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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 only on its compiled-in defaults, ignoring the settings in any option files, use this command:

  mysqld --no-defaults --verbose --help

• To see the current values used by a running server, use theSHOW VARIABLES statement or the Performance Schema system variable tables. SeeSection 29.12.14, “Performance Schema System Variable Tables”.

• Section 7.1.9, “Using System Variables”, discusses the syntax for setting and displaying system variable values.

• Section 7.1.9.2, “Dynamic System Variables”, lists the variables that can be set at runtime.

• Information on tuning system variables can be found inSection 7.1.1, “Configuring the Server”.

• Section 17.14, “InnoDB Startup Options and System Variables”, listsInnoDB system variables.

• Section 25.4.3.9.2, “NDB Cluster System Variables”, lists system variables which are specific to NDB Cluster.

• For information on server system variables specific to replication, seeSection 19.1.6, “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 6.2.2.4, “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.

• activate_all_roles_on_login

  Command-Line Format	--activate-all-roles-on-login[={OFF|ON}]
  System Variable	activate_all_roles_on_login
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  Whether to enable automatic activation of all granted roles when users log in to the server:

  • Ifactivate_all_roles_on_login is enabled, the server activates all roles granted to each account at login time. This takes precedence over default roles specified withSET DEFAULT ROLE.

  • Ifactivate_all_roles_on_login is disabled, the server activates the default roles specified withSET DEFAULT ROLE, if any, at login time.

  Granted roles include those granted explicitly to the user and those named in themandatory_roles system variable value.

  activate_all_roles_on_login applies only at login time, and at the beginning of execution for stored programs and views that execute in definer context. To change the active roles within a session, useSET ROLE. To change the active roles for a stored program, the program body should executeSET ROLE.

• admin_address

  Command-Line Format	--admin-address=addr
  Introduced	8.0.14
  System Variable	admin_address
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	String

  The IP address on which to listen for TCP/IP connections on the administrative network interface (seeSection 7.1.12.1, “Connection Interfaces”). There is no defaultadmin_address value. If this variable is not specified at startup, the server maintains no administrative interface. The server also has abind_address system variable for configuring regular (nonadministrative) client TCP/IP connections. SeeSection 7.1.12.1, “Connection Interfaces”.

  Ifadmin_address is specified, its value must satisfy these requirements:

  • The value must be a single IPv4 address, IPv6 address, or host name.

  • The value cannot specify a wildcard address format (*,0.0.0.0, or::).

  • As of MySQL 8.0.22, the value may include a network namespace specifier.

  An IP address can be specified as an IPv4 or IPv6 address. If the value 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 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.

  These rules apply to specifying a network namespace for an address:

  • A network namespace can be specified for an IP address or a host name.

  • A network namespace cannot be specified for a wildcard IP address.

  • For a given address, the network namespace is optional. If given, it must be specified as a/ns suffix immediately following the address.

  • An address with no/ns suffix uses the host system global namespace. The global namespace is therefore the default.

  • An address with a/ns suffix uses the namespace namedns.

  • The host system must support network namespaces and each named namespace must previously have been set up. Naming a nonexistent namespace produces an error.

  For additional information about network namespaces, seeSection 7.1.14, “Network Namespace Support”.

  If binding to the address fails, the server produces an error and does not start.

  Theadmin_address system variable is similar to thebind_address system variable that binds the server to an address for ordinary client connections, but with these differences:

  • bind_address permits multiple addresses.admin_address permits a single address.

  • bind_address permits wildcard addresses.admin_address does not.

• admin_port

  Command-Line Format	--admin-port=port_num
  Introduced	8.0.14
  System Variable	admin_port
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	33062
  Minimum Value	0
  Maximum Value	65535

  The TCP/IP port number to use for connections on the administrative network interface (seeSection 7.1.12.1, “Connection Interfaces”). Setting this variable to 0 causes the default value to be used.

  Settingadmin_port has no effect ifadmin_address is not specified because in that case the server maintains no administrative network interface.

• admin_ssl_ca

  Command-Line Format	--admin-ssl-ca=file_name
  Introduced	8.0.21
  System Variable	admin_ssl_ca
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	File name
  Default Value	NULL

  Theadmin_ssl_ca system variable is likessl_ca, except that it applies to the administrative connection interface rather than the main connection interface. For information about configuring encryption support for the administrative interface, seeAdministrative Interface Support for Encrypted Connections.

• admin_ssl_capath

  Command-Line Format	--admin-ssl-capath=dir_name
  Introduced	8.0.21
  System Variable	admin_ssl_capath
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Directory name
  Default Value	NULL

  Theadmin_ssl_capath system variable is likessl_capath, except that it applies to the administrative connection interface rather than the main connection interface. For information about configuring encryption support for the administrative interface, seeAdministrative Interface Support for Encrypted Connections.

• admin_ssl_cert

  Command-Line Format	--admin-ssl-cert=file_name
  Introduced	8.0.21
  System Variable	admin_ssl_cert
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	File name
  Default Value	NULL

  Theadmin_ssl_cert system variable is likessl_cert, except that it applies to the administrative connection interface rather than the main connection interface. For information about configuring encryption support for the administrative interface, seeAdministrative Interface Support for Encrypted Connections.

• admin_ssl_cipher

  Command-Line Format	--admin-ssl-cipher=name
  Introduced	8.0.21
  System Variable	admin_ssl_cipher
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	String
  Default Value	NULL

  Theadmin_ssl_cipher system variable is likessl_cipher, except that it applies to the administrative connection interface rather than the main connection interface. For information about configuring encryption support for the administrative interface, seeAdministrative Interface Support for Encrypted Connections.

• admin_ssl_crl

  Command-Line Format	--admin-ssl-crl=file_name
  Introduced	8.0.21
  System Variable	admin_ssl_crl
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	File name
  Default Value	NULL

  Theadmin_ssl_crl system variable is likessl_crl, except that it applies to the administrative connection interface rather than the main connection interface. For information about configuring encryption support for the administrative interface, seeAdministrative Interface Support for Encrypted Connections.

• admin_ssl_crlpath

  Command-Line Format	--admin-ssl-crlpath=dir_name
  Introduced	8.0.21
  System Variable	admin_ssl_crlpath
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Directory name
  Default Value	NULL

  Theadmin_ssl_crlpath system variable is likessl_crlpath, except that it applies to the administrative connection interface rather than the main connection interface. For information about configuring encryption support for the administrative interface, seeAdministrative Interface Support for Encrypted Connections.

