The MySQL server maintains many system variables that affect its
operation. Most system variables can be set at server startup
using options on the command line or in an option file. Most of
them can be changed dynamically at runtime using the
SET
statement, which enables you to modify operation of the server
without having to stop and restart it. Some variables are
read-only, and their values are determined by the system
environment, by how MySQL is installed on the system, or possibly
by the options used to compile MySQL. Most system variables have a
default value, but there are exceptions, including read-only
variables. You can also use system variable values in expressions.
At runtime, setting a global system variable value requires the
SUPER
privilege. Setting a session
system variable value normally requires no special privileges and
can be done by any user, although there are exceptions. For more
information, see Section 5.1.8.1, “System Variable Privileges”
There are several ways to see the names and values of system variables:
To see the values that a server uses 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 uses based on only its compiled-in defaults, ignoring the settings in any option files, use this command:
mysqld --no-defaults --verbose --help
To see the current values used by a running server, use the
SHOW VARIABLES
statement or the Performance Schema system variable tables. See Section 25.12.13, “Performance Schema System Variable Tables”.
This section provides a description of each system variable. For a system variable summary table, see Section 5.1.4, “Server System Variable Reference”. For more information about manipulation of system variables, see Section 5.1.8, “Using System Variables”.
For additional system variable information, see these sections:
Section 5.1.8, “Using System Variables”, discusses the syntax for setting and displaying system variable values.
Section 5.1.8.2, “Dynamic System Variables”, lists the variables that can be set at runtime.
Information on tuning system variables can be found in Section 5.1.1, “Configuring the Server”.
Section 14.15, “InnoDB Startup Options and System Variables”, lists
InnoDB
system variables.Section 21.4.3.9.2, “NDB Cluster System Variables”, lists system variables which are specific to NDB Cluster.
For information on server system variables specific to replication, see Section 16.1.6, “Replication and Binary Logging Options and Variables”.
Some of the following variable descriptions refer to
“enabling” or “disabling” a variable.
These variables can be enabled with the
SET
statement by setting them to ON
or
1
, or disabled by setting them to
OFF
or 0
. Boolean
variables can be set at startup to the values
ON
, TRUE
,
OFF
, and FALSE
(not
case-sensitive), as well as 1
and
0
. See Section 4.2.2.4, “Program Option Modifiers”.
Some system variables control the size of buffers or caches. For a given buffer, the server might need to allocate internal data structures. These structures typically are allocated from the total memory allocated to the buffer, and the amount of space required might be platform dependent. This means that when you assign a value to a system variable that controls a buffer size, the amount of space actually available might differ from the value assigned. In some cases, the amount might be less than the value assigned. It is also possible for the server to adjust a value upward. For example, if you assign a value of 0 to a variable for which the minimal value is 1024, the server sets the value to 1024.
Values for buffer sizes, lengths, and stack sizes are given in bytes unless otherwise specified.
Some system variable descriptions include a block size, in which
case a value that is not an integer multiple of the stated block
size is rounded down to the next lower multiple of the block
size before being stored by the server, that is to
FLOOR(
value
)*
.
block_size
Example: Suppose that the block size for a given variable is given as 4096, and you set the value of the variable to 100000 (we assume that the variable's maximum value is greater than this number). Since 100000 / 4096 = 24.4140625, the server automatically lowers the value to 98304 (24 * 4096) before storing it.
In some cases, the stated maximum for a variable is the maximum allowed by the MySQL parser, but is not an exact multiple of the block size. In such cases, the effective maximum is the next lower multiple of the block size.
Example: A system variable's maxmum value is shown as 4294967295 (232-1), and its block size is 1024. 4294967295 / 1024 = 4194303.9990234375, so if you set this variable to its stated maximum, the value actually stored is 4194303 * 1024 = 4294966272.
Some system variables take file name values. Unless otherwise
specified, the default file location is the data directory if the
value is a relative path name. To specify the location explicitly,
use an absolute path name. Suppose that the data directory is
/var/mysql/data
. If a file-valued variable is
given as a relative path name, it is located under
/var/mysql/data
. If the value is an absolute
path name, its location is as given by the path name.
authentication_windows_log_level
Command-Line Format --authentication-windows-log-level=#
System Variable authentication_windows_log_level
Scope Global Dynamic No Type Integer Default Value 2
Minimum Value 0
Maximum Value 4
This variable is available only if the
authentication_windows
Windows authentication plugin is enabled and debugging code is enabled. See Section 6.4.1.8, “Windows Pluggable Authentication”.This variable sets the logging level for the Windows authentication plugin. The following table shows the permitted values.
Value Description 0 No logging 1 Log only error messages 2 Log level 1 messages and warning messages 3 Log level 2 messages and information notes 4 Log level 3 messages and debug messages authentication_windows_use_principal_name
Command-Line Format --authentication-windows-use-principal-name[={OFF|ON}]
System Variable authentication_windows_use_principal_name
Scope Global Dynamic No Type Boolean Default Value ON
This variable is available only if the
authentication_windows
Windows authentication plugin is enabled. See Section 6.4.1.8, “Windows Pluggable Authentication”.A client that authenticates using the
InitSecurityContext()
function should provide a string identifying the service to which it connects (targetName
). MySQL uses the principal name (UPN) of the account under which the server is running. The UPN has the form
and need not be registered anywhere to be used. This UPN is sent by the server at the beginning of authentication handshake.user_id
@computer_name
This variable controls whether the server sends the UPN in the initial challenge. By default, the variable is enabled. For security reasons, it can be disabled to avoid sending the server's account name to a client as cleartext. If the variable is disabled, the server always sends a
0x00
byte in the first challenge, the client does not specifytargetName
, and as a result, NTLM authentication is used.If the server fails to obtain its UPN (which happens primarily in environments that do not support Kerberos authentication), the UPN is not sent by the server and NTLM authentication is used.
-
Command-Line Format --autocommit[={OFF|ON}]
System Variable autocommit
Scope Global, Session Dynamic Yes Type Boolean Default Value ON
The autocommit mode. If set to 1, all changes to a table take effect immediately. If set to 0, you must use
COMMIT
to accept a transaction orROLLBACK
to cancel it. Ifautocommit
is 0 and you change it to 1, MySQL performs an automaticCOMMIT
of any open transaction. Another way to begin a transaction is to use aSTART TRANSACTION
orBEGIN
statement. See Section 13.3.1, “START TRANSACTION, COMMIT, and ROLLBACK Statements”.By default, client connections begin with
autocommit
set to 1. To cause clients to begin with a default of 0, set the globalautocommit
value by starting the server with the--autocommit=0
option. To set the variable using an option file, include these lines:[mysqld] autocommit=0
-
Command-Line Format --automatic-sp-privileges[={OFF|ON}]
System Variable automatic_sp_privileges
Scope Global Dynamic Yes Type Boolean Default Value ON
When this variable has a value of 1 (the default), the server automatically grants the
EXECUTE
andALTER ROUTINE
privileges to the creator of a stored routine, if the user cannot already execute and alter or drop the routine. (TheALTER ROUTINE
privilege is required to drop the routine.) The server also automatically drops those privileges from the creator when the routine is dropped. Ifautomatic_sp_privileges
is 0, the server does not automatically add or drop these privileges.The creator of a routine is the account used to execute the
CREATE
statement for it. This might not be the same as the account named as theDEFINER
in the routine definition.If you start mysqld with
--skip-new
,automatic_sp_privileges
is set toOFF
.See also Section 23.2.2, “Stored Routines and MySQL Privileges”.
-
Command-Line Format --auto-generate-certs[={OFF|ON}]
System Variable auto_generate_certs
Scope Global Dynamic No Type Boolean Default Value ON
This variable is available if the server was compiled using OpenSSL (see Section 6.3.4, “SSL Library-Dependent Capabilities”). It controls whether the server autogenerates SSL key and certificate files in the data directory, if they do not already exist.
At startup, the server automatically generates server-side and client-side SSL certificate and key files in the data directory if the
auto_generate_certs
system variable is enabled, no SSL options other than--ssl
are specified, and the server-side SSL files are missing from the data directory. These files enable secure client connections using SSL; see Section 6.3.1, “Configuring MySQL to Use Encrypted Connections”.For more information about SSL file autogeneration, including file names and characteristics, see Section 6.3.3.1, “Creating SSL and RSA Certificates and Keys using MySQL”
The
sha256_password_auto_generate_rsa_keys
system variable is related but controls autogeneration of RSA key-pair files needed for secure password exchange using RSA over unencypted connections. -
Command-Line Format --avoid-temporal-upgrade[={OFF|ON}]
Deprecated Yes System Variable avoid_temporal_upgrade
Scope Global Dynamic Yes Type Boolean Default Value OFF
This variable controls whether
ALTER TABLE
implicitly upgrades temporal columns found to be in pre-5.6.4 format (TIME
,DATETIME
, andTIMESTAMP
columns without support for fractional seconds precision). Upgrading such columns requires a table rebuild, which prevents any use of fast alterations that might otherwise apply to the operation to be performed.This variable is disabled by default. Enabling it causes
ALTER TABLE
not to rebuild temporal columns and thereby be able to take advantage of possible fast alterations.This variable is deprecated; expect it to be removed in a future release of MySQL.
-
Command-Line Format --back-log=#
System Variable back_log
Scope Global Dynamic No Type Integer Default Value -1
(signifies autosizing; do not assign this literal value)Minimum Value 1
Maximum Value 65535
The number of outstanding connection requests MySQL can have. This comes into play when the main MySQL thread gets very many connection requests in a very short time. It then takes some time (although very little) for the main thread to check the connection and start a new thread. The
back_log
value indicates how many requests can be stacked during this short time before MySQL momentarily stops answering new requests. You need to increase this only if you expect a large number of connections in a short period of time.In other words, this value is the size of the listen queue for incoming TCP/IP connections. Your operating system has its own limit on the size of this queue. The manual page for the Unix
listen()
system call should have more details. Check your OS documentation for the maximum value for this variable.back_log
cannot be set higher than your operating system limit.The default value is based on the following formula, capped to a limit of 900:
50 + (max_connections / 5)
-
Command-Line Format --basedir=dir_name
System Variable basedir
Scope Global Dynamic No Type Directory name Default Value configuration-dependent default
The path to the MySQL installation base directory.
-
Command-Line Format --big-tables[={OFF|ON}]
System Variable big_tables
Scope Global, Session Dynamic Yes Type Boolean Default Value OFF
If enabled, the server stores all temporary tables on disk rather than in memory. This prevents most
The table
errors fortbl_name
is fullSELECT
operations that require a large temporary table, but also slows down queries for which in-memory tables would suffice.The default value for new connections is
OFF
(use in-memory temporary tables). Normally, it should never be necessary to enable this variable because the server is able to handle large result sets automatically by using memory for small temporary tables and switching to disk-based tables as required. -
Command-Line Format --bind-address=addr
System Variable bind_address
Scope Global Dynamic No Type String Default Value *
The MySQL server listens on a single network socket for TCP/IP connections. This socket is bound to a single address, but it is possible for an address to map onto multiple network interfaces. To specify an address, set
bind_address=
at server startup, whereaddr
addr
is an IPv4 or IPv6 address or a host name. Ifaddr
is a host name, the server resolves the name to an IP address and binds to that address. If a host name resolves to multiple IP addresses, the server uses the first IPv4 address if there are any, or the first IPv6 address otherwise.The server treats different types of addresses as follows:
If the address is
*
, the server accepts TCP/IP connections on all server host IPv4 interfaces, and, if the server host supports IPv6, on all IPv6 interfaces. Use this address to permit both IPv4 and IPv6 connections on all server interfaces. This value is the default.If the address is
0.0.0.0
, the server accepts TCP/IP connections on all server host IPv4 interfaces.If the address is
::
, the server accepts TCP/IP connections on all server host IPv4 and IPv6 interfaces.If the address is an IPv4-mapped address, the server accepts TCP/IP connections for that address, in either IPv4 or IPv6 format. For example, if the server is bound to
::ffff:127.0.0.1
, clients can connect using--host=127.0.0.1
or--host=::ffff:127.0.0.1
.If the address is a “regular” IPv4 or IPv6 address (such as
127.0.0.1
or::1
), the server accepts TCP/IP connections only for that IPv4 or IPv6 address.
If binding to the address fails, the server produces an error and does not start.
If you intend to bind the server to a specific address, be sure that the
mysql.user
system table contains an account with administrative privileges that you can use to connect to that address. Otherwise, you cannot shut down the server. For example, if you bind the server to*
, you can connect to it using all existing accounts. But if you bind the server to::1
, it accepts connections only on that address. In that case, first make sure that the'root'@'::1'
account is present in themysql.user
table so you can still connect to the server to shut it down.This variable has no effect for the embedded server (
libmysqld
) and is not visible within the embedded server. -
Command-Line Format --block-encryption-mode=#
System Variable block_encryption_mode
Scope Global, Session Dynamic Yes Type String Default Value aes-128-ecb
This variable controls the block encryption mode for block-based algorithms such as AES. It affects encryption for
AES_ENCRYPT()
andAES_DECRYPT()
.block_encryption_mode
takes a value inaes-
format, wherekeylen
-mode
keylen
is the key length in bits andmode
is the encryption mode. The value is not case-sensitive. Permittedkeylen
values are 128, 192, and 256. Permitted encryption modes depend on whether MySQL was compiled using OpenSSL or yaSSL:For OpenSSL, permitted
mode
values are:ECB
,CBC
,CFB1
,CFB8
,CFB128
,OFB
For yaSSL, permitted
mode
values are:ECB
,CBC
For example, this statement causes the AES encryption functions to use a key length of 256 bits and the CBC mode:
SET block_encryption_mode = 'aes-256-cbc';
An error occurs for attempts to set
block_encryption_mode
to a value containing an unsupported key length or a mode that the SSL library does not support. -
Command-Line Format --bulk-insert-buffer-size=#
System Variable bulk_insert_buffer_size
Scope Global, Session Dynamic Yes Type Integer Default Value 8388608
Minimum Value 0
Maximum Value (64-bit platforms) 18446744073709551615
Maximum Value (32-bit platforms) 4294967295
Unit bytes/thread MyISAM
uses a special tree-like cache to make bulk inserts faster forINSERT ... SELECT
,INSERT ... VALUES (...), (...), ...
, andLOAD DATA
when adding data to nonempty tables. This variable limits the size of the cache tree in bytes per thread. Setting it to 0 disables this optimization. The default value is 8MB. -
System Variable character_set_client
Scope Global, Session Dynamic Yes Type String Default Value utf8
The character set for statements that arrive from the client. The session value of this variable is set using the character set requested by the client when the client connects to the server. (Many clients support a
--default-character-set
option to enable this character set to be specified explicitly. See also Section 10.4, “Connection Character Sets and Collations”.) The global value of the variable is used to set the session value in cases when the client-requested value is unknown or not available, or the server is configured to ignore client requests:The client requests a character set not known to the server. For example, a Japanese-enabled client requests
sjis
when connecting to a server not configured withsjis
support.The client is from a version of MySQL older than MySQL 4.1, and thus does not request a character set.
mysqld was started with the
--skip-character-set-client-handshake
option, which causes it to ignore client character set configuration. This reproduces MySQL 4.0 behavior and is useful should you wish to upgrade the server without upgrading all the clients.
Some character sets cannot be used as the client character set. Attempting to use them as the
character_set_client
value produces an error. See Impermissible Client Character Sets. -
System Variable character_set_connection
Scope Global, Session Dynamic Yes Type String Default Value utf8
The character set used for literals specified without a character set introducer and for number-to-string conversion. For information about introducers, see Section 10.3.8, “Character Set Introducers”.
-
System Variable character_set_database
Scope Global, Session Dynamic Yes Type String Default Value latin1
Footnote This option is dynamic, but should be set only by server. You should not set this variable manually. The character set used by the default database. The server sets this variable whenever the default database changes. If there is no default database, the variable has the same value as
character_set_server
.The global
character_set_database
andcollation_database
system variables are deprecated in MySQL 5.7; expect them to be removed in a future version of MySQL.Assigning a value to the session
character_set_database
andcollation_database
system variables is deprecated in MySQL 5.7 and assignments produce a warning. You should expect the session variables to become read only in a future version of MySQL and assignments to produce an error, while remaining possible to access the session variables to determine the database character set and collation for the default database. -
Command-Line Format --character-set-filesystem=name
System Variable character_set_filesystem
Scope Global, Session Dynamic Yes Type String Default Value binary
The file system character set. This variable is used to interpret string literals that refer to file names, such as in the
LOAD DATA
andSELECT ... INTO OUTFILE
statements and theLOAD_FILE()
function. Such file names are converted fromcharacter_set_client
tocharacter_set_filesystem
before the file opening attempt occurs. The default value isbinary
, which means that no conversion occurs. For systems on which multibyte file names are permitted, a different value may be more appropriate. For example, if the system represents file names using UTF-8, setcharacter_set_filesystem
to'utf8mb4'
. -
System Variable character_set_results
Scope Global, Session Dynamic Yes Type String Default Value utf8
The character set used for returning query results to the client. This includes result data such as column values, result metadata such as column names, and error messages.
-
Command-Line Format --character-set-server=name
System Variable character_set_server
Scope Global, Session Dynamic Yes Type String Default Value latin1
The servers default character set. See Section 10.15, “Character Set Configuration”. If you set this variable, you should also set
collation_server
to specify the collation for the character set. -
System Variable character_set_system
Scope Global Dynamic No Type String Default Value utf8
The character set used by the server for storing identifiers. The value is always
utf8
. -
Command-Line Format --character-sets-dir=dir_name
System Variable character_sets_dir
Scope Global Dynamic No Type Directory name The directory where character sets are installed. See Section 10.15, “Character Set Configuration”.
-
Command-Line Format --check-proxy-users[={OFF|ON}]
System Variable check_proxy_users
Scope Global Dynamic Yes Type Boolean Default Value OFF
Some authentication plugins implement proxy user mapping for themselves (for example, the PAM and Windows authentication plugins). Other authentication plugins do not support proxy users by default. Of these, some can request that the MySQL server itself map proxy users according to granted proxy privileges:
mysql_native_password
,sha256_password
.If the
check_proxy_users
system variable is enabled, the server performs proxy user mapping for any authentication plugins that make such a request. However, it may also be necessary to enable plugin-specific system variables to take advantage of server proxy user mapping support:For the
mysql_native_password
plugin, enablemysql_native_password_proxy_users
.For the
sha256_password
plugin, enablesha256_password_proxy_users
.
For information about user proxying, see Section 6.2.14, “Proxy Users”.
-
System Variable collation_connection
Scope Global, Session Dynamic Yes Type String The collation of the connection character set.
collation_connection
is important for comparisons of literal strings. For comparisons of strings with column values,collation_connection
does not matter because columns have their own collation, which has a higher collation precedence (see Section 10.8.4, “Collation Coercibility in Expressions”). -
System Variable collation_database
Scope Global, Session Dynamic Yes Type String Default Value latin1_swedish_ci
Footnote This option is dynamic, but should be set only by server. You should not set this variable manually. The collation used by the default database. The server sets this variable whenever the default database changes. If there is no default database, the variable has the same value as
collation_server
.The global
character_set_database
andcollation_database
system variables are deprecated in MySQL 5.7; expect them to be removed in a future version of MySQL.Assigning a value to the session
character_set_database
andcollation_database
system variables is deprecated in MySQL 5.7 and assignments produce a warning. Expect the session variables to become read only in a future version of MySQL and assignments to produce an error, while remaining possible to access the session variables to determine the database character set and collation for the default database. -
Command-Line Format --collation-server=name
System Variable collation_server
Scope Global, Session Dynamic Yes Type String Default Value latin1_swedish_ci
The server's default collation. See Section 10.15, “Character Set Configuration”.
-
Command-Line Format --completion-type=#
System Variable completion_type
Scope Global, Session Dynamic Yes Type Enumeration Default Value NO_CHAIN
Valid Values NO_CHAIN
CHAIN
RELEASE
0
1
2
The transaction completion type. This variable can take the values shown in the following table. The variable can be assigned using either the name values or corresponding integer values.
Value Description NO_CHAIN
(or 0)COMMIT
andROLLBACK
are unaffected. This is the default value.CHAIN
(or 1)COMMIT
andROLLBACK
are equivalent toCOMMIT AND CHAIN
andROLLBACK AND CHAIN
, respectively. (A new transaction starts immediately with the same isolation level as the just-terminated transaction.)RELEASE
(or 2)COMMIT
andROLLBACK
are equivalent toCOMMIT RELEASE
andROLLBACK RELEASE
, respectively. (The server disconnects after terminating the transaction.)completion_type
affects transactions that begin withSTART TRANSACTION
orBEGIN
and end withCOMMIT
orROLLBACK
. It does not apply to implicit commits resulting from execution of the statements listed in Section 13.3.3, “Statements That Cause an Implicit Commit”. It also does not apply forXA COMMIT
,XA ROLLBACK
, or whenautocommit=1
. -
Command-Line Format --concurrent-insert[=value]
System Variable concurrent_insert
Scope Global Dynamic Yes Type Enumeration Default Value AUTO
Valid Values NEVER
AUTO
ALWAYS
0
1
2
If
AUTO
(the default), MySQL permitsINSERT
andSELECT
statements to run concurrently forMyISAM
tables that have no free blocks in the middle of the data file.This variable can take the values shown in the following table. The variable can be assigned using either the name values or corresponding integer values.
Value Description NEVER
(or 0)Disables concurrent inserts AUTO
(or 1)(Default) Enables concurrent insert for MyISAM
tables that do not have holesALWAYS
(or 2)Enables concurrent inserts for all MyISAM
tables, even those that have holes. For a table with a hole, new rows are inserted at the end of the table if it is in use by another thread. Otherwise, MySQL acquires a normal write lock and inserts the row into the hole.If you start mysqld with
--skip-new
,concurrent_insert
is set toNEVER
.See also Section 8.11.3, “Concurrent Inserts”.
-
Command-Line Format --connect-timeout=#
System Variable connect_timeout
Scope Global Dynamic Yes Type Integer Default Value 10
Minimum Value 2
Maximum Value 31536000
Unit seconds The number of seconds that the mysqld server waits for a connect packet before responding with
Bad handshake
. The default value is 10 seconds.Increasing the
connect_timeout
value might help if clients frequently encounter errors of the formLost connection to MySQL server at '
.XXX
', system error:errno
-
System Variable core_file
Scope Global Dynamic No Type Boolean Default Value OFF
Whether to write a core file if the server unexpectedly exits. This variable is set by the
--core-file
option. -
Command-Line Format --datadir=dir_name
System Variable datadir
Scope Global Dynamic No Type Directory name The path to the MySQL server data directory. Relative paths are resolved with respect to the current directory. If you expect the server to be started automatically (that is, in contexts for which you cannot assume what the current directory is), it is best to specify the
datadir
value as an absolute path. This variable is unused. It is deprecated and is removed in MySQL 8.0.
This variable is unused. It is deprecated and is removed in MySQL 8.0.
-
Command-Line Format --debug[=debug_options]
System Variable debug
Scope Global, Session Dynamic Yes Type String Default Value (Unix) d:t:i:o,/tmp/mysqld.trace
Default Value (Windows) d:t:i:O,\mysqld.trace
This variable indicates the current debugging settings. It is available only for servers built with debugging support. The initial value comes from the value of instances of the
--debug
option given at server startup. The global and session values may be set at runtime.Setting the session value of this system variable is a restricted operation. The session user must have privileges sufficient to set restricted session variables. See Section 5.1.8.1, “System Variable Privileges”.
