Innodb_buffer_pool_pages_dirty
The number of pages currently dirty. Added in MySQL 5.0.2.
Innodb_buffer_pool_pages_flushed
The number of buffer pool page-flush requests. Added in MySQL 5.0.2.
The number of free pages. Added in MySQL 5.0.2.
Innodb_buffer_pool_pages_latched
The number of latched pages in InnoDB
buffer pool. These are pages currently being read or written
or that cannot be flushed or removed for some other reason.
Added in MySQL 5.0.2.
The number of pages that are busy because they have been
allocated for administrative overhead such as row locks or
the adaptive hash index. This value can also be calculated
as Innodb_buffer_pool_pages_total –
Innodb_buffer_pool_pages_free –
Innodb_buffer_pool_pages_data. Added in
MySQL 5.0.2.
Innodb_buffer_pool_pages_total
The total size of buffer pool, in pages. Added in MySQL 5.0.2.
Innodb_buffer_pool_read_ahead_rnd
The number of “random” read-aheads initiated by
InnoDB. This happens when a query scans a
large portion of a table but in random order. Added in MySQL
5.0.2.
Innodb_buffer_pool_read_ahead_seq
The number of sequential read-aheads initiated by
InnoDB. This happens when
InnoDB does a sequential full table scan.
Added in MySQL 5.0.2.
Innodb_buffer_pool_read_requests
The number of logical read requests
InnoDB has done. Added in MySQL 5.0.2.
The number of logical reads that InnoDB
could not satisfy from the buffer pool and had to do a
single-page read. Added in MySQL 5.0.2.
Normally, writes to the InnoDB buffer
pool happen in the background. However, if it is necessary
to read or create a page and no clean pages are available,
it is also necessary to wait for pages to be flushed first.
This counter counts instances of these waits. If the buffer
pool size has been set properly, this value should be small.
Added in MySQL 5.0.2.
Innodb_buffer_pool_write_requests
The number writes done to the InnoDB
buffer pool. Added in MySQL 5.0.2.
The number of fsync() operations so far.
Added in MySQL 5.0.2.
The current number of pending fsync()
operations. Added in MySQL 5.0.2.
The current number of pending reads. Added in MySQL 5.0.2.
The current number of pending writes. Added in MySQL 5.0.2.
The amount of data read so far, in bytes. Added in MySQL 5.0.2.
The total number of data reads. Added in MySQL 5.0.2.
The total number of data writes. Added in MySQL 5.0.2.
The amount of data written so far, in bytes. Added in MySQL 5.0.2.
Innodb_dblwr_writes,
Innodb_dblwr_pages_written
The number of doublewrite operations that have been
performed and the number of pages that have been written for
this purpose. Added in MySQL 5.0.2. See
Section 13.2.14.1, “InnoDB Disk I/O”.
The number of times that the log buffer was too small and a wait was required for it to be flushed before continuing. Added in MySQL 5.0.2.
The number of log write requests. Added in MySQL 5.0.2.
The number of physical writes to the log file. Added in MySQL 5.0.2.
The number of fsync() writes done to the
log file. Added in MySQL 5.0.2.
The number of pending log file fsync()
operations. Added in MySQL 5.0.2.
The number of pending log file writes. Added in MySQL 5.0.2.
The number of bytes written to the log file. Added in MySQL 5.0.2.
The compiled-in InnoDB page size (default
16KB). Many values are counted in pages; the page size
allows them to be easily converted to bytes. Added in MySQL
5.0.2.
The number of pages created. Added in MySQL 5.0.2.
The number of pages read. Added in MySQL 5.0.2.
The number of pages written. Added in MySQL 5.0.2.
The number of row locks currently being waited for. Added in MySQL 5.0.3.
The total time spent in acquiring row locks, in milliseconds. Added in MySQL 5.0.3.
The average time to acquire a row lock, in milliseconds. Added in MySQL 5.0.3.
The maximum time to acquire a row lock, in milliseconds. Added in MySQL 5.0.3.
The number of times a row lock had to be waited for. Added in MySQL 5.0.3.
The number of rows deleted from InnoDB
tables. Added in MySQL 5.0.2.
The number of rows inserted into InnoDB
tables. Added in MySQL 5.0.2.
The number of rows read from InnoDB
tables. Added in MySQL 5.0.2.