• admin_ssl_key

  Command-Line Format	--admin-ssl-key=file_name
  Introduced	8.0.21
  System Variable	admin_ssl_key
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	File name
  Default Value	NULL

  Theadmin_ssl_key system variable is likessl_key, except that it applies to the administrative connection interface rather than the main connection interface. For information about configuring encryption support for the administrative interface, seeAdministrative Interface Support for Encrypted Connections.

• admin_tls_ciphersuites

  Command-Line Format	--admin-tls-ciphersuites=ciphersuite_list
  Introduced	8.0.21
  System Variable	admin_tls_ciphersuites
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	String
  Default Value	NULL

  Theadmin_tls_ciphersuites system variable is liketls_ciphersuites, except that it applies to the administrative connection interface rather than the main connection interface. For information about configuring encryption support for the administrative interface, seeAdministrative Interface Support for Encrypted Connections.

• admin_tls_version

  Command-Line Format	--admin-tls-version=protocol_list
  Introduced	8.0.21
  System Variable	admin_tls_version
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	String
  Default Value (≥ 8.0.28)	TLSv1.2,TLSv1.3
  Default Value (≥ 8.0.21, ≤ 8.0.27)	TLSv1,TLSv1.1,TLSv1.2,TLSv1.3

  Theadmin_tls_version system variable is liketls_version, except that it applies to the administrative connection interface rather than the main connection interface. For information about configuring encryption support for the administrative interface, seeAdministrative Interface Support for Encrypted Connections.

  Important

  • Support for the TLSv1 and TLSv1.1 connection protocols is removed from MySQL Server as of MySQL 8.0.28. The protocols were deprecated from MySQL 8.0.26. SeeRemoval of Support for the TLSv1 and TLSv1.1 Protocols for more information.

  • Support for the TLSv1.3 protocol is available in MySQL Server as of MySQL 8.0.16, provided that MySQL Server was compiled using OpenSSL 1.1.1 or higher. The server checks the version of OpenSSL at startup, and if it is lower than 1.1.1, TLSv1.3 is removed from the default value for the system variable. In that case, the defaults are“TLSv1,TLSv1.1,TLSv1.2” up to and including MySQL 8.0.27, and“TLSv1.2” from MySQL 8.0.28.

• authentication_policy

  Command-Line Format	--authentication-policy=value
  Introduced	8.0.27
  System Variable	authentication_policy
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	String
  Default Value	*,,

  This variable is used to administer multifactor authentication (MFA) capabilities. It applies to the authentication factor-related clauses ofCREATE USER andALTER USER statements used to manage MySQL account definitions, where“factor” corresponds to an authentication method or plugin associated with an account:

  • authentication_policy controls the number of authentication factors that accounts may have. That is, it controls which factors are required or permitted.

  • authentication_policy also controls, for each factor, which plugins (or methods) are permitted.

  • authentication_policy, in conjunction withdefault_authentication_plugin, determines the default authentication plugin for authentication specifications that do not name a plugin explicitly.

  Becauseauthentication_policy applies only when accounts are created or altered, changes to its value have no effect on existing user accounts.

  Note

  Although theauthentication_policy system variable places certain constraints on the authentication-related clauses ofCREATE USER andALTER USER statements, a user who has theAUTHENTICATION_POLICY_ADMIN privilege is not subject to the constraints. (A warning does occur for statements that otherwise would not be permitted.)

  The value ofauthentication_policy is a list of 1, 2, or 3 comma-separated elements. Each element present can be an authentication plugin name, an asterisk (*), empty, or missing. (Exception: Element 1 cannot be empty or missing.) In all cases, an element may be surrounded by whitespace characters and the entire list is enclosed in single quotes.

  The type of value specified for elementN in the list has implications for whether factorN must be present in account definitions, and which authentication plugins can be used:

  • If elementN is an authentication plugin name, an authentication method for factorN is required and must use the named plugin.

    In addition, the plugin becomes the default plugin for factorN authentication methods that do not name a plugin explicitly. For details, seeThe Default Authentication Plugin.

    Authentication plugins that use internal credentials storage can be specified for the first element only, and cannot repeat. For example, the following settings are not permitted:

    • authentication_policy = 'caching_sha2_password, sha256_password'

    • authentication_policy = 'caching_sha2_password, authentication_fido, sha256_password'

  • If elementN is an asterisk (*), an authentication method for factorN is required. It may use any authentication plugin that is valid for elementN (as described later).

  • If elementN is empty, an authentication method for factorN is optional. If given, it may use any authentication plugin that is valid for elementN (as described later).

  • If elementN is missing from the list (that is, there are fewer thanN−1 commas in the value), an authentication method for factorN is forbidden. For example, a value of'*' permits only a single factor and thus enforces single-factor authentication (1FA) for new accounts created withCREATE USER or changes to existing accounts made withALTER USER. In this case, such statements cannot specify authentication for factors 2 or 3.

  When anauthentication_policy element names an authentication plugin, the permitted plugin names for the element are subject to these conditions:

  • Element 1 must name a plugin that does not require a registration step. For example,authentication_fido cannot be named.

  • Elements 2 and 3 must name a plugin that does not use internal credentials storage.

    For information about which authentication plugins use internal credentials storage, seeSection 8.2.15, “Password Management”.

  Whenauthentication_policy elementN is*, the permitted plugin names for factorN in account definitions are subject to these conditions:

  • For factor 1, account definitions can use any plugin. Default authentication plugin rules apply for authentication specifications that do not name a plugin. SeeThe Default Authentication Plugin.

  • For factors 2 and 3, account definitions cannot name a plugin that uses internal credentials storage. For example, with '*,*', '*,*,*', '*,', '*,,'authentication_policy settings, plugins that use internal credentials storage are only permitted for the first factor and cannot repeat.

  Whenauthentication_policy elementN is empty, the permitted plugin names for factorN in account definitions are subject to these conditions:

  • For factor 1, this does not apply because element 1 cannot be empty.

  • For factors 2 and 3, account definitions cannot name a plugin that uses internal credentials storage.

  Empty elements must occur at the end of the list, following a nonempty element. In other words, the first element cannot be empty, and either no element is empty or the last element is empty or the last two elements are empty. For example, a value of',,' is not permitted because it would signify that all factors are optional. That cannot be; accounts must have at least one authentication factor.

