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• 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 theSHOW VARIABLES statement or the Performance Schema system variable tables. SeeSection 25.12.13, “Performance Schema System Variable Tables”.

• 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 inSection 5.1.1, “Configuring the Server”.

• Section 14.15, “InnoDB Startup Options and System Variables”, listsInnoDB 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, seeSection 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 theSET statement by setting them toON or1, or disabled by setting them toOFF or0. Boolean variables can be set at startup to the valuesON,TRUE,OFF, andFALSE (not case-sensitive), as well as1 and0. SeeSection 4.2.2.4, “Program Option Modifiers”.

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 toFLOOR(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.

• 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 theauthentication_windows Windows authentication plugin is enabled and debugging code is enabled. SeeSection 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 theauthentication_windows Windows authentication plugin is enabled. SeeSection 6.4.1.8, “Windows Pluggable Authentication”.

  A client that authenticates using theInitSecurityContext() 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 formuser_id@computer_name and need not be registered anywhere to be used. This UPN is sent by the server at the beginning of authentication handshake.

  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 a0x00 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.

• autocommit

  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 useCOMMIT 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. SeeSection 13.3.1, “START TRANSACTION, COMMIT, and ROLLBACK Statements”.

  By default, client connections begin withautocommit 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

• automatic_sp_privileges

  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 theEXECUTE 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 theCREATE statement for it. This might not be the same as the account named as theDEFINER in the routine definition.

  If you startmysqld with--skip-new,automatic_sp_privileges is set toOFF.

  See alsoSection 23.2.2, “Stored Routines and MySQL Privileges”.

• auto_generate_certs

  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 (seeSection 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 theauto_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; seeSection 6.3.1, “Configuring MySQL to Use Encrypted Connections”.

  For more information about SSL file autogeneration, including file names and characteristics, seeSection 6.3.3.1, “Creating SSL and RSA Certificates and Keys using MySQL”

  Thesha256_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.

• avoid_temporal_upgrade

  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 whetherALTER 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 causesALTER 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.

• back_log

  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. Theback_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 Unixlisten() 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)

• basedir

  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.

• big_tables

  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 mostThe tabletbl_name is full errors forSELECT 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 isOFF (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.

• bind_address

  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, setbind_address=addr at server startup, whereaddr 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 is0.0.0.0, 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 as127.0.0.1 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 themysql.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.

• block_encryption_mode

  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 forAES_ENCRYPT() andAES_DECRYPT().

  block_encryption_mode takes a value inaes-keylen-mode format, wherekeylen 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, permittedmode values are:ECB,CBC,CFB1,CFB8,CFB128,OFB

  • For yaSSL, permittedmode 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 setblock_encryption_mode to a value containing an unsupported key length or a mode that the SSL library does not support.

• bulk_insert_buffer_size

  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.

• character_set_client

  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 alsoSection 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 requestssjis 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 thecharacter_set_client value produces an error. SeeImpermissible Client Character Sets.

• character_set_connection

  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, seeSection 10.3.8, “Character Set Introducers”.

• character_set_database

  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 ascharacter_set_server.

  The globalcharacter_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 sessioncharacter_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.

• character_set_filesystem

  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 theLOAD 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'.

• character_set_results

  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.

• character_set_server

  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. SeeSection 10.15, “Character Set Configuration”. If you set this variable, you should also setcollation_server to specify the collation for the character set.

• character_set_system

  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 alwaysutf8.

• character_sets_dir

  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. SeeSection 10.15, “Character Set Configuration”.

• check_proxy_users

  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 thecheck_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 themysql_native_password plugin, enablemysql_native_password_proxy_users.

  • For thesha256_password plugin, enablesha256_password_proxy_users.

  For information about user proxying, seeSection 6.2.14, “Proxy Users”.

• collation_connection

  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 (seeSection 10.8.4, “Collation Coercibility in Expressions”).

• collation_database

  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 ascollation_server.

  The globalcharacter_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 sessioncharacter_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.

• collation_server

  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. SeeSection 10.15, “Character Set Configuration”.

• completion_type

  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 inSection 13.3.3, “Statements That Cause an Implicit Commit”. It also does not apply forXA COMMIT,XA ROLLBACK, or whenautocommit=1.

• concurrent_insert

  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

  IfAUTO (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 forMyISAM tables that do not have holes
  ALWAYS (or 2)	Enables concurrent inserts for allMyISAM 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 startmysqld with--skip-new,concurrent_insert is set toNEVER.

  See alsoSection 8.11.3, “Concurrent Inserts”.

• connect_timeout

  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 themysqld server waits for a connect packet before responding withBad handshake. The default value is 10 seconds.

  Increasing theconnect_timeout value might help if clients frequently encounter errors of the formLost connection to MySQL server at 'XXX', system error:errno.

• core_file

  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.

• datadir

  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 thedatadir value as an absolute path.

• date_format

  This variable is unused. It is deprecated and is removed in MySQL 8.0.

• datetime_format

  This variable is unused. It is deprecated and is removed in MySQL 8.0.

• debug

  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. SeeSection 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, seeSection 5.8.3, “The DBUG Package”.

• debug_sync

  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=ONCMake option (seeSection 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 ofdebug_sync isOFF. If the server is started with--debug-sync-timeout=N, whereN 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. SeeSection 5.1.8.1, “System Variable Privileges”.

  For a description of the Debug Sync facility and how to use synchronization points, seeMySQL Server Doxygen Documentation.

• default_authentication_plugin

  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; seeSection 6.4.1.1, “Native Pluggable Authentication”.

  • sha256_password: Use SHA-256 passwords; seeSection 6.4.1.5, “SHA-256 Pluggable Authentication”.

  Note

  If this variable has a value other thanmysql_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.

  Thedefault_authentication_plugin value affects these aspects of server operation:

  • It determines which authentication plugin the server assigns to new accounts created byCREATE USER andGRANT statements that do not explicitly specify an authentication plugin.

  • Theold_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.

• default_password_lifetime

  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 defaultdefault_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 theALTER USER statement. SeeSection 6.2.11, “Password Management”.

  Note

  Prior to MySQL 5.7.11, the defaultdefault_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 thedefault_password_lifetime variable to0, thus disabling automatic password expiration for all users.

• default_storage_engine

  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. SeeChapter 15,Alternative Storage Engines. This variable sets the storage engine for permanent tables only. To set the storage engine forTEMPORARY tables, set thedefault_tmp_storage_engine system variable.

  To see which storage engines are available and enabled, use theSHOW ENGINES statement or query theINFORMATION_SCHEMAENGINES table.

  If you disable the default storage engine at server startup, you must set the default engine for both permanent andTEMPORARY tables to a different engine or the server cannot start.