The number of rows updated in InnoDB
tables. Added in MySQL 5.0.2.
The number of key blocks in the key cache that have changed but have not yet been flushed to disk.
The number of unused blocks in the key cache. You can use
this value to determine how much of the key cache is in use;
see the discussion of key_buffer_size in
Section 5.1.3, “System Variables”.
The number of used blocks in the key cache. This value is a high-water mark that indicates the maximum number of blocks that have ever been in use at one time.
The number of requests to read a key block from the cache.
The number of physical reads of a key block from disk. If
Key_reads is large, then your
key_buffer_size value is probably too
small. The cache miss rate can be calculated as
Key_reads/Key_read_requests.
The number of requests to write a key block to the cache.
The number of physical writes of a key block to disk.
The total cost of the last compiled query as computed by the
query optimizer. This is useful for comparing the cost of
different query plans for the same query. The default value
of 0 means that no query has been compiled yet. This
variable was added in MySQL 5.0.1, with a default value of
-1. In MySQL 5.0.7, the default was changed to 0; also in
version 5.0.7, the scope of
Last_query_cost was changed to session
rather than global.
The Last_query_cost value can be computed
accurately only for simple “flat” queries, not
complex queries such as those with subqueries or
UNION. For the latter, the value is set
to 0.
Prior to MySQL 5.0.16, this variable was not updated for queries served from the query cache.
The maximum number of connections that have been in use simultaneously since the server started.
The number of rows waiting to be written in INSERT
DELAY queues.
The number of files that are open.
The number of streams that are open (used mainly for logging).
The number of tables that are open.
The number of tables that have been opened. If
Opened_tables is big, your
table_cache value is probably too small.
The current number of prepared statements. (The maximum
number of statements is given by the
max_prepared_stmt_count system variable.)
This variable was added in MySQL 5.0.32.
The number of free memory blocks in the query cache.
The amount of free memory for the query cache.
The number of query cache hits.
The number of queries added to the query cache.
The number of queries that were deleted from the query cache because of low memory.
The number of non-cached queries (not cacheable, or not
cached due to the query_cache_type
setting).
The number of queries registered in the query cache.
The total number of blocks in the query cache.
The number of statements that clients have sent to the server.
The status of fail-safe replication (not yet implemented).
The number of joins that perform table scans because they do not use indexes. If this value is not 0, you should carefully check the indexes of your tables.
The number of joins that used a range search on a reference table.
The number of joins that used ranges on the first table. This is normally not a critical issue even if the value is quite large.
The number of joins without keys that check for key usage after each row. If this is not 0, you should carefully check the indexes of your tables.
The number of joins that did a full scan of the first table.
The number of temporary tables that the slave SQL thread currently has open.
This is ON if this server is a slave that
is connected to a master.
The total number of times since startup that the replication slave SQL thread has retried transactions. This variable was added in version 5.0.4.
The number of threads that have taken more than
slow_launch_time seconds to create.
The number of queries that have taken more than
long_query_time seconds. See
Section 5.2.4, “The Slow Query Log”.
The number of merge passes that the sort algorithm has had
to do. If this value is large, you should consider
increasing the value of the
sort_buffer_size system variable.
The number of sorts that were done using ranges.
The number of sorted rows.
The number of sorts that were done by scanning the table.
Ssl_
xxx
Variables used for SSL connections.
The number of times that a table lock was acquired immediately.
The number of times that a table lock could not be acquired immediately and a wait was needed. If this is high and you have performance problems, you should first optimize your queries, and then either split your table or tables or use replication.
For the memory-mapped implementation of the log that is used
by mysqld when it acts as the transaction
coordinator for recovery of internal XA transactions, this
variable indicates the largest number of pages used for the
log since the server started. If the product of
Tc_log_max_pages_used and
Tc_log_page_size is always significantly
less than the log size, the size is larger than necessary
and can be reduced. (The size is set by the
--log-tc-size option. Currently, this
variable is unused: It is unneeded for binary log-based
recovery, and the memory-mapped recovery log method is not
used unless the number of storage engines capable of
two-phase commit is greater than one.
(InnoDB is the only applicable engine.)
Added in MySQL 5.0.3.
The page size used for the memory-mapped implementation of
the XA recovery log. The default value is determined using
getpagesize(). Currently, this variable
is unused for the same reasons as described for
Tc_log_max_pages_used. Added in MySQL
5.0.3.