  The default value ofauthentication_policy is'*,,'. This means that factor 1 is required in account definitions and can use any authentication plugin, and that factors 2 and 3 are optional and each can use any authentication plugin that does not use internal credentials storage.

  The following table shows someauthentication_policy values and the policy that each establishes for creating or altering accounts.

  Table 7.4 Example authentication_policy Values

  authentication_policy Value	Effective Policy
  '*'	Permit only creating or altering accounts with one factor.
  '*,*'	Permit only creating or altering accounts with two factors.
  '*,*,*'	Permit only creating or altering accounts with three factors.
  '*,'	Permit creating or altering accounts with one or two factors.
  '*,,'	Permit creating or altering accounts with one, two, or three factors.
  '*,*,'	Permit creating or altering accounts with two or three factors.
  '*,auth_plugin'	Permit creating or altering accounts with two factors, where the first factor can be any authentication method, and the second factor must be the named plugin.
  'auth_plugin,*,'	Permit creating or altering accounts with two or three factors, where the first factor must be the named plugin.
  'auth_plugin,'	Permit creating or altering accounts with one or two factors, where the first factor must be the named plugin.
  'auth_plugin,auth_plugin,auth_plugin'	Permits creating or altering accounts with three factors, where the factors must use the named plugins.

  
  

• authentication_windows_log_level

  Command-Line Format	--authentication-windows-log-level=#
  System Variable	authentication_windows_log_level
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	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 8.4.1.6, “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
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  This variable is available only if theauthentication_windows Windows authentication plugin is enabled. SeeSection 8.4.1.6, “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
  SET_VAR Hint Applies	No
  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 15.3.1, “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
  SET_VAR Hint Applies	No
  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 27.2.2, “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
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  This variable 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 8.3.1, “Configuring MySQL to Use Encrypted Connections”.

  For more information about SSL file autogeneration, including file names and characteristics, seeSection 8.3.3.1, “Creating SSL and RSA Certificates and Keys using MySQL”

  Thesha256_password_auto_generate_rsa_keys andcaching_sha2_password_auto_generate_rsa_keys system variables are related but control autogeneration of RSA key-pair files needed for secure password exchange using RSA over unencrypted connections.

• avoid_temporal_upgrade

  Command-Line Format	--avoid-temporal-upgrade[={OFF|ON}]
  Deprecated	Yes
  System Variable	avoid_temporal_upgrade
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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 MySQL release.

• back_log

  Command-Line Format	--back-log=#
  System Variable	back_log
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	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 the value ofmax_connections, which enables the permitted backlog to adjust to the maximum permitted number of connections.

• basedir

  Command-Line Format	--basedir=dir_name
  System Variable	basedir
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Directory name
  Default Value	parent of mysqld installation directory

  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
  SET_VAR Hint Applies	No
  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. When in-memoryinternal temporary tables are managed by theTempTable storage engine (the default), and the maximum amount of memory that can be occupied by theTempTable storage engine is exceeded, theTempTable storage engine starts storing data to temporary files on disk. When in-memory temporary tables are managed by theMEMORY storage engine, in-memory tables are automatically converted to disk-based tables as required. For more information, seeSection 10.4.4, “Internal Temporary Table Use in MySQL”.

• bind_address

  Command-Line Format	--bind-address=addr
  System Variable	bind_address
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	String
  Default Value	*

  The MySQL server listens on one or more network sockets for TCP/IP connections. Each socket is bound to one address, but it is possible for an address to map onto multiple network interfaces. To specify how the server should listen for TCP/IP connections, set thebind_address system variable at server startup. The server also has anadmin_address system variable that enables administrative connections on a dedicated interface. SeeSection 7.1.12.1, “Connection Interfaces”.

  Ifbind_address is specified, its value must satisfy these requirements:

  • Prior to MySQL 8.0.13,bind_address accepts a single address value, which may specify a single non-wildcard IP address or host name, or one of the wildcard address formats that permit listening on multiple network interfaces (*,0.0.0.0, or::).

  • As of MySQL 8.0.13,bind_address accepts either a single value as just described, or a list of comma-separated values. When the variable names a list of multiple values, each value must specify a single non-wildcard IP address (either IPv4 or IPv6) or a host name. Wildcard address formats (*,0.0.0.0, or::) are not allowed in a list of values.

  • As of MySQL 8.0.22, addresses may include a network namespace specifier.

  IP addresses can be specified as IPv4 or IPv6 addresses. For any value that 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 variable specifies a list of multiple values, this value is not permitted.

  • If the address is0.0.0.0, the server accepts TCP/IP connections on all server host IPv4 interfaces. If the variable specifies a list of multiple values, this value is not permitted.

  • If the address is::, the server accepts TCP/IP connections on all server host IPv4 and IPv6 interfaces. If the variable specifies a list of multiple values, this value is not permitted.

  • 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.

  These rules apply to specifying a network namespace for an address:

  • A network namespace can be specified for an IP address or a host name.

  • A network namespace cannot be specified for a wildcard IP address.

  • For a given address, the network namespace is optional. If given, it must be specified as a/ns suffix immediately following the address.

  • An address with no/ns suffix uses the host system global namespace. The global namespace is therefore the default.

  • An address with a/ns suffix uses the namespace namedns.

  • The host system must support network namespaces and each named namespace must previously have been set up. Naming a nonexistent namespace produces an error.

  • If the variable value specifies multiple addresses, it can include addresses in the global namespace, in named namespaces, or a mix.

  For additional information about network namespaces, seeSection 7.1.14, “Network Namespace Support”.

  If binding to any address fails, the server produces an error and does not start.

  Examples:

  • bind_address=*

    The server listens on all IPv4 or IPv6 addresses, as specified by the* wildcard.

  • bind_address=198.51.100.20

    The server listens only on the198.51.100.20 IPv4 address.

  • bind_address=198.51.100.20,2001:db8:0:f101::1

    The server listens on the198.51.100.20 IPv4 address and the2001:db8:0:f101::1 IPv6 address.

  • bind_address=198.51.100.20,*

    This produces an error because wildcard addresses are not permitted whenbind_address names a list of multiple values.

  • bind_address=198.51.100.20/red,2001:db8:0:f101::1/blue,192.0.2.50

    The server listens on the198.51.100.20 IPv4 address in thered namespace, the2001:db8:0:f101::1 IPv6 address in theblue namespace, and the192.0.2.50 IPv4 address in the global namespace.