• default_tmp_storage_engine

  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 forTEMPORARY 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 andTEMPORARY tables to a different engine or the server cannot start.

• default_week_format

  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 theWEEK() function. SeeSection 12.7, “Date and Time Functions”.

• delay_key_write

  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 toMyISAM tables. Delayed key writing causes key buffers not to be flushed between writes. See alsoSection 15.2.1, “MyISAM Startup Options”.

  This variable can have one of the following values to affect handling of theDELAY_KEY_WRITE table option that can be used inCREATE TABLE statements.

  Option	Description
  OFF	DELAY_KEY_WRITE is ignored.
  ON	MySQL honors anyDELAY_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 theDELAY_KEY_WRITE option enabled.

  Note

  If you set this variable toALL, you should not useMyISAM tables from within another program (such as another MySQL server ormyisamchk) when the tables are in use. Doing so leads to index corruption.

  IfDELAY_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'). SeeSection 5.1.7, “Server System Variables”, andSection 15.2.1, “MyISAM Startup Options”.

  If you startmysqld with--skip-new,delay_key_write is set toOFF.

  Warning

  If you enable external locking with--external-locking, there is no protection against index corruption for tables that use delayed key writes.

• delayed_insert_limit

  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 (becauseDELAYED inserts are not supported); expect it to be removed in a future release.

• delayed_insert_timeout

  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 (becauseDELAYED inserts are not supported); expect it to be removed in a future release.

• delayed_queue_size

  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 (becauseDELAYED inserts are not supported); expect it to be removed in a future release.

• disabled_storage_engines

  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 newMyISAM 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 ... ENGINEpermitted_engine.

  It is permitted to set thedefault_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.

  Note

  Settingdisabled_storage_engines might cause an issue withmysql_upgrade. For details, seeSection 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 ofdisconnect_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 ofdisconnect_on_expired_password:

    • Ifdisconnect_on_expired_password: is enabled, the server disconnects the client.

    • Ifdisconnect_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, seeSection 6.2.12, “Server Handling of Expired Passwords”.

• div_precision_increment

  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 |+----------------+

• end_markers_in_json

  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. SeeSection 8.15.9, “The end_markers_in_json System Variable”.

• eq_range_index_dive_limit

  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 upcol_name values:

  col_name IN(val1, ...,valN)col_name =val1 OR ... ORcol_name =valN

  In both cases, the expression containsN 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, seeEquality Range Optimization of Many-Valued Comparisons.

  To update table index statistics for best estimates, useANALYZE TABLE.

• error_count

  The number of errors that resulted from the last statement that generated messages. This variable is read only. SeeSection 13.7.5.17, “SHOW ERRORS Statement”.

• event_scheduler

  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 areON,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 inSection 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 andNULL-value handling inTIMESTAMP columns. By default,explicit_defaults_for_timestamp is disabled, which enables the nonstandard behaviors.

  Ifexplicit_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 firstTIMESTAMP 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 theNO_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. SeeSection 5.1.10, “Server SQL Modes”.

  The nonstandard behaviors just described are deprecated; expect them to be removed in a future release of MySQL.

  Ifexplicit_defaults_for_timestamp is enabled, the server disables the nonstandard behaviors and handlesTIMESTAMP columns as follows:

  • It is not possible to assign aTIMESTAMP 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.

  • NoTIMESTAMP column is automatically declared with theDEFAULT CURRENT_TIMESTAMP orON UPDATE CURRENT_TIMESTAMP attributes. Those attributes must be explicitly specified.

  • The firstTIMESTAMP column in a table is not handled differently fromTIMESTAMP columns following the first one.

  Ifexplicit_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 (seedocumentation for more details).

  As indicated by the warning, to disable the deprecated nonstandard behaviors, enable theexplicit_defaults_for_timestamp system variable at server startup.

  Note

  explicit_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, seeSection 11.2.6, “Automatic Initialization and Updating for TIMESTAMP and DATETIME”.

• external_user

  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 isNULL. SeeSection 6.2.14, “Proxy Users”.

• flush

  Command-Line Format	--flush[={OFF|ON}]
  System Variable	flush
  Scope	Global
  Dynamic	Yes
  Type	Boolean
  Default Value	OFF

  IfON, 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. SeeSection B.3.3.3, “What to Do If MySQL Keeps Crashing”. This variable is set toON if you startmysqld with the--flush option.

  Note

  Ifflush is enabled, the value offlush_time does not matter and changes toflush_time have no effect on flush behavior.

• flush_time

  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 everyflush_time seconds to free up resources and synchronize unflushed data to disk. This option is best used only on systems with minimal resources.

  Note

  Ifflush is enabled, the value offlush_time does not matter and changes toflush_time have no effect on flush behavior.

• foreign_key_checks

  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, anALTER TABLE operation returns an error if a foreign key definition is incorrectly formed. For more information, seeSection 13.1.18.5, “FOREIGN KEY Constraints”.

  Setting this variable has the same effect onNDB tables as it does forInnoDB tables. Typically you leave this setting enabled during normal operation, to enforcereferential integrity. Disabling foreign key checking can be useful for reloadingInnoDB tables in an order different from that required by their parent/child relationships. SeeSection 13.1.18.5, “FOREIGN KEY Constraints”.

  Settingforeign_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.

  Note

  Settingforeign_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 withforeign_key_checks=0. The foreign key constraint must be removed before dropping the index (Bug #70260).

• ft_boolean_syntax

  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 usingIN BOOLEAN MODE. SeeSection 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.

• ft_max_word_len

  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 aMyISAMFULLTEXT index.

  Note

  FULLTEXT indexes onMyISAM tables must be rebuilt after changing this variable. UseREPAIR TABLEtbl_name QUICK.

• ft_min_word_len

  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 aMyISAMFULLTEXT index.

  Note

  FULLTEXT indexes onMyISAM tables must be rebuilt after changing this variable. UseREPAIR TABLEtbl_name QUICK.

• ft_query_expansion_limit

  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 usingWITH QUERY EXPANSION.

• ft_stopword_file

  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 onMyISAM 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 arenot 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 alsoSection 12.9.4, “Full-Text Stopwords”.

  Note

  FULLTEXT indexes onMyISAM tables must be rebuilt after changing this variable or the contents of the stopword file. UseREPAIR TABLEtbl_name QUICK.

• general_log

  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 (orOFF) 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.

• general_log_file

  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 ishost_name.log, but the initial value can be changed with the--general_log_file option.

• group_concat_max_len

  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 theGROUP_CONCAT() function. The default is 1024.

• have_compress

  YES if thezlib compression library is available to the server,NO if not. If not, theCOMPRESS() andUNCOMPRESS() functions cannot be used.