For the memory-mapped implementation of the recovery log,
this variable increments each time the server was not able
to commit a transaction and had to wait for a free page in
the log. If this value is large, you might want to increase
the log size (with the --log-tc-size
option). For binary log-based recovery, this variable
increments each time the binary log cannot be closed because
there are two-phase commits in progress. (The close
operation waits until all such transactions are finished.)
Added in MySQL 5.0.3.
The number of threads in the thread cache.
The number of currently open connections.
The number of threads created to handle connections. If
Threads_created is big, you may want to
increase the thread_cache_size value. The
cache miss rate can be calculated as
Threads_created/Connections.
The number of threads that are not sleeping.
The number of seconds that the server has been up.
The MySQL server can operate in different SQL modes, and can apply these modes differently for different clients. This capability enables each application to tailor the server's operating mode to its own requirements.
For answers to some questions that are often asked about server SQL modes in MySQL, see Section A.3, “MySQL 5.0 FAQ — Server SQL Mode”.
Modes define what SQL syntax MySQL should support and what kind of data validation checks it should perform. This makes it easier to use MySQL in different environments and to use MySQL together with other database servers.
You can set the default SQL mode by starting
mysqld with the
--sql-mode="
option, or by using
modes"sql-mode=" in
modes"my.cnf (Unix operating systems) or
my.ini (Windows).
modes is a list of different modes
separated by comma (“,”)
characters. The default value is empty (no modes set). The
modes value also can be empty
(--sql-mode="" on the command line, or
sql-mode="" in my.cnf on
Unix systems or in my.ini on Windows) if
you want to clear it explicitly.
You can change the SQL mode at runtime by using a SET
[GLOBAL|SESSION]
sql_mode=' statement
to set the modes'sql_mode system value. Setting the
GLOBAL variable requires the
SUPER privilege and affects the operation of
all clients that connect from that time on. Setting the
SESSION variable affects only the current
client. Any client can change its own session
sql_mode value at any time.
You can retrieve the current global or session
sql_mode value with the following statements:
SELECT @@global.sql_mode; SELECT @@session.sql_mode;
The most important sql_mode values are
probably these:
This mode changes syntax and behavior to conform more closely to standard SQL.
If a value could not be inserted as given into a transactional table, abort the statement. For a non-transactional table, abort the statement if the value occurs in a single-row statement or the first row of a multiple-row statement. More detail is given later in this section. (Implemented in MySQL 5.0.2)
Make MySQL behave like a “traditional” SQL database system. A simple description of this mode is “give an error instead of a warning” when inserting an incorrect value into a column.
The INSERT/UPDATE
aborts as soon as the error is noticed. This may not be
what you want if you are using a non-transactional storage
engine, because data changes made prior to the error may
not be rolled back, resulting in a “partially
done” update. (Added in MySQL 5.0.2)
When this manual refers to “strict mode,” it means
a mode where at least one of
STRICT_TRANS_TABLES or
STRICT_ALL_TABLES is enabled.
The following list describes all supported modes:
Don't do full checking of dates. Check only that the month
is in the range from 1 to 12 and the day is in the range
from 1 to 31. This is very convenient for Web applications
where you obtain year, month, and day in three different
fields and you want to store exactly what the user inserted
(without date validation). This mode applies to
DATE and DATETIME
columns. It does not apply TIMESTAMP
columns, which always require a valid date.
This mode is implemented in MySQL 5.0.2. Before 5.0.2, this
was the default MySQL date-handling mode. As of 5.0.2, the
server requires that month and day values be legal, and not
merely in the range 1 to 12 and 1 to 31, respectively. With
strict mode disabled, invalid dates such as
'2004-04-31' are converted to
'0000-00-00' and a warning is generated.
With strict mode enabled, invalid dates generate an error.
To allow such dates, enable
ALLOW_INVALID_DATES.
Treat “"” as an identifier
quote character (like the
“`” quote character) and not
as a string quote character. You can still use
“`” to quote identifiers
with this mode enabled. With ANSI_QUOTES
enabled, you cannot use double quotes to quote literal
strings, because it is interpreted as an identifier.