  Whenbind_address names a single value (wildcard or non-wildcard), the server listens on a single socket, which for a wildcard address may be bound to multiple network interfaces. Whenbind_address names a list of multiple values, the server listens on one socket per value, with each socket bound to a single network interface. The number of sockets is linear with the number of values specified. Depending on operating system connection-acceptance efficiency, long value lists might incur a performance penalty for accepting TCP/IP connections.

  Because file descriptors are allocated for listening sockets and network namespace files, it may be necessary to increase theopen_files_limit system variable.

  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.

• block_encryption_mode

  Command-Line Format	--block-encryption-mode=#
  System Variable	block_encryption_mode
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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. Permittedmode values areECB,CBC,CFB1,CFB8,CFB128, andOFB.

  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.

• build_id

  Introduced	8.0.31
  System Variable	build_id
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Platform Specific	Linux

  This is a 160-bitSHA1 signature which is generated by the linker when compiling the server on Linux systems with-DWITH_BUILD_ID=ON (enabled by default), and converted to a hexadecimal string. This read-only value serves as a unique build ID, and is written into the server log at startup.

  build_id is not supported on platforms other than Linux.

• bulk_insert_buffer_size

  Command-Line Format	--bulk-insert-buffer-size=#
  System Variable	bulk_insert_buffer_size
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	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.

  As of MySQL 8.0.14, 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 7.1.9.1, “System Variable Privileges”.

• caching_sha2_password_digest_rounds

  Command-Line Format	--caching-sha2-password-digest-rounds=#
  Introduced	8.0.24
  System Variable	caching_sha2_password_digest_rounds
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	5000
  Minimum Value	5000
  Maximum Value	4095000

  The number of hash rounds used by thecaching_sha2_password authentication plugin for password storage.

  Increasing the number of hashing rounds above the default value incurs a performance penalty that correlates with the amount of increase:

  • Creating an account that uses thecaching_sha2_password plugin has no impact on the client session within which the account is created, but the server must perform the hashing rounds to complete the operation.

  • For client connections that use the account, the server must perform the hashing rounds and save the result in the cache. The result is longer login time for the first client connection, but not for subsequent connections. This behavior occurs after each server restart.

• caching_sha2_password_auto_generate_rsa_keys

  Command-Line Format	--caching-sha2-password-auto-generate-rsa-keys[={OFF|ON}]
  System Variable	caching_sha2_password_auto_generate_rsa_keys
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  The server uses this variable to determine whether to autogenerate 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 all of these conditions are true: Thesha256_password_auto_generate_rsa_keys orcaching_sha2_password_auto_generate_rsa_keys system variable is enabled; no RSA options are specified; the RSA files are missing from the data directory. These key-pair files enable secure password exchange using RSA over unencrypted connections for accounts authenticated by thesha256_password orcaching_sha2_password plugin; seeSection 8.4.1.3, “SHA-256 Pluggable Authentication”, andSection 8.4.1.2, “Caching SHA-2 Pluggable Authentication”.

  For more information about RSA file autogeneration, including file names and characteristics, seeSection 8.3.3.1, “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.

• caching_sha2_password_private_key_path

  Command-Line Format	--caching-sha2-password-private-key-path=file_name
  System Variable	caching_sha2_password_private_key_path
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	File name
  Default Value	private_key.pem

  This variable specifies the path name of the RSA private key file for thecaching_sha2_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 aboutcaching_sha2_password, seeSection 8.4.1.2, “Caching SHA-2 Pluggable Authentication”.

• caching_sha2_password_public_key_path

  Command-Line Format	--caching-sha2-password-public-key-path=file_name
  System Variable	caching_sha2_password_public_key_path
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	File name
  Default Value	public_key.pem

  This variable specifies the path name of the RSA public key file for thecaching_sha2_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.

  For information aboutcaching_sha2_password, including information about how clients request the RSA public key, seeSection 8.4.1.2, “Caching SHA-2 Pluggable Authentication”.

• character_set_client

  System Variable	character_set_client
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	String
  Default Value	utf8mb4

  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 12.4, “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.

  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
  SET_VAR Hint Applies	No
  Type	String
  Default Value	utf8mb4

  The character set used for literals specified without a character set introducer and for number-to-string conversion. For information about introducers, seeSection 12.3.8, “Character Set Introducers”.

• character_set_database

  System Variable	character_set_database
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	String
  Default Value	utf8mb4
  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.

  As of MySQL 8.0.14, 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 7.1.9.1, “System Variable Privileges”.

  The globalcharacter_set_database andcollation_database system variables are deprecated; 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 and assignments produce a warning. Expect the session variables to become read-only (and assignments to them to produce an error) in a future version of MySQL in which it remains 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
  SET_VAR Hint Applies	No
  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'.

  As of MySQL 8.0.14, 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 7.1.9.1, “System Variable Privileges”.

• character_set_results

  System Variable	character_set_results
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	String
  Default Value	utf8mb4

  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
  SET_VAR Hint Applies	No
  Type	String
  Default Value	utf8mb4

  The servers default character set. SeeSection 12.15, “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
  SET_VAR Hint Applies	No
  Type	String
  Default Value	utf8mb3

  The character set used by the server for storing identifiers. The value is alwaysutf8mb3.

• character_sets_dir

  Command-Line Format	--character-sets-dir=dir_name
  System Variable	character_sets_dir
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Directory name

  The directory where character sets are installed. SeeSection 12.15, “Character Set Configuration”.

• check_proxy_users

  Command-Line Format	--check-proxy-users[={OFF|ON}]
  System Variable	check_proxy_users
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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 8.2.19, “Proxy Users”.

• collation_connection

  System Variable	collation_connection
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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 12.8.4, “Collation Coercibility in Expressions”).

  In MySQL 8.0.33 and later, using the name of a user-defined collation for this variable raises a warning.

• collation_database

  System Variable	collation_database
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	String
  Default Value	utf8mb4_0900_ai_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.

  As of MySQL 8.0.18, setting the session value of this system variable is no longer a restricted operation.

  The globalcharacter_set_database andcollation_database system variables are deprecated; 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 and assignments produce a warning. Expect the session variables to become read-only (and assignments to produce an error) in a future version of MySQL in which it remains possible to access the session variables to determine the database character set and collation for the default database.