• have_crypt

  YES if thecrypt() system call is available to the server,NO if not. If not, theENCRYPT() function cannot be used.

  Note

  TheENCRYPT() 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.

• have_dynamic_loading

  YES ifmysqld 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.

• have_geometry

  YES if the server supports spatial data types,NO if not.

• have_openssl

  This variable is a synonym forhave_ssl.

• have_profiling

  YES if statement profiling capability is present,NO if not. If present, theprofiling system variable controls whether this capability is enabled or disabled. SeeSection 13.7.5.31, “SHOW PROFILES Statement”.

  This variable is deprecated; expect it to be removed in a future release of MySQL.

• have_query_cache

  YES ifmysqld supports the query cache,NO if not.

  Note

  The query cache is deprecated as of MySQL 5.7.20, and is removed in MySQL 8.0. Deprecation includeshave_query_cache.

• have_rtree_keys

  YES ifRTREE indexes are available,NO if not. (These are used for spatial indexes inMyISAM tables.)

• have_ssl

  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 ifmysqld 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, seeSection 2.8.6, “Configuring SSL Library Support”.

• have_statement_timeout

  System Variable	have_statement_timeout
  Scope	Global
  Dynamic	No
  Type	Boolean

  Whether the statement execution timeout feature is available (seeStatement Execution Time Optimizer Hints). The value can beNO if the background thread used by this feature could not be initialized.

• have_symlink

  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.

• host_cache_size

  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; seeSection 5.1.11.2, “DNS Lookups and the Host Cache”.

  Thehost_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 thehost_cache table, and unblocks any blocked hosts.

  The default value is autosized to 128, plus 1 for a value ofmax_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 thehost_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.

• hostname

  System Variable	hostname
  Scope	Global
  Dynamic	No
  Type	String

  The server sets this variable to the server host name at startup.

• identity

  This variable is a synonym for thelast_insert_id variable. It exists for compatibility with other database systems. You can read its value withSELECT @@identity, and set it usingSET identity.

• ignore_db_dirs

  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 withmysqld --initialize to specify directories that the server should ignore for purposes of assessing whether an existing data directory is considered empty. SeeSection 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.

• init_connect

  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 theSUPER 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 ofinit_connect.

• init_file

  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. SeeSection 16.1.3, “Replication with Global Transaction Identifiers”.

• innodb_xxx

  InnoDB system variables are listed inSection 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.

• insert_id

  The value to be used by the followingINSERT orALTER TABLE statement when inserting anAUTO_INCREMENT value. This is mainly used with the binary log.

• interactive_timeout

  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 theCLIENT_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 (seeSection 8.4.4, “Internal Temporary Table Use in MySQL”). Permitted values areMYISAM andINNODB (the default).

  Theoptimizer uses the storage engine defined byinternal_tmp_disk_storage_engine for on-disk internal temporary tables.

  When usinginternal_tmp_disk_storage_engine=INNODB (the default), queries that generate on-disk internal temporary tables that exceedInnoDB row or column limits returnRow size too large orToo many columns errors. The workaround is to setinternal_tmp_disk_storage_engine toMYISAM.

• join_buffer_size

  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 ofjoin_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 forjoin_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 ofjoin_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, seeSection 8.2.1.6, “Nested-Loop Join Algorithms”. For information about Batched Key Access, seeSection 8.2.1.11, “Block Nested-Loop and Batched Key Access Joins”.

• keep_files_on_create

  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 aMyISAM 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 aMyISAM 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.

• key_buffer_size

  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 forMyISAM 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 setkey_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 forkey_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 theMyISAM 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, useLOCK TABLES. SeeSection 8.2.4.1, “Optimizing INSERT Statements”.

  You can check the performance of the key buffer by issuing aSHOW STATUS statement and examining theKey_read_requests,Key_reads,Key_write_requests, andKey_writes status variables. (SeeSection 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 usingkey_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 multipleMyISAM key caches. The size limit of 4GB applies to each cache individually, not as a group. SeeSection 8.10.2, “The MyISAM Key Cache”.

• key_cache_age_threshold

  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. SeeSection 8.10.2, “The MyISAM Key Cache”.

• key_cache_block_size

  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. SeeSection 8.10.2, “The MyISAM Key Cache”.

• key_cache_division_limit

  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. SeeSection 8.10.2, “The MyISAM Key Cache”.

• large_files_support

  System Variable	large_files_support
  Scope	Global
  Dynamic	No
  Type	Boolean

  Whethermysqld was compiled with options for large file support.

• large_pages

  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). SeeSection 8.12.4.3, “Enabling Large Page Support”.

• large_page_size

  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. SeeSection 8.12.4.3, “Enabling Large Page Support”.

• last_insert_id

  The value to be returned fromLAST_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.

• lc_messages

  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 isen_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. SeeSection 10.12, “Setting the Error Message Language”.

• lc_messages_dir

  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 oflc_messages to produce the location for the error message file. SeeSection 10.12, “Setting the Error Message Language”.

• lc_time_names

  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 theDATE_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, seeSection 10.16, “MySQL Server Locale Support”.

• license

  System Variable	license
  Scope	Global
  Dynamic	No
  Type	String
  Default Value	GPL

  The type of license the server has.

• local_infile

  Command-Line Format	--local-infile[={OFF|ON}]
  System Variable	local_infile
  Scope	Global
  Dynamic	Yes
  Type	Boolean
  Default Value	ON

  This variable controls server-sideLOCAL 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 permitLOAD DATA LOCAL statements (regardless of how client programs and libraries are configured at build time or runtime), startmysqld withlocal_infile disabled or enabled, respectively.local_infile can also be set at runtime. For more information, seeSection 6.1.6, “Security Considerations for LOAD DATA LOCAL”.

• lock_wait_timeout

  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 asLOCK TABLES,FLUSH TABLES WITH READ LOCK, andHANDLER statements.

  This timeout does not apply to implicit accesses to system tables in themysql 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 thelock_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.

• locked_in_memory

  System Variable	locked_in_memory
  Scope	Global
  Dynamic	No
  Type	Boolean
  Default Value	OFF

  Whethermysqld was locked in memory with--memlock.

• log_error

  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 isstderr. Otherwise, the destination is a file and thelog_error value is the file name. SeeSection 5.4.2, “The Error Log”.

• log_error_verbosity

  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.

• log_output

  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 fromTABLE,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 thegeneral_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, seeSection 5.4.1, “Selecting General Query Log and Slow Query Log Output Destinations”.

• log_queries_not_using_indexes

  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. SeeSection 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.