Assigning a value that begins with
+
or-
cause the value to added to or subtracted from the current value:mysql> SET debug = 'T'; mysql> SELECT @@debug; +---------+ | @@debug | +---------+ | T | +---------+ mysql> SET debug = '+P'; mysql> SELECT @@debug; +---------+ | @@debug | +---------+ | P:T | +---------+ mysql> SET debug = '-P'; mysql> SELECT @@debug; +---------+ | @@debug | +---------+ | T | +---------+
For more information, see Section 5.8.3, “The DBUG Package”.
-
System Variable debug_sync
Scope Session Dynamic Yes Type String This variable is the user interface to the Debug Sync facility. Use of Debug Sync requires that MySQL be configured with the
-DWITH_DEBUG=ON
CMake option (see Section 2.8.7, “MySQL Source-Configuration Options”); otherwise, this system variable is not available.The global variable value is read only and indicates whether the facility is enabled. By default, Debug Sync is disabled and the value of
debug_sync
isOFF
. If the server is started with--debug-sync-timeout=
, whereN
N
is a timeout value greater than 0, Debug Sync is enabled and the value ofdebug_sync
isON - current signal
followed by the signal name. Also,N
becomes the default timeout for individual synchronization points.The session value can be read by any user and has the same value as the global variable. The session value can be set to control synchronization points.
Setting the session value of this system variable is a restricted operation. The session user must have privileges sufficient to set restricted session variables. See Section 5.1.8.1, “System Variable Privileges”.
For a description of the Debug Sync facility and how to use synchronization points, see MySQL Server Doxygen Documentation.
-
Command-Line Format --default-authentication-plugin=plugin_name
System Variable default_authentication_plugin
Scope Global Dynamic No Type Enumeration Default Value mysql_native_password
Valid Values mysql_native_password
sha256_password
The default authentication plugin. These values are permitted:
mysql_native_password
: Use MySQL native passwords; see Section 6.4.1.1, “Native Pluggable Authentication”.sha256_password
: Use SHA-256 passwords; see Section 6.4.1.5, “SHA-256 Pluggable Authentication”.
NoteIf this variable has a value other than
mysql_native_password
, clients older than MySQL 5.5.7 cannot connect because, of the permitted default authentication plugins, they understand only themysql_native_password
authentication protocol.The
default_authentication_plugin
value affects these aspects of server operation:It determines which authentication plugin the server assigns to new accounts created by
CREATE USER
andGRANT
statements that do not explicitly specify an authentication plugin.The
old_passwords
system variable affects password hashing for accounts that use themysql_native_password
orsha256_password
authentication plugin. If the default authentication plugin is one of those plugins, the server setsold_passwords
at startup to the value required by the plugin password hashing method.For an account created with either of the following statements, the server associates the account with the default authentication plugin and assigns the account the given password, hashed as required by that plugin:
CREATE USER ... IDENTIFIED BY 'cleartext password'; GRANT ... IDENTIFIED BY 'cleartext password';
For an account created with either of the following statements, the server associates the account with the default authentication plugin and assigns the account the given password hash, if the password hash has the format required by the plugin:
CREATE USER ... IDENTIFIED BY PASSWORD 'encrypted password'; GRANT ... IDENTIFIED BY PASSWORD 'encrypted password';
If the password hash is not in the format required by the default authentication plugin, the statement fails.
-
Command-Line Format --default-password-lifetime=#
System Variable default_password_lifetime
Scope Global Dynamic Yes Type Integer Default Value (≥ 5.7.11) 0
Default Value (≤ 5.7.10) 360
Minimum Value 0
Maximum Value 65535
Unit days This variable defines the global automatic password expiration policy. The default
default_password_lifetime
value is 0, which disables automatic password expiration. If the value ofdefault_password_lifetime
is a positive integerN
, it indicates the permitted password lifetime; passwords must be changed everyN
days.The global password expiration policy can be overridden as desired for individual accounts using the password expiration options of the
ALTER USER
statement. See Section 6.2.11, “Password Management”.NotePrior to MySQL 5.7.11, the default
default_password_lifetime
value is 360 (passwords must be changed approximately once per year). For those versions, be aware that, if you make no changes to thedefault_password_lifetime
variable or to individual user accounts, all user passwords expire after 360 days, and all user accounts start running in restricted mode when this happens. Clients (which are effectively users) connecting to the server then get an error indicating that the password must be changed:ERROR 1820 (HY000): You must reset your password using ALTER USER statement before executing this statement.
However, this is easy to miss for clients that automatically connect to the server, such as connections made from scripts. To avoid having such clients suddenly stop working due to a password expiring, make sure to change the password expiration settings for those clients, like this:
ALTER USER 'script'@'localhost' PASSWORD EXPIRE NEVER;
Alternatively, set the
default_password_lifetime
variable to0
, thus disabling automatic password expiration for all users. -
Command-Line Format --default-storage-engine=name
System Variable default_storage_engine
Scope Global, Session Dynamic Yes Type Enumeration Default Value InnoDB
The default storage engine for tables. See Chapter 15, Alternative Storage Engines. This variable sets the storage engine for permanent tables only. To set the storage engine for
TEMPORARY
tables, set thedefault_tmp_storage_engine
system variable.To see which storage engines are available and enabled, use the
SHOW ENGINES
statement or query theINFORMATION_SCHEMA
ENGINES
table.If you disable the default storage engine at server startup, you must set the default engine for both permanent and
TEMPORARY
tables to a different engine or the server cannot start. -
Command-Line Format --default-tmp-storage-engine=name
System Variable default_tmp_storage_engine
Scope Global, Session Dynamic Yes Type Enumeration Default Value InnoDB
The default storage engine for
TEMPORARY
tables (created withCREATE TEMPORARY TABLE
). To set the storage engine for permanent tables, set thedefault_storage_engine
system variable. Also see the discussion of that variable regarding possible values.If you disable the default storage engine at server startup, you must set the default engine for both permanent and
TEMPORARY
tables to a different engine or the server cannot start. -
Command-Line Format --default-week-format=#
System Variable default_week_format
Scope Global, Session Dynamic Yes Type Integer Default Value 0
Minimum Value 0
Maximum Value 7
The default mode value to use for the
WEEK()
function. See Section 12.7, “Date and Time Functions”. -
Command-Line Format --delay-key-write[={OFF|ON|ALL}]
System Variable delay_key_write
Scope Global Dynamic Yes Type Enumeration Default Value ON
Valid Values OFF
ON
ALL
This variable specifies how to use delayed key writes. It applies only to
MyISAM
tables. Delayed key writing causes key buffers not to be flushed between writes. See also Section 15.2.1, “MyISAM Startup Options”.This variable can have one of the following values to affect handling of the
DELAY_KEY_WRITE
table option that can be used inCREATE TABLE
statements.Option Description OFF
DELAY_KEY_WRITE
is ignored.ON
MySQL honors any DELAY_KEY_WRITE
option specified inCREATE 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.NoteIf you set this variable to
ALL
, you should not useMyISAM
tables from within another program (such as another MySQL server or myisamchk) when the tables are in use. Doing so leads to index corruption.If
DELAY_KEY_WRITE
is enabled for a table, the key buffer is not flushed for the table on every index update, but only when the table is closed. This speeds up writes on keys a lot, but if you use this feature, you should add automatic checking of allMyISAM
tables by starting the server with themyisam_recover_options
system variable set (for example,myisam_recover_options='BACKUP,FORCE'
). See Section 5.1.7, “Server System Variables”, and Section 15.2.1, “MyISAM Startup Options”.If you start mysqld with
--skip-new
,delay_key_write
is set toOFF
.WarningIf you enable external locking with
--external-locking
, there is no protection against index corruption for tables that use delayed key writes. -
Command-Line Format --delayed-insert-limit=#
Deprecated Yes System Variable delayed_insert_limit
Scope Global Dynamic Yes Type Integer Default Value 100
Minimum Value 1
Maximum Value (64-bit platforms) 18446744073709551615
Maximum Value (32-bit platforms) 4294967295
This system variable is deprecated (because
DELAYED
inserts are not supported); expect it to be removed in a future release. -
Command-Line Format --delayed-insert-timeout=#
Deprecated Yes System Variable delayed_insert_timeout
Scope Global Dynamic Yes Type Integer Default Value 300
Minimum Value 1
Maximum Value 31536000
Unit seconds This system variable is deprecated (because
DELAYED
inserts are not supported); expect it to be removed in a future release. -
Command-Line Format --delayed-queue-size=#
Deprecated Yes System Variable delayed_queue_size
Scope Global Dynamic Yes Type Integer Default Value 1000
Minimum Value 1
Maximum Value (64-bit platforms) 18446744073709551615
Maximum Value (32-bit platforms) 4294967295
This system variable is deprecated (because
DELAYED
inserts are not supported); expect it to be removed in a future release. -
Command-Line Format --disabled-storage-engines=engine[,engine]...
System Variable disabled_storage_engines
Scope Global Dynamic No Type String Default Value empty string
This variable indicates which storage engines cannot be used to create tables or tablespaces. For example, to prevent new
MyISAM
orFEDERATED
tables from being created, start the server with these lines in the server option file:[mysqld] disabled_storage_engines="MyISAM,FEDERATED"
By default,
disabled_storage_engines
is empty (no engines disabled), but it can be set to a comma-separated list of one or more engines (not case-sensitive). Any engine named in the value cannot be used to create tables or tablespaces withCREATE TABLE
orCREATE TABLESPACE
, and cannot be used withALTER TABLE ... ENGINE
orALTER TABLESPACE ... ENGINE
to change the storage engine of existing tables or tablespaces. Attempts to do so result in anER_DISABLED_STORAGE_ENGINE
error.disabled_storage_engines
does not restrict other DDL statements for existing tables, such asCREATE INDEX
,TRUNCATE TABLE
,ANALYZE TABLE
,DROP TABLE
, orDROP TABLESPACE
. This permits a smooth transition so that existing tables or tablespaces that use a disabled engine can be migrated to a permitted engine by means such asALTER TABLE ... ENGINE
.permitted_engine
It is permitted to set the
default_storage_engine
ordefault_tmp_storage_engine
system variable to a storage engine that is disabled. This could cause applications to behave erratically or fail, although that might be a useful technique in a development environment for identifying applications that use disabled engines, so that they can be modified.disabled_storage_engines
is disabled and has no effect if the server is started with any of these options:--bootstrap
,--initialize
,--initialize-insecure
,--skip-grant-tables
.NoteSetting
disabled_storage_engines
might cause an issue with mysql_upgrade. For details, see Section 4.4.7, “mysql_upgrade — Check and Upgrade MySQL Tables”. disconnect_on_expired_password
Command-Line Format --disconnect-on-expired-password[={OFF|ON}]
System Variable disconnect_on_expired_password
Scope Global Dynamic No Type Boolean Default Value ON
This variable controls how the server handles clients with expired passwords:
If the client indicates that it can handle expired passwords, the value of
disconnect_on_expired_password
is irrelevant. The server permits the client to connect but puts it in sandbox mode.If the client does not indicate that it can handle expired passwords, the server handles the client according to the value of
disconnect_on_expired_password
:If
disconnect_on_expired_password
: is enabled, the server disconnects the client.If
disconnect_on_expired_password
: is disabled, the server permits the client to connect but puts it in sandbox mode.
For more information about the interaction of client and server settings relating to expired-password handling, see Section 6.2.12, “Server Handling of Expired Passwords”.
-
Command-Line Format --div-precision-increment=#
System Variable div_precision_increment
Scope Global, Session Dynamic Yes Type Integer Default Value 4
Minimum Value 0
Maximum Value 30
This variable indicates the number of digits by which to increase the scale of the result of division operations performed with the
/
operator. The default value is 4. The minimum and maximum values are 0 and 30, respectively. The following example illustrates the effect of increasing the default value.mysql> SELECT 1/7; +--------+ | 1/7 | +--------+ | 0.1429 | +--------+ mysql> SET div_precision_increment = 12; mysql> SELECT 1/7; +----------------+ | 1/7 | +----------------+ | 0.142857142857 | +----------------+
-
Command-Line Format --end-markers-in-json[={OFF|ON}]
System Variable end_markers_in_json
Scope Global, Session Dynamic Yes Type Boolean Default Value OFF
Whether optimizer JSON output should add end markers. See MySQL Internals: The end_markers_in_json System Variable.
-
Command-Line Format --eq-range-index-dive-limit=#
System Variable eq_range_index_dive_limit
Scope Global, Session Dynamic Yes Type Integer Default Value 200
Minimum Value 0
Maximum Value 4294967295
This variable indicates the number of equality ranges in an equality comparison condition when the optimizer should switch from using index dives to index statistics in estimating the number of qualifying rows. It applies to evaluation of expressions that have either of these equivalent forms, where the optimizer uses a nonunique index to look up
col_name
values:col_name IN(val1, ..., valN) col_name = val1 OR ... OR col_name = valN
In both cases, the expression contains
N
equality ranges. The optimizer can make row estimates using index dives or index statistics. Ifeq_range_index_dive_limit
is greater than 0, the optimizer uses existing index statistics instead of index dives if there areeq_range_index_dive_limit
or more equality ranges. Thus, to permit use of index dives for up toN
equality ranges, seteq_range_index_dive_limit
toN
+ 1. To disable use of index statistics and always use index dives regardless ofN
, seteq_range_index_dive_limit
to 0.For more information, see Equality Range Optimization of Many-Valued Comparisons.
To update table index statistics for best estimates, use
ANALYZE TABLE
. The number of errors that resulted from the last statement that generated messages. This variable is read only. See Section 13.7.5.17, “SHOW ERRORS Statement”.
-
Command-Line Format --event-scheduler[=value]
System Variable event_scheduler
Scope Global Dynamic Yes Type Enumeration Default Value OFF
Valid Values OFF
ON
DISABLED
This variable enables or disables, and starts or stops, the Event Scheduler. The possible status values are
ON
,OFF
, andDISABLED
. Turning the Event SchedulerOFF
is not the same as disabling the Event Scheduler, which requires setting the status toDISABLED
. This variable and its effects on the Event Scheduler's operation are discussed in greater detail in Section 23.4.2, “Event Scheduler Configuration” explicit_defaults_for_timestamp
Command-Line Format --explicit-defaults-for-timestamp[={OFF|ON}]
Deprecated Yes System Variable explicit_defaults_for_timestamp
Scope Global, Session Dynamic Yes Type Boolean Default Value OFF
This system variable determines whether the server enables certain nonstandard behaviors for default values and
NULL
-value handling inTIMESTAMP
columns. By default,explicit_defaults_for_timestamp
is disabled, which enables the nonstandard behaviors.If
explicit_defaults_for_timestamp
is disabled, the server enables the nonstandard behaviors and handlesTIMESTAMP
columns as follows:TIMESTAMP
columns not explicitly declared with theNULL
attribute are automatically declared with theNOT NULL
attribute. Assigning such a column a value ofNULL
is permitted and sets the column to the current timestamp.The first
TIMESTAMP
column in a table, if not explicitly declared with theNULL
attribute or an explicitDEFAULT
orON UPDATE
attribute, is automatically declared with theDEFAULT CURRENT_TIMESTAMP
andON UPDATE CURRENT_TIMESTAMP
attributes.TIMESTAMP
columns following the first one, if not explicitly declared with theNULL
attribute or an explicitDEFAULT
attribute, are automatically declared asDEFAULT '0000-00-00 00:00:00'
(the “zero” timestamp). For inserted rows that specify no explicit value for such a column, the column is assigned'0000-00-00 00:00:00'
and no warning occurs.Depending on whether strict SQL mode or the
NO_ZERO_DATE
SQL mode is enabled, a default value of'0000-00-00 00:00:00'
may be invalid. Be aware that theTRADITIONAL
SQL mode includes strict mode andNO_ZERO_DATE
. See Section 5.1.10, “Server SQL Modes”.
The nonstandard behaviors just described are deprecated; expect them to be removed in a future release of MySQL.
If
explicit_defaults_for_timestamp
is enabled, the server disables the nonstandard behaviors and handlesTIMESTAMP
columns as follows:It is not possible to assign a
TIMESTAMP
column a value ofNULL
to set it to the current timestamp. To assign the current timestamp, set the column toCURRENT_TIMESTAMP
or a synonym such asNOW()
.TIMESTAMP
columns not explicitly declared with theNOT NULL
attribute are automatically declared with theNULL
attribute and permitNULL
values. Assigning such a column a value ofNULL
sets it toNULL
, not the current timestamp.TIMESTAMP
columns declared with theNOT NULL
attribute do not permitNULL
values. For inserts that specifyNULL
for such a column, the result is either an error for a single-row insert if strict SQL mode is enabled, or'0000-00-00 00:00:00'
is inserted for multiple-row inserts with strict SQL mode disabled. In no case does assigning the column a value ofNULL
set it to the current timestamp.TIMESTAMP
columns explicitly declared with theNOT NULL
attribute and without an explicitDEFAULT
attribute are treated as having no default value. For inserted rows that specify no explicit value for such a column, the result depends on the SQL mode. If strict SQL mode is enabled, an error occurs. If strict SQL mode is not enabled, the column is declared with the implicit default of'0000-00-00 00:00:00'
and a warning occurs. This is similar to how MySQL treats other temporal types such asDATETIME
.No
TIMESTAMP
column is automatically declared with theDEFAULT CURRENT_TIMESTAMP
orON UPDATE CURRENT_TIMESTAMP
attributes. Those attributes must be explicitly specified.The first
TIMESTAMP
column in a table is not handled differently fromTIMESTAMP
columns following the first one.
If
explicit_defaults_for_timestamp
is disabled at server startup, this warning appears in the error log:[Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details).
As indicated by the warning, to disable the deprecated nonstandard behaviors, enable the
explicit_defaults_for_timestamp
system variable at server startup.Noteexplicit_defaults_for_timestamp
is itself deprecated because its only purpose is to permit control over deprecatedTIMESTAMP
behaviors that are to be removed in a future release of MySQL. When removal of those behaviors occurs,explicit_defaults_for_timestamp
no longer has any purpose, and you can expect it to be removed as well.For additional information, see Section 11.2.6, “Automatic Initialization and Updating for TIMESTAMP and DATETIME”.
-
System Variable external_user
Scope Session Dynamic No Type String The external user name used during the authentication process, as set by the plugin used to authenticate the client. With native (built-in) MySQL authentication, or if the plugin does not set the value, this variable is
NULL
. See Section 6.2.14, “Proxy Users”. -
Command-Line Format --flush[={OFF|ON}]
System Variable flush
Scope Global Dynamic Yes Type Boolean Default Value OFF
If
ON
, the server flushes (synchronizes) all changes to disk after each SQL statement. Normally, MySQL does a write of all changes to disk only after each SQL statement and lets the operating system handle the synchronizing to disk. See Section B.3.3.3, “What to Do If MySQL Keeps Crashing”. This variable is set toON
if you start mysqld with the--flush
option.NoteIf
flush
is enabled, the value offlush_time
does not matter and changes toflush_time
have no effect on flush behavior. -
Command-Line Format --flush-time=#
System Variable flush_time
Scope Global Dynamic Yes Type Integer Default Value 0
Minimum Value 0
Maximum Value 31536000
Unit seconds If this is set to a nonzero value, all tables are closed every
flush_time
seconds to free up resources and synchronize unflushed data to disk. This option is best used only on systems with minimal resources.NoteIf
flush
is enabled, the value offlush_time
does not matter and changes toflush_time
have no effect on flush behavior. -
System Variable foreign_key_checks
Scope Global, Session Dynamic Yes Type Boolean Default Value ON
If set to 1 (the default), foreign key constraints are checked. If set to 0, foreign key constraints are ignored, with a couple of exceptions. When re-creating a table that was dropped, an error is returned if the table definition does not conform to the foreign key constraints referencing the table. Likewise, an
ALTER TABLE
operation returns an error if a foreign key definition is incorrectly formed. For more information, see Section 13.1.18.5, “FOREIGN KEY Constraints”.Setting this variable has the same effect on
NDB
tables as it does forInnoDB
tables. Typically you leave this setting enabled during normal operation, to enforce referential integrity. Disabling foreign key checking can be useful for reloadingInnoDB
tables in an order different from that required by their parent/child relationships. See Section 13.1.18.5, “FOREIGN KEY Constraints”.Setting
foreign_key_checks
to 0 also affects data definition statements:DROP SCHEMA
drops a schema even if it contains tables that have foreign keys that are referred to by tables outside the schema, andDROP TABLE
drops tables that have foreign keys that are referred to by other tables.NoteSetting
foreign_key_checks
to 1 does not trigger a scan of the existing table data. Therefore, rows added to the table whileforeign_key_checks=0
are not verified for consistency.Dropping an index required by a foreign key constraint is not permitted, even with
foreign_key_checks=0
. The foreign key constraint must be removed before dropping the index (Bug #70260). -
Command-Line Format --ft-boolean-syntax=name
System Variable ft_boolean_syntax
Scope Global Dynamic Yes Type String Default Value + -><()~*:""&|
The list of operators supported by boolean full-text searches performed using
IN BOOLEAN MODE
. See Section 12.9.2, “Boolean Full-Text Searches”.The default variable value is
'+ -><()~*:""&|'
. The rules for changing the value are as follows:Operator function is determined by position within the string.
The replacement value must be 14 characters.
Each character must be an ASCII nonalphanumeric character.
Either the first or second character must be a space.
No duplicates are permitted except the phrase quoting operators in positions 11 and 12. These two characters are not required to be the same, but they are the only two that may be.
Positions 10, 13, and 14 (which by default are set to
:
,&
, and|
) are reserved for future extensions.
-
Command-Line Format --ft-max-word-len=#
System Variable ft_max_word_len
Scope Global Dynamic No Type Integer Default Value 84
Minimum Value 10
Maximum Value 84
The maximum length of the word to be included in a
MyISAM
FULLTEXT
index.NoteFULLTEXT
indexes onMyISAM
tables must be rebuilt after changing this variable. UseREPAIR TABLE
.tbl_name
QUICK -
Command-Line Format --ft-min-word-len=#
System Variable ft_min_word_len
Scope Global Dynamic No Type Integer Default Value 4
Minimum Value 1
Maximum Value 82
The minimum length of the word to be included in a
MyISAM
FULLTEXT
index.NoteFULLTEXT
indexes onMyISAM
tables must be rebuilt after changing this variable. UseREPAIR TABLE
.tbl_name
QUICK -
Command-Line Format --ft-query-expansion-limit=#
System Variable ft_query_expansion_limit
Scope Global Dynamic No Type Integer Default Value 20
Minimum Value 0
Maximum Value 1000
The number of top matches to use for full-text searches performed using
WITH QUERY EXPANSION
. -
Command-Line Format --ft-stopword-file=file_name
System Variable ft_stopword_file
Scope Global Dynamic No Type File name The file from which to read the list of stopwords for full-text searches on
MyISAM
tables. The server looks for the file in the data directory unless an absolute path name is given to specify a different directory. All the words from the file are used; comments are not honored. By default, a built-in list of stopwords is used (as defined in thestorage/myisam/ft_static.c
file). Setting this variable to the empty string (''
) disables stopword filtering. See also Section 12.9.4, “Full-Text Stopwords”.NoteFULLTEXT
indexes onMyISAM
tables must be rebuilt after changing this variable or the contents of the stopword file. UseREPAIR TABLE
.tbl_name
QUICK -
Command-Line Format --general-log[={OFF|ON}]
System Variable general_log
Scope Global Dynamic Yes Type Boolean Default Value OFF
Whether the general query log is enabled. The value can be 0 (or
OFF
) to disable the log or 1 (orON
) to enable the log. The destination for log output is controlled by thelog_output
system variable; if that value isNONE
, no log entries are written even if the log is enabled. -
Command-Line Format --general-log-file=file_name
System Variable general_log_file
Scope Global Dynamic Yes Type File name Default Value host_name.log
The name of the general query log file. The default value is
, but the initial value can be changed with thehost_name
.log--general_log_file
option. -
Command-Line Format --group-concat-max-len=#
System Variable group_concat_max_len
Scope Global, Session Dynamic Yes Type Integer Default Value 1024
Minimum Value 4
Maximum Value (64-bit platforms) 18446744073709551615
Maximum Value (32-bit platforms) 4294967295
The maximum permitted result length in bytes for the
GROUP_CONCAT()
function. The default is 1024. YES
if thezlib
compression library is available to the server,NO
if not. If not, theCOMPRESS()
andUNCOMPRESS()
functions cannot be used.YES
if thecrypt()
system call is available to the server,NO
if not. If not, theENCRYPT()
function cannot be used.NoteThe
ENCRYPT()
function is deprecated in MySQL 5.7, will be removed in a future release of MySQL, and should no longer be used. (For one-way hashing, consider usingSHA2()
instead.) Consequently,have_crypt
also is deprecated; expect it to be removed in a future release.YES
if mysqld supports dynamic loading of plugins,NO
if not. If the value isNO
, you cannot use options such as--plugin-load
to load plugins at server startup, or theINSTALL PLUGIN
statement to load plugins at runtime.YES
if the server supports spatial data types,NO
if not.This variable is a synonym for
have_ssl
.YES
if statement profiling capability is present,NO
if not. If present, theprofiling
system variable controls whether this capability is enabled or disabled. See Section 13.7.5.31, “SHOW PROFILES Statement”.This variable is deprecated; expect it to be removed in a future release of MySQL.