  In MySQL 8.0.33 and later, using the name of a user-defined collation forcollation_database raises a warning.

• collation_server

  Command-Line Format	--collation-server=name
  System Variable	collation_server
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	String
  Default Value	utf8mb4_0900_ai_ci

  The server's default collation. SeeSection 12.15, “Character Set Configuration”.

  Beginning with MySQL 8.0.33, setting this to the name of a user-defined collation raises a warning.

• completion_type

  Command-Line Format	--completion-type=#
  System Variable	completion_type
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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 15.3.3, “Statements That Cause an Implicit Commit”. It also does not apply forXA COMMIT,XA ROLLBACK, or whenautocommit=1.

• component_scheduler.enabled

  Command-Line Format	--component-scheduler.enabled[=value]
  Introduced	8.0.34
  System Variable	component_scheduler.enabled
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  When set toOFF at startup, the background thread does not start. Tasks can still be scheduled, but they do not run untilcomponent_scheduler is enabled. When set toON at startup, the component is fully operational.

  It is also possible to set the value dynamically to get the following effects:

  • ON starts the background thread that begins servicing the queue immediately.

  • OFF signals a termination of the background thread, which waits for it to end. The background thread checks the termination flag before accessing the queue to check for tasks to execute.

• concurrent_insert

  Command-Line Format	--concurrent-insert[=value]
  System Variable	concurrent_insert
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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 10.11.3, “Concurrent Inserts”.

• connect_timeout

  Command-Line Format	--connect-timeout=#
  System Variable	connect_timeout
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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.

• connection_memory_chunk_size

  Command-Line Format	--connection-memory-chunk-size=#
  Introduced	8.0.28
  System Variable	connection_memory_chunk_size
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value (≥ 8.0.34)	8192
  Default Value (≥ 8.0.28, ≤ 8.0.33)	8912
  Minimum Value	0
  Maximum Value	536870912
  Unit	bytes

  Set the chunking size for updates to the global memory usage counterGlobal_connection_memory. The status variable is updated only when total memory consumption by all user connections changes by more than this amount. Disable updates by settingconnection_memory_chunk_size = 0.

  The memory calculation is exclusive of any memory used by system users such as the MySQL root user. Memory used by theInnoDB buffer pool is also not included.

  You must have theSYSTEM_VARIABLES_ADMIN orSUPER privilege to set this variable.

• connection_memory_limit

  Command-Line Format	--connection-memory-limit=#
  Introduced	8.0.28
  System Variable	connection_memory_limit
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	18446744073709551615
  Minimum Value	2097152
  Maximum Value	18446744073709551615
  Unit	bytes

  Set the maximum amount of memory that can be used by a single user connection. If any user connection uses more than this amount, all queries from this connection are rejected withER_CONN_LIMIT, including any queries currently running.

  The limit set by this variable does not apply to system users, or to the MySQL root account. Memory used by theInnoDB buffer pool is also not included.

  You must have theSYSTEM_VARIABLES_ADMIN orSUPER privilege to set this variable.

• core_file

  System Variable	core_file
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	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.

• create_admin_listener_thread

  Command-Line Format	--create-admin-listener-thread[={OFF|ON}]
  Introduced	8.0.14
  System Variable	create_admin_listener_thread
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  Whether to use a dedicated listening thread for client connections on the administrative network interface (seeSection 7.1.12.1, “Connection Interfaces”). The default isOFF; that is, the manager thread for ordinary connections on the main interface also handles connections for the administrative interface.

  Depending on factors such as platform type and workload, you may find one setting for this variable yields better performance than the other setting.

  Settingcreate_admin_listener_thread has no effect ifadmin_address is not specified because in that case the server maintains no administrative network interface.

• cte_max_recursion_depth

  Command-Line Format	--cte-max-recursion-depth=#
  System Variable	cte_max_recursion_depth
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	1000
  Minimum Value	0
  Maximum Value	4294967295

  The common table expression (CTE) maximum recursion depth. The server terminates execution of any CTE that recurses more levels than the value of this variable. For more information, seeLimiting Common Table Expression Recursion.

• datadir

  Command-Line Format	--datadir=dir_name
  System Variable	datadir
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	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 know the current directory in advance), it is best to specify thedatadir value as an absolute path.

• debug

  Command-Line Format	--debug[=debug_options]
  System Variable	debug
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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 7.1.9.1, “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 7.9.4, “The DBUG Package”.

• debug_sync

  System Variable	debug_sync
  Scope	Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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 7.1.9.1, “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
  Deprecated	8.0.27
  System Variable	default_authentication_plugin
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Enumeration
  Default Value	caching_sha2_password
  Valid Values	mysql_native_password sha256_password caching_sha2_password

  The default authentication plugin. This must be a plugin that uses internal credentials storage, so these values are permitted:

  • mysql_native_password: Use MySQL native passwords; seeSection 8.4.1.1, “Native Pluggable Authentication”.

  • sha256_password: Use SHA-256 passwords; seeSection 8.4.1.3, “SHA-256 Pluggable Authentication”.

  • caching_sha2_password: Use SHA-256 passwords; seeSection 8.4.1.2, “Caching SHA-2 Pluggable Authentication”.

  For information about which authentication plugins use internal credentials storage, seeSection 8.2.15, “Password Management”.

  Note

  In MySQL 8.0,caching_sha2_password is the default authentication plugin rather thanmysql_native_password. For information about the implications of this change for server operation and compatibility of the server with clients and connectors, seecaching_sha2_password as the Preferred Authentication Plugin.

  Prior to MySQL 8.0.27, thedefault_authentication_plugin value affects these aspects of server operation:

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

  • For an account created with a statement of the following form, 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';

  As of MySQL 8.0.27, which introduces multifactor authentication,default_authentication_plugin is still used, but in conjunction with and at a lower precedence than theauthentication_policy system variable. For details, seeThe Default Authentication Plugin. Because of this diminished role,default_authentication_plugin is deprecated as of MySQL 8.0.27 and subject to removal in a future MySQL version.

• default_collation_for_utf8mb4

  System Variable	default_collation_for_utf8mb4
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Enumeration
  Default Value	utf8mb4_0900_ai_ci
  Valid Values	utf8mb4_0900_ai_ci utf8mb4_general_ci

  Important

  Thedefault_collation_for_utf8mb4 system variable is for internal use by MySQL Replication only.