• log_slow_admin_statements

  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 includeALTER TABLE,ANALYZE TABLE,CHECK TABLE,CREATE INDEX,DROP INDEX,OPTIMIZE TABLE, andREPAIR TABLE.

• log_syslog

  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, andsyslog 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. SeeSection 5.4.2, “The Error Log”.

• log_syslog_facility

  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 tosyslog (what type of program is sending the message). This variable has no effect unless thelog_syslog system variable is enabled. SeeSection 5.4.2.3, “Error Logging to the System Log”.

  The permitted values can vary per operating system; consult your systemsyslog documentation.

  This variable does not exist on Windows.

• log_syslog_include_pid

  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 tosyslog. This variable has no effect unless thelog_syslog system variable is enabled. SeeSection 5.4.2.3, “Error Logging to the System Log”.

  This variable does not exist on Windows.

• log_syslog_tag

  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 tosyslog. This variable has no effect unless thelog_syslog system variable is enabled. SeeSection 5.4.2.3, “Error Logging to the System Log”.

  By default, the server identifier ismysqld 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.

• log_timestamps

  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.

  Permittedlog_timestamps values areUTC (the default) andSYSTEM (local system time zone).

  Timestamps are written using ISO 8601 / RFC 3339 format:YYYY-MM-DDThh:mm:ss.uuuuuu plus a tail value ofZ 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

  Iflog_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, seeSection 5.4.5, “The Slow Query Log”.

• log_warnings

  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 bylog_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. SeeSection 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 withlog_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 tolog_warnings assigns a value tolog_error_verbosity and vice versa. The variables are related as follows:

  • Suppression of alllog_warnings items, achieved withlog_warnings=0, is achieved withlog_error_verbosity=1 (errors only).

  • Items printed forlog_warnings=1 or higher count as warnings and are printed forlog_error_verbosity=2 or higher.

  • Items printed forlog_warnings=2 count as notes and are printed forlog_error_verbosity=3.

  As of MySQL 5.7.2, the default log level is controlled bylog_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 oflog_warnings is still permitted but maps onto use oflog_error_verbosity as follows:

  • Settinglog_warnings=0 is equivalent tolog_error_verbosity=1 (errors only).

  • Settinglog_warnings=1 is equivalent tolog_error_verbosity=2 (errors, warnings).

  • Settinglog_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.

• long_query_time

  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 theSlow_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. SeeSection 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.

• low_priority_updates

  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 to1, 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). SeeSection 8.11.2, “Table Locking Issues”.

• lower_case_file_system

  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.

• lower_case_table_names

  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, seeSection 9.2.3, “Identifier Case Sensitivity”.

  The default value of this variable is platform-dependent (seelower_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 shouldnot setlower_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 ... FROMtbl_name operation with the wrongtbl_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, seeSection 16.2.5, “How Servers Evaluate Replication Filtering Rules”.

• max_allowed_packet

  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 themysql_stmt_send_long_data() C API function. The default is 4MB.

  The packet message buffer is initialized tonet_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 largeBLOB 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 themax_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 andmysqldump 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 globalmax_allowed_packet value. (The global value could be less than the session value if the global value is changed after the client connects.)

• max_connect_errors

  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

  Aftermax_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; seeFlushing the Host Cache.

• max_connections

  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 ofopen_files_limit - 810, and the value actually set formax_connections.

  For more information, seeSection 5.1.11.1, “Connection Interfaces”.

• max_delayed_threads

  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 (becauseDELAYED inserts are not supported); expect it to be removed in a future release.

• max_digest_length

  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.

  The length used for calculating a normalized statement digest is the sum of the length of the normalized statement digest and the length of the statement digest. Since the length of the statement digest is always 64, when the value ofmax_digest_length is 1024 (the default), the maximum length for a normalized SQL statement before truncation occurs is 1024 - 64 = 960 bytes.

  Warning

  Settingmax_digest_length to zero disables digest production, which also disables server functionality that requires digests, such as MySQL Enterprise Firewall.

  Decreasing themax_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 theperformance_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, seeSection 25.10, “Performance Schema Statement Digests”.

• max_error_count

  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 theSHOW 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.

• max_execution_time

  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 forSELECT statements, in milliseconds. If the value is 0, timeouts are not enabled.

  max_execution_time applies as follows:

  • The globalmax_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(N) optimizer hint or for whichN 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.

• max_heap_table_size

  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-createdMEMORY 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 existingMEMORY 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 withtmp_table_size to limit the size of internal in-memory tables. SeeSection 8.4.4, “Internal Temporary Table Use in MySQL”.

  max_heap_table_size is not replicated. SeeSection 16.4.1.20, “Replication and MEMORY Tables”, andSection 16.4.1.37, “Replication and Variables”, for more information.

• max_insert_delayed_threads

  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 formax_delayed_threads.

  This system variable is deprecated (becauseDELAYED inserts are not supported); expect it to be removed in a future release.

• max_join_size

  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 thanmax_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, seeUsing Safe-Updates Mode (--safe-updates).

  Setting this variable to a value other thanDEFAULT 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.

• max_length_for_sort_data

  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 whichfilesort algorithm to use. SeeSection 8.2.1.14, “ORDER BY Optimization”.

• max_points_in_geometry

  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 thepoints_per_circle argument to theST_Buffer_Strategy() function.

• max_prepared_stmt_count

  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.

• max_seeks_for_key

  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 (seeSection 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.

• max_sort_length

  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 firstmax_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 ofmax_sort_length may require increasing the value ofsort_buffer_size as well. For details, seeSection 8.2.1.14, “ORDER BY Optimization”

• max_sp_recursion_depth

  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 ofmax_sp_recursion_depth, it may be necessary to increase thread stack size by increasing the value ofthread_stack at server startup.

• max_tmp_tables

  This variable is unused. It is deprecated and is removed in MySQL 8.0.

• max_user_connections

  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 nonzeroMAX_USER_CONNECTIONS resource limit, the sessionmax_user_connections value is set to that limit.

  • Otherwise, the sessionmax_user_connections value is set to the global value.

  Account resource limits are specified using theCREATE USER orALTER USER statement. SeeSection 6.2.16, “Setting Account Resource Limits”.

• max_write_lock_count

  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, ifmax_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.

• mecab_rc_file

  Command-Line Format	--mecab-rc-file=file_name
  System Variable	mecab_rc_file
  Scope	Global
  Dynamic	No
  Type	File name

  Themecab_rc_file option is used when setting up the MeCab full-text parser.

  Themecab_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, seeSection 12.9.9, “MeCab Full-Text Parser Plugin”.

  For information about options that can be specified in the MeCabmecabrc configuration file, refer to theMeCab Documentation on theGoogle Developers site.