Produce an error in strict mode (otherwise a warning) when a
division by zero (or
MOD(X,0)) occurs during an
INSERT or UPDATE. If
this mode is not enabled, MySQL instead returns
NULL for divisions by zero. For
INSERT IGNORE or UPDATE
IGNORE, MySQL generates a warning for divisions by
zero, but the result of the operation is
NULL. (Implemented in MySQL 5.0.2)
From MySQL 5.0.2 on, the precedence of the
NOT operator is such that
expressions such as NOT a BETWEEN b AND c
are parsed as NOT (a BETWEEN b AND c).
Before MySQL 5.0.2, the expression is parsed as
(NOT a) BETWEEN b AND c. The old
higher-precedence behavior can be obtained by enabling the
HIGH_NOT_PRECEDENCE SQL mode. (Added in
MySQL 5.0.2)
mysql>SET sql_mode = '';mysql>SELECT NOT 1 BETWEEN -5 AND 5;-> 0 mysql>SET sql_mode = 'HIGH_NOT_PRECEDENCE';mysql>SELECT NOT 1 BETWEEN -5 AND 5;-> 1
Allow spaces between a function name and the
“(” character. This causes
built-in function names to be treated as reserved words. As
a result, identifiers that are the same as function names
must be quoted as described in
Section 8.2, “Schema Object Names”. For example, because there is
a COUNT() function, the use
of count as a table name in the following
statement causes an error:
mysql> CREATE TABLE count (i INT);
ERROR 1064 (42000): You have an error in your SQL syntax
The table name should be quoted:
mysql> CREATE TABLE `count` (i INT);
Query OK, 0 rows affected (0.00 sec)
The IGNORE_SPACE SQL mode applies to
built-in functions, not to user-defined functions or stored
functions. It is always allowable to have spaces after a UDF
or stored function name, regardless of whether
IGNORE_SPACE is enabled.
For further discussion of IGNORE_SPACE,
see Section 8.2.3, “Function Name Parsing and Resolution”.
Prevent the GRANT statement from
automatically creating new users if it would otherwise do
so, unless a non-empty password also is specified. (Added in
MySQL 5.0.2)
NO_AUTO_VALUE_ON_ZERO affects handling of
AUTO_INCREMENT columns. Normally, you
generate the next sequence number for the column by
inserting either NULL or
0 into it.
NO_AUTO_VALUE_ON_ZERO suppresses this
behavior for 0 so that only
NULL generates the next sequence number.
This mode can be useful if 0 has been
stored in a table's AUTO_INCREMENT
column. (Storing 0 is not a recommended
practice, by the way.) For example, if you dump the table
with mysqldump and then reload it, MySQL
normally generates new sequence numbers when it encounters
the 0 values, resulting in a table with
contents different from the one that was dumped. Enabling
NO_AUTO_VALUE_ON_ZERO before reloading
the dump file solves this problem.
mysqldump now automatically includes in
its output a statement that enables
NO_AUTO_VALUE_ON_ZERO, to avoid this
problem.
Disable the use of the backslash character
(“\”) as an escape character
within strings. With this mode enabled, backslash becomes an
ordinary character like any other. (Implemented in MySQL
5.0.1)
When creating a table, ignore all INDEX
DIRECTORY and DATA DIRECTORY
directives. This option is useful on slave replication
servers.
NO_ENGINE_SUBSTITUTION
Control automatic substitution of the default storage engine
when a statement such as CREATE TABLE or
ALTER TABLE specifies a storage engine
that is disabled or not compiled in. (Implemented in MySQL
5.0.8)
With NO_ENGINE_SUBSTITUTION disabled, the
default engine is used and a warning occurs if the desired
engine is known but disabled or not compiled in. If the
desired engine is invalid (not a known engine name), an
error occurs and the table is not created or altered.
With NO_ENGINE_SUBSTITUTION enabled, an
error occurs and the table is not created or altered if the
desired engine is unavailable for any reason (whether
disabled or invalid).
Do not print MySQL-specific column options in the output of
SHOW CREATE TABLE. This mode is used by
mysqldump in portability mode.
Do not print MySQL-specific index options in the output of
SHOW CREATE TABLE. This mode is used by
mysqldump in portability mode.
Do not print MySQL-specific table options (such as
ENGINE) in the output of SHOW
CREATE TABLE. This mode is used by
mysqldump in portability mode.