YES
if mysqld supports the query cache,NO
if not.NoteThe query cache is deprecated as of MySQL 5.7.20, and is removed in MySQL 8.0. Deprecation includes
have_query_cache
.YES
ifRTREE
indexes are available,NO
if not. (These are used for spatial indexes inMyISAM
tables.)-
System Variable have_ssl
Scope Global Dynamic No Type String Valid Values YES
(SSL support available)DISABLED
(SSL support was compiled into server, but server was not started with necessary options to enable it)YES
if mysqld supports SSL connections,DISABLED
if the server was compiled with SSL support, but was not started with the appropriate connection-encryption options. For more information, see Section 2.8.6, “Configuring SSL Library Support”. -
System Variable have_statement_timeout
Scope Global Dynamic No Type Boolean Whether the statement execution timeout feature is available (see Statement Execution Time Optimizer Hints). The value can be
NO
if the background thread used by this feature could not be initialized. YES
if symbolic link support is enabled,NO
if not. This is required on Unix for support of theDATA DIRECTORY
andINDEX DIRECTORY
table options. If the server is started with the--skip-symbolic-links
option, the value isDISABLED
.This variable has no meaning on Windows.
-
Command-Line Format --host-cache-size=#
System Variable host_cache_size
Scope Global Dynamic Yes Type Integer Default Value -1
(signifies autosizing; do not assign this literal value)Minimum Value 0
Maximum Value 65536
The MySQL server maintains an in-memory host cache that contains client host name and IP address information and is used to avoid Domain Name System (DNS) lookups; see Section 5.1.11.2, “DNS Lookups and the Host Cache”.
The
host_cache_size
variable controls the size of the host cache, as well as the size of the Performance Schemahost_cache
table that exposes the cache contents. Settinghost_cache_size
has these effects:Setting the size to 0 disables the host cache. With the cache disabled, the server performs a DNS lookup every time a client connects.
Changing the size at runtime causes an implicit host cache flushing operation that clears the host cache, truncates the
host_cache
table, and unblocks any blocked hosts.
The default value is autosized to 128, plus 1 for a value of
max_connections
up to 500, plus 1 for every increment of 20 over 500 in themax_connections
value, capped to a limit of 2000.Using the
--skip-host-cache
option is similar to setting thehost_cache_size
system variable to 0, buthost_cache_size
is more flexible because it can also be used to resize, enable, and disable the host cache at runtime, not just at server startup.Starting the server with
--skip-host-cache
does not prevent runtime changes to the value ofhost_cache_size
, but such changes have no effect and the cache is not re-enabled even ifhost_cache_size
is set larger than 0.Setting the
host_cache_size
system variable rather than the--skip-host-cache
option is preferred for the reasons given in the previous paragraph. In addition, the--skip-host-cache
option is deprecated in MySQL 8.0, and its removal is expected in a future version of MySQL. -
System Variable hostname
Scope Global Dynamic No Type String The server sets this variable to the server host name at startup.
This variable is a synonym for the
last_insert_id
variable. It exists for compatibility with other database systems. You can read its value withSELECT @@identity
, and set it usingSET identity
.-
Deprecated 5.7.16 System Variable ignore_db_dirs
Scope Global Dynamic No Type String A comma-separated list of names that are not considered as database directories in the data directory. The value is set from any instances of
--ignore-db-dir
given at server startup.As of MySQL 5.7.11,
--ignore-db-dir
can be used at data directory initialization time with mysqld --initialize to specify directories that the server should ignore for purposes of assessing whether an existing data directory is considered empty. See Section 2.9.1, “Initializing the Data Directory”.This system variable is deprecated in MySQL 5.7. With the introduction of the data dictionary in MySQL 8.0, it became superfluous and was removed in that version.
-
Command-Line Format --init-connect=name
System Variable init_connect
Scope Global Dynamic Yes Type String A string to be executed by the server for each client that connects. The string consists of one or more SQL statements, separated by semicolon characters.
For users that have the
SUPER
privilege, the content ofinit_connect
is not executed. This is done so that an erroneous value forinit_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 executinginit_connect
for users that have theSUPER
privilege enables them to open a connection and fix theinit_connect
value.As of MySQL 5.7.22,
init_connect
execution is skipped for any client user with an expired password. This is done because such a user cannot execute arbitrary statements, and thusinit_connect
execution fails, leaving the client unable to connect. Skippinginit_connect
execution enables the user to connect and change password.The server discards any result sets produced by statements in the value of
init_connect
. -
Command-Line Format --init-file=file_name
System Variable init_file
Scope Global Dynamic No Type File name If specified, this variable names a file containing SQL statements to be read and executed during the startup process. Each statement must be on a single line and should not include comments.
If the server is started with any of the
--bootstrap
,--initialize
, or--initialize-insecure
options, it operates in bootstap mode and some functionality is unavailable that limits the statements permitted in the file. These include statements that relate to account management (such asCREATE USER
orGRANT
), replication, and global transaction identifiers. See Section 16.1.3, “Replication with Global Transaction Identifiers”. innodb_
xxx
InnoDB
system variables are listed in Section 14.15, “InnoDB Startup Options and System Variables”. These variables control many aspects of storage, memory use, and I/O patterns forInnoDB
tables, and are especially important now thatInnoDB
is the default storage engine.The value to be used by the following
INSERT
orALTER TABLE
statement when inserting anAUTO_INCREMENT
value. This is mainly used with the binary log.-
Command-Line Format --interactive-timeout=#
System Variable interactive_timeout
Scope Global, Session Dynamic Yes Type Integer Default Value 28800
Minimum Value 1
Maximum Value 31536000
Unit seconds 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 tomysql_real_connect()
. See alsowait_timeout
. internal_tmp_disk_storage_engine
Command-Line Format --internal-tmp-disk-storage-engine=#
System Variable internal_tmp_disk_storage_engine
Scope Global Dynamic Yes Type Enumeration Default Value INNODB
Valid Values MYISAM
INNODB
The storage engine for on-disk internal temporary tables (see Section 8.4.4, “Internal Temporary Table Use in MySQL”). Permitted values are
MYISAM
andINNODB
(the default).The optimizer uses the storage engine defined by
internal_tmp_disk_storage_engine
for on-disk internal temporary tables.When using
internal_tmp_disk_storage_engine=INNODB
(the default), queries that generate on-disk internal temporary tables that exceedInnoDB
row or column limits return Row size too large or Too many columns errors. The workaround is to setinternal_tmp_disk_storage_engine
toMYISAM
.-
Command-Line Format --join-buffer-size=#
System Variable join_buffer_size
Scope Global, Session Dynamic Yes Type Integer Default Value 262144
Minimum Value 128
Maximum Value (Windows) 4294967168
Maximum Value (Other, 64-bit platforms) 18446744073709551488
Maximum Value (Other, 32-bit platforms) 4294967168
Unit bytes Block Size 128
The minimum size of the buffer that is used for plain index scans, range index scans, and joins that do not use indexes and thus perform full table scans. Normally, the best way to get fast joins is to add indexes. Increase the value of
join_buffer_size
to get a faster full join when adding indexes is not possible. One join buffer is allocated for each full join between two tables. For a complex join between several tables for which indexes are not used, multiple join buffers might be necessary.The default is 256KB. The maximum permissible setting for
join_buffer_size
is 4GB−1. Larger values are permitted for 64-bit platforms (except 64-bit Windows, for which large values are truncated to 4GB−1 with a warning). The block size is 128, and a value that is not an exact multiple of the block size is rounded down to the next lower multiple of the block size by MySQL Server before storing the value for the system variable. The parser allows values up to the maximum unsigned integer value for the platform (4294967295 or 232−1 for a 32-bit system, 18446744073709551615 or 264−1 for a 64-bit system) but the actual maximum is a block size lower.Unless a Block Nested-Loop or Batched Key Access algorithm is used, there is no gain from setting the buffer larger than required to hold each matching row, and all joins allocate at least the minimum size, so use caution in setting this variable to a large value globally. It is better to keep the global setting small and change the session setting to a larger value only in sessions that are doing large joins. Memory allocation time can cause substantial performance drops if the global size is larger than needed by most queries that use it.
When Block Nested-Loop is used, a larger join buffer can be beneficial up to the point where all required columns from all rows in the first table are stored in the join buffer. This depends on the query; the optimal size may be smaller than holding all rows from the first tables.
When Batched Key Access is used, the value of
join_buffer_size
defines how large the batch of keys is in each request to the storage engine. The larger the buffer, the more sequential access is made to the right hand table of a join operation, which can significantly improve performance.For additional information about join buffering, see Section 8.2.1.6, “Nested-Loop Join Algorithms”. For information about Batched Key Access, see Section 8.2.1.11, “Block Nested-Loop and Batched Key Access Joins”.
-
Command-Line Format --keep-files-on-create[={OFF|ON}]
System Variable keep_files_on_create
Scope Global, Session Dynamic Yes Type Boolean Default Value OFF
If a
MyISAM
table is created with noDATA DIRECTORY
option, the.MYD
file is created in the database directory. By default, ifMyISAM
finds an existing.MYD
file in this case, it overwrites it. The same applies to.MYI
files for tables created with noINDEX DIRECTORY
option. To suppress this behavior, set thekeep_files_on_create
variable toON
(1), in which caseMyISAM
does not overwrite existing files and returns an error instead. The default value isOFF
(0).If a
MyISAM
table is created with aDATA DIRECTORY
orINDEX DIRECTORY
option and an existing.MYD
or.MYI
file is found, MyISAM always returns an error. It does not overwrite a file in the specified directory. -
Command-Line Format --key-buffer-size=#
System Variable key_buffer_size
Scope Global Dynamic Yes Type Integer Default Value 8388608
Minimum Value 0
Maximum Value (64-bit platforms) OS_PER_PROCESS_LIMIT
Maximum Value (32-bit platforms) 4294967295
Unit bytes 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 minimum permissible setting is 0, but you cannot set
key_buffer_size
to 0 dynamically. A setting of 0 drops the key cache, which is not permitted at runtime. Settingkey_buffer_size
to 0 is permitted only at startup, in which case the key cache is not initialized. Changing thekey_buffer_size
setting at runtime from a value of 0 to a permitted non-zero value initializes the key cache.key_buffer_size
can be increased or decreased only in increments or multiples of 4096 bytes. Increasing or decreasing the setting by a nonconforming value produces a warning and truncates the setting to a conforming value.The maximum permissible setting for
key_buffer_size
is 4GB−1 on 32-bit platforms. Larger values are permitted for 64-bit platforms. The effective maximum size might be less, depending on your available physical RAM and per-process RAM limits imposed by your operating system or hardware platform. The value of this variable indicates the amount of memory requested. Internally, the server allocates as much memory as possible up to this amount, but the actual allocation might be less.You can increase the value to get better index handling for all reads and multiple writes; on a system whose primary function is to run MySQL using the
MyISAM
storage engine, 25% of the machine's total memory is an acceptable value for this variable. However, you should be aware that, if you make the value too large (for example, more than 50% of the machine's total memory), your system might start to page and become extremely slow. This is because MySQL relies on the operating system to perform file system caching for data reads, so you must leave some room for the file system cache. You should also consider the memory requirements of any other storage engines that you may be using in addition toMyISAM
.For even more speed when writing many rows at the same time, use
LOCK TABLES
. See Section 8.2.4.1, “Optimizing INSERT Statements”.You can check the performance of the key buffer by issuing a
SHOW STATUS
statement and examining theKey_read_requests
,Key_reads
,Key_write_requests
, andKey_writes
status variables. (See Section 13.7.5, “SHOW Statements”.) TheKey_reads/Key_read_requests
ratio should normally be less than 0.01. TheKey_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 theDELAY_KEY_WRITE
table option.The fraction of the key buffer in use can be determined using
key_buffer_size
in conjunction with theKey_blocks_unused
status variable and the buffer block size, which is available from thekey_cache_block_size
system variable:1 - ((Key_blocks_unused * key_cache_block_size) / key_buffer_size)
This value is an approximation because some space in the key buffer is allocated internally for administrative structures. Factors that influence the amount of overhead for these structures include block size and pointer size. As block size increases, the percentage of the key buffer lost to overhead tends to decrease. Larger blocks results in a smaller number of read operations (because more keys are obtained per read), but conversely an increase in reads of keys that are not examined (if not all keys in a block are relevant to a query).
It is possible to create multiple
MyISAM
key caches. The size limit of 4GB applies to each cache individually, not as a group. See Section 8.10.2, “The MyISAM Key Cache”. -
Command-Line Format --key-cache-age-threshold=#
System Variable key_cache_age_threshold
Scope Global Dynamic Yes Type Integer Default Value 300
Minimum Value 100
Maximum Value (64-bit platforms) 18446744073709551516
Maximum Value (32-bit platforms) 4294967196
Block Size 100
This value controls the demotion of buffers from the hot sublist of a key cache to the warm sublist. Lower values cause demotion to happen more quickly. The minimum value is 100. The default value is 300. See Section 8.10.2, “The MyISAM Key Cache”.
-
Command-Line Format --key-cache-block-size=#
System Variable key_cache_block_size
Scope Global Dynamic Yes Type Integer Default Value 1024
Minimum Value 512
Maximum Value 16384
Unit bytes Block Size 512
The size in bytes of blocks in the key cache. The default value is 1024. See Section 8.10.2, “The MyISAM Key Cache”.
-
Command-Line Format --key-cache-division-limit=#
System Variable key_cache_division_limit
Scope Global Dynamic Yes Type Integer Default Value 100
Minimum Value 1
Maximum Value 100
The division point between the hot and warm sublists of the key cache buffer list. The value is the percentage of the buffer list to use for the warm sublist. Permissible values range from 1 to 100. The default value is 100. See Section 8.10.2, “The MyISAM Key Cache”.
-
System Variable large_files_support
Scope Global Dynamic No Type Boolean Whether mysqld was compiled with options for large file support.
-
Command-Line Format --large-pages[={OFF|ON}]
System Variable large_pages
Scope Global Dynamic No Platform Specific Linux Type Boolean Default Value OFF
Whether large page support is enabled (via the
--large-pages
option). See Section 8.12.4.3, “Enabling Large Page Support”. -
System Variable large_page_size
Scope Global Dynamic No Type Integer Default Value 0
Minimum Value 0
Maximum Value 65535
Unit bytes If large page support is enabled, this shows the size of memory pages. Large memory pages are supported only on Linux; on other platforms, the value of this variable is always 0. See Section 8.12.4.3, “Enabling Large Page Support”.
The value to be returned from
LAST_INSERT_ID()
. This is stored in the binary log when you useLAST_INSERT_ID()
in a statement that updates a table. Setting this variable does not update the value returned by themysql_insert_id()
C API function.-
Command-Line Format --lc-messages=name
System Variable lc_messages
Scope Global, Session Dynamic Yes Type String Default Value en_US
The locale to use for error messages. The default is
en_US
. The server converts the argument to a language name and combines it with the value oflc_messages_dir
to produce the location for the error message file. See Section 10.12, “Setting the Error Message Language”. -
Command-Line Format --lc-messages-dir=dir_name
System Variable lc_messages_dir
Scope Global Dynamic No Type Directory name The directory where error messages are located. The server uses the value together with the value of
lc_messages
to produce the location for the error message file. See Section 10.12, “Setting the Error Message Language”. -
Command-Line Format --lc-time-names=value
System Variable lc_time_names
Scope Global, Session Dynamic Yes Type String This variable specifies the locale that controls the language used to display day and month names and abbreviations. This variable affects the output from the
DATE_FORMAT()
,DAYNAME()
andMONTHNAME()
functions. Locale names are POSIX-style values such as'ja_JP'
or'pt_BR'
. The default value is'en_US'
regardless of your system's locale setting. For further information, see Section 10.16, “MySQL Server Locale Support”. -
System Variable license
Scope Global Dynamic No Type String Default Value GPL
The type of license the server has.
-
Command-Line Format --local-infile[={OFF|ON}]
System Variable local_infile
Scope Global Dynamic Yes Type Boolean Default Value ON
This variable controls server-side
LOCAL
capability forLOAD DATA
statements. Depending on thelocal_infile
setting, the server refuses or permits local data loading by clients that haveLOCAL
enabled on the client side.To explicitly cause the server to refuse or permit
LOAD DATA LOCAL
statements (regardless of how client programs and libraries are configured at build time or runtime), start mysqld withlocal_infile
disabled or enabled, respectively.local_infile
can also be set at runtime. For more information, see Section 6.1.6, “Security Considerations for LOAD DATA LOCAL”. -
Command-Line Format --lock-wait-timeout=#
System Variable lock_wait_timeout
Scope Global, Session Dynamic Yes Type Integer Default Value 31536000
Minimum Value 1
Maximum Value 31536000
Unit seconds This variable specifies the timeout in seconds for attempts to acquire metadata locks. The permissible values range from 1 to 31536000 (1 year). The default is 31536000.
This timeout applies to all statements that use metadata locks. These include DML and DDL operations on tables, views, stored procedures, and stored functions, as well as
LOCK TABLES
,FLUSH TABLES WITH READ LOCK
, andHANDLER
statements.This timeout does not apply to implicit accesses to system tables in the
mysql
database, such as grant tables modified byGRANT
orREVOKE
statements or table logging statements. The timeout does apply to system tables accessed directly, such as withSELECT
orUPDATE
.The timeout value applies separately for each metadata lock attempt. A given statement can require more than one lock, so it is possible for the statement to block for longer than the
lock_wait_timeout
value before reporting a timeout error. When lock timeout occurs,ER_LOCK_WAIT_TIMEOUT
is reported.lock_wait_timeout
does not apply to delayed inserts, which always execute with a timeout of 1 year. This is done to avoid unnecessary timeouts because a session that issues a delayed insert receives no notification of delayed insert timeouts. -
System Variable locked_in_memory
Scope Global Dynamic No Type Boolean Default Value OFF
-
Command-Line Format --log-error[=file_name]
System Variable log_error
Scope Global Dynamic No Type File name The error log output destination. If the destination is the console, the value is
stderr
. Otherwise, the destination is a file and thelog_error
value is the file name. See Section 5.4.2, “The Error Log”. -
Command-Line Format --log-error-verbosity=#
System Variable log_error_verbosity
Scope Global Dynamic Yes Type Integer Default Value 3
Minimum Value 1
Maximum Value 3
The verbosity of the server in writing error, warning, and note messages to the error log. The following table shows the permitted values. The default is 3.
log_error_verbosity Value Permitted Messages 1 Error messages 2 Error and warning messages 3 Error, warning, and information messages log_error_verbosity
was added in MySQL 5.7.2. It is preferred over, and should be used instead of, the olderlog_warnings
system variable. See the description oflog_warnings
for information about how that variable relates tolog_error_verbosity
. In particular, assigning a value tolog_warnings
assigns a value tolog_error_verbosity
and vice versa. -
Command-Line Format --log-output=name
System Variable log_output
Scope Global Dynamic Yes Type Set Default Value FILE
Valid Values TABLE
FILE
NONE
The destination or destinations for general query log and slow query log output. The value is a list one or more comma-separated words chosen from
TABLE
,FILE
, andNONE
.TABLE
selects logging to thegeneral_log
andslow_log
tables in themysql
system database.FILE
selects logging to log files.NONE
disables logging. IfNONE
is present in the value, it takes precedence over any other words that are present.TABLE
andFILE
can both be given to select both log output destinations.This variable selects log output destinations, but does not enable log output. To do that, enable the
general_log
andslow_query_log
system variables. ForFILE
logging, thegeneral_log_file
andslow_query_log_file
system variables determine the log file locations. For more information, see Section 5.4.1, “Selecting General Query Log and Slow Query Log Output Destinations”. -
Command-Line Format --log-queries-not-using-indexes[={OFF|ON}]
System Variable log_queries_not_using_indexes
Scope Global Dynamic Yes Type Boolean Default Value OFF
If you enable this variable with the slow query log enabled, queries that are expected to retrieve all rows are logged. See Section 5.4.5, “The Slow Query Log”. This option does not necessarily mean that no index is used. For example, a query that uses a full index scan uses an index but would be logged because the index would not limit the number of rows.
-
Command-Line Format --log-slow-admin-statements[={OFF|ON}]
System Variable log_slow_admin_statements
Scope Global Dynamic Yes Type Boolean Default Value OFF
Include slow administrative statements in the statements written to the slow query log. Administrative statements include
ALTER TABLE
,ANALYZE TABLE
,CHECK TABLE
,CREATE INDEX
,DROP INDEX
,OPTIMIZE TABLE
, andREPAIR TABLE
. -
Command-Line Format --log-syslog[={OFF|ON}]
System Variable log_syslog
Scope Global Dynamic Yes Type Boolean Default Value (Unix) OFF
Default Value (Windows) ON
Whether to write error log output to the system log. This is the Event Log on Windows, and
syslog
on Unix and Unix-like systems. The default value is platform specific:On Windows, Event Log output is enabled by default.
On Unix and Unix-like systems,
syslog
output is disabled by default.
Regardless of the default,
log_syslog
can be set explicitly to control output on any supported platform.System log output control is distinct from sending error output to a file or the console. Error output can be directed to a file or the console in addition to or instead of the system log as desired. See Section 5.4.2, “The Error Log”.
-
Command-Line Format --log-syslog-facility=value
System Variable log_syslog_facility
Scope Global Dynamic Yes Type String Default Value daemon
The facility for error log output written to
syslog
(what type of program is sending the message). This variable has no effect unless thelog_syslog
system variable is enabled. See Section 5.4.2.3, “Error Logging to the System Log”.The permitted values can vary per operating system; consult your system
syslog
documentation.This variable does not exist on Windows.