• metadata_locks_cache_size

  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.

• metadata_locks_hash_instances

  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. Themetadata_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.

• min_examined_row_limit

  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.

• multi_range_count

  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.

• myisam_data_pointer_size

  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 byCREATE 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. SeeSection B.3.2.10, “The table is full”.

• myisam_max_sort_file_size

  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 aMyISAM 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.

  IfMyISAM 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.

• myisam_mmap_size

  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 compressedMyISAM files. If many compressedMyISAM tables are used, the value can be decreased to reduce the likelihood of memory-swapping problems.

• myisam_recover_options

  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 theMyISAM 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 timemysqld 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 thetbl_name.MYD file astbl_name-datetime.BAK.
  FORCE	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 optionsBACKUP,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.

  SeeSection 15.2.1, “MyISAM Startup Options”.

• myisam_repair_threads

  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

  Note

  This 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.

  Note

  Multithreaded repair isbeta-quality code.

• myisam_sort_buffer_size

  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 sortingMyISAM indexes during aREPAIR TABLE or when creating indexes withCREATE INDEX orALTER TABLE.

• myisam_stats_method

  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 treatsNULL 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 inSection 8.3.7, “InnoDB and MyISAM Index Statistics Collection”.

• myisam_use_mmap

  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 writingMyISAM 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 themysql_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, seeSection 6.2.14, “Proxy Users”.

• named_pipe

  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.

• named_pipe_full_access_group

  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 thenamed_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.

• net_buffer_length

  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 bynet_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 whichnet_buffer_length can be set is 1MB.

  The session value of this variable is read only.

• net_read_timeout

  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.

• net_retry_count

  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.

• net_write_timeout

  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 alsonet_read_timeout.

• new

  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 alwaysOFF.

  In NDB Cluster, setting this variable toON 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, seeUser-defined partitioning and the NDB storage engine (NDB Cluster).

• ngram_token_size

  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. Thengram_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, seeSection 12.9.8, “ngram Full-Text Parser”.

• offline_mode

  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 theSUPER 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 theSUPER 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 theSUPER 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.

• old

  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.

  Whenold 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. (SeeSection 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.

• old_alter_table

  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 anALTER 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, seeSection 13.1.8, “ALTER TABLE Statement”.

• old_passwords

  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

  Note

  This 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 thePASSWORD() 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 ofold_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 setold_passwords=2, follow the instructions for using thesha256_password plugin atSection 6.4.1.5, “SHA-256 Pluggable Authentication”.

  The server sets the globalold_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 sessionold_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, seeSection 6.2.13, “Pluggable Authentication”, andSection 6.1.2.4, “Password Hashing in MySQL”.

• open_files_limit

  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 tomysqld from the operating system:

  • At startup,mysqld reserves descriptors withsetrlimit(), using the value requested at by setting this variable directly or by using the--open-files-limit option tomysqld_safe. Ifmysqld 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 ofopen_files_limit indicates the number of file descriptors actually permitted tomysqld 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 effectiveopen_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 theulimit -n command. On Linux systems usingsystemd, the value cannot be set greater thanLimitNOFile (this isDefaultLimitNOFILE, ifLimitNOFile is not set); otherwise, on Linux, the value ofopen_files_limit cannot exceedulimit -n.

• optimizer_prune_level

  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.

• optimizer_search_depth

  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.

• optimizer_switch

  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}

  Theoptimizer_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, seeSection 8.9.2, “Switchable Optimizations”.

• optimizer_trace

  Command-Line Format	--optimizer-trace=value
  System Variable	optimizer_trace
  Scope	Global, Session
  Dynamic	Yes
  Type	String

  This variable controls optimizer tracing. For details, seeSection 8.15, “Tracing the Optimizer”.

• optimizer_trace_features

  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, seeSection 8.15, “Tracing the Optimizer”.

• optimizer_trace_limit

  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, seeSection 8.15, “Tracing the Optimizer”.

• optimizer_trace_max_mem_size

  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, seeSection 8.15, “Tracing the Optimizer”.

• optimizer_trace_offset

  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, seeSection 8.15, “Tracing the Optimizer”.

• performance_schema_xxx

  Performance Schema system variables are listed inSection 25.15, “Performance Schema System Variables”. These variables may be used to configure Performance Schema operation.

• parser_max_mem_size

  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.

• pid_file

  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 ofhost_name.pid, wherehost_name is the name of the host machine.

  The process ID file is used by other programs such asmysqld_safe to determine the server's process ID. On Windows, this variable also affects the default error log file name. SeeSection 5.4.2, “The Error Log”.

• plugin_dir

  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 usingSELECT ... 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.

• port

  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.

• preload_buffer_size

  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.

• profiling

  If set to 0 orOFF (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. SeeSection 13.7.5.31, “SHOW PROFILES Statement”.

  This variable is deprecated; expect it to be removed in a future release of MySQL.

• profiling_history_size

  The number of statements for which to maintain profiling information ifprofiling is enabled. The default value is 15. The maximum value is 100. Setting the value to 0 effectively disables profiling. SeeSection 13.7.5.31, “SHOW PROFILES Statement”.

  This variable is deprecated; expect it to be removed in a future release of MySQL.

• protocol_version

  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.

• proxy_user

  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 isNULL. SeeSection 6.2.14, “Proxy Users”.

• pseudo_slave_mode

  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-useBINLOG 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.

• pseudo_thread_id

  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.

  Warning

  Changing the session value of thepseudo_thread_id system variable changes the value returned by theCONNECTION_ID() function.

• query_alloc_block_size

  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.

• query_cache_limit

  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.

  Note

  The query cache is deprecated as of MySQL 5.7.20, and is removed in MySQL 8.0. Deprecation includesquery_cache_limit.

• query_cache_min_res_unit

  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 inSection 8.10.3.3, “Query Cache Configuration”.

  Note

  The query cache is deprecated as of MySQL 5.7.20, and is removed in MySQL 8.0. Deprecation includesquery_cache_min_res_unit.

• query_cache_size

  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 forquery_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 ofquery_cache_size, that many bytes of memory are allocated even ifquery_cache_type=0. SeeSection 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 ofquery_cache_size too small, a warning occurs, as described inSection 8.10.3.3, “Query Cache Configuration”.

  Note

  The query cache is deprecated as of MySQL 5.7.20, and is removed in MySQL 8.0. Deprecation includesquery_cache_size.

• query_cache_type

  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 theGLOBAL 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 setquery_cache_size to 0.
  1 orON	Cache all cacheable query results except for those that begin withSELECT SQL_NO_CACHE.
  2 orDEMAND	Cache results only for cacheable queries that begin withSELECT SQL_CACHE.