  This variable is set by the server to the default collation for theutf8mb4 character set. The value of the variable is replicated from a source to a replica so that the replica can correctly process data originating from a source with a different default collation forutf8mb4. This variable is primarily intended to support replication from a MySQL 5.7 or older replication source server to a MySQL 8.0 replica server, or group replication with a MySQL 5.7 primary node and one or more MySQL 8.0 secondaries. The default collation forutf8mb4 in MySQL 5.7 isutf8mb4_general_ci, bututf8mb4_0900_ai_ci in MySQL 8.0. The variable is not present in releases earlier than MySQL 8.0, so if the replica does not receive a value for the variable, it assumes the source is from an earlier release and sets the value to the previous default collationutf8mb4_general_ci.

  As of MySQL 8.0.18, setting the session value of this system variable is no longer a restricted operation.

  The defaultutf8mb4 collation is used in the following statements:

  • SHOW COLLATION andSHOW CHARACTER SET.

  • CREATE TABLE andALTER TABLE having aCHARACTER SET utf8mb4 clause without aCOLLATION clause, either for the table character set or for a column character set.

  • CREATE DATABASE andALTER DATABASE having aCHARACTER SET utf8mb4 clause without aCOLLATION clause.

  • Any statement containing a string literal of the form_utf8mb4'some text' without aCOLLATE clause.

  See alsoSection 12.9, “Unicode Support”.

• default_password_lifetime

  Command-Line Format	--default-password-lifetime=#
  System Variable	default_password_lifetime
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	0
  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 option of theCREATE USER andALTER USER statements. SeeSection 8.2.15, “Password Management”.

• default_storage_engine

  Command-Line Format	--default-storage-engine=name
  System Variable	default_storage_engine
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Enumeration
  Default Value	InnoDB

  The default storage engine for tables. SeeChapter 18,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 else the server does not start.

• default_table_encryption

  Command-Line Format	--default-table-encryption[={OFF|ON}]
  Introduced	8.0.16
  System Variable	default_table_encryption
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	Yes
  Type	Boolean
  Default Value	OFF

  Defines the default encryption setting applied to schemas and general tablespaces when they are created without specifying anENCRYPTION clause.

  Thedefault_table_encryption variable is only applicable to user-created schemas and general tablespaces. It does not govern encryption of themysql system tablespace.

  Setting the runtime value ofdefault_table_encryption requires theSYSTEM_VARIABLES_ADMIN andTABLE_ENCRYPTION_ADMIN privileges, or the deprecatedSUPER privilege.

  The value ofdefault_table_encryption cannot be changed while Group Replication is running.

  default_table_encryption supportsSET PERSIST andSET PERSIST_ONLY syntax. SeeSection 7.1.9.3, “Persisted System Variables”.

  For more information, seeDefining an Encryption Default for Schemas and General Tablespaces.

• default_tmp_storage_engine

  Command-Line Format	--default-tmp-storage-engine=name
  System Variable	default_tmp_storage_engine
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	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 else the server does not start.

• default_week_format

  Command-Line Format	--default-week-format=#
  System Variable	default_week_format
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	0
  Minimum Value	0
  Maximum Value	7

  The default mode value to use for theWEEK() function. SeeSection 14.7, “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
  SET_VAR Hint Applies	No
  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 18.2.1, “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 7.1.8, “Server System Variables”, andSection 18.2.1, “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
  SET_VAR Hint Applies	No
  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), and you should 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
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	300
  Minimum Value	1
  Maximum Value	31536000
  Unit	seconds

  This system variable is deprecated (becauseDELAYED inserts are not supported), and you should 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
  SET_VAR Hint Applies	No
  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), and you should 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
  SET_VAR Hint Applies	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:--initialize,--initialize-insecure,--skip-grant-tables.

  Note

  Settingdisabled_storage_engines might cause an issue withmysql_upgrade. For details, seeSection 6.4.5, “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
  SET_VAR Hint Applies	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 8.2.16, “Server Handling of Expired Passwords”.

• div_precision_increment

  Command-Line Format	--div-precision-increment=#
  System Variable	div_precision_increment
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	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 |+----------------+

• dragnet.log_error_filter_rules

  Command-Line Format	--dragnet.log-error-filter-rules=value
  System Variable	dragnet.log_error_filter_rules
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	String
  Default Value	IF prio>=INFORMATION THEN drop. IF EXISTS source_line THEN unset source_line.

  The filter rules that control operation of thelog_filter_dragnet error log filter component. Iflog_filter_dragnet is not installed,dragnet.log_error_filter_rules is unavailable. Iflog_filter_dragnet is installed but not enabled, changes todragnet.log_error_filter_rules have no effect.

  The effect of the default value is similar to the filtering performed by thelog_sink_internal filter with a setting oflog_error_verbosity=2.

  As of MySQL 8.0.12, thedragnet.Status status variable can be consulted to determine the result of the most recent assignment todragnet.log_error_filter_rules.

  Prior to MySQL 8.0.12, successful assignments todragnet.log_error_filter_rules at runtime produce a note confirming the new value:

  mysql> SET GLOBAL dragnet.log_error_filter_rules = 'IF prio <> 0 THEN unset prio.';Query OK, 0 rows affected, 1 warning (0.00 sec)mysql> SHOW WARNINGS\G*************************** 1. row ***************************  Level: Note   Code: 4569Message: filter configuration accepted:         SET @@GLOBAL.dragnet.log_error_filter_rules=         'IF prio!=ERROR THEN unset prio.';

  The value displayed bySHOW WARNINGS indicates the“decompiled” canonical representation after the rule set has been successfully parsed and compiled into internal form. Semantically, this canonical form is identical to the value assigned todragnet.log_error_filter_rules, but there may be some differences between the assigned and canonical values, as illustrated by the preceding example:

  • The<> operator is changed to!=.

  • The numeric priority of 0 is changed to the corresponding priority symbolERROR.

  • Optional spaces are removed.

  For additional information, seeSection 7.4.2.4, “Types of Error Log Filtering”, andSection 7.5.3, “Error Log Components”.

• enterprise_encryption.maximum_rsa_key_size

  Command-Line Format	--enterprise-encryption.maximum-rsa-key-size=#
  Introduced	8.0.30
  System Variable	enterprise_encryption.maximum_rsa_key_size
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	4096
  Minimum Value	2048
  Maximum Value	16384

  This variable limits the maximum size of RSA keys generated by MySQL Enterprise Encryption. The variable is available only if the MySQL Enterprise Encryption componentcomponent_enterprise_encryption is installed, which is available from MySQL 8.0.30. The variable is not available if theopenssl_udf shared library is used to provide MySQL Enterprise Encryption functions.