-
Command-Line Format --log-syslog-include-pid[={OFF|ON}]
System Variable log_syslog_include_pid
Scope Global Dynamic Yes Type Boolean Default Value ON
Whether to include the server process ID in each line of error log output written to
syslog
. This variable has no effect unless thelog_syslog
system variable is enabled. See Section 5.4.2.3, “Error Logging to the System Log”.This variable does not exist on Windows.
-
Command-Line Format --log-syslog-tag=tag
System Variable log_syslog_tag
Scope Global Dynamic Yes Type String Default Value empty string
The tag to be added to the server identifier in error log output written to
syslog
. This variable has no effect unless thelog_syslog
system variable is enabled. See Section 5.4.2.3, “Error Logging to the System Log”.By default, the server identifier is
mysqld
with no tag. If a tag value oftag
is specified, it is appended to the server identifier with a leading hyphen, resulting in an identifier ofmysqld-
.tag
On Windows, to use a tag that does not already exist, the server must be run from an account with Administrator privileges, to permit creation of a registry entry for the tag. Elevated privileges are not required if the tag already exists.
-
Command-Line Format --log-timestamps=#
System Variable log_timestamps
Scope Global Dynamic Yes Type Enumeration Default Value UTC
Valid Values UTC
SYSTEM
This variable controls the time zone of timestamps in messages written to the error log, and in general query log and slow query log messages written to files. It does not affect the time zone of general query log and slow query log messages written to tables (
mysql.general_log
,mysql.slow_log
). Rows retrieved from those tables can be converted from the local system time zone to any desired time zone withCONVERT_TZ()
or by setting the sessiontime_zone
system variable.Permitted
log_timestamps
values areUTC
(the default) andSYSTEM
(local system time zone).Timestamps are written using ISO 8601 / RFC 3339 format:
plus a tail value ofYYYY-MM-DD
Thh:mm:ss.uuuuuu
Z
signifying Zulu time (UTC) or±hh:mm
(an offset from UTC). log_throttle_queries_not_using_indexes
Command-Line Format --log-throttle-queries-not-using-indexes=#
System Variable log_throttle_queries_not_using_indexes
Scope Global Dynamic Yes Type Integer Default Value 0
Minimum Value 0
Maximum Value 4294967295
If
log_queries_not_using_indexes
is enabled, thelog_throttle_queries_not_using_indexes
variable limits the number of such queries per minute that can be written to the slow query log. A value of 0 (the default) means “no limit”. For more information, see Section 5.4.5, “The Slow Query Log”.-
Command-Line Format --log-warnings[=#]
Deprecated Yes System Variable log_warnings
Scope Global Dynamic Yes Type Integer Default Value 2
Minimum Value 0
Maximum Value (64-bit platforms) 18446744073709551615
Maximum Value (32-bit platforms) 4294967295
Whether to produce additional warning messages to the error log. As of MySQL 5.7.2, information items previously governed by
log_warnings
are governed bylog_error_verbosity
, which is preferred over, and should be used instead of, the olderlog_warnings
system variable. (Thelog_warnings
system variable and--log-warnings
command-line option are deprecated; expect them to be removed in a future release of MySQL.)log_warnings
is enabled by default (the default is 1 before MySQL 5.7.2, 2 as of 5.7.2). To disable it, set it to 0. If the value is greater than 0, the server logs messages about statements that are unsafe for statement-based logging. If the value is greater than 1, the server logs aborted connections and access-denied errors for new connection attempts. See Section B.3.2.9, “Communication Errors and Aborted Connections”.If you use replication, enabling this variable by setting it greater than 0 is recommended, to get more information about what is happening, such as messages about network failures and reconnections.
If a replica server is started with
log_warnings
enabled, the replica prints messages to the error log to provide information about its status, such as the binary log and relay log coordinates where it starts its job, when it is switching to another relay log, when it reconnects after a disconnect, and so forth.Assigning a value to
log_warnings
assigns a value tolog_error_verbosity
and vice versa. The variables are related as follows:Suppression of all
log_warnings
items, achieved withlog_warnings=0
, is achieved withlog_error_verbosity=1
(errors only).Items printed for
log_warnings=1
or higher count as warnings and are printed forlog_error_verbosity=2
or higher.Items printed for
log_warnings=2
count as notes and are printed forlog_error_verbosity=3
.
As of MySQL 5.7.2, the default log level is controlled by
log_error_verbosity
, which has a default of 3. In addition, the default forlog_warnings
changes from 1 to 2, which corresponds tolog_error_verbosity=3
. To achieve a logging level similar to the previous default, setlog_error_verbosity=2
.In MySQL 5.7.2 and higher, use of
log_warnings
is still permitted but maps onto use oflog_error_verbosity
as follows:Setting
log_warnings=0
is equivalent tolog_error_verbosity=1
(errors only).Setting
log_warnings=1
is equivalent tolog_error_verbosity=2
(errors, warnings).Setting
log_warnings=2
(or higher) is equivalent tolog_error_verbosity=3
(errors, warnings, notes), and the server setslog_warnings
to 2 if a larger value is specified.
-
Command-Line Format --long-query-time=#
System Variable long_query_time
Scope Global, Session Dynamic Yes Type Numeric Default Value 10
Minimum Value 0
Maximum Value 31536000
Unit seconds If a query takes longer than this many seconds, the server increments the
Slow_queries
status variable. If the slow query log is enabled, 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 and default values oflong_query_time
are 0 and 10, respectively. The maximum is 31536000, which is 365 days in seconds. The value can be specified to a resolution of microseconds. See Section 5.4.5, “The Slow Query Log”.Smaller values of this variable result in more statements being considered long-running, with the result that more space is required for the slow query log. For very small values (less than one second), the log may grow quite large in a small time. Increasing the number of statements considered long-running may also result in false positives for the “excessive Number of Long Running Processes” alert in MySQL Enterprise Monitor, especially if Group Replication is enabled. For these reasons, very small values should be used in test environments only, or, in production environments, only for a short period.
-
Command-Line Format --low-priority-updates[={OFF|ON}]
System Variable low_priority_updates
Scope Global, Session Dynamic Yes Type Boolean Default Value OFF
If set to
1
, allINSERT
,UPDATE
,DELETE
, andLOCK TABLE WRITE
statements wait until there is no pendingSELECT
orLOCK TABLE READ
on the affected table. The same effect can be obtained using{INSERT | REPLACE | DELETE | UPDATE} LOW_PRIORITY ...
to lower the priority of only one query. This variable affects only storage engines that use only table-level locking (such asMyISAM
,MEMORY
, andMERGE
). See Section 8.11.2, “Table Locking Issues”. -
System Variable lower_case_file_system
Scope Global Dynamic No Type Boolean This variable describes the case sensitivity of file names on the file system where the data directory is located.
OFF
means file names are case-sensitive,ON
means they are not case-sensitive. This variable is read only because it reflects a file system attribute and setting it would have no effect on the file system. -
Command-Line Format --lower-case-table-names[=#]
System Variable lower_case_table_names
Scope Global Dynamic No Type Integer Default Value (macOS) 2
Default Value (Unix) 0
Default Value (Windows) 1
Minimum Value 0
Maximum Value 2
If set to 0, table names are stored as specified and comparisons are case-sensitive. If set to 1, table names are stored in lowercase on disk and 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. For additional details, see Section 9.2.3, “Identifier Case Sensitivity”.
The default value of this variable is platform-dependent (see
lower_case_file_system
). On Linux and other Unix-like systems, the default is0
. On Windows the default value is1
. On macOS, the default value is2
. On Linux (and other Unix-like systems), setting the value to2
is not supported; the server forces the value to0
instead.You should not set
lower_case_table_names
to 0 if you are running MySQL on a system where the data directory resides on a case-insensitive file system (such as on Windows or macOS). It is an unsupported combination that could result in a hang condition when running anINSERT INTO ... SELECT ... FROM
operation with the wrongtbl_name
tbl_name
lettercase. WithMyISAM
, accessing table names using different lettercases could cause index corruption.An error message is printed and the server exits if you attempt to start the server with
--lower_case_table_names=0
on a case-insensitive file system.The setting of this variable affects the behavior of replication filtering options with regard to case sensitivity. For more information, see Section 16.2.5, “How Servers Evaluate Replication Filtering Rules”.
-
Command-Line Format --max-allowed-packet=#
System Variable max_allowed_packet
Scope Global, Session Dynamic Yes Type Integer Default Value 4194304
Minimum Value 1024
Maximum Value 1073741824
Unit bytes Block Size 1024
The maximum size of one packet or any generated/intermediate string, or any parameter sent by the
mysql_stmt_send_long_data()
C API function. The default is 4MB.The packet message buffer is initialized to
net_buffer_length
bytes, but can grow up tomax_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 largestBLOB
you want to use. The protocol limit formax_allowed_packet
is 1GB. The value should be a multiple of 1024; nonmultiples are rounded down to the nearest multiple.When you change the message buffer size by changing the value of the
max_allowed_packet
variable, you should also change the buffer size on the client side if your client program permits it. The defaultmax_allowed_packet
value built in to the client library is 1GB, but individual client programs might override this. For example, mysql and mysqldump have defaults of 16MB and 24MB, respectively. They also enable you to change the client-side value by settingmax_allowed_packet
on the command line or in an option file.The session value of this variable is read only. The client can receive up to as many bytes as the session value. However, the server cannot send to the client more bytes than the current global
max_allowed_packet
value. (The global value could be less than the session value if the global value is changed after the client connects.) -
Command-Line Format --max-connect-errors=#
System Variable max_connect_errors
Scope Global Dynamic Yes Type Integer Default Value 100
Minimum Value 1
Maximum Value (64-bit platforms) 18446744073709551615
Maximum Value (32-bit platforms) 4294967295
After
max_connect_errors
successive connection requests from a host are interrupted without a successful connection, the server blocks that host from further connections. If a connection from a host is established successfully within fewer thanmax_connect_errors
attempts after a previous connection was interrupted, the error count for the host is cleared to zero. To unblock blocked hosts, flush the host cache; see Flushing the Host Cache. -
Command-Line Format --max-connections=#
System Variable max_connections
Scope Global Dynamic Yes Type Integer Default Value 151
Minimum Value 1
Maximum Value 100000
The maximum permitted number of simultaneous client connections. The maximum effective value is the lesser of the effective value of
open_files_limit
- 810
, and the value actually set formax_connections
.For more information, see Section 5.1.11.1, “Connection Interfaces”.
-
Command-Line Format --max-delayed-threads=#
Deprecated Yes System Variable max_delayed_threads
Scope Global, Session Dynamic Yes Type Integer Default Value 20
Minimum Value 0
Maximum Value 16384
This system variable is deprecated (because
DELAYED
inserts are not supported); expect it to be removed in a future release. -
Command-Line Format --max-digest-length=#
System Variable max_digest_length
Scope Global Dynamic No Type Integer Default Value 1024
Minimum Value 0
Maximum Value 1048576
Unit bytes The maximum number of bytes of memory reserved per session for computation of normalized statement digests. Once that amount of space is used during digest computation, truncation occurs: no further tokens from a parsed statement are collected or figure into its digest value. Statements that differ only after that many bytes of parsed tokens produce the same normalized statement digest and are considered identical if compared or if aggregated for digest statistics.
WarningSetting
max_digest_length
to zero disables digest production, which also disables server functionality that requires digests, such as MySQL Enterprise Firewall.Decreasing the
max_digest_length
value reduces memory use but causes the digest value of more statements to become indistinguishable if they differ only at the end. Increasing the value permits longer statements to be distinguished but increases memory use, particularly for workloads that involve large numbers of simultaneous sessions (the server allocatesmax_digest_length
bytes per session).The parser uses this system variable as a limit on the maximum length of normalized statement digests that it computes. The Performance Schema, if it tracks statement digests, makes a copy of the digest value, using the
performance_schema_max_digest_length
. system variable as a limit on the maximum length of digests that it stores. Consequently, ifperformance_schema_max_digest_length
is less thanmax_digest_length
, digest values stored in the Performance Schema are truncated relative to the original digest values.For more information about statement digesting, see Section 25.10, “Performance Schema Statement Digests”.
-
Command-Line Format --max-error-count=#
System Variable max_error_count
Scope Global, Session Dynamic Yes Type Integer Default Value 64
Minimum Value 0
Maximum Value 65535
The maximum number of error, warning, and information messages to be stored for display by the
SHOW ERRORS
andSHOW WARNINGS
statements. This is the same as the number of condition areas in the diagnostics area, and thus the number of conditions that can be inspected byGET DIAGNOSTICS
. -
Command-Line Format --max-execution-time=#
System Variable max_execution_time
Scope Global, Session Dynamic Yes Type Integer Default Value 0
Minimum Value 0
Maximum Value 4294967295
Unit milliseconds The execution timeout for
SELECT
statements, in milliseconds. If the value is 0, timeouts are not enabled.max_execution_time
applies as follows:The global
max_execution_time
value provides the default for the session value for new connections. The session value applies toSELECT
executions executed within the session that include noMAX_EXECUTION_TIME(
optimizer hint or for whichN
)N
is 0.max_execution_time
applies to read-onlySELECT
statements. Statements that are not read only are those that invoke a stored function that modifies data as a side effect.max_execution_time
is ignored forSELECT
statements in stored programs.
-
Command-Line Format --max-heap-table-size=#
System Variable max_heap_table_size
Scope Global, Session Dynamic Yes Type Integer Default Value 16777216
Minimum Value 16384
Maximum Value (64-bit platforms) 18446744073709550592
Maximum Value (32-bit platforms) 4294966272
Unit bytes Block Size 1024
This variable sets the maximum size to which user-created
MEMORY
tables are permitted to grow. The value of the variable is used to calculateMEMORY
tableMAX_ROWS
values.Setting this variable has no effect on any existing
MEMORY
table, unless the table is re-created with a statement such asCREATE TABLE
or altered withALTER TABLE
orTRUNCATE TABLE
. A server restart also sets the maximum size of existingMEMORY
tables to the globalmax_heap_table_size
value.This variable is also used in conjunction with
tmp_table_size
to limit the size of internal in-memory tables. See Section 8.4.4, “Internal Temporary Table Use in MySQL”.max_heap_table_size
is not replicated. See Section 16.4.1.20, “Replication and MEMORY Tables”, and Section 16.4.1.37, “Replication and Variables”, for more information. -
Deprecated Yes System Variable max_insert_delayed_threads
Scope Global, Session Dynamic Yes Type Integer Default Value 0
Minimum Value 20
Maximum Value 16384
This variable is a synonym for
max_delayed_threads
.This system variable is deprecated (because
DELAYED
inserts are not supported); expect it to be removed in a future release. -
Command-Line Format --max-join-size=#
System Variable max_join_size
Scope Global, Session Dynamic Yes Type Integer Default Value 18446744073709551615
Minimum Value 1
Maximum Value 18446744073709551615
Do not permit 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 thanmax_join_size
disk seeks. By setting this value, you can catch 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 aWHERE
clause, that take a long time, or that return millions of rows. For more information, see Using Safe-Updates Mode (--safe-updates).Setting this variable to a value other than
DEFAULT
resets the value ofsql_big_selects
to0
. If you set thesql_big_selects
value again, themax_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.
-
Command-Line Format --max-length-for-sort-data=#
System Variable max_length_for_sort_data
Scope Global, Session Dynamic Yes Type Integer Default Value 1024
Minimum Value 4
Maximum Value 8388608
Unit bytes The cutoff on the size of index values that determines which
filesort
algorithm to use. See Section 8.2.1.14, “ORDER BY Optimization”. -
Command-Line Format --max-points-in-geometry=#
System Variable max_points_in_geometry
Scope Global, Session Dynamic Yes Type Integer Default Value 65536
Minimum Value 3
Maximum Value 1048576
The maximum value of the
points_per_circle
argument to theST_Buffer_Strategy()
function. -
Command-Line Format --max-prepared-stmt-count=#
System Variable max_prepared_stmt_count
Scope Global Dynamic Yes Type Integer Default Value 16382
Minimum Value 0
Maximum Value 1048576
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. 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. Setting the value to 0 disables prepared statements.
-
Command-Line Format --max-seeks-for-key=#
System Variable max_seeks_for_key
Scope Global, Session Dynamic Yes Type Integer Default Value (Windows) 4294967295
Default Value (Other, 64-bit platforms) 18446744073709551615
Default Value (Other, 32-bit platforms) 4294967295
Minimum Value 1
Maximum Value (Windows) 4294967295
Maximum Value (Other, 64-bit platforms) 18446744073709551615
Maximum Value (Other, 32-bit platforms) 4294967295
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 13.7.5.22, “SHOW INDEX Statement”). By setting this to a low value (say, 100), you can force MySQL to prefer indexes instead of table scans.
-
Command-Line Format --max-sort-length=#
System Variable max_sort_length
Scope Global, Session Dynamic Yes Type Integer Default Value 1024
Minimum Value 4
Maximum Value 8388608
Unit bytes The number of bytes to use when sorting data values. The server uses only the first
max_sort_length
bytes of each value and ignores the rest. Consequently, values that differ only after the firstmax_sort_length
bytes compare as equal forGROUP BY
,ORDER BY
, andDISTINCT
operations.Increasing the value of
max_sort_length
may require increasing the value ofsort_buffer_size
as well. For details, see Section 8.2.1.14, “ORDER BY Optimization” -
Command-Line Format --max-sp-recursion-depth[=#]
System Variable max_sp_recursion_depth
Scope Global, Session Dynamic Yes Type Integer Default Value 0
Minimum Value 0
Maximum Value 255
The number of times that any given stored procedure may be called recursively. The default value for this option is 0, which completely disables 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 ofthread_stack
at server startup. This variable is unused. It is deprecated and is removed in MySQL 8.0.
-
Command-Line Format --max-user-connections=#
System Variable max_user_connections
Scope Global, Session Dynamic Yes Type Integer Default Value 0
Minimum Value 0
Maximum Value 4294967295
The maximum number of simultaneous connections permitted to any given MySQL user account. A value of 0 (the default) means “no limit.”
This variable has a global value that can be set at server startup or runtime. It also has a read-only session value that indicates the effective simultaneous-connection limit that applies to the account associated with the current session. The session value is initialized as follows:
If the user account has a nonzero
MAX_USER_CONNECTIONS
resource limit, the sessionmax_user_connections
value is set to that limit.Otherwise, the session
max_user_connections
value is set to the global value.
Account resource limits are specified using the
CREATE USER
orALTER USER
statement. See Section 6.2.16, “Setting Account Resource Limits”. -
Command-Line Format --max-write-lock-count=#
System Variable max_write_lock_count
Scope Global Dynamic Yes Type Integer Default Value (Windows) 4294967295
Default Value (Other, 64-bit platforms) 18446744073709551615
Default Value (Other, 32-bit platforms) 4294967295
Minimum Value 1
Maximum Value (Windows) 4294967295
Maximum Value (Other, 64-bit platforms) 18446744073709551615
Maximum Value (Other, 32-bit platforms) 4294967295
After this many write locks, permit some pending read lock requests to be processed in between. Write lock requests have higher priority than read lock requests. However, if
max_write_lock_count
is set to some low value (say, 10), read lock requests may be preferred over pending write lock requests if the read lock requests have already been passed over in favor of 10 write lock requests. Normally this behavior does not occur becausemax_write_lock_count
by default has a very large value. -
Command-Line Format --mecab-rc-file=file_name
System Variable mecab_rc_file
Scope Global Dynamic No Type File name The
mecab_rc_file
option is used when setting up the MeCab full-text parser.The
mecab_rc_file
option defines the path to themecabrc
configuration file, which is the configuration file for MeCab. The option is read-only and can only be set at startup. Themecabrc
configuration file is required to initialize MeCab.For information about the MeCab full-text parser, see Section 12.9.9, “MeCab Full-Text Parser Plugin”.
For information about options that can be specified in the MeCab
mecabrc
configuration file, refer to the MeCab Documentation on the Google Developers site. -
Command-Line Format --metadata-locks-cache-size=#
Deprecated Yes System Variable metadata_locks_cache_size
Scope Global Dynamic No Type Integer Default Value 1024
Minimum Value 1
Maximum Value 1048576
Unit bytes The size of the metadata locks cache. The server uses this cache to avoid creation and destruction of synchronization objects. This is particularly helpful on systems where such operations are expensive, such as Windows XP.
In MySQL 5.7.4, metadata locking implementation changes make this variable unnecessary, and so it is deprecated; expect it to be removed in a future release of MySQL.
-
Command-Line Format --metadata-locks-hash-instances=#
Deprecated Yes System Variable metadata_locks_hash_instances
Scope Global Dynamic No Type Integer Default Value 8
Minimum Value 1
Maximum Value 1024
The set of metadata locks can be partitioned into separate hashes to permit connections accessing different objects to use different locking hashes and reduce contention. The
metadata_locks_hash_instances
system variable specifies the number of hashes (default 8).In MySQL 5.7.4, metadata locking implementation changes make this variable unnecessary, and so it is deprecated; expect it to be removed in a future release of MySQL.
-
Command-Line Format --min-examined-row-limit=#
System Variable min_examined_row_limit
Scope Global, Session Dynamic Yes Type Integer Default Value 0
Minimum Value 0
Maximum Value (64-bit platforms) 18446744073709551615
Maximum Value (32-bit platforms) 4294967295
Queries that examine fewer than this number of rows are not logged to the slow query log.
-
Command-Line Format --multi-range-count=#
Deprecated Yes System Variable multi_range_count
Scope Global, Session Dynamic Yes Type Integer Default Value 256
Minimum Value 1
Maximum Value 4294967295
This variable has no effect. It is deprecated and is removed in MySQL 8.0.
-
Command-Line Format --myisam-data-pointer-size=#
System Variable myisam_data_pointer_size
Scope Global Dynamic Yes Type Integer Default Value 6
Minimum Value 2
Maximum Value 7
Unit bytes The default pointer size in bytes, to be used by
CREATE TABLE
forMyISAM
tables when noMAX_ROWS
option is specified. This variable cannot be less than 2 or larger than 7. The default value is 6. See Section B.3.2.10, “The table is full”. -
Command-Line Format --myisam-max-sort-file-size=#
System Variable myisam_max_sort_file_size
Scope Global Dynamic Yes Type Integer Default Value (Windows) 2146435072
Default Value (Other, 64-bit platforms) 9223372036853727232
Default Value (Other, 32-bit platforms) 2147483648
Minimum Value 0
Maximum Value (Windows) 2146435072
Maximum Value (Other, 64-bit platforms) 9223372036853727232
Maximum Value (Other, 32-bit platforms) 2147483648
Unit bytes The maximum size of the temporary file that MySQL is permitted to use while re-creating a
MyISAM
index (duringREPAIR TABLE
,ALTER TABLE
, orLOAD DATA
). 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.If
MyISAM
index files exceed this size and disk space is available, increasing the value may help performance. The space must be available in the file system containing the directory where the original index file is located. -
Command-Line Format --myisam-mmap-size=#
System Variable myisam_mmap_size
Scope Global Dynamic No Type Integer Default Value (64-bit platforms) 18446744073709551615
Default Value (32-bit platforms) 4294967295
Minimum Value 7
Maximum Value (64-bit platforms) 18446744073709551615
Maximum Value (32-bit platforms) 4294967295
Unit bytes The maximum amount of memory to use for memory mapping compressed
MyISAM
files. If many compressedMyISAM
tables are used, the value can be decreased to reduce the likelihood of memory-swapping problems. -
Command-Line Format --myisam-recover-options[=list]
System Variable myisam_recover_options
Scope Global Dynamic No Type Enumeration Default Value OFF
Valid Values OFF
DEFAULT
BACKUP
FORCE
QUICK
Set the
MyISAM
storage engine recovery mode. The variable value is any combination of the values ofOFF
,DEFAULT
,BACKUP
,FORCE
, orQUICK
. If you specify multiple values, separate them by commas. Specifying the variable with no value at server startup is the same as specifyingDEFAULT
, and specifying with an explicit value of""
disables recovery (same as a value ofOFF
). If recovery is enabled, each time mysqld opens aMyISAM
table, it checks whether the table is marked as crashed or was not 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 OFF
No recovery. DEFAULT
Recovery without backup, forcing, or quick checking. BACKUP
If the data file was changed during recovery, save a backup of the
file astbl_name
.MYD
.tbl_name-datetime
.BAKFORCE
Run recovery even if we would lose more than one row from the .MYD
file.QUICK
Do not check the rows in the table if there are not 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. -
Command-Line Format --myisam-repair-threads=#
Deprecated 5.7.38 (removed in 5.7.39) System Variable myisam_repair_threads
Scope Global, Session Dynamic Yes Type Integer Default Value 1
Minimum Value 1
Maximum Value (64-bit platforms) 18446744073709551615
Maximum Value (32-bit platforms) 4294967295
NoteThis system variable is deprecated in MySQL 5.7; expect it to be removed in a future release of MySQL.