  This variable defaults toOFF.

  If the server is started withquery_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.

  Note

  The query cache is deprecated as of MySQL 5.7.20, and is removed in MySQL 8.0. Deprecation includesquery_cache_type.

• query_cache_wlock_invalidate

  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 aWRITE 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.

  Note

  The query cache is deprecated as of MySQL 5.7.20, and is removed in MySQL 8.0. Deprecation includesquery_cache_wlock_invalidate.

• query_prealloc_size

  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 largerquery_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.

• rand_seed1

  System Variable	rand_seed1
  Scope	Session
  Dynamic	Yes
  Type	Integer
  Default Value	N/A
  Minimum Value	0
  Maximum Value	4294967295

  Therand_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 theRAND() 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.

• rand_seed2

  See the description forrand_seed1.

• range_alloc_block_size

  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.

• range_optimizer_max_mem_size

  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, seeLimiting Memory Use for Range Optimization.

• rbr_exec_mode

  System Variable	rbr_exec_mode
  Scope	Session
  Dynamic	Yes
  Type	Enumeration
  Default Value	STRICT
  Valid Values	STRICT IDEMPOTENT

  For internal use bymysqlbinlog. This variable switches the server betweenIDEMPOTENT mode andSTRICT mode.IDEMPOTENT mode causes suppression of duplicate-key and no-key-found errors inBINLOG statements generated bymysqlbinlog. 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;

• read_buffer_size

  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 aMyISAM 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 forORDER 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, seeSection 8.12.4.1, “How MySQL Uses Memory”.

• read_only

  Command-Line Format	--read-only[={OFF|ON}]
  System Variable	read_only
  Scope	Global
  Dynamic	Yes
  Type	Boolean
  Default Value	OFF

  If theread_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 asuper_read_only system variable (disabled by default), which has these effects:

  • Ifsuper_read_only is enabled, the server prohibits client updates, even from users who have theSUPER privilege.

  • Settingsuper_read_only toON implicitly forcesread_only toON.

  • Settingread_only toOFF implicitly forcessuper_read_only toOFF.

  Even withread_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 enableread_only on replica servers to ensure that replicas accept updates only from the source server and not from clients.

  • Use ofANALYZE 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 withmysqlcheck--all-databases--analyze.

  • Use ofFLUSH STATUS statements, which are always written to the binary log.

  • Operations onTEMPORARY tables.

  • Inserts into the log tables (mysql.general_log andmysql.slow_log); seeSection 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 asUPDATE orTRUNCATE TABLE operations.

  Changes toread_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 enableread_only (including implicit attempts resulting from enablingsuper_read_only):

  • The attempt fails and an error occurs if you have any explicit locks (acquired withLOCK TABLES) or have a pending transaction.

  • The attempt blocks while other clients have any ongoing statement, activeLOCK 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.

• read_rnd_buffer_size

  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 fromMyISAM tables, and, for any storage engine, for Multi-Range Read optimization.

  When reading rows from aMyISAM table in sorted order following a key-sorting operation, the rows are read through this buffer to avoid disk seeks. SeeSection 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, seeSection 8.12.4.1, “How MySQL Uses Memory”. For information about Multi-Range Read optimization, seeSection 8.2.1.10, “Multi-Range Read Optimization”.

• require_secure_transport

  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 anER_SECURE_TRANSPORT_REQUIRED error.

  This capability supplements per-account SSL requirements, which take precedence. For example, if an account is defined withREQUIRE 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 theshared_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.

  See alsoConfiguring Encrypted Connections as Mandatory.

• secure_auth

  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. SeeSection 6.4.1.3, “Migrating Away from Pre-4.1 Password Hashing and the mysql_old_password Plugin”.

  Note

  Passwords 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, seeSection 6.4.1.3, “Migrating Away from Pre-4.1 Password Hashing and the mysql_old_password Plugin”.

• secure_file_priv

  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 theLOAD 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 toNULL, the server disables import and export operations.

  The default value is platform specific and depends on the value of theINSTALL_LAYOUTCMake 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_PRIVDIRCMake option.

  INSTALL_LAYOUT Value	Defaultsecure_file_priv Value
  STANDALONE,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 value

  To set the defaultsecure_file_priv value for thelibmysqld embedded server, use theINSTALL_SECURE_FILE_PRIV_EMBEDDEDDIRCMake option. The default value for this option isNULL.

  The server checks the value ofsecure_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.

• session_track_gtids

  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 forsession_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, seeSection 5.1.15, “Server Tracking of Client Session State”.

• session_track_schema

  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, seeSection 5.1.15, “Server Tracking of Client Session State”.

• session_track_state_change

  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.

  Thesession_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.

  Note

  Assigning a value tosession_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, seeSection 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 fortime_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, setsession_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, seeSection 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. Thesesession_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 LEVELREAD ONLYREAD WRITEWITH 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 thetransaction_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, seeSection 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 (seeSection 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 thesha256_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; seeSection 6.4.1.5, “SHA-256 Pluggable Authentication”.

  For more information about RSA file autogeneration, including file names and characteristics, seeSection 6.3.3.1, “Creating SSL and RSA Certificates and Keys using MySQL”

  Theauto_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 (seeSection 6.3.4, “SSL Library-Dependent Capabilities”). Its value is the path name of the RSA private key file for thesha256_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.

  Important

  Because this file stores a private key, its access mode should be restricted so that only the MySQL server can read it.

  For information aboutsha256_password, seeSection 6.4.1.5, “SHA-256 Pluggable Authentication”.

• sha256_password_proxy_users

  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 thesha256_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, seeSection 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 (seeSection 6.3.4, “SSL Library-Dependent Capabilities”). Its value is the path name of the RSA public key file for thesha256_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 aboutsha256_password, including information about how clients specify the RSA public key, seeSection 6.4.1.5, “SHA-256 Pluggable Authentication”.

• shared_memory

  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.

• shared_memory_base_name

  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 isMYSQL. The name is case-sensitive.

  This variable applies only if the server is started with theshared_memory system variable enabled to support shared-memory connections.

• show_compatibility_56

  Command-Line Format	--show-compatibility-56[={OFF|ON}]
  Deprecated	Yes
  System Variable	show_compatibility_56
  Scope	Global
  Dynamic	Yes
  Type	Boolean
  Default Value	OFF

  TheINFORMATION_SCHEMA has tables that contain system and status variable information (seeSection 24.3.11, “The INFORMATION_SCHEMA GLOBAL_VARIABLES and SESSION_VARIABLES Tables”, andSection 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 (seeSection 25.12.13, “Performance Schema System Variable Tables”, andSection 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 theINFORMATION_SCHEMA tables to the Performance Schema tables, seeSection 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.