  The lowest setting is 2048 bits, which is the minimum RSA key length that is acceptable by current best practice. The default setting is 4096 bits. The highest setting is 16384 bits. Generating longer keys can consume significant CPU resources, so you can use this setting to limit keys to a length that provides adequate security for your requirements while balancing this with resource usage. Note that the functions provided by theopenssl_udf shared library allow key lengths starting at 1024 bits, and following an upgrade to the component, the minimum key length is greater than this. SeeSection 8.6.2, “Configuring MySQL Enterprise Encryption” for more information.

• enterprise_encryption.rsa_support_legacy_padding

  Command-Line Format	--enterprise-encryption.rsa_support_legacy_padding[={OFF|ON}]
  Introduced	8.0.30
  System Variable	enterprise_encryption.rsa_support_legacy_padding
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  This variable controls whether encrypted data and signatures that MySQL Enterprise Encryption produced with theopenssl_udf shared library functions used before MySQL 8.0.30, can be decrypted or verified by the functions of the MySQL Enterprise Encryption componentcomponent_enterprise_encryption, which is available from MySQL 8.0.30. The variable is available only if the MySQL Enterprise Encryption component is installed, and it is not available if theopenssl_udf shared library is used to provide MySQL Enterprise Encryption functions.

  For the component functions to support decryption and verification for content produced by the legacyopenssl_udf shared library functions, you must set the system variable padding toON. WhenON is set, if the component functions cannot decrypt or verify content when assuming it has the RSAES-OAEP or RSASSA-PSS scheme (as used by the component), they make another attempt assuming it has the RSAES-PKCS1-v1_5 or RSASSA-PKCS1-v1_5 scheme (as used by theopenssl_udf shared library functions). WhenOFF is set, if the component functions cannot decrypt or verify content using their normal schemes, they return null output. SeeSection 8.6.2, “Configuring MySQL Enterprise Encryption” for more information.

• end_markers_in_json

  Command-Line Format	--end-markers-in-json[={OFF|ON}]
  System Variable	end_markers_in_json
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	Yes
  Type	Boolean
  Default Value	OFF

  Whether optimizer JSON output should add end markers. SeeSection 10.15.9, “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
  SET_VAR Hint Applies	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 15.7.7.17, “SHOW ERRORS Statement”.

• event_scheduler

  Command-Line Format	--event-scheduler[=value]
  System Variable	event_scheduler
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Enumeration
  Default Value	ON
  Valid Values	ON OFF 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 27.4.2, “Event Scheduler Configuration”

• explain_format

  Command-Line Format	--explain-format=format
  Introduced	8.0.32
  System Variable	explain_format
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Enumeration
  Default Value	TRADITIONAL
  Valid Values	TRADITIONAL (DEFAULT) JSON TREE

  This variable determines the default output format used byEXPLAIN in the absence of aFORMAT option when displaying a query execution plan. Possible values and their effects are listed here:

  • TRADITIONAL: Use MySQL's traditional table-based output, as ifFORMAT=TRADITIONAL had been specified as part of theEXPLAIN statement. This is the variable's default value.DEFAULT is also supported as a synonym forTRADITIONAL, and has exactly the same effect.

    Note

    DEFAULT cannot be used as part of anEXPLAIN statement'sFORMAT option.

  • JSON: Use the JSON output format, as ifFORMAT=JSON had been specified.

  • TREE: Use the tree-based output format, as ifFORMAT=TREE had been specified.

  The setting for this variable also affectsEXPLAIN ANALYZE. For this purpose,DEFAULT andTRADITIONAL are interpeted asTREE. If the value ofexplain_format isJSON and anEXPLAIN ANALYZE statement having noFORMAT option is issued, the statement raises an error (ER_NOT_SUPPORTED_YET).

  Using a format specifier withEXPLAIN orEXPLAIN ANALYZE overrides any setting forexplain_format.

  Theexplain_format system variable has no effect onEXPLAIN output when this statement is used to display information about table columns.

  Setting the session value ofexplain_format requires no special privileges; setting it on the global level requiresSYSTEM_VARIABLES_ADMIN (or the deprecatedSUPER privilege). SeeSection 7.1.9.1, “System Variable Privileges”.

  For more information and examples, seeObtaining Execution Plan Information.

• 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
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  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 enabled, which disables the nonstandard behaviors. Disablingexplicit_defaults_for_timestamp results in a warning.

  As of MySQL 8.0.18, setting the session value of this system variable is no longer a restricted operation.

  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.Exception: As of MySQL 8.0.22, attempting to insertNULL into a generated column declared asTIMESTAMP NOT NULL is rejected with an error.

  • 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 7.1.11, “Server SQL Modes”.

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

  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 MySQL release. When removal of those behaviors occurs, expectexplicit_defaults_for_timestamp to be removed as well.

  For additional information, seeSection 13.2.5, “Automatic Initialization and Updating for TIMESTAMP and DATETIME”.

• external_user

  System Variable	external_user
  Scope	Session
  Dynamic	No
  SET_VAR Hint Applies	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 8.2.19, “Proxy Users”.

• flush

  Command-Line Format	--flush[={OFF|ON}]
  System Variable	flush
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  Applies to MyISAM, only.

  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
  SET_VAR Hint Applies	No
  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
  SET_VAR Hint Applies	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 15.1.20.5, “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 15.1.20.5, “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.

• ft_boolean_syntax

  Command-Line Format	--ft-boolean-syntax=name
  System Variable	ft_boolean_syntax
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	String
  Default Value	+ -><()~*:""&|

  The list of operators supported by boolean full-text searches performed usingIN BOOLEAN MODE. SeeSection 14.9.2, “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
  SET_VAR Hint Applies	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
  SET_VAR Hint Applies	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
  SET_VAR Hint Applies	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
  SET_VAR Hint Applies	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 14.9.4, “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
  SET_VAR Hint Applies	No
  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
  SET_VAR Hint Applies	No
  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.

• generated_random_password_length

  Command-Line Format	--generated-random-password-length=#
  Introduced	8.0.18
  System Variable	generated_random_password_length
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	20
  Minimum Value	5
  Maximum Value	255

  The maximum number of characters permitted in random passwords generated forCREATE USER,ALTER USER, andSET PASSWORD statements. For more information, seeRandom Password Generation.