From MySQL 5.7.38, values other than 1 produce a warning.
If this value is greater than 1,
MyISAM
table indexes are created in parallel (each index in its own thread) during theRepair by sorting
process. The default value is 1.NoteMultithreaded repair is beta-quality code.
-
Command-Line Format --myisam-sort-buffer-size=#
System Variable myisam_sort_buffer_size
Scope Global, Session Dynamic Yes Type Integer Default Value 8388608
Minimum Value 4096
Maximum Value (64-bit platforms) 18446744073709551615
Maximum Value (32-bit platforms) 4294967295
Unit bytes The size of the buffer that is allocated when sorting
MyISAM
indexes during aREPAIR TABLE
or when creating indexes withCREATE INDEX
orALTER TABLE
. -
Command-Line Format --myisam-stats-method=name
System Variable myisam_stats_method
Scope Global, Session Dynamic Yes Type Enumeration Default Value nulls_unequal
Valid Values nulls_unequal
nulls_equal
nulls_ignored
How the server treats
NULL
values when collecting statistics about the distribution of index values forMyISAM
tables. This variable has three possible values,nulls_equal
,nulls_unequal
, andnulls_ignored
. Fornulls_equal
, allNULL
index values are considered equal and form a single value group that has a size equal to the number ofNULL
values. Fornulls_unequal
,NULL
values are considered unequal, and eachNULL
forms a distinct value group of size 1. Fornulls_ignored
,NULL
values are ignored.The method that is used for generating table statistics influences how the optimizer chooses indexes for query execution, as described in Section 8.3.7, “InnoDB and MyISAM Index Statistics Collection”.
-
Command-Line Format --myisam-use-mmap[={OFF|ON}]
System Variable myisam_use_mmap
Scope Global Dynamic Yes Type Boolean Default Value OFF
Use memory mapping for reading and writing
MyISAM
tables. mysql_native_password_proxy_users
Command-Line Format --mysql-native-password-proxy-users[={OFF|ON}]
System Variable mysql_native_password_proxy_users
Scope Global Dynamic Yes Type Boolean Default Value OFF
This variable controls whether the
mysql_native_password
built-in authentication plugin supports proxy users. It has no effect unless thecheck_proxy_users
system variable is enabled. For information about user proxying, see Section 6.2.14, “Proxy Users”.-
Command-Line Format --named-pipe[={OFF|ON}]
System Variable named_pipe
Scope Global Dynamic No Platform Specific Windows Type Boolean Default Value OFF
(Windows only.) Indicates whether the server supports connections over named pipes.
-
Command-Line Format --named-pipe-full-access-group=value
Introduced 5.7.25 System Variable named_pipe_full_access_group
Scope Global Dynamic No Platform Specific Windows Type String Default Value empty string
Valid Values empty string
valid Windows local group name
*everyone*
(Windows only.) The access control granted to clients on the named pipe created by the MySQL server is set to the minimum necessary for successful communication when the
named_pipe
system variable is enabled to support named-pipe connections. Some MySQL client software can open named pipe connections without any additional configuration; however, other client software may still require full access to open a named pipe connection.This variable sets the name of a Windows local group whose members are granted sufficient access by the MySQL server to use named-pipe clients. As of MySQL 5.7.34, the default value is set to an empty string, which means that no Windows user is granted full access to the named pipe.
A new Windows local group name (for example,
mysql_access_client_users
) can be created in Windows and then used to replace the default value when access is absolutely necessary. In this case, limit the membership of the group to as few users as possible, removing users from the group when their client software is upgraded. A non-member of the group who attempts to open a connection to MySQL with the affected named-pipe client is denied access until a Windows administrator adds the user to the group. Newly added users must log out and log in again to join the group (required by Windows).Setting the value to
'*everyone*'
provides a language-independent way of referring to the Everyone group on Windows. The Everyone group is not secure by default. -
Command-Line Format --net-buffer-length=#
System Variable net_buffer_length
Scope Global, Session Dynamic Yes Type Integer Default Value 16384
Minimum Value 1024
Maximum Value 1048576
Unit bytes Block Size 1024
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 tomax_allowed_packet
bytes as needed. The result buffer shrinks tonet_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.The session value of this variable is read only.
-
Command-Line Format --net-read-timeout=#
System Variable net_read_timeout
Scope Global, Session Dynamic Yes Type Integer Default Value 30
Minimum Value 1
Maximum Value 31536000
Unit seconds The number of seconds to wait for more data from a connection before aborting the read. 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 alsoslave_net_timeout
. -
Command-Line Format --net-retry-count=#
System Variable net_retry_count
Scope Global, Session Dynamic Yes Type Integer Default Value 10
Minimum Value 1
Maximum Value (64-bit platforms) 18446744073709551615
Maximum Value (32-bit platforms) 4294967295
If a read or write 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.
-
Command-Line Format --net-write-timeout=#
System Variable net_write_timeout
Scope Global, Session Dynamic Yes Type Integer Default Value 60
Minimum Value 1
Maximum Value 31536000
Unit seconds The number of seconds to wait for a block to be written to a connection before aborting the write. See also
net_read_timeout
. -
Command-Line Format --new[={OFF|ON}]
System Variable new
Scope Global, Session Dynamic Yes Disabled by skip-new
Type Boolean Default Value OFF
This variable was used in MySQL 4.0 to turn on some 4.1 behaviors, and is retained for backward compatibility. Its value is always
OFF
.In NDB Cluster, setting this variable to
ON
makes it possible to employ partitioning types other thanKEY
orLINEAR KEY
withNDB
tables. This experimental feature is not supported in production, and is now deprecated and thus subject to removal in a future release. For additional information, see User-defined partitioning and the NDB storage engine (NDB Cluster). -
Command-Line Format --ngram-token-size=#
System Variable ngram_token_size
Scope Global Dynamic No Type Integer Default Value 2
Minimum Value 1
Maximum Value 10
Defines the n-gram token size for the n-gram full-text parser. The
ngram_token_size
option is read-only and can only be modified at startup. The default value is 2 (bigram). The maximum value is 10.For more information about how to configure this variable, see Section 12.9.8, “ngram Full-Text Parser”.
-
Command-Line Format --offline-mode[={OFF|ON}]
System Variable offline_mode
Scope Global Dynamic Yes Type Boolean Default Value OFF
Whether the server is in “offline mode”, which has these characteristics:
Connected client users who do not have the
SUPER
privilege are disconnected on the next request, with an appropriate error. Disconnection includes terminating running statements and releasing locks. Such clients also cannot initiate new connections, and receive an appropriate error.Connected client users who have the
SUPER
privilege are not disconnected, and can initiate new connections to manage the server.Replica threads are permitted to keep applying data to the server.
Only users who have the
SUPER
privilege can control offline mode. To put a server in offline mode, change the value of theoffline_mode
system variable fromOFF
toON
. To resume normal operations, changeoffline_mode
fromON
toOFF
. In offline mode, clients that are refused access receive anER_SERVER_OFFLINE_MODE
error. -
Command-Line Format --old[={OFF|ON}]
System Variable old
Scope Global Dynamic No Type Boolean Default Value OFF
old
is a compatibility variable. It is disabled by default, but can be enabled at startup to revert the server to behaviors present in older versions.When
old
is enabled, it changes the default scope of index hints to that used prior to MySQL 5.1.17. That is, index hints with noFOR
clause apply only to how indexes are used for row retrieval and not to resolution ofORDER BY
orGROUP BY
clauses. (See Section 8.9.4, “Index Hints”.) Take care about enabling this in a replication setup. With statement-based binary logging, having different modes for the source and replicas might lead to replication errors. -
Command-Line Format --old-alter-table[={OFF|ON}]
System Variable old_alter_table
Scope Global, Session Dynamic Yes Type Boolean Default Value OFF
When this variable is enabled, the server does not use the optimized method of processing an
ALTER TABLE
operation. It reverts to using a temporary table, copying over the data, and then renaming the temporary table to the original, as used by MySQL 5.0 and earlier. For more information on the operation ofALTER TABLE
, see Section 13.1.8, “ALTER TABLE Statement”. -
Command-Line Format --old-passwords=value
Deprecated Yes System Variable old_passwords
Scope Global, Session Dynamic Yes Type Enumeration Default Value 0
Valid Values 0
2
NoteThis system variable is deprecated in MySQL 5.7; expect it to be removed in a future release of MySQL.
This variable controls the password hashing method used by the
PASSWORD()
function. It also influences password hashing performed byCREATE USER
andGRANT
statements that specify a password using anIDENTIFIED BY
clause.The following table shows, for each password hashing method, the permitted value of
old_passwords
and which authentication plugins use the hashing method.Password Hashing Method old_passwords Value Associated Authentication Plugin MySQL 4.1 native hashing 0 mysql_native_password
SHA-256 hashing 2 sha256_password
If you set
old_passwords=2
, follow the instructions for using thesha256_password
plugin at Section 6.4.1.5, “SHA-256 Pluggable Authentication”.The server sets the global
old_passwords
value during startup to be consistent with the password hashing method required by the authentication plugin indicated by thedefault_authentication_plugin
system variable.When a client successfully connects to the server, the server sets the session
old_passwords
value appropriately for the account authentication method. For example, if the account uses thesha256_password
authentication plugin, the server setsold_passwords=2
.For additional information about authentication plugins and hashing formats, see Section 6.2.13, “Pluggable Authentication”, and Section 6.1.2.4, “Password Hashing in MySQL”.
-
Command-Line Format --open-files-limit=#
System Variable open_files_limit
Scope Global Dynamic No Type Integer Default Value 5000, with possible adjustment
Minimum Value 0
Maximum Value platform dependent
The number of file descriptors available to mysqld from the operating system:
At startup, mysqld reserves descriptors with
setrlimit()
, using the value requested at by setting this variable directly or by using the--open-files-limit
option to mysqld_safe. If mysqld produces the errorToo many open files
, try increasing theopen_files_limit
value. Internally, the maximum value for this variable is the maximum unsigned integer value, but the actual maximum is platform dependent.At runtime, the value of
open_files_limit
indicates the number of file descriptors actually permitted to mysqld by the operating system, which might differ from the value requested at startup. If the number of file descriptors requested during startup cannot be allocated, mysqld writes a warning to the error log.
The effective
open_files_limit
value is based on the value specified at system startup (if any) and the values ofmax_connections
andtable_open_cache
, using these formulas:10 + max_connections + (table_open_cache * 2)
max_connections * 5
The operating system limit if that limit is positive but not Infinity.
If the operating system limit is Infinity:
open_files_limit
value if specified at startup, 5000 if not.
The server attempts to obtain the number of file descriptors using the maximum of those values. If that many descriptors cannot be obtained, the server attempts to obtain as many as the system permits.
The effective value is 0 on systems where MySQL cannot change the number of open files.
On Unix, the value cannot be set greater than the value displayed by the ulimit -n command. On Linux systems using
systemd
, the value cannot be set greater thanLimitNOFile
(this isDefaultLimitNOFILE
, ifLimitNOFile
is not set); otherwise, on Linux, the value ofopen_files_limit
cannot exceed ulimit -n. -
Command-Line Format --optimizer-prune-level=#
System Variable optimizer_prune_level
Scope Global, Session Dynamic Yes Type Integer Default Value 1
Minimum Value 0
Maximum Value 1
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.
-
Command-Line Format --optimizer-search-depth=#
System Variable optimizer_search_depth
Scope Global, Session Dynamic Yes Type Integer Default Value 62
Minimum Value 0
Maximum Value 62
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.
-
Command-Line Format --optimizer-switch=value
System Variable optimizer_switch
Scope Global, Session Dynamic Yes Type Set Valid Values (≥ 5.7.33) batched_key_access={on|off}
block_nested_loop={on|off}
condition_fanout_filter={on|off}
derived_merge={on|off}
duplicateweedout={on|off}
engine_condition_pushdown={on|off}
firstmatch={on|off}
index_condition_pushdown={on|off}
index_merge={on|off}
index_merge_intersection={on|off}
index_merge_sort_union={on|off}
index_merge_union={on|off}
loosescan={on|off}
materialization={on|off}
mrr={on|off}
mrr_cost_based={on|off}
prefer_ordering_index={on|off}
semijoin={on|off}
subquery_materialization_cost_based={on|off}
use_index_extensions={on|off}
Valid Values (≤ 5.7.32) batched_key_access={on|off}
block_nested_loop={on|off}
condition_fanout_filter={on|off}
derived_merge={on|off}
duplicateweedout={on|off}
engine_condition_pushdown={on|off}
firstmatch={on|off}
index_condition_pushdown={on|off}
index_merge={on|off}
index_merge_intersection={on|off}
index_merge_sort_union={on|off}
index_merge_union={on|off}
loosescan={on|off}
materialization={on|off}
mrr={on|off}
mrr_cost_based={on|off}
semijoin={on|off}
subquery_materialization_cost_based={on|off}
use_index_extensions={on|off}
The
optimizer_switch
system variable enables control over optimizer behavior. The value of this variable is a set of flags, each of which has a value ofon
oroff
to indicate whether the corresponding optimizer behavior is enabled or disabled. This variable has global and session values and can be changed at runtime. The global default can be set at server startup.To see the current set of optimizer flags, select the variable value:
mysql> SELECT @@optimizer_switch\G *************************** 1. row *************************** @@optimizer_switch: index_merge=on,index_merge_union=on, index_merge_sort_union=on, index_merge_intersection=on, engine_condition_pushdown=on, index_condition_pushdown=on, mrr=on,mrr_cost_based=on, block_nested_loop=on,batched_key_access=off, materialization=on,semijoin=on,loosescan=on, firstmatch=on,duplicateweedout=on, subquery_materialization_cost_based=on, use_index_extensions=on, condition_fanout_filter=on,derived_merge=on, prefer_ordering_index=on
For more information about the syntax of this variable and the optimizer behaviors that it controls, see Section 8.9.2, “Switchable Optimizations”.
-
Command-Line Format --optimizer-trace=value
System Variable optimizer_trace
Scope Global, Session Dynamic Yes Type String This variable controls optimizer tracing. For details, see MySQL Internals: Tracing the Optimizer.
-
Command-Line Format --optimizer-trace-features=value
System Variable optimizer_trace_features
Scope Global, Session Dynamic Yes Type String This variable enables or disables selected optimizer tracing features. For details, see MySQL Internals: Tracing the Optimizer.
-
Command-Line Format --optimizer-trace-limit=#
System Variable optimizer_trace_limit
Scope Global, Session Dynamic Yes Type Integer Default Value 1
Minimum Value 0
Maximum Value 2147483647
The maximum number of optimizer traces to display. For details, see MySQL Internals: Tracing the Optimizer.
-
Command-Line Format --optimizer-trace-max-mem-size=#
System Variable optimizer_trace_max_mem_size
Scope Global, Session Dynamic Yes Type Integer Default Value 16384
Minimum Value 0
Maximum Value 4294967295
Unit bytes The maximum cumulative size of stored optimizer traces. For details, see MySQL Internals: Tracing the Optimizer.
-
Command-Line Format --optimizer-trace-offset=#
System Variable optimizer_trace_offset
Scope Global, Session Dynamic Yes Type Integer Default Value -1
Minimum Value -2147483647
Maximum Value 2147483647
The offset of optimizer traces to display. For details, see MySQL Internals: Tracing the Optimizer.
performance_schema_
xxx
Performance Schema system variables are listed in Section 25.15, “Performance Schema System Variables”. These variables may be used to configure Performance Schema operation.
-
Command-Line Format --parser-max-mem-size=#
Introduced 5.7.12 System Variable parser_max_mem_size
Scope Global, Session Dynamic Yes Type Integer Default Value (64-bit platforms) 18446744073709551615
Default Value (32-bit platforms) 4294967295
Minimum Value 10000000
Maximum Value (64-bit platforms) 18446744073709551615
Maximum Value (32-bit platforms) 4294967295
Unit bytes The maximum amount of memory available to the parser. The default value places no limit on memory available. The value can be reduced to protect against out-of-memory situations caused by parsing long or complex SQL statements.
-
Command-Line Format --pid-file=file_name
System Variable pid_file
Scope Global Dynamic No Type File name The path name of the file in which the server writes its process ID. The server creates the file in the data directory unless an absolute path name is given to specify a different directory. If you specify this variable, you must specify a value. If you do not specify this variable, MySQL uses a default value of
, wherehost_name
.pidhost_name
is the name of the host machine.The process ID file is used by other programs such as mysqld_safe to determine the server's process ID. On Windows, this variable also affects the default error log file name. See Section 5.4.2, “The Error Log”.
-
Command-Line Format --plugin-dir=dir_name
System Variable plugin_dir
Scope Global Dynamic No Type Directory name Default Value BASEDIR/lib/plugin
The path name of the plugin directory.
If the plugin directory is writable by the server, it may be possible for a user to write executable code to a file in the directory using
SELECT ... INTO DUMPFILE
. This can be prevented by makingplugin_dir
read only to the server or by settingsecure_file_priv
to a directory whereSELECT
writes can be made safely. -
Command-Line Format --port=port_num
System Variable port
Scope Global Dynamic No Type Integer Default Value 3306
Minimum Value 0
Maximum Value 65535
The number of the port on which the server listens for TCP/IP connections. This variable can be set with the
--port
option. -
Command-Line Format --preload-buffer-size=#
System Variable preload_buffer_size
Scope Global, Session Dynamic Yes Type Integer Default Value 32768
Minimum Value 1024
Maximum Value 1073741824
Unit bytes The size of the buffer that is allocated when preloading indexes.
If set to 0 or
OFF
(the default), statement profiling is disabled. If set to 1 orON
, statement profiling is enabled and theSHOW PROFILE
andSHOW PROFILES
statements provide access to profiling information. See Section 13.7.5.31, “SHOW PROFILES Statement”.This variable is deprecated; expect it to be removed in a future release of MySQL.
The number of statements for which to maintain profiling information if
profiling
is enabled. The default value is 15. The maximum value is 100. Setting the value to 0 effectively disables profiling. See Section 13.7.5.31, “SHOW PROFILES Statement”.This variable is deprecated; expect it to be removed in a future release of MySQL.
-
System Variable protocol_version
Scope Global Dynamic No Type Integer Default Value 10
Minimum Value 0
Maximum Value 4294967295
The version of the client/server protocol used by the MySQL server.
-
System Variable proxy_user
Scope Session Dynamic No Type String If the current client is a proxy for another user, this variable is the proxy user account name. Otherwise, this variable is
NULL
. See Section 6.2.14, “Proxy Users”. -
System Variable pseudo_slave_mode
Scope Session Dynamic Yes Type Boolean This system variable is for internal server use.
pseudo_slave_mode
assists with the correct handling of transactions that originated on older or newer servers than the server currently processing them. mysqlbinlog sets the value ofpseudo_slave_mode
to true before executing any SQL statements.pseudo_slave_mode
has the following effects on the handling of prepared XA transactions, which can be attached to or detached from the handling session (by default, the session that issuesXA START
):If true, and the handling session has executed an internal-use
BINLOG
statement, XA transactions are automatically detached from the session as soon as the first part of the transaction up toXA PREPARE
finishes, so they can be committed or rolled back by any session that has theXA_RECOVER_ADMIN
privilege.If false, XA transactions remain attached to the handling session as long as that session is alive, during which time no other session can commit the transaction. The prepared transaction is only detached if the session disconnects or the server restarts.
-
System Variable pseudo_thread_id
Scope Session Dynamic Yes Type Integer Default Value 2147483647
Minimum Value 0
Maximum Value 2147483647
This variable is for internal server use.
WarningChanging the session value of the
pseudo_thread_id
system variable changes the value returned by theCONNECTION_ID()
function. -
Command-Line Format --query-alloc-block-size=#
System Variable query_alloc_block_size
Scope Global, Session Dynamic Yes Type Integer Default Value 8192
Minimum Value 1024
Maximum Value 4294966272
Unit bytes Block Size 1024
The allocation size in bytes 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 parameter.
The block size for the byte number is 1024. A value that is not an exact multiple of the block size is rounded down to the next lower multiple of the block size by MySQL Server before storing the value for the system variable. The parser allows values up to the maximum unsigned integer value for the platform (4294967295 or 232−1 for a 32-bit system, 18446744073709551615 or 264−1 for a 64-bit system) but the actual maximum is a block size lower.
-
Command-Line Format --query-cache-limit=#
Deprecated 5.7.20 System Variable query_cache_limit
Scope Global Dynamic Yes Type Integer Default Value 1048576
Minimum Value 0
Maximum Value (64-bit platforms) 18446744073709551615
Maximum Value (32-bit platforms) 4294967295
Unit bytes Do not cache results that are larger than this number of bytes. The default value is 1MB.
NoteThe query cache is deprecated as of MySQL 5.7.20, and is removed in MySQL 8.0. Deprecation includes
query_cache_limit
. -
Command-Line Format --query-cache-min-res-unit=#
Deprecated 5.7.20 System Variable query_cache_min_res_unit
Scope Global Dynamic Yes Type Integer Default Value 4096
Minimum Value 512
Maximum Value (64-bit platforms) 18446744073709551615
Maximum Value (32-bit platforms) 4294967295
Unit bytes 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 8.10.3.3, “Query Cache Configuration”.