  Note

  show_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 ofshow_compatibility_56:

  • Overview of show_compatibility_56 Effects

  • Effect of show_compatibility_56 on SHOW Statements

  • Effect of show_compatibility_56 on INFORMATION_SCHEMA Tables

  • Effect of show_compatibility_56 on Performance Schema Tables

  • Effect of show_compatibility_56 on Slave Status Variables

  • Effect of show_compatibility_56 on FLUSH STATUS

  For better understanding, it is strongly recommended that you also read these sections:

  • Section 25.12.13, “Performance Schema System Variable Tables”

  • Section 25.12.14, “Performance Schema Status Variable Tables”

  • Section 25.12.15.10, “Status Variable Summary Tables”

  Overview of show_compatibility_56 Effects

  Theshow_compatibility_56 system variable affects these aspects of server operation regarding system and status variables:

  • Information available from theSHOW VARIABLES andSHOW STATUS statements

  • Information available from theINFORMATION_SCHEMA tables that provide system and status variable information

  • Information available from the Performance Schema tables that provide system and status variable information

  • The effect of theFLUSH STATUS statement on status variables

  This list summarizes the effects ofshow_compatibility_56, with additional details given later:

  • Whenshow_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.

  • Whenshow_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 Whenshow_compatibility_56=OFF, use the Performance Schema tables or theSHOW statements.

    Note

    Whenshow_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 theSELECT 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.

  • SeveralSlave_xxx status variables are available fromSHOW 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 settingshow_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_xxx statement execution counters.

    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_xxx statement execution counters. (In MySQL 5.7.6 and 5.7.7,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 theSHOW 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 forCom_xxx status variables in the status variable tables. To obtain global and per-session statement execution counts, use theevents_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_xxx status variables are available fromSHOW 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_xxx status variables become unavailable inSHOW STATUS and their locations in Performance Schema replication tables.

    Status Variable	Performance Schema Location
    Slave_heartbeat_period	replication_connection_configuration table,HEARTBEAT_INTERVAL column
    Slave_last_heartbeat	replication_connection_status table,LAST_HEARTBEAT_TIMESTAMP column
    Slave_received_heartbeats	replication_connection_status table,COUNT_RECEIVED_HEARTBEATS column
    Slave_retried_transactions	replication_applier_status table,COUNT_TRANSACTIONS_RETRIES column
    Slave_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.

• show_create_table_verbosity

  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.

• show_old_temporals

  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

  WhetherSHOW 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 theCOLUMN_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.

• skip_external_locking

  Command-Line Format	--skip-external-locking[={OFF|ON}]
  System Variable	skip_external_locking
  Scope	Global
  Dynamic	No
  Type	Boolean
  Default Value	ON

  This isOFF ifmysqld 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 onlyMyISAM table access. For more information, including conditions under which it can and cannot be used, seeSection 8.11.5, “External Locking”.

• skip_name_resolve

  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 isOFF,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. SeeSection 5.1.11.2, “DNS Lookups and the Host Cache”.

  Depending on the network configuration of your system and theHost 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 host127.0.0.1 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';

• skip_networking

  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 withmysqld 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. SeeSection 5.1.11.2, “DNS Lookups and the Host Cache”.

• skip_show_database

  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 theSHOW 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.

  Caution

  Because a global privilege is considered a privilege for all databases,any global privilege enables a user to see all database names withSHOW DATABASES or by examining theINFORMATION_SCHEMASCHEMATA table.

• slow_launch_time

  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 theSlow_launch_threads status variable.

• slow_query_log

  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 (orOFF) 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 thelong_query_time variable. SeeSection 5.4.5, “The Slow Query Log”.

• slow_query_log_file

  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 ishost_name-slow.log, but the initial value can be changed with the--slow_query_log_file option.

• socket

  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 isMySQL (not case-sensitive).

• sort_buffer_size

  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, seeSection 8.2.1.14, “ORDER BY Optimization”

  If you see manySort_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. SeeSection B.3.3.5, “Where MySQL Stores Temporary Files”.

  The maximum permissible setting forsort_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).

• sql_auto_is_null

  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 generatedAUTO_INCREMENT value, you can find that value by issuing a statement of the following form:

  SELECT * FROMtbl_name WHEREauto_col IS NULL

  If the statement returns a row, the value returned is the same as if you invoked theLAST_INSERT_ID() function. For details, including the return value after a multiple-row insert, seeSection 12.15, “Information Functions”. If noAUTO_INCREMENT value was successfully inserted, theSELECT statement returns no row.

  The behavior of retrieving anAUTO_INCREMENT value by using anIS NULL comparison is used by some ODBC programs, such as Access. SeeObtaining Auto-Increment Values. This behavior can be disabled by settingsql_auto_is_null toOFF.

  The default value ofsql_auto_is_null isOFF.

• sql_big_selects

  System Variable	sql_big_selects
  Scope	Global, Session
  Dynamic	Yes
  Type	Boolean
  Default Value	ON

  If set toOFF, 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 themax_join_size system variable to a value other thanDEFAULT,sql_big_selects is set toOFF.

• sql_buffer_result

  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.

• sql_log_off

  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 isOFF (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. SeeSection 5.1.8.1, “System Variable Privileges”.

• sql_mode

  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, seeSection 5.1.10, “Server SQL Modes”.

  Note

  MySQL installation programs may configure the SQL mode during the installation process. If the SQL mode differs from the default or from what you expect, check for a setting in an option file that the server reads at startup.

• sql_notes

  System Variable	sql_notes
  Scope	Global, Session
  Dynamic	Yes
  Type	Boolean
  Default Value	ON

  If enabled (the default), diagnostics ofNote 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.

• sql_quote_show_create

  System Variable	sql_quote_show_create
  Scope	Global, Session
  Dynamic	Yes
  Type	Boolean
  Default Value	ON

  If enabled (the default), the server quotes identifiers forSHOW 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. SeeSection 13.7.5.10, “SHOW CREATE TABLE Statement”, andSection 13.7.5.6, “SHOW CREATE DATABASE Statement”.

• sql_safe_updates

  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 themysql client,sql_safe_updates can be enabled by using the--safe-updates option. For more information, seeUsing Safe-Updates Mode (--safe-updates).

• sql_select_limit

  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 fromSELECT statements. For more information, seeUsing 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 ofDEFAULT.

  If aSELECT has aLIMIT clause, theLIMIT takes precedence over the value ofsql_select_limit.

• sql_warnings

  System Variable	sql_warnings
  Scope	Global, Session
  Dynamic	Yes
  Type	Boolean
  Default Value	OFF

  This variable controls whether single-rowINSERT statements produce an information string if warnings occur. The default isOFF. Set the value toON to produce an information string.