In integer subtraction operations, do not mark the result as
UNSIGNED if one of the operands is
unsigned. In other words, the result of a
subtraction is always signed whenever this mode is in
effect, even if one of the operands is unsigned.
For example, compare the type of column
c2 in table t1 with
that of column c2 in table
t2:
mysql>SET SQL_MODE='';mysql>CREATE TABLE test (c1 BIGINT UNSIGNED NOT NULL);mysql>CREATE TABLE t1 SELECT c1 - 1 AS c2 FROM test;mysql>DESCRIBE t1;+-------+---------------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+---------------------+------+-----+---------+-------+ | c2 | bigint(21) unsigned | | | 0 | | +-------+---------------------+------+-----+---------+-------+ mysql>SET SQL_MODE='NO_UNSIGNED_SUBTRACTION';mysql>CREATE TABLE t2 SELECT c1 - 1 AS c2 FROM test;mysql>DESCRIBE t2;+-------+------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +-------+------------+------+-----+---------+-------+ | c2 | bigint(21) | | | 0 | | +-------+------------+------+-----+---------+-------+
Note that this means that BIGINT UNSIGNED
is not 100% usable in all contexts. See
Section 11.9, “Cast Functions and Operators”.
mysql>SET SQL_MODE = '';mysql>SELECT CAST(0 AS UNSIGNED) - 1;+-------------------------+ | CAST(0 AS UNSIGNED) - 1 | +-------------------------+ | 18446744073709551615 | +-------------------------+ mysql>SET SQL_MODE = 'NO_UNSIGNED_SUBTRACTION';mysql>SELECT CAST(0 AS UNSIGNED) - 1;+-------------------------+ | CAST(0 AS UNSIGNED) - 1 | +-------------------------+ | -1 | +-------------------------+
In strict mode, don't allow '0000-00-00'
as a valid date. You can still insert zero dates with the
IGNORE option. When not in strict mode,
the date is accepted but a warning is generated. (Added in
MySQL 5.0.2)
In strict mode, do not accept dates where the year part is
non-zero but the the month or day part is 0 (for example,
'0000-00-00' is legal but
'2010-00-01' and
'2010-01-00' are not). If used with the
IGNORE option, MySQL inserts a
'0000-00-00' date for any such date. When
not in strict mode, the date is accepted but a warning is
generated. (Added in MySQL 5.0.2)
Do not allow queries for which the SELECT
list refers to non-aggregated columns that are not named in
the GROUP BY clause. The following query
is invalid with this mode enabled because
address is not named in the
GROUP BY clause:
SELECT name, address, MAX(age) FROM t GROUP BY name;
As of MySQL 5.0.23, this mode also restricts references to
non-aggregated columns in the HAVING
clause that are not named in the GROUP BY
clause.
Treat || as
a string concatenation operator (same as
CONCAT()) rather than as a
synonym for OR.
Treat REAL as a synonym for
FLOAT. By default, MySQL treats
REAL as a synonym for
DOUBLE.
Enable strict mode for all storage engines. Invalid data values are rejected. Additional detail follows. (Added in MySQL 5.0.2)
Enable strict mode for transactional storage engines, and when possible for non-transactional storage engines. Additional details follow. (Implemented in MySQL 5.0.2)
Strict mode controls how MySQL handles input values that are
invalid or missing. A value can be invalid for several reasons.
For example, it might have the wrong data type for the column,
or it might be out of range. A value is missing when a new row
to be inserted does not contain a value for a
non-NULL column that has no explicit
DEFAULT clause in its definition. (For a
NULL column, NULL is
inserted if the value is missing.)
For transactional tables, an error occurs for invalid or missing
values in a statement when either of the
STRICT_ALL_TABLES or
STRICT_TRANS_TABLES modes are enabled. The
statement is aborted and rolled back.
For non-transactional tables, the behavior is the same for either mode, if the bad value occurs in the first row to be inserted or updated. The statement is aborted and the table remains unchanged. If the statement inserts or modifies multiple rows and the bad value occurs in the second or later row, the result depends on which strict option is enabled:
For STRICT_ALL_TABLES, MySQL returns an
error and ignores the rest of the rows. However, in this
case, the earlier rows still have been inserted or updated.
This means that you might get a partial update, which might
not be what you want. To avoid this, it's best to use
single-row statements because these can be aborted without
changing the table.