NoteThe query cache is deprecated as of MySQL 5.7.20, and is removed in MySQL 8.0. Deprecation includes
query_cache_min_res_unit
. -
Command-Line Format --query-cache-size=#
Deprecated 5.7.20 System Variable query_cache_size
Scope Global Dynamic Yes Type Integer Default Value 1048576
Minimum Value 0
Maximum Value (64-bit platforms) 18446744073709551615
Maximum Value (32-bit platforms) 4294967295
Unit bytes The amount of memory allocated for caching query results. By default, the query cache is disabled. This is achieved using a default value of 1M, with a default for
query_cache_type
of 0. (To reduce overhead significantly if you set the size to 0, you should also start the server withquery_cache_type=0
.The permissible values are multiples of 1024; other values are rounded down to the nearest multiple. For nonzero values of
query_cache_size
, that many bytes of memory are allocated even ifquery_cache_type=0
. See Section 8.10.3.3, “Query Cache Configuration”, for more information.The query cache needs a minimum size of about 40KB to allocate its structures. (The exact size depends on system architecture.) If you set the value of
query_cache_size
too small, a warning occurs, as described in Section 8.10.3.3, “Query Cache Configuration”.NoteThe query cache is deprecated as of MySQL 5.7.20, and is removed in MySQL 8.0. Deprecation includes
query_cache_size
. -
Command-Line Format --query-cache-type=#
Deprecated 5.7.20 System Variable query_cache_type
Scope Global, Session Dynamic Yes Type Enumeration Default Value 0
Valid Values 0
1
2
Set the query cache type. Setting the
GLOBAL
value sets the type for all clients that connect thereafter. Individual clients can set theSESSION
value to affect their own use of the query cache. Possible values are shown in the following table.Option Description 0
orOFF
Do not 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
orON
Cache all cacheable query results except for those that begin with SELECT SQL_NO_CACHE
.2
orDEMAND
Cache results only for cacheable queries that begin with SELECT SQL_CACHE
.This variable defaults to
OFF
.If the server is started with
query_cache_type
set to 0, it does not acquire the query cache mutex at all, which means that the query cache cannot be enabled at runtime and there is reduced overhead in query execution.NoteThe query cache is deprecated as of MySQL 5.7.20, and is removed in MySQL 8.0. Deprecation includes
query_cache_type
. -
Command-Line Format --query-cache-wlock-invalidate[={OFF|ON}]
Deprecated 5.7.20 System Variable query_cache_wlock_invalidate
Scope Global, Session Dynamic Yes Type Boolean Default Value OFF
Normally, when one client acquires a
WRITE
lock on a 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 aWRITE
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.NoteThe query cache is deprecated as of MySQL 5.7.20, and is removed in MySQL 8.0. Deprecation includes
query_cache_wlock_invalidate
. -
Command-Line Format --query-prealloc-size=#
System Variable query_prealloc_size
Scope Global, Session Dynamic Yes Type Integer Default Value 8192
Minimum Value 8192
Maximum Value (64-bit platforms) 18446744073709550592
Maximum Value (32-bit platforms) 4294966272
Unit bytes Block Size 1024
The size in bytes 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. You should be aware that doing this does not necessarily eliminate allocation completely; the server may still allocate memory in some situations, such as for operations relating to transactions, or to stored programs. -
System Variable rand_seed1
Scope Session Dynamic Yes Type Integer Default Value N/A
Minimum Value 0
Maximum Value 4294967295
The
rand_seed1
andrand_seed2
variables exist as session variables only, and can be set but not read. The variables—but not their values—are shown in the output ofSHOW VARIABLES
.The purpose of these variables is to support replication of the
RAND()
function. For statements that invokeRAND()
, the source passes two values to the replica, where they are used to seed the random number generator. The replica uses these values to set the session variablesrand_seed1
andrand_seed2
so thatRAND()
on the replica generates the same value as on the source. See the description for
rand_seed1
.-
Command-Line Format --range-alloc-block-size=#
System Variable range_alloc_block_size
Scope Global, Session Dynamic Yes Type Integer Default Value 4096
Minimum Value 4096
Maximum Value (64-bit platforms) 18446744073709550592
Maximum Value 4294966272
Unit bytes Block Size 1024
The size in bytes of blocks that are allocated when doing range optimization.
The block size for the byte number is 1024. A value that is not an exact multiple of the block size is rounded down to the next lower multiple of the block size by MySQL Server before storing the value for the system variable. The parser allows values up to the maximum unsigned integer value for the platform (4294967295 or 232−1 for a 32-bit system, 18446744073709551615 or 264−1 for a 64-bit system) but the actual maximum is a block size lower.
-
Command-Line Format --range-optimizer-max-mem-size=#
System Variable range_optimizer_max_mem_size
Scope Global, Session Dynamic Yes Type Integer Default Value (≥ 5.7.12) 8388608
Default Value (≤ 5.7.11) 1536000
Minimum Value 0
Maximum Value 18446744073709551615
Unit bytes The limit on memory consumption for the range optimizer. A value of 0 means “no limit.” If an execution plan considered by the optimizer uses the range access method but the optimizer estimates that the amount of memory needed for this method would exceed the limit, it abandons the plan and considers other plans. For more information, see Limiting Memory Use for Range Optimization.
-
System Variable rbr_exec_mode
Scope Session Dynamic Yes Type Enumeration Default Value STRICT
Valid Values STRICT
IDEMPOTENT
For internal use by mysqlbinlog. This variable switches the server between
IDEMPOTENT
mode andSTRICT
mode.IDEMPOTENT
mode causes suppression of duplicate-key and no-key-found errors inBINLOG
statements generated by mysqlbinlog. This mode is useful when replaying a row-based binary log on a server that causes conflicts with existing data. mysqlbinlog sets this mode when you specify the--idempotent
option by writing the following to the output:SET SESSION RBR_EXEC_MODE=IDEMPOTENT;
-
Command-Line Format --read-buffer-size=#
System Variable read_buffer_size
Scope Global, Session Dynamic Yes Type Integer Default Value 131072
Minimum Value 8192
Maximum Value 2147479552
Unit bytes Block Size 4096
Each thread that does a sequential scan for a
MyISAM
table 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 is rounded down to the nearest multiple of 4KB.This option is also used in the following context for all storage engines:
For caching the indexes in a temporary file (not a temporary table), when sorting rows for
ORDER BY
.For bulk insert into partitions.
For caching results of nested queries.
read_buffer_size
is also used in one other storage engine-specific way: to determine the memory block size forMEMORY
tables.For more information about memory use during different operations, see Section 8.12.4.1, “How MySQL Uses Memory”.
-
Command-Line Format --read-only[={OFF|ON}]
System Variable read_only
Scope Global Dynamic Yes Type Boolean Default Value OFF
If the
read_only
system variable is enabled, the server permits no client updates except from users who have theSUPER
privilege. This variable is disabled by default.The server also supports a
super_read_only
system variable (disabled by default), which has these effects:If
super_read_only
is enabled, the server prohibits client updates, even from users who have theSUPER
privilege.Setting
super_read_only
toON
implicitly forcesread_only
toON
.Setting
read_only
toOFF
implicitly forcessuper_read_only
toOFF
.
Even with
read_only
enabled, the server permits these operations:Updates performed by replication threads, if the server is a replica. In replication setups, it can be useful to enable
read_only
on replica servers to ensure that replicas accept updates only from the source server and not from clients.Use of
ANALYZE TABLE
orOPTIMIZE TABLE
statements. The purpose of read-only mode is to prevent changes to table structure or contents. Analysis and optimization do not qualify as such changes. This means, for example, that consistency checks on read-only replicas can be performed with mysqlcheck--all-databases
--analyze
.Use of
FLUSH STATUS
statements, which are always written to the binary log.Operations on
TEMPORARY
tables.Inserts into the log tables (
mysql.general_log
andmysql.slow_log
); see Section 5.4.1, “Selecting General Query Log and Slow Query Log Output Destinations”.As of MySQL 5.7.16, updates to Performance Schema tables, such as
UPDATE
orTRUNCATE TABLE
operations.
Changes to
read_only
on a replication source server are not replicated to replica servers. The value can be set on a replica independent of the setting on the source.The following conditions apply to attempts to enable
read_only
(including implicit attempts resulting from enablingsuper_read_only
):The attempt fails and an error occurs if you have any explicit locks (acquired with
LOCK TABLES
) or have a pending transaction.The attempt blocks while other clients have any ongoing statement, active
LOCK TABLES WRITE
, or ongoing commit, until the locks are released and the statements and transactions end. While the attempt to enableread_only
is pending, requests by other clients for table locks or to begin transactions also block untilread_only
has been set.The attempt blocks if there are active transactions that hold metadata locks, until those transactions end.
read_only
can be enabled while you hold a global read lock (acquired withFLUSH TABLES WITH READ LOCK
) because that does not involve table locks.
-
Command-Line Format --read-rnd-buffer-size=#
System Variable read_rnd_buffer_size
Scope Global, Session Dynamic Yes Type Integer Default Value 262144
Minimum Value 1
Maximum Value 2147483647
Unit bytes This variable is used for reads from
MyISAM
tables, and, for any storage engine, for Multi-Range Read optimization.When reading rows from a
MyISAM
table in sorted order following a key-sorting operation, the rows are read through this buffer to avoid disk seeks. See Section 8.2.1.14, “ORDER BY Optimization”. Setting the variable to a large value can improveORDER 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.For more information about memory use during different operations, see Section 8.12.4.1, “How MySQL Uses Memory”. For information about Multi-Range Read optimization, see Section 8.2.1.10, “Multi-Range Read Optimization”.
-
Command-Line Format --require-secure-transport[={OFF|ON}]
System Variable require_secure_transport
Scope Global Dynamic Yes Type Boolean Default Value OFF
Whether client connections to the server are required to use some form of secure transport. When this variable is enabled, the server permits only TCP/IP connections encrypted using TLS/SSL, or connections that use a socket file (on Unix) or shared memory (on Windows). The server rejects nonsecure connection attempts, which fail with an
ER_SECURE_TRANSPORT_REQUIRED
error.This capability supplements per-account SSL requirements, which take precedence. For example, if an account is defined with
REQUIRE SSL
, enablingrequire_secure_transport
does not make it possible to use the account to connect using a Unix socket file.It is possible for a server to have no secure transports available. For example, a server on Windows supports no secure transports if started without specifying any SSL certificate or key files and with the
shared_memory
system variable disabled. Under these conditions, attempts to enablerequire_secure_transport
at startup cause the server to write a message to the error log and exit. Attempts to enable the variable at runtime fail with anER_NO_SECURE_TRANSPORTS_CONFIGURED
error. -
Command-Line Format --secure-auth[={OFF|ON}]
Deprecated Yes System Variable secure_auth
Scope Global Dynamic Yes Type Boolean Default Value ON
Valid Values ON
If this variable is enabled, the server blocks connections by clients that attempt to use accounts that have passwords stored in the old (pre-4.1) format. Enable this variable to prevent all use of passwords employing the old format (and hence insecure communication over the network).
This variable is deprecated; expect it to be removed in a future release of MySQL. It is always enabled and attempting to disable it produces an error.
Server startup fails with an error if this variable is enabled and the privilege tables are in pre-4.1 format. See Section 6.4.1.3, “Migrating Away from Pre-4.1 Password Hashing and the mysql_old_password Plugin”.
NotePasswords that use the pre-4.1 hashing method are less secure than passwords that use the native password hashing method and should be avoided. Pre-4.1 passwords are deprecated and support for them is removed in MySQL 5.7.5. For account upgrade instructions, see Section 6.4.1.3, “Migrating Away from Pre-4.1 Password Hashing and the mysql_old_password Plugin”.
-
Command-Line Format --secure-file-priv=dir_name
System Variable secure_file_priv
Scope Global Dynamic No Type String Default Value platform specific
Valid Values empty string
dirname
NULL
This variable is used to limit the effect of data import and export operations, such as those performed by the
LOAD DATA
andSELECT ... INTO OUTFILE
statements and theLOAD_FILE()
function. These operations are permitted only to users who have theFILE
privilege.secure_file_priv
may be set as follows:If empty, the variable has no effect. This is not a secure setting.
If set to the name of a directory, the server limits import and export operations to work only with files in that directory. The directory must exist; the server does not create it.
If set to
NULL
, the server disables import and export operations.
The default value is platform specific and depends on the value of the
INSTALL_LAYOUT
CMake option, as shown in the following table. To specify the defaultsecure_file_priv
value explicitly if you are building from source, use theINSTALL_SECURE_FILE_PRIVDIR
CMake option.INSTALL_LAYOUT
ValueDefault secure_file_priv
ValueSTANDALONE
,WIN
NULL
(>= MySQL 5.7.16), empty (< MySQL 5.7.16)DEB
,RPM
,SLES
,SVR4
/var/lib/mysql-files
Otherwise mysql-files
under theCMAKE_INSTALL_PREFIX
valueTo set the default
secure_file_priv
value for thelibmysqld
embedded server, use theINSTALL_SECURE_FILE_PRIV_EMBEDDEDDIR
CMake option. The default value for this option isNULL
.The server checks the value of
secure_file_priv
at startup and writes a warning to the error log if the value is insecure. A non-NULL
value is considered insecure if it is empty, or the value is the data directory or a subdirectory of it, or a directory that is accessible by all users. Ifsecure_file_priv
is set to a nonexistent path, the server writes an error message to the error log and exits. -
Command-Line Format --session-track-gtids=value
System Variable session_track_gtids
Scope Global, Session Dynamic Yes Type Enumeration Default Value OFF
Valid Values OFF
OWN_GTID
ALL_GTIDS
Controls whether the server returns GTIDs to the client, enabling the client to use them to track the server state. Depending on the variable value, at the end of executing each transaction, the server’s GTIDs are captured and returned to the client as part of the acknowledgement. The possible values for
session_track_gtids
are as follows:OFF
: The server does not return GTIDs to the client. This is the default.OWN_GTID
: The server returns the GTIDs for all transactions that were successfully committed by this client in its current session since the last acknowledgement. Typically, this is the single GTID for the last transaction committed, but if a single client request resulted in multiple transactions, the server returns a GTID set containing all the relevant GTIDs.ALL_GTIDS
: The server returns the global value of itsgtid_executed
system variable, which it reads at a point after the transaction is successfully committed. As well as the GTID for the transaction just committed, this GTID set includes all transactions committed on the server by any client, and can include transactions committed after the point when the transaction currently being acknowledged was committed.
session_track_gtids
cannot be set within transactional context.For more information about session state tracking, see Section 5.1.15, “Server Tracking of Client Session State”.
-
Command-Line Format --session-track-schema[={OFF|ON}]
System Variable session_track_schema
Scope Global, Session Dynamic Yes Type Boolean Default Value ON
Controls whether the server tracks when the default schema (database) is set within the current session and notifies the client to make the schema name available.
If the schema name tracker is enabled, name notification occurs each time the default schema is set, even if the new schema name is the same as the old.
For more information about session state tracking, see Section 5.1.15, “Server Tracking of Client Session State”.
-
Command-Line Format --session-track-state-change[={OFF|ON}]
System Variable session_track_state_change
Scope Global, Session Dynamic Yes Type Boolean Default Value OFF
Controls whether the server tracks changes to the state of the current session and notifies the client when state changes occur. Changes can be reported for these attributes of client session state:
The default schema (database).
Session-specific values for system variables.
User-defined variables.
Temporary tables.
Prepared statements.
If the session state tracker is enabled, notification occurs for each change that involves tracked session attributes, even if the new attribute values are the same as the old. For example, setting a user-defined variable to its current value results in a notification.
The
session_track_state_change
variable controls only notification of when changes occur, not what the changes are. For example, state-change notifications occur when the default schema is set or tracked session system variables are assigned, but the notification does not include the schema name or variable values. To receive notification of the schema name or session system variable values, use thesession_track_schema
orsession_track_system_variables
system variable, respectively.NoteAssigning a value to
session_track_state_change
itself is not considered a state change and is not reported as such. However, if its name listed in the value ofsession_track_system_variables
, any assignments to it do result in notification of the new value.For more information about session state tracking, see Section 5.1.15, “Server Tracking of Client Session State”.
session_track_system_variables
Command-Line Format --session-track-system-variables=#
System Variable session_track_system_variables
Scope Global, Session Dynamic Yes Type String Default Value time_zone, autocommit, character_set_client, character_set_results, character_set_connection
Controls whether the server tracks assignments to session system variables and notifies the client of the name and value of each assigned variable. The variable value is a comma-separated list of variables for which to track assignments. By default, notification is enabled for
time_zone
,autocommit
,character_set_client
,character_set_results
, andcharacter_set_connection
. (The latter three variables are those affected bySET NAMES
.)The special value
*
causes the server to track assignments to all session variables. If given, this value must be specified by itself without specific system variable names.To disable notification of session variable assignments, set
session_track_system_variables
to the empty string.If session system variable tracking is enabled, notification occurs for all assignments to tracked session variables, even if the new values are the same as the old.
For more information about session state tracking, see Section 5.1.15, “Server Tracking of Client Session State”.
session_track_transaction_info
Command-Line Format --session-track-transaction-info=value
System Variable session_track_transaction_info
Scope Global, Session Dynamic Yes Type Enumeration Default Value OFF
Valid Values OFF
STATE
CHARACTERISTICS
Controls whether the server tracks the state and characteristics of transactions within the current session and notifies the client to make this information available. These
session_track_transaction_info
values are permitted:OFF
: Disable transaction state tracking. This is the default.STATE
: Enable transaction state tracking without characteristics tracking. State tracking enables the client to determine whether a transaction is in progress and whether it could be moved to a different session without being rolled back.CHARACTERISTICS
: Enable transaction state tracking, including characteristics tracking. Characteristics tracking enables the client to determine how to restart a transaction in another session so that it has the same characteristics as in the original session. The following characteristics are relevant for this purpose:ISOLATION LEVEL READ ONLY READ WRITE WITH CONSISTENT SNAPSHOT
For a client to safely relocate a transaction to another session, it must track not only transaction state but also transaction characteristics. In addition, the client must track the
transaction_isolation
andtransaction_read_only
system variables to correctly determine the session defaults. (To track these variables, list them in the value of thesession_track_system_variables
system variable.)For more information about session state tracking, see Section 5.1.15, “Server Tracking of Client Session State”.
sha256_password_auto_generate_rsa_keys
Command-Line Format --sha256-password-auto-generate-rsa-keys[={OFF|ON}]
System Variable sha256_password_auto_generate_rsa_keys
Scope Global Dynamic No Type Boolean Default Value ON
This variable is available if the server was compiled using OpenSSL (see Section 6.3.4, “SSL Library-Dependent Capabilities”). It controls whether the server autogenerates RSA private/public key-pair files in the data directory, if they do not already exist.
At startup, the server automatically generates RSA private/public key-pair files in the data directory if the
sha256_password_auto_generate_rsa_keys
system variable is enabled, no RSA options are specified, and the RSA files are missing from the data directory. These files enable secure password exchange using RSA over unencrypted connections for accounts authenticated by thesha256_password
plugin; see Section 6.4.1.5, “SHA-256 Pluggable Authentication”.For more information about RSA file autogeneration, including file names and characteristics, see Section 6.3.3.1, “Creating SSL and RSA Certificates and Keys using MySQL”
The
auto_generate_certs
system variable is related but controls autogeneration of SSL certificate and key files needed for secure connections using SSL.sha256_password_private_key_path
Command-Line Format --sha256-password-private-key-path=file_name
System Variable sha256_password_private_key_path
Scope Global Dynamic No Type File name Default Value private_key.pem
This variable is available if MySQL was compiled using OpenSSL (see Section 6.3.4, “SSL Library-Dependent Capabilities”). Its value is the path name of the RSA private key file for the
sha256_password
authentication plugin. If the file is named as a relative path, it is interpreted relative to the server data directory. The file must be in PEM format.ImportantBecause this file stores a private key, its access mode should be restricted so that only the MySQL server can read it.
For information about
sha256_password
, see Section 6.4.1.5, “SHA-256 Pluggable Authentication”.-
Command-Line Format --sha256-password-proxy-users[={OFF|ON}]
System Variable sha256_password_proxy_users
Scope Global Dynamic Yes Type Boolean Default Value OFF
This variable controls whether the
sha256_password
built-in authentication plugin supports proxy users. It has no effect unless thecheck_proxy_users
system variable is enabled. For information about user proxying, see Section 6.2.14, “Proxy Users”. sha256_password_public_key_path
Command-Line Format --sha256-password-public-key-path=file_name
System Variable sha256_password_public_key_path
Scope Global Dynamic No Type File name Default Value public_key.pem
This variable is available if MySQL was compiled using OpenSSL (see Section 6.3.4, “SSL Library-Dependent Capabilities”). Its value is the path name of the RSA public key file for the
sha256_password
authentication plugin. If the file is named as a relative path, it is interpreted relative to the server data directory. The file must be in PEM format. Because this file stores a public key, copies can be freely distributed to client users. (Clients that explicitly specify a public key when connecting to the server using RSA password encryption must use the same public key as that used by the server.)For information about
sha256_password
, including information about how clients specify the RSA public key, see Section 6.4.1.5, “SHA-256 Pluggable Authentication”.-
Command-Line Format --shared-memory[={OFF|ON}]
System Variable shared_memory
Scope Global Dynamic No Platform Specific Windows Type Boolean Default Value OFF
(Windows only.) Whether the server permits shared-memory connections.
-
Command-Line Format --shared-memory-base-name=name
System Variable shared_memory_base_name
Scope Global Dynamic No Platform Specific Windows Type String Default Value MYSQL
(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 variable applies only if the server is started with the
shared_memory
system variable enabled to support shared-memory connections. -
Command-Line Format --show-compatibility-56[={OFF|ON}]
Deprecated Yes System Variable show_compatibility_56
Scope Global Dynamic Yes Type Boolean Default Value OFF
The
INFORMATION_SCHEMA
has tables that contain system and status variable information (see Section 24.3.11, “The INFORMATION_SCHEMA GLOBAL_VARIABLES and SESSION_VARIABLES Tables”, and Section 24.3.10, “The INFORMATION_SCHEMA GLOBAL_STATUS and SESSION_STATUS Tables”). As of MySQL 5.7.6, the Performance Schema also contains system and status variable tables (see Section 25.12.13, “Performance Schema System Variable Tables”, and Section 25.12.14, “Performance Schema Status Variable Tables”). The Performance Schema tables are intended to replace theINFORMATION_SCHEMA
tables, which are deprecated as of MySQL 5.7.6 and are removed in MySQL 8.0.For advice on migrating away from the
INFORMATION_SCHEMA
tables to the Performance Schema tables, see Section 25.20, “Migrating to Performance Schema System and Status Variable Tables”. To assist in the migration, you can use theshow_compatibility_56
system variable, which affects whether MySQL 5.6 compatibility is enabled with respect to how system and status variable information is provided by theINFORMATION_SCHEMA
and Performance Schema tables, and also by theSHOW VARIABLES
andSHOW STATUS
statements.Noteshow_compatibility_56
is deprecated because its only purpose is to permit control over deprecated system and status variable information sources which you can expect to be removed in a future release of MySQL. When those sources are removed,show_compatibility_56
no longer has any purpose, and you can expect it be removed as well.The following discussion describes the effects of
show_compatibility_56
:For better understanding, it is strongly recommended that you also read these sections:
Overview of show_compatibility_56 Effects
The
show_compatibility_56
system variable affects these aspects of server operation regarding system and status variables:Information available from the
SHOW VARIABLES
andSHOW STATUS
statementsInformation available from the
INFORMATION_SCHEMA
tables that provide system and status variable informationInformation available from the Performance Schema tables that provide system and status variable information
The effect of the
FLUSH STATUS
statement on status variables
This list summarizes the effects of
show_compatibility_56
, with additional details given later:When
show_compatibility_56
isON
, compatibility with MySQL 5.6 is enabled. Older variable information sources (SHOW
statements,INFORMATION_SCHEMA
tables) produce the same output as in MySQL 5.6.When
show_compatibility_56
isOFF
, compatibility with MySQL 5.6 is disabled. Selecting from theINFORMATION_SCHEMA
tables produces an error because the Performance Schema tables are intended to replace them. TheINFORMATION_SCHEMA
tables are deprecated as of MySQL 5.7.6 and are removed in MySQL 8.0.To obtain system and status variable information When
show_compatibility_56=OFF
, use the Performance Schema tables or theSHOW
statements.NoteWhen
show_compatibility_56=OFF
, theSHOW VARIABLES
andSHOW STATUS
statements display rows from the Performance Schemaglobal_variables
,session_variables
,global_status
, andsession_status
tables.As of MySQL 5.7.9, those tables are world readable and accessible without the
SELECT
privilege, which means thatSELECT
is not needed to use theSHOW
statements, either. Before MySQL 5.7.9, theSELECT
privilege is required to access those Performance Schema tables, either directly, or indirectly through theSHOW
statements.Several
Slave_
status variables are available fromxxx
SHOW STATUS
whenshow_compatibility_56
isON
. Whenshow_compatibility_56
isOFF
, some of those variables are not exposed toSHOW STATUS
. The information they provide is available in replication-related Performance Schema tables, as described later.show_compatibility_56
has no effect on system variable access using@@
notation:@@GLOBAL.