• ssl_ca

  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.

• ssl_capath

  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. You must run OpenSSLrehash on the directory specified by this option prior to using it. On Linux systems, you can invokerehash like this:

  $> openssl rehashpath/to/directory

  On Windows platforms, you can use thec_rehash script in a command prompt, like this:

  \> c_rehashpath/to/directory

  Seeopenssl-rehash for complete syntax and other information.

  Support for this capability depends on the SSL library used to compile MySQL; seeSection 6.3.4, “SSL Library-Dependent Capabilities”.

• ssl_cert

  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 withssl_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, seeConnection Cipher Configuration.

• ssl_cipher

  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 athttps://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, seeSection 6.3.2, “Encrypted Connection TLS Protocols and Ciphers”.

• ssl_crl

  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. SeeSection 6.3.4, “SSL Library-Dependent Capabilities”.

• ssl_crlpath

  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. SeeSection 6.3.4, “SSL Library-Dependent Capabilities”.

• ssl_key

  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.

• stored_program_cache

  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.

• super_read_only

  Command-Line Format	--super-read-only[={OFF|ON}]
  System Variable	super_read_only
  Scope	Global
  Dynamic	Yes
  Type	Boolean
  Default Value	OFF

  If theread_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 whensuper_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 tosuper_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.

• sync_frm

  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_time_zone

  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 setsystem_time_zone. To explicitly specify the system time zone, set theTZ environment variable or use the--timezone option of themysqld_safe script.

  Thesystem_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. SeeSection 5.1.13, “MySQL Server Time Zone Support”.

• table_definition_cache

  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)

  ForInnoDB, 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 theInnoDB 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 thetable_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.

• table_open_cache

  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 thatmysqld requires. The effective value of this variable is the greater of the effective value ofopen_files_limit - 10 - the effective value ofmax_connections / 2, and 400; that is

  MAX(    (open_files_limit - 10 - max_connections) / 2,    400   )

  You can check whether you need to increase the table cache by checking theOpened_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, seeSection 8.4.3.1, “How MySQL Opens and Closes Tables”.

• table_open_cache_instances

  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 sizetable_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 fortable_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.

• thread_cache_size

  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 thanthread_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, seeSection 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.

• thread_handling

  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 areno-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; seeSection 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.

• thread_pool_algorithm

  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. SeeSection 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. SeeSection 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 ofN 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. SeeSection 5.5.3, “MySQL Enterprise Thread Pool”.

• thread_pool_prio_kickup_timer

  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. SeeSection 5.5.3, “MySQL Enterprise Thread Pool”.

• thread_pool_size

  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. SeeSection 5.5.3, “MySQL Enterprise Thread Pool”.

• thread_pool_stall_limit

  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. SeeSection 5.5.3, “MySQL Enterprise Thread Pool”.

• thread_stack

  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.

• time_format

  This variable is unused. It is deprecated and is removed in MySQL 8.0.

• time_zone

  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. SeeSection 5.1.13, “MySQL Server Time Zone Support”.

  Note

  If set toSYSTEM, 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.

• timestamp

  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'YYYY-MM-DD hh:mm:ss' format) orDEFAULT.

  Settingtimestamp 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.

• tls_version

  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, seeSection 6.3.2, “Encrypted Connection TLS Protocols and Ciphers”.

  Note

  As 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. SeeDeprecated TLS Protocols.

  Setting this variable to an empty string disables encrypted connections.

• tmp_table_size

  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-createdMEMORY tables.

  The actual limit is the smaller oftmp_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 oftmp_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 comparingCreated_tmp_disk_tables andCreated_tmp_tables values.

  See alsoSection 8.4.4, “Internal Temporary Table Use in MySQL”.

• tmpdir

  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, seeSection B.3.3.5, “Where MySQL Stores Temporary Files”.

• transaction_alloc_block_size

  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 oftransaction_prealloc_size.

• transaction_isolation

  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 isREPEATABLE-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 theSET 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 globaltransaction_isolation value sets the isolation level for all subsequent sessions. Existing sessions are unaffected.

  To set the session or next-leveltransaction_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 SESSIONvar_name =value;SETvar_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 toSET 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 toSET TRANSACTION ISOLATION LEVEL (without theSESSION keyword).

  For more information aboutSET TRANSACTION and its relationship to thetransaction_isolation system variable, seeSection 13.3.6, “SET TRANSACTION Statement”.

  Note

  transaction_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.

• transaction_prealloc_size

  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 istransaction_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 makingtransaction_prealloc_size sufficiently large to contain all statements within a single transaction, you can avoid manymalloc() calls.

• transaction_read_only

  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 beOFF (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 theSET 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 globaltransaction_read_only value sets the access mode for all subsequent sessions. Existing sessions are unaffected.

  To set the session or next-leveltransaction_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 SESSIONvar_name =value;SETvar_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 toSET 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 toSET TRANSACTION {READ WRITE | READ ONLY} (without theSESSION keyword).

  For more information aboutSET TRANSACTION and its relationship to thetransaction_read_only system variable, seeSection 13.3.6, “SET TRANSACTION Statement”.

  Note

  transaction_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.

• tx_isolation

  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 toREPEATABLE-READ.

  Note

  transaction_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.

• tx_read_only

  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 beOFF (read/write, the default) orON (read only).

  Note

  transaction_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.

• unique_checks

  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 inInnoDB 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 notrequire storage engines to ignore duplicate keys. An engine is still permitted to check for them and issue duplicate-key errors if it detects them.

• updatable_views_with_limit

  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 aLIMIT 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

  Thevalidate_password plugin implements a set of system variables having names of the formvalidate_password_xxx. These variables affect password testing by that plugin; seeSection 6.4.3.2, “Password Validation Plugin Options and Variables”.

• version

  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.

• version_comment

  System Variable	version_comment
  Scope	Global
  Dynamic	No
  Type	String

  TheCMake configuration program has aCOMPILATION_COMMENT option that permits a comment to be specified when building MySQL. This variable contains the value of that comment. SeeSection 2.8.7, “MySQL Source-Configuration Options”.

• version_compile_machine

  System Variable	version_compile_machine
  Scope	Global
  Dynamic	No
  Type	String

  The type of the server binary.

• version_compile_os

  System Variable	version_compile_os
  Scope	Global
  Dynamic	No
  Type	String

  The type of operating system on which MySQL was built.

• wait_timeout

  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 sessionwait_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.

• warning_count

  The number of errors, warnings, and notes that resulted from the last statement that generated messages. This variable is read only. SeeSection 13.7.5.40, “SHOW WARNINGS Statement”.