For STRICT_TRANS_TABLES, MySQL converts
an invalid value to the closest valid value for the column
and insert the adjusted value. If a value is missing, MySQL
inserts the implicit default value for the column data type.
In either case, MySQL generates a warning rather than an
error and continues processing the statement. Implicit
defaults are described in
Section 10.1.4, “Data Type Default Values”.
Strict mode disallows invalid date values such as
'2004-04-31'. It does not disallow dates with
zero month or day parts such as '2004-04-00'
or “zero” dates. To disallow these as well, enable
the NO_ZERO_IN_DATE and
NO_ZERO_DATE SQL modes in addition to strict
mode.
If you are not using strict mode (that is, neither
STRICT_TRANS_TABLES nor
STRICT_ALL_TABLES is enabled), MySQL inserts
adjusted values for invalid or missing values and produces
warnings. In strict mode, you can produce this behavior by using
INSERT IGNORE or UPDATE
IGNORE. See Section 12.5.4.28, “SHOW WARNINGS Syntax”.
The following special modes are provided as shorthand for
combinations of mode values from the preceding list. All are
available in MySQL 5.0 beginning with version
5.0.0, except for TRADITIONAL, which was
implemented in MySQL 5.0.2.
The descriptions include all mode values that are available in the most recent version of MySQL. For older versions, a combination mode does not include individual mode values that are not available except in newer versions.
Equivalent to REAL_AS_FLOAT,
PIPES_AS_CONCAT,
ANSI_QUOTES,
IGNORE_SPACE. Before MySQL 5.0.3,
ANSI also includes
ONLY_FULL_GROUP_BY.
As of MySQL 5.0.40, ANSI mode also causes
the server to return an error for queries where a set
function S with an outer
reference
S(outer_ref)
SELECT * FROM t1 WHERE t1.a IN (SELECT MAX(t1.b) FROM t2 WHERE ...);
Here, MAX(t1.b) cannot
aggregated in the outer query because it appears in the
WHERE clause of that query. Standard SQL
requires an error in this situation. If
ANSI mode is not enabled, the server
treats
S(outer_ref)S(const)
Equivalent to PIPES_AS_CONCAT,
ANSI_QUOTES,
IGNORE_SPACE,
NO_KEY_OPTIONS,
NO_TABLE_OPTIONS,
NO_FIELD_OPTIONS.
Equivalent to PIPES_AS_CONCAT,
ANSI_QUOTES,
IGNORE_SPACE,
NO_KEY_OPTIONS,
NO_TABLE_OPTIONS,
NO_FIELD_OPTIONS,
NO_AUTO_CREATE_USER.
Equivalent to PIPES_AS_CONCAT,
ANSI_QUOTES,
IGNORE_SPACE,
NO_KEY_OPTIONS,
NO_TABLE_OPTIONS,
NO_FIELD_OPTIONS.
Equivalent to NO_FIELD_OPTIONS,
HIGH_NOT_PRECEDENCE.
Equivalent to NO_FIELD_OPTIONS,
HIGH_NOT_PRECEDENCE.
Equivalent to PIPES_AS_CONCAT,
ANSI_QUOTES,
IGNORE_SPACE,
NO_KEY_OPTIONS,
NO_TABLE_OPTIONS,
NO_FIELD_OPTIONS,
NO_AUTO_CREATE_USER.
Equivalent to PIPES_AS_CONCAT,
ANSI_QUOTES,
IGNORE_SPACE,
NO_KEY_OPTIONS,
NO_TABLE_OPTIONS,
NO_FIELD_OPTIONS.
Equivalent to STRICT_TRANS_TABLES,
STRICT_ALL_TABLES,
NO_ZERO_IN_DATE,
NO_ZERO_DATE,
ERROR_FOR_DIVISION_BY_ZERO,
NO_AUTO_CREATE_USER.
MySQL Server supports a HELP statement that
returns online information from the MySQL Reference manual (see
Section 12.3.3, “HELP Syntax”). The proper operation of this statement
requires that the help tables in the mysql
database be initialized with help topic information, which is
done by processing the contents of the
fill_help_tables.sql script.
For a MySQL binary distribution on Unix, help table setup occurs when you run mysql_install_db. For an RPM distribution on Linux or binary distribution on Windows, help table setup occurs as part of the MySQL installation process.