,var_name
@@SESSION.
,var_name
@@
.var_name
show_compatibility_56
has no effect for the embedded server, which produces 5.6-compatible output in all cases.
The following descriptions detail the effect of setting
show_compatibility_56
toON
orOFF
in the contexts in which this variable applies.Effect of show_compatibility_56 on SHOW Statements
SHOW GLOBAL VARIABLES
statement:ON
: MySQL 5.6 output.OFF
: Output displays rows from the Performance Schemaglobal_variables
table.
SHOW [SESSION | LOCAL] VARIABLES
statement:ON
: MySQL 5.6 output.OFF
: Output displays rows from the Performance Schemasession_variables
table. (In MySQL 5.7.6 and 5.7.7,OFF
output does not fully reflect all system variable values in effect for the current session; it includes no rows for global variables that have no session counterpart. This is corrected in MySQL 5.7.8.)
SHOW GLOBAL STATUS
statement:ON
: MySQL 5.6 output.OFF
: Output displays rows from the Performance Schemaglobal_status
table, plus theCom_
statement execution counters.xxx
OFF
output includes no rows for session variables that have no global counterpart, unlikeON
output.
SHOW [SESSION | LOCAL] STATUS
statement:ON
: MySQL 5.6 output.OFF
: Output displays rows from the Performance Schemasession_status
table, plus theCom_
statement execution counters. (In MySQL 5.7.6 and 5.7.7,xxx
OFF
output does not fully reflect all status variable values in effect for the current session; it includes no rows for global variables that have no session counterpart. This is corrected in MySQL 5.7.8.)
In MySQL 5.7.6 and 5.7.7, for each of the
SHOW
statements just described, use of aWHERE
clause produces a warning whenshow_compatibility_56=ON
and an error whenshow_compatibility_56=OFF
. (This applies toWHERE
clauses that are not optimized away. For example,WHERE 1
is trivially true, is optimized away, and thus produces no warning or error.) This behavior does not occur as of MySQL 5.7.8;WHERE
is supported as before 5.7.6.Effect of show_compatibility_56 on INFORMATION_SCHEMA Tables
INFORMATION_SCHEMA
tables (GLOBAL_VARIABLES
,SESSION_VARIABLES
,GLOBAL_STATUS
, andSESSION_STATUS
):ON
: MySQL 5.6 output, with a deprecation warning.OFF
: Selecting from these tables produces an error. (Before 5.7.9, selecting from these tables produces no output, with a deprecation warning.)
Effect of show_compatibility_56 on Performance Schema Tables
Performance Schema system variable tables:
OFF
:global_variables
: Global system variables only.session_variables
: System variables in effect for the current session: A row for each session variable, and a row for each global variable that has no session counterpart.variables_by_thread
: Session system variables only, for each active session.
ON
: Same output as forOFF
. (Before 5.7.8, these tables produce no output.)
Performance Schema status variable tables:
OFF
:global_status
: Global status variables only.session_status
: Status variables in effect the current session: A row for each session variable, and a row for each global variable that has no session counterpart.status_by_account
Session status variables only, aggregated per account.status_by_host
: Session status variables only, aggregated per host name.status_by_thread
: Session status variables only, for each active session.status_by_user
: Session status variables only, aggregated per user name.
The Performance Schema does not collect statistics for
Com_
status variables in the status variable tables. To obtain global and per-session statement execution counts, use thexxx
events_statements_summary_global_by_event_name
andevents_statements_summary_by_thread_by_event_name
tables, respectively.ON
: Same output as forOFF
. (Before 5.7.9, these tables produce no output.)
Effect of show_compatibility_56 on Slave Status Variables
Replica status variables:
ON
: SeveralSlave_
status variables are available fromxxx
SHOW STATUS
.OFF
: Some of those replica variables are not exposed toSHOW STATUS
or the Performance Schema status variable tables. The information they provide is available in replication-related Performance Schema tables. The following table shows whichSlave_
status variables become unavailable inxxx
SHOW STATUS
and their locations in Performance Schema replication tables.Status Variable Performance Schema Location Slave_heartbeat_period
replication_connection_configuration
table,HEARTBEAT_INTERVAL
columnSlave_last_heartbeat
replication_connection_status
table,LAST_HEARTBEAT_TIMESTAMP
columnSlave_received_heartbeats
replication_connection_status
table,COUNT_RECEIVED_HEARTBEATS
columnSlave_retried_transactions
replication_applier_status
table,COUNT_TRANSACTIONS_RETRIES
columnSlave_running
replication_connection_status
andreplication_applier_status
tables,SERVICE_STATE
column
Effect of show_compatibility_56 on FLUSH STATUS
FLUSH STATUS
statement:ON
: This statement produces MySQL 5.6 behavior. It adds the current thread's session status variable values to the global values and resets the session values to zero. Some global variables may be reset to zero as well. It also resets the counters for key caches (default and named) to zero and setsMax_used_connections
to the current number of open connections.OFF
: This statement adds the session status from all active sessions to the global status variables, resets the status of all active sessions, and resets account, host, and user status values aggregated from disconnected sessions.
-
Command-Line Format --show-create-table-verbosity[={OFF|ON}]
Introduced 5.7.22 System Variable show_create_table_verbosity
Scope Global, Session Dynamic Yes Type Boolean Default Value OFF
SHOW CREATE TABLE
normally does not show theROW_FORMAT
table option if the row format is the default format. Enabling this variable causesSHOW CREATE TABLE
to displayROW_FORMAT
regardless of whether it is the default format. -
Command-Line Format --show-old-temporals[={OFF|ON}]
Deprecated Yes System Variable show_old_temporals
Scope Global, Session Dynamic Yes Type Boolean Default Value OFF
Whether
SHOW CREATE TABLE
output includes comments to flag temporal columns found to be in pre-5.6.4 format (TIME
,DATETIME
, andTIMESTAMP
columns without support for fractional seconds precision). This variable is disabled by default. If enabled,SHOW CREATE TABLE
output looks like this:CREATE TABLE `mytbl` ( `ts` timestamp /* 5.5 binary format */ NOT NULL DEFAULT CURRENT_TIMESTAMP, `dt` datetime /* 5.5 binary format */ DEFAULT NULL, `t` time /* 5.5 binary format */ DEFAULT NULL ) DEFAULT CHARSET=latin1
Output for the
COLUMN_TYPE
column of the Information SchemaCOLUMNS
table is affected similarly.This variable is deprecated; expect it to be removed in a future release of MySQL.
-
Command-Line Format --skip-external-locking[={OFF|ON}]
System Variable skip_external_locking
Scope Global Dynamic No Type Boolean Default Value ON
This is
OFF
if mysqld uses external locking (system locking),ON
if external locking is disabled. This affects onlyMyISAM
table access.This variable is set by the
--external-locking
or--skip-external-locking
option. External locking is disabled by default.External locking affects only
MyISAM
table access. For more information, including conditions under which it can and cannot be used, see Section 8.11.5, “External Locking”. -
Command-Line Format --skip-name-resolve[={OFF|ON}]
System Variable skip_name_resolve
Scope Global Dynamic No Type Boolean Default Value OFF
Whether to resolve host names when checking client connections. If this variable is
OFF
, mysqld resolves host names when checking client connections. If it isON
, mysqld uses only IP numbers; in this case, allHost
column values in the grant tables must be IP addresses. See Section 5.1.11.2, “DNS Lookups and the Host Cache”.Depending on the network configuration of your system and the
Host
values for your accounts, clients may need to connect using an explicit--host
option, such as--host=127.0.0.1
or--host=::1
.An attempt to connect to the host
127.0.0.1
normally resolves to thelocalhost
account. However, this fails if the server is run withskip_name_resolve
enabled. If you plan to do that, make sure an account exists that can accept a connection. For example, to be able to connect asroot
using--host=127.0.0.1
or--host=::1
, create these accounts:CREATE USER 'root'@'127.0.0.1' IDENTIFIED BY 'root-password'; CREATE USER 'root'@'::1' IDENTIFIED BY 'root-password';
-
Command-Line Format --skip-networking[={OFF|ON}]
System Variable skip_networking
Scope Global Dynamic No Type Boolean Default Value OFF
This variable controls whether the server permits TCP/IP connections. By default, it is disabled (permit TCP connections). If enabled, the server permits only local (non-TCP/IP) connections and all interaction with mysqld must be made using 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 permitted. See Section 5.1.11.2, “DNS Lookups and the Host Cache”.
-
Command-Line Format --skip-show-database
System Variable skip_show_database
Scope Global Dynamic No Type Boolean Default Value OFF
This prevents people from using the
SHOW DATABASES
statement if they do not have theSHOW 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 theSHOW DATABASES
privilege: If the variable value isON
, theSHOW DATABASES
statement is permitted only to users who have theSHOW DATABASES
privilege, and the statement displays all database names. If the value isOFF
,SHOW DATABASES
is permitted to all users, but displays the names of only those databases for which the user has theSHOW DATABASES
or other privilege.CautionBecause a global privilege is considered a privilege for all databases, any global privilege enables a user to see all database names with
SHOW DATABASES
or by examining theINFORMATION_SCHEMA
SCHEMATA
table. -
Command-Line Format --slow-launch-time=#
System Variable slow_launch_time
Scope Global Dynamic Yes Type Integer Default Value 2
Minimum Value 0
Maximum Value 31536000
Unit seconds If creating a thread takes longer than this many seconds, the server increments the
Slow_launch_threads
status variable. -
Command-Line Format --slow-query-log[={OFF|ON}]
System Variable slow_query_log
Scope Global Dynamic Yes Type Boolean Default Value OFF
Whether the slow query log is enabled. The value can be 0 (or
OFF
) to disable the log or 1 (orON
) to enable the log. The destination for log output is controlled by thelog_output
system variable; if that value isNONE
, no log entries are written even if the log is enabled.“Slow” is determined by the value of the
long_query_time
variable. See Section 5.4.5, “The Slow Query Log”. -
Command-Line Format --slow-query-log-file=file_name
System Variable slow_query_log_file
Scope Global Dynamic Yes Type File name Default Value host_name-slow.log
The name of the slow query log file. The default value is
, but the initial value can be changed with thehost_name
-slow.log--slow_query_log_file
option. -
Command-Line Format --socket={file_name|pipe_name}
System Variable socket
Scope Global Dynamic No Type String Default Value (Windows) MySQL
Default Value (Other) /tmp/mysql.sock
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). -
Command-Line Format --sort-buffer-size=#
System Variable sort_buffer_size
Scope Global, Session Dynamic Yes Type Integer Default Value 262144
Minimum Value 32768
Maximum Value (Windows) 4294967295
Maximum Value (Other, 64-bit platforms) 18446744073709551615
Maximum Value (Other, 32-bit platforms) 4294967295
Unit bytes Each session that must perform a sort allocates a buffer of this size.
sort_buffer_size
is not specific to any storage engine and applies in a general manner for optimization. At minimum thesort_buffer_size
value must be large enough to accommodate fifteen tuples in the sort buffer. Also, increasing the value ofmax_sort_length
may require increasing the value ofsort_buffer_size
. For more information, see Section 8.2.1.14, “ORDER BY Optimization”If you see many
Sort_merge_passes
per second inSHOW GLOBAL STATUS
output, you can consider increasing thesort_buffer_size
value to speed upORDER BY
orGROUP BY
operations that cannot be improved with query optimization or improved indexing.The optimizer tries to work out how much space is needed but can allocate more, up to the limit. Setting it larger than required globally slows down most queries that sort. It is best to increase it as a session setting, and only for the sessions that need a larger size. On Linux, there are thresholds of 256KB and 2MB where larger values may significantly slow down memory allocation, so you should consider staying below one of those values. Experiment to find the best value for your workload. See Section B.3.3.5, “Where MySQL Stores Temporary Files”.
The maximum permissible setting for
sort_buffer_size
is 4GB−1. Larger values are permitted for 64-bit platforms (except 64-bit Windows, for which large values are truncated to 4GB−1 with a warning). -
System Variable sql_auto_is_null
Scope Global, Session Dynamic Yes Type Boolean Default Value OFF
If this variable is enabled, then after a statement that successfully inserts an automatically generated
AUTO_INCREMENT
value, you can find that value by issuing a statement of the following form:SELECT * FROM tbl_name WHERE auto_col IS NULL
If the statement returns a row, the value returned is the same as if you invoked the
LAST_INSERT_ID()
function. For details, including the return value after a multiple-row insert, see Section 12.15, “Information Functions”. If noAUTO_INCREMENT
value was successfully inserted, theSELECT
statement returns no row.The behavior of retrieving an
AUTO_INCREMENT
value by using anIS NULL
comparison is used by some ODBC programs, such as Access. See Obtaining Auto-Increment Values. This behavior can be disabled by settingsql_auto_is_null
toOFF
.The default value of
sql_auto_is_null
isOFF
. -
System Variable sql_big_selects
Scope Global, Session Dynamic Yes Type Boolean Default Value ON
If set to
OFF
, MySQL abortsSELECT
statements that are likely to take a very long time to execute (that is, statements for which the optimizer estimates that the number of examined rows exceeds the value ofmax_join_size
). This is useful when an inadvisableWHERE
statement has been issued. The default value for a new connection isON
, which permits allSELECT
statements.If you set the
max_join_size
system variable to a value other thanDEFAULT
,sql_big_selects
is set toOFF
. -
System Variable sql_buffer_result
Scope Global, Session Dynamic Yes Type Boolean Default Value OFF
If enabled,
sql_buffer_result
forces results fromSELECT
statements to be put into temporary tables. This helps MySQL free the table locks early and can be beneficial in cases where it takes a long time to send results to the client. The default value isOFF
. -
System Variable sql_log_off
Scope Global, Session Dynamic Yes Type Boolean Default Value OFF
Valid Values OFF
(enable logging)ON
(disable logging)This variable controls whether logging to the general query log is disabled for the current session (assuming that the general query log itself is enabled). The default value is
OFF
(that is, enable logging). To disable or enable general query logging for the current session, set the sessionsql_log_off
variable toON
orOFF
.Setting the session value of this system variable is a restricted operation. The session user must have privileges sufficient to set restricted session variables. See Section 5.1.8.1, “System Variable Privileges”.
-
Command-Line Format --sql-mode=name
System Variable sql_mode
Scope Global, Session Dynamic Yes Type Set Default Value ONLY_FULL_GROUP_BY STRICT_TRANS_TABLES NO_ZERO_IN_DATE NO_ZERO_DATE ERROR_FOR_DIVISION_BY_ZERO NO_AUTO_CREATE_USER NO_ENGINE_SUBSTITUTION
Valid Values ALLOW_INVALID_DATES
ANSI_QUOTES
ERROR_FOR_DIVISION_BY_ZERO
HIGH_NOT_PRECEDENCE
IGNORE_SPACE
NO_AUTO_CREATE_USER
NO_AUTO_VALUE_ON_ZERO
NO_BACKSLASH_ESCAPES
NO_DIR_IN_CREATE
NO_ENGINE_SUBSTITUTION
NO_FIELD_OPTIONS
NO_KEY_OPTIONS
NO_TABLE_OPTIONS
NO_UNSIGNED_SUBTRACTION
NO_ZERO_DATE
NO_ZERO_IN_DATE
ONLY_FULL_GROUP_BY
PAD_CHAR_TO_FULL_LENGTH
PIPES_AS_CONCAT
REAL_AS_FLOAT
STRICT_ALL_TABLES
STRICT_TRANS_TABLES
The current server SQL mode, which can be set dynamically. For details, see Section 5.1.10, “Server SQL Modes”.
NoteMySQL installation programs may configure the SQL mode during the installation process. If the SQL mode differs from the default or from what you expect, check for a setting in an option file that the server reads at startup.
-
System Variable sql_notes
Scope Global, Session Dynamic Yes Type Boolean Default Value ON
If enabled (the default), diagnostics of
Note
level incrementwarning_count
and the server records them. If disabled,Note
diagnostics do not incrementwarning_count
and the server does not record them. mysqldump includes output to disable this variable so that reloading the dump file does not produce warnings for events that do not affect the integrity of the reload operation. -
System Variable sql_quote_show_create
Scope Global, Session Dynamic Yes Type Boolean Default Value ON
If enabled (the default), the server quotes identifiers for
SHOW CREATE TABLE
andSHOW CREATE DATABASE
statements. If disabled, quoting is disabled. This option is enabled by default so that replication works for identifiers that require quoting. See Section 13.7.5.10, “SHOW CREATE TABLE Statement”, and Section 13.7.5.6, “SHOW CREATE DATABASE Statement”. -
System Variable sql_safe_updates
Scope Global, Session Dynamic Yes Type Boolean Default Value OFF
If this variable is enabled,
UPDATE
andDELETE
statements that do not use a key in theWHERE
clause or aLIMIT
clause produce an error. This makes it possible to catchUPDATE
andDELETE
statements where keys are not used properly and that would probably change or delete a large number of rows. The default value isOFF
.For the mysql client,
sql_safe_updates
can be enabled by using the--safe-updates
option. For more information, see Using Safe-Updates Mode (--safe-updates). -
System Variable sql_select_limit
Scope Global, Session Dynamic Yes Type Integer Default Value 18446744073709551615
Minimum Value 0
Maximum Value 18446744073709551615
The maximum number of rows to return from
SELECT
statements. For more information, see Using Safe-Updates Mode (--safe-updates).The default value for a new connection is the maximum number of rows that the server permits per table. Typical default values are (232)−1 or (264)−1. If you have changed the limit, the default value can be restored by assigning a value of
DEFAULT
.If a
SELECT
has aLIMIT
clause, theLIMIT
takes precedence over the value ofsql_select_limit
. -
System Variable sql_warnings
Scope Global, Session Dynamic Yes Type Boolean Default Value OFF
This variable controls whether single-row
INSERT
statements produce an information string if warnings occur. The default isOFF
. Set the value toON
to produce an information string. -
Command-Line Format --ssl-ca=file_name
System Variable ssl_ca
Scope Global Dynamic No Type File name Default Value NULL
The path name of the Certificate Authority (CA) certificate file in PEM format. The file contains a list of trusted SSL Certificate Authorities.
-
Command-Line Format --ssl-capath=dir_name
System Variable ssl_capath
Scope Global Dynamic No Type Directory name Default Value NULL
The path name of the directory that contains trusted SSL Certificate Authority (CA) certificate files in PEM format. Support for this capability depends on the SSL library used to compile MySQL; see Section 6.3.4, “SSL Library-Dependent Capabilities”.
-
Command-Line Format --ssl-cert=file_name
System Variable ssl_cert
Scope Global Dynamic No Type File name Default Value NULL
The path name of the server SSL public key certificate file in PEM format.
If the server is started with
ssl_cert
set to a certificate that uses any restricted cipher or cipher category, the server starts with support for encrypted connections disabled. For information about cipher restrictions, see Connection Cipher Configuration. -
Command-Line Format --ssl-cipher=name
System Variable ssl_cipher
Scope Global Dynamic No Type String Default Value NULL
The list of permissible ciphers for connection encryption. If no cipher in the list is supported, encrypted connections do not work.
For greatest portability, the cipher list should be a list of one or more cipher names, separated by colons. This format is understood both by OpenSSL and yaSSL. The following example shows two cipher names separated by a colon:
[mysqld] ssl_cipher="DHE-RSA-AES128-GCM-SHA256:AES128-SHA"
OpenSSL supports a more flexible syntax for specifying ciphers, as described in the OpenSSL documentation at https://www.openssl.org/docs/manmaster/man1/openssl-ciphers.html. yaSSL does not, so attempts to use that extended syntax fail for a MySQL distribution compiled using yaSSL.
For information about which encryption ciphers MySQL supports, see Section 6.3.2, “Encrypted Connection TLS Protocols and Ciphers”.
-
Command-Line Format --ssl-crl=file_name
System Variable ssl_crl
Scope Global Dynamic No Type File name Default Value NULL
The path name of the file containing certificate revocation lists in PEM format. Support for revocation-list capability depends on the SSL library used to compile MySQL. See Section 6.3.4, “SSL Library-Dependent Capabilities”.
-
Command-Line Format --ssl-crlpath=dir_name
System Variable ssl_crlpath
Scope Global Dynamic No Type Directory name Default Value NULL
The path of the directory that contains certificate revocation-list files in PEM format. Support for revocation-list capability depends on the SSL library used to compile MySQL. See Section 6.3.4, “SSL Library-Dependent Capabilities”.
-
Command-Line Format --ssl-key=file_name
System Variable ssl_key
Scope Global Dynamic No Type File name Default Value NULL
The path name of the server SSL private key file in PEM format. For better security, use a certificate with an RSA key size of at least 2048 bits.
If the key file is protected by a passphrase, the server prompts the user for the passphrase. The password must be given interactively; it cannot be stored in a file. If the passphrase is incorrect, the program continues as if it could not read the key.
-
Command-Line Format --stored-program-cache=#
System Variable stored_program_cache
Scope Global Dynamic Yes Type Integer Default Value 256
Minimum Value 16
Maximum Value 524288
Sets a soft upper limit for the number of cached stored routines per connection. The value of this variable is specified in terms of the number of stored routines held in each of the two caches maintained by the MySQL Server for, respectively, stored procedures and stored functions.
Whenever a stored routine is executed this cache size is checked before the first or top-level statement in the routine is parsed; if the number of routines of the same type (stored procedures or stored functions according to which is being executed) exceeds the limit specified by this variable, the corresponding cache is flushed and memory previously allocated for cached objects is freed. This allows the cache to be flushed safely, even when there are dependencies between stored routines.
-
Command-Line Format --super-read-only[={OFF|ON}]
System Variable super_read_only
Scope Global Dynamic Yes Type Boolean Default Value OFF
If the
read_only
system variable is enabled, the server permits no client updates except from users who have theSUPER
privilege. If thesuper_read_only
system variable is also enabled, the server prohibits client updates even from users who haveSUPER
. See the description of theread_only
system variable for a description of read-only mode and information about howread_only
andsuper_read_only
interact.Client updates prevented when
super_read_only
is enabled include operations that do not necessarily appear to be updates, such asCREATE FUNCTION
(to install a loadable function) andINSTALL PLUGIN
. These operations are prohibited because they involve changes to tables in themysql
system database.Changes to
super_read_only
on a replication source server are not replicated to replica servers. The value can be set on a replica independent of the setting on the source. -
Command-Line Format --sync-frm[={OFF|ON}]
Deprecated Yes System Variable sync_frm
Scope Global Dynamic Yes Type Boolean Default Value ON
If this variable is set to 1, when any nontemporary table is created its
.frm
file is synchronized to disk (usingfdatasync()
). This is slower but safer in case of a crash. The default is 1.This variable is deprecated in MySQL 5.7 and is removed in MySQL 8.0 (when
.frm
files become obsolete). -
System Variable system_time_zone
Scope Global Dynamic No Type String 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
. To explicitly specify the system time zone, set theTZ
environment variable or use the--timezone
option of the mysqld_safe script.The
system_time_zone
variable differs from thetime_zone
variable. Although they might have the same value, the latter variable is used to initialize the time zone for each client that connects. See Section 5.1.13, “MySQL Server Time Zone Support”. -
Command-Line Format --table-definition-cache=#
System Variable table_definition_cache
Scope Global Dynamic Yes Type Integer Default Value -1
(signifies autosizing; do not assign this literal value)Minimum Value 400
Maximum Value 524288
The number of table definitions (from
.frm
files) that can be stored in the table definition cache. If you use a large number of tables, you can create a large table definition cache to speed up opening of tables. The table definition cache takes less space and does not use file descriptors, unlike the normal table cache. The minimum value is 400. The default value is based on the following formula, capped to a limit of 2000:400 + (table_open_cache / 2)
For
InnoDB
, thetable_definition_cache
setting acts as a soft limit for the number of table instances in theInnoDB
data dictionary cache and the number file-per-table tablespaces that can be open at one time.If the number of table instances in the
InnoDB
data dictionary cache exceeds thetable_definition_cache
limit, an LRU mechanism begins marking table instances for eviction and eventually removes them from the InnoDB data dictionary cache. The number of open tables with cached metadata can be higher than thetable_definition_cache
limit due to table instances with foreign key relationships, which are not placed on the LRU list.The number of file-per-table tablespaces that can be open at one time is limited by both the
table_definition_cache
andinnodb_open_files
settings. If both variables are set, the highest setting is used. If neither variable is set, thetable_definition_cache
setting, which has a higher default value, is used. If the number of open tablespaces exceeds the limit defined bytable_definition_cache
orinnodb_open_files
, an LRU mechanism searches the LRU list for tablespace files that are fully flushed and not currently being extended. This process is performed each time a new tablespace is opened. Only inactive tablespaces are closed. -
Command-Line Format --table-open-cache=#
System Variable table_open_cache
Scope Global Dynamic Yes Type Integer Default Value 2000
Minimum Value 1
Maximum Value 524288
The number of open tables for all threads. Increasing this value increases the number of file descriptors that mysqld requires. The effective value of this variable is the greater of the effective value of
open_files_limit
- 10 -
the effective value ofmax_connections
/ 2
, and 400; that isMAX( (open_files_limit - 10 - max_connections) / 2, 400 )
You can check whether you need to increase the table cache by checking the
Opened_tables
status variable. If the value ofOpened_tables
is large and you do not useFLUSH TABLES
often (which just forces all tables to be closed and reopened), then you should increase the value of thetable_open_cache
variable. For more information about the table cache, see Section 8.4.3.1, “How MySQL Opens and Closes Tables”. -
Command-Line Format --table-open-cache-instances=#
System Variable table_open_cache_instances
Scope Global Dynamic No Type Integer Default Value 16
Minimum Value 1
Maximum Value 64
The number of open tables cache instances. To improve scalability by reducing contention among sessions, the open tables cache can be partitioned into several smaller cache instances of size
table_open_cache
/table_open_cache_instances
. A session needs to lock only one instance to access it for DML statements. This segments cache access among instances, permitting higher performance for operations that use the cache when there are many sessions accessing tables. (DDL statements still require a lock on the entire cache, but such statements are much less frequent than DML statements.)A value of 8 or 16 is recommended on systems that routinely use 16 or more cores. However, if you have many large triggers on your tables that cause a high memory load, the default setting for
table_open_cache_instances
might lead to excessive memory usage. In that situation, it can be helpful to settable_open_cache_instances
to 1 in order to restrict memory usage. -
Command-Line Format --thread-cache-size=#
System Variable thread_cache_size
Scope Global Dynamic Yes Type Integer Default Value -1
(signifies autosizing; do not assign this literal value)Minimum Value 0
Maximum Value 16384
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 does not provide a notable performance improvement if you have a good thread implementation. However, if your server sees hundreds of connections per second you should normally setthread_cache_size
high enough so that most new connections use cached threads. By examining the difference between theConnections
andThreads_created
status variables, you can see how efficient the thread cache is. For details, see Section 5.1.9, “Server Status Variables”.The default value is based on the following formula, capped to a limit of 100:
8 + (max_connections / 100)
This variable has no effect for the embedded server (
libmysqld
) and as of MySQL 5.7.2 is no longer visible within the embedded server. -
Command-Line Format --thread-handling=name
System Variable thread_handling
Scope Global Dynamic No Type Enumeration Default Value one-thread-per-connection
Valid Values no-threads
one-thread-per-connection
loaded-dynamically
The thread-handling model used by the server for connection threads. The permissible values are
no-threads
(the server uses a single thread to handle one connection),one-thread-per-connection
(the server uses one thread to handle each client connection), andloaded-dynamically
(set by the thread pool plugin when it initializes).no-threads
is useful for debugging under Linux; see Section 5.8, “Debugging MySQL”.This variable has no effect for the embedded server (
libmysqld
) and as of MySQL 5.7.2 is no longer visible within the embedded server. -
Command-Line Format --thread-pool-algorithm=#
System Variable thread_pool_algorithm
Scope Global Dynamic No Type Integer Default Value 0
Minimum Value 0
Maximum Value 1
This variable controls which algorithm the thread pool plugin uses:
A value of 0 (the default) uses a conservative low-concurrency algorithm which is most well tested and is known to produce very good results.
A value of 1 increases the concurrency and uses a more aggressive algorithm which at times has been known to perform 5–10% better on optimal thread counts, but has degrading performance as the number of connections increases. Its use should be considered as experimental and not supported.
This variable is available only if the thread pool plugin is enabled. See Section 5.5.3, “MySQL Enterprise Thread Pool”.
thread_pool_high_priority_connection
Command-Line Format --thread-pool-high-priority-connection=#
System Variable thread_pool_high_priority_connection
Scope Global, Session Dynamic Yes Type Integer Default Value 0
Minimum Value 0
Maximum Value 1
This variable affects queuing of new statements prior to execution. If the value is 0 (false, the default), statement queuing uses both the low-priority and high-priority queues. If the value is 1 (true), queued statements always go to the high-priority queue.
This variable is available only if the thread pool plugin is enabled. See Section 5.5.3, “MySQL Enterprise Thread Pool”.
thread_pool_max_unused_threads
Command-Line Format --thread-pool-max-unused-threads=#
System Variable thread_pool_max_unused_threads
Scope Global Dynamic Yes Type Integer Default Value 0
Minimum Value 0
Maximum Value 4096
The maximum permitted number of unused threads in the thread pool. This variable makes it possible to limit the amount of memory used by sleeping threads.
A value of 0 (the default) means no limit on the number of sleeping threads. A value of
N
whereN
is greater than 0 means 1 consumer thread andN
−1 reserve threads. In this case, if a thread is ready to sleep but the number of sleeping threads is already at the maximum, the thread exits rather than going to sleep.A sleeping thread is either sleeping as a consumer thread or a reserve thread. The thread pool permits one thread to be the consumer thread when sleeping. If a thread goes to sleep and there is no existing consumer thread, it sleeps as a consumer thread. When a thread must be woken up, a consumer thread is selected if there is one. A reserve thread is selected only when there is no consumer thread to wake up.
This variable is available only if the thread pool plugin is enabled. See Section 5.5.3, “MySQL Enterprise Thread Pool”.
-
Command-Line Format --thread-pool-prio-kickup-timer=#
System Variable thread_pool_prio_kickup_timer
Scope Global Dynamic Yes Type Integer Default Value 1000
Minimum Value 0
Maximum Value 4294967294
Unit milliseconds This variable affects statements waiting for execution in the low-priority queue. The value is the number of milliseconds before a waiting statement is moved to the high-priority queue. The default is 1000 (1 second).
This variable is available only if the thread pool plugin is enabled. See Section 5.5.3, “MySQL Enterprise Thread Pool”.
-
Command-Line Format --thread-pool-size=#
System Variable thread_pool_size
Scope Global Dynamic No Type Integer Default Value 16
Minimum Value 1
Maximum Value 64
The number of thread groups in the thread pool. This is the most important parameter controlling thread pool performance. It affects how many statements can execute simultaneously. If a value outside the range of permissible values is specified, the thread pool plugin does not load and the server writes a message to the error log.
This variable is available only if the thread pool plugin is enabled. See Section 5.5.3, “MySQL Enterprise Thread Pool”.
-
Command-Line Format --thread-pool-stall-limit=#
System Variable thread_pool_stall_limit
Scope Global Dynamic Yes Type Integer Default Value 6
Minimum Value 4
Maximum Value 600
Unit milliseconds * 10 This variable affects executing statements. The value is the amount of time a statement has to finish after starting to execute before it becomes defined as stalled, at which point the thread pool permits the thread group to begin executing another statement. The value is measured in 10 millisecond units, so the default of 6 means 60ms. Short wait values permit threads to start more quickly. Short values are also better for avoiding deadlock situations. Long wait values are useful for workloads that include long-running statements, to avoid starting too many new statements while the current ones execute.
This variable is available only if the thread pool plugin is enabled. See Section 5.5.3, “MySQL Enterprise Thread Pool”.
-
Command-Line Format --thread-stack=#
System Variable thread_stack
Scope Global Dynamic No Type Integer Default Value (64-bit platforms) 262144
Default Value (32-bit platforms) 196608
Minimum Value 131072
Maximum Value (64-bit platforms) 18446744073709550592
Maximum Value (32-bit platforms) 4294966272
Unit bytes Block Size 1024
The stack size for each thread. The default 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 unused. It is deprecated and is removed in MySQL 8.0.
-
System Variable time_zone
Scope Global, Session Dynamic Yes Type String Default Value SYSTEM
Minimum Value -12:59
Maximum Value +13:00
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 ofsystem_time_zone
”). The value can be specified explicitly at server startup with the--default-time-zone
option. See Section 5.1.13, “MySQL Server Time Zone Support”.NoteIf set to
SYSTEM
, every MySQL function call that requires a time zone calculation makes a system library call to determine the current system time zone. This call may be protected by a global mutex, resulting in contention. -
System Variable timestamp
Scope Session Dynamic Yes Type Numeric Default Value UNIX_TIMESTAMP()
Minimum Value 1
Maximum Value 2147483647
Set the time for this client. This is used to get the original timestamp if you use the binary log to restore rows.
timestamp_value
should be a Unix epoch timestamp (a value like that returned byUNIX_TIMESTAMP()
, not a value in'
format) orYYYY-MM-DD hh:mm:ss
'DEFAULT
.Setting
timestamp
to a constant value causes it to retain that value until it is changed again. Settingtimestamp
toDEFAULT
causes its value to be the current date and time as of the time it is accessed. The maximum value corresponds to'2038-01-19 03:14:07'
UTC, the same as for theTIMESTAMP
data type.timestamp
is aDOUBLE
rather thanBIGINT
because its value includes a microseconds part.SET timestamp
affects the value returned byNOW()
but not bySYSDATE()
. This means that timestamp settings in the binary log have no effect on invocations ofSYSDATE()
. The server can be started with the--sysdate-is-now
option to causeSYSDATE()
to be a synonym forNOW()
, in which caseSET timestamp
affects both functions. -
Command-Line Format --tls-version=protocol_list
Introduced 5.7.10 System Variable tls_version
Scope Global Dynamic No Type String Default Value (≥ 5.7.28) TLSv1,TLSv1.1,TLSv1.2
Default Value (≤ 5.7.27) TLSv1,TLSv1.1,TLSv1.2
(OpenSSL)TLSv1,TLSv1.1
(yaSSL)Which protocols the server permits for encrypted connections. The value is a comma-separated list containing one or more protocol versions. The protocols that can be named for this variable depend on the SSL library used to compile MySQL. Permitted protocols should be chosen such as not to leave “holes” in the list. For details, see Section 6.3.2, “Encrypted Connection TLS Protocols and Ciphers”.
NoteAs of MySQL 5.7.35, the TLSv1 and TLSv1.1 connection protocols are deprecated and support for them is subject to removal in a future version of MySQL. See Deprecated TLS Protocols.
Setting this variable to an empty string disables encrypted connections.
-
Command-Line Format --tmp-table-size=#
System Variable tmp_table_size
Scope Global, Session Dynamic Yes Type Integer Default Value 16777216
Minimum Value 1024
Maximum Value 18446744073709551615
Unit bytes The maximum size of internal in-memory temporary tables. This variable does not apply to user-created
MEMORY
tables.The actual limit is the smaller of
tmp_table_size
andmax_heap_table_size
. When an in-memory temporary table exceeds the limit, MySQL automatically converts it to an on-disk temporary table. Theinternal_tmp_disk_storage_engine
option defines the storage engine used for on-disk temporary tables.Increase the value of
tmp_table_size
(andmax_heap_table_size
if necessary) if you do many advancedGROUP BY
queries and you have lots of memory.You can compare the number of internal on-disk temporary tables created to the total number of internal temporary tables created by comparing
Created_tmp_disk_tables
andCreated_tmp_tables
values.See also Section 8.4.4, “Internal Temporary Table Use in MySQL”.
-
Command-Line Format --tmpdir=dir_name
System Variable tmpdir
Scope Global Dynamic No Type Directory name The path of the directory to use for creating temporary files. It might be useful if your default
/tmp
directory resides on a partition that is too small to hold temporary tables. This 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.tmpdir
can be a non-permanent location, such as a directory on a memory-based file system or a directory that is cleared when the server host restarts. If the MySQL server is acting as a replica, and you are using a non-permanent location fortmpdir
, consider setting a different temporary directory for the replica using theslave_load_tmpdir
variable. For a replica, the temporary files used to replicateLOAD DATA
statements are stored in this directory, so with a permanent location they can survive machine restarts, although replication can now continue after a restart if the temporary files have been removed.For more information about the storage location of temporary files, see Section B.3.3.5, “Where MySQL Stores Temporary Files”.
-
Command-Line Format --transaction-alloc-block-size=#
System Variable transaction_alloc_block_size
Scope Global, Session Dynamic Yes Type Integer Default Value 8192
Minimum Value 1024
Maximum Value 131072
Unit bytes Block Size 1024
The amount in bytes by which to increase a per-transaction memory pool which needs memory. See the description of
transaction_prealloc_size
. -
Command-Line Format --transaction-isolation=name
System Variable (≥ 5.7.20) transaction_isolation
Scope (≥ 5.7.20) Global, Session Dynamic (≥ 5.7.20) Yes Type Enumeration Default Value REPEATABLE-READ
Valid Values READ-UNCOMMITTED
READ-COMMITTED
REPEATABLE-READ
SERIALIZABLE
The transaction isolation level. The default is
REPEATABLE-READ
.The transaction isolation level has three scopes: global, session, and next transaction. This three-scope implementation leads to some nonstandard isolation-level assignment semantics, as described later.
To set the global transaction isolation level at startup, use the
--transaction-isolation
server option.At runtime, the isolation level can be set directly using the
SET
statement to assign a value to thetransaction_isolation
system variable, or indirectly using theSET TRANSACTION
statement. If you settransaction_isolation
directly to an isolation level name that contains a space, the name should be enclosed within quotation marks, with the space replaced by a dash. For example, use thisSET
statement to set the global value:SET GLOBAL transaction_isolation = 'READ-COMMITTED';
Setting the global
transaction_isolation
value sets the isolation level for all subsequent sessions. Existing sessions are unaffected.To set the session or next-level
transaction_isolation
value, use theSET
statement. For most session system variables, these statements are equivalent ways to set the value:SET @@SESSION.var_name = value; SET SESSION var_name = value; SET var_name = value; SET @@var_name = value;
As mentioned previously, the transaction isolation level has a next-transaction scope, in addition to the global and session scopes. To enable the next-transaction scope to be set,
SET
syntax for assigning session system variable values has nonstandard semantics fortransaction_isolation
:To set the session isolation level, use any of these syntaxes:
SET @@SESSION.transaction_isolation = value; SET SESSION transaction_isolation = value; SET transaction_isolation = value;
For each of those syntaxes, these semantics apply:
Sets the isolation level for all subsequent transactions performed within the session.
Permitted within transactions, but does not affect the current ongoing transaction.
If executed between transactions, overrides any preceding statement that sets the next-transaction isolation level.
Corresponds to
SET SESSION TRANSACTION ISOLATION LEVEL
(with theSESSION
keyword).
To set the next-transaction isolation level, use this syntax:
SET @@transaction_isolation = value;
For that syntax, these semantics apply:
Sets the isolation level only for the next single transaction performed within the session.
Subsequent transactions revert to the session isolation level.
Not permitted within transactions.
Corresponds to
SET TRANSACTION ISOLATION LEVEL
(without theSESSION
keyword).
For more information about
SET TRANSACTION
and its relationship to thetransaction_isolation
system variable, see Section 13.3.6, “SET TRANSACTION Statement”.Notetransaction_isolation
was added in MySQL 5.7.20 as a synonym fortx_isolation
, which is now deprecated and is removed in MySQL 8.0. Applications should be adjusted to usetransaction_isolation
in preference totx_isolation
. -
Command-Line Format --transaction-prealloc-size=#
System Variable transaction_prealloc_size
Scope Global, Session Dynamic Yes Type Integer Default Value 4096
Minimum Value 1024
Maximum Value 131072
Unit bytes Block Size 1024
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 bytransaction_alloc_block_size
bytes. When the transaction ends, the pool is truncated totransaction_prealloc_size
bytes.By making
transaction_prealloc_size
sufficiently large to contain all statements within a single transaction, you can avoid manymalloc()
calls. -
Command-Line Format --transaction-read-only[={OFF|ON}]
System Variable (≥ 5.7.20) transaction_read_only
Scope (≥ 5.7.20) Global, Session Dynamic (≥ 5.7.20) Yes Type Boolean Default Value OFF
The transaction access mode. The value can be
OFF
(read/write; the default) orON
(read only).The transaction access mode has three scopes: global, session, and next transaction. This three-scope implementation leads to some nonstandard access-mode assignment semantics, as described later.
To set the global transaction access mode at startup, use the
--transaction-read-only
server option.At runtime, the access mode can be set directly using the
SET
statement to assign a value to thetransaction_read_only
system variable, or indirectly using theSET TRANSACTION
statement. For example, use thisSET
statement to set the global value:SET GLOBAL transaction_read_only = ON;
Setting the global
transaction_read_only
value sets the access mode for all subsequent sessions. Existing sessions are unaffected.To set the session or next-level
transaction_read_only
value, use theSET
statement. For most session system variables, these statements are equivalent ways to set the value:SET @@SESSION.var_name = value; SET SESSION var_name = value; SET var_name = value; SET @@var_name = value;
As mentioned previously, the transaction access mode has a next-transaction scope, in addition to the global and session scopes. To enable the next-transaction scope to be set,
SET
syntax for assigning session system variable values has nonstandard semantics fortransaction_read_only
,To set the session access mode, use any of these syntaxes:
SET @@SESSION.transaction_read_only = value; SET SESSION transaction_read_only = value; SET transaction_read_only = value;
For each of those syntaxes, these semantics apply:
Sets the access mode for all subsequent transactions performed within the session.
Permitted within transactions, but does not affect the current ongoing transaction.
If executed between transactions, overrides any preceding statement that sets the next-transaction access mode.
Corresponds to
SET SESSION TRANSACTION {READ WRITE | READ ONLY}
(with theSESSION
keyword).
To set the next-transaction access mode, use this syntax:
SET @@transaction_read_only = value;
For that syntax, these semantics apply:
Sets the access mode only for the next single transaction performed within the session.
Subsequent transactions revert to the session access mode.
Not permitted within transactions.
Corresponds to
SET TRANSACTION {READ WRITE | READ ONLY}
(without theSESSION
keyword).
For more information about
SET TRANSACTION
and its relationship to thetransaction_read_only
system variable, see Section 13.3.6, “SET TRANSACTION Statement”.Notetransaction_read_only
was added in MySQL 5.7.20 as a synonym fortx_read_only
, which is now deprecated and is removed in MySQL 8.0. Applications should be adjusted to usetransaction_read_only
in preference totx_read_only
. -
Deprecated 5.7.20 System Variable tx_isolation
Scope Global, Session Dynamic Yes Type Enumeration Default Value REPEATABLE-READ
Valid Values READ-UNCOMMITTED
READ-COMMITTED
REPEATABLE-READ
SERIALIZABLE
The default transaction isolation level. Defaults to
REPEATABLE-READ
.Notetransaction_isolation
was added in MySQL 5.7.20 as a synonym fortx_isolation
, which is now deprecated and is removed in MySQL 8.0. Applications should be adjusted to usetransaction_isolation
in preference totx_isolation
. See the description oftransaction_isolation
for details. -
Deprecated 5.7.20 System Variable tx_read_only
Scope Global, Session Dynamic Yes Type Boolean Default Value OFF
The default transaction access mode. The value can be
OFF
(read/write, the default) orON
(read only).Notetransaction_read_only
was added in MySQL 5.7.20 as a synonym fortx_read_only
, which is now deprecated and is removed in MySQL 8.0. Applications should be adjusted to usetransaction_read_only
in preference totx_read_only
. See the description oftransaction_read_only
for details. -
System Variable unique_checks
Scope Global, Session Dynamic Yes Type Boolean Default Value ON
If set to 1 (the default), uniqueness checks for secondary indexes in
InnoDB
tables are performed. If set to 0, storage engines are permitted to assume that duplicate keys are not present in input data. If you know for certain that your data does not contain uniqueness violations, you can set this to 0 to speed up large table imports toInnoDB
.Setting this variable to 0 does not require storage engines to ignore duplicate keys. An engine is still permitted to check for them and issue duplicate-key errors if it detects them.
-
Command-Line Format --updatable-views-with-limit[={OFF|ON}]
System Variable updatable_views_with_limit
Scope Global, Session Dynamic Yes Type Boolean Default Value 1
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 anUPDATE
orDELETE
statement. Primary key here means aPRIMARY KEY
, or aUNIQUE
index in which no column can containNULL
.The variable can have two values:
1
orYES
: Issue a warning only (not an error message). This is the default value.0
orNO
: Prohibit the update.
validate_password_
xxx
The
validate_password
plugin implements a set of system variables having names of the formvalidate_password_
. These variables affect password testing by that plugin; see Section 6.4.3.2, “Password Validation Plugin Options and Variables”.xxx
The version number for the server. The value might also include a suffix indicating server build or configuration information.
-log
indicates that one or more of the general log, slow query log, or binary log are enabled.-debug
indicates that the server was built with debugging support enabled.-
System Variable version_comment
Scope Global Dynamic No Type String The CMake configuration program has a
COMPILATION_COMMENT
option that permits a comment to be specified when building MySQL. This variable contains the value of that comment. See Section 2.8.7, “MySQL Source-Configuration Options”. -
System Variable version_compile_machine
Scope Global Dynamic No Type String The type of the server binary.
-
System Variable version_compile_os
Scope Global Dynamic No Type String The type of operating system on which MySQL was built.
-
Command-Line Format --wait-timeout=#
System Variable wait_timeout
Scope Global, Session Dynamic Yes Type Integer Default Value 28800
Minimum Value 1
Maximum Value (Windows) 2147483
Maximum Value (Other) 31536000
Unit seconds The number of seconds the server waits for activity on a noninteractive connection before closing it.
On thread startup, the session
wait_timeout
value is initialized from the globalwait_timeout
value or from the globalinteractive_timeout
value, depending on the type of client (as defined by theCLIENT_INTERACTIVE
connect option tomysql_real_connect()
). See alsointeractive_timeout
. The number of errors, warnings, and notes that resulted from the last statement that generated messages. This variable is read only. See Section 13.7.5.40, “SHOW WARNINGS Statement”.