For a MySQL source distribution, you can find the
fill_help_tables.sql file in the
scripts directory. To load the file
manually, make sure that you have initialized the
mysql database by running
mysql_install_db, and then process the file
with the mysql client as follows:
shell> mysql -u root mysql < fill_help_tables.sql
If you are working with BitKeeper and a MySQL development source
tree, the tree doesn't contain
fill_help_tables.sql. You can download the
proper file for your version of MySQL from
http://dev.mysql.com/doc/. After downloading and
uncompressing the file, process it with mysql
as just described.
On Unix, signals can be sent to processes. mysqld responds to signals sent to it as follows:
SIGTERM causes the server to shut down.
SIGHUP causes the server to reload the
grant tables and flush the logs (like FLUSH
PRIVILEGES and FLUSH LOGS). It
also writes a status report to the error log that has this
format:
Status information: Current dir: /var/mysql/data/ Running threads: 0 Stack size: 196608 Current locks: Key caches: default Buffer_size: 8388600 Block_size: 1024 Division_limit: 100 Age_limit: 300 blocks used: 0 not flushed: 0 w_requests: 0 writes: 0 r_requests: 0 reads: 0 handler status: read_key: 0 read_next: 0 read_rnd 0 read_first: 1 write: 0 delete 0 update: 0 Table status: Opened tables: 5 Open tables: 0 Open files: 7 Open streams: 0 Alarm status: Active alarms: 1 Max used alarms: 2 Next alarm time: 67
On some Mac OS X 10.3 versions, mysqld
ignores SIGHUP and
SIGQUIT.
The server shutdown process takes place as follows:
The shutdown process is initiated.
Server shutdown can be initiated several ways. For example,
a user with the SHUTDOWN privilege can
execute a mysqladmin shutdown command.
mysqladmin can be used on any platform
supported by MySQL. Other operating system-specific shutdown
initiation methods are possible as well: The server shuts
down on Unix when it receives a SIGTERM
signal. A server running as a service on Windows shuts down
when the services manager tells it to.
The server creates a shutdown thread if necessary.
Depending on how shutdown was initiated, the server might
create a thread to handle the shutdown process. If shutdown
was requested by a client, a shutdown thread is created. If
shutdown is the result of receiving a
SIGTERM signal, the signal thread might
handle shutdown itself, or it might create a separate thread
to do so. If the server tries to create a shutdown thread
and cannot (for example, if memory is exhausted), it issues
a diagnostic message that appears in the error log:
Error: Can't create thread to kill server
The server stops accepting new connections.
To prevent new activity from being initiated during shutdown, the server stops accepting new client connections. It does this by closing the network connections to which it normally listens for connections: the TCP/IP port, the Unix socket file, the Windows named pipe, and shared memory on Windows.
The server terminates current activity.
For each thread that is associated with a client connection,
the connection to the client is broken and the thread is
marked as killed. Threads die when they notice that they are
so marked. Threads for idle connections die quickly. Threads
that currently are processing statements check their state
periodically and take longer to die. For additional
information about thread termination, see
Section 12.5.5.3, “KILL Syntax”, in particular for the instructions
about killed REPAIR TABLE or
OPTIMIZE TABLE operations on
MyISAM tables.
For threads that have an open transaction, the transaction
is rolled back. Note that if a thread is updating a
non-transactional table, an operation such as a multiple-row
UPDATE or INSERT may
leave the table partially updated, because the operation can
terminate before completion.
If the server is a master replication server, threads associated with currently connected slaves are treated like other client threads. That is, each one is marked as killed and exits when it next checks its state.
If the server is a slave replication server, the I/O and SQL threads, if active, are stopped before client threads are marked as killed. The SQL thread is allowed to finish its current statement (to avoid causing replication problems), and then stops. If the SQL thread was in the middle of a transaction at this point, the transaction is rolled back.
Storage engines are shut down or closed.
At this stage, the table cache is flushed and all open tables are closed.
Each storage engine performs any actions necessary for
tables that it manages. For example,
MyISAM flushes any pending index writes
for a table. InnoDB flushes its buffer
pool to disk (starting from 5.0.5: unless
innodb_fast_shutdown is 2), writes the
current LSN to the tablespace, and terminates its own
internal threads.
The server exits.