• global_connection_memory_limit

  Command-Line Format	--global-connection-memory-limit=#
  Introduced	8.0.28
  System Variable	global_connection_memory_limit
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	18446744073709551615
  Minimum Value	16777216
  Maximum Value	18446744073709551615
  Unit	bytes

  Set the total amount of memory that can be used by all user connections; that is,Global_connection_memory should not exceed this amount. Any time that it does, all queries (including any currently running) from regular users are rejected withER_GLOBAL_CONN_LIMIT.

  Memory used by the system users such as the MySQL root user is included in this total, but is not counted towards the disconnection limit; such users are never disconnected due to memory usage.

  Memory used by theInnoDB buffer pool is excluded from the total.

  You must have theSYSTEM_VARIABLES_ADMIN orSUPER privilege to set this variable.

• global_connection_memory_tracking

  Command-Line Format	--global-connection-memory-tracking={TRUE|FALSE}
  Introduced	8.0.28
  System Variable	global_connection_memory_tracking
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	FALSE

  Determines whether the server calculatesGlobal_connection_memory. This variable must be enabled explicitly; otherwise, the memory calculation is not performed, andGlobal_connection_memory is not set.

  You must have theSYSTEM_VARIABLES_ADMIN orSUPER privilege to set this variable.

• group_concat_max_len

  Command-Line Format	--group-concat-max-len=#
  System Variable	group_concat_max_len
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	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_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.

  As of MySQL 8.0.26,have_openssl is deprecated and subject to removal in a future MySQL version. For information about TLS properties of MySQL connection interfaces, use thetls_channel_status table.

• 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 15.7.7.31, “SHOW PROFILES Statement”.

  This variable is deprecated and you should expect it to be removed in a future MySQL release.

• have_query_cache

  The query cache was removed in MySQL 8.0.3.have_query_cache is deprecated, always has a value ofNO, and you should expect it to be removed in a future MySQL release.

• have_rtree_keys

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

• have_ssl

  Deprecated	8.0.26
  System Variable	have_ssl
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	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”.

  As of MySQL 8.0.26,have_ssl is deprecated and subject to removal in a future MySQL version. For information about TLS properties of MySQL connection interfaces, use thetls_channel_status table.

• have_statement_timeout

  System Variable	have_statement_timeout
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	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.

  Note

  Symbolic link support, along with the--symbolic-links option that controls it, is deprecated; expect these to be removed in a future version of MySQL. In addition, the option is disabled by default. The relatedhave_symlink system variable also is deprecated and you should expect it to be removed in a future version of MySQL.

• histogram_generation_max_mem_size

  Command-Line Format	--histogram-generation-max-mem-size=#
  System Variable	histogram_generation_max_mem_size
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	20000000
  Minimum Value	1000000
  Maximum Value (64-bit platforms)	18446744073709551615
  Maximum Value (32-bit platforms)	4294967295
  Unit	bytes

  The maximum amount of memory available for generating histogram statistics. SeeSection 10.9.6, “Optimizer Statistics”, andSection 15.7.3.1, “ANALYZE TABLE Statement”.

  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 7.1.9.1, “System Variable Privileges”.

• host_cache_size

  Command-Line Format	--host-cache-size=#
  System Variable	host_cache_size
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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 7.1.12.3, “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 and its removal is expected in a future version of MySQL; in MySQL 8.0.29 and later, using the option raises a warning.

• hostname

  System Variable	hostname
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	String

  The server sets this variable to the server host name at startup. The maximum length is 255 characters as of MySQL 8.0.17, per RFC 1034, and 60 characters before that.

• 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.

• init_connect

  Command-Line Format	--init-connect=name
  System Variable	init_connect
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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 theCONNECTION_ADMIN privilege (or the deprecatedSUPER 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 theCONNECTION_ADMIN orSUPER privilege enables them to open a connection and fix theinit_connect value.

  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.

• information_schema_stats_expiry

  Command-Line Format	--information-schema-stats-expiry=#
  System Variable	information_schema_stats_expiry
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	86400
  Minimum Value	0
  Maximum Value	31536000
  Unit	seconds

  SomeINFORMATION_SCHEMA tables contain columns that provide table statistics:

  STATISTICS.CARDINALITYTABLES.AUTO_INCREMENTTABLES.AVG_ROW_LENGTHTABLES.CHECKSUMTABLES.CHECK_TIMETABLES.CREATE_TIMETABLES.DATA_FREETABLES.DATA_LENGTHTABLES.INDEX_LENGTHTABLES.MAX_DATA_LENGTHTABLES.TABLE_ROWSTABLES.UPDATE_TIME

  Those columns represent dynamic table metadata; that is, information that changes as table contents change.

  By default, MySQL retrieves cached values for those columns from themysql.index_stats andmysql.table_stats dictionary tables when the columns are queried, which is more efficient than retrieving statistics directly from the storage engine. If cached statistics are not available or have expired, MySQL retrieves the latest statistics from the storage engine and caches them in themysql.index_stats andmysql.table_stats dictionary tables. Subsequent queries retrieve the cached statistics until the cached statistics expire. A server restart or the first opening of themysql.index_stats andmysql.table_stats tables do not update cached statistics automatically.

  Theinformation_schema_stats_expiry session variable defines the period of time before cached statistics expire. The default is 86400 seconds (24 hours), but the time period can be extended to as much as one year.

  To update cached values at any time for a given table, useANALYZE TABLE.

  To always retrieve the latest statistics directly from the storage engine and bypass cached values, setinformation_schema_stats_expiry to0.

  Querying statistics columns does not store or update statistics in themysql.index_stats andmysql.table_stats dictionary tables under these circumstances:

  • When cached statistics have not expired.

  • Wheninformation_schema_stats_expiry is set to 0.

  • When the server is inread_only,super_read_only,transaction_read_only, orinnodb_read_only mode.

  • When the query also fetches Performance Schema data.

  The statistics cache may be updated during a multiple-statement transaction before it is known whether the transaction commits. As a result, the cache may contain information that does not correspond to a known committed state. This can occur withautocommit=0 or afterSTART TRANSACTION.

  information_schema_stats_expiry is a session variable, and each client session can define its own expiration value. Statistics that are retrieved from the storage engine and cached by one session are available to other sessions.

  For related information, seeSection 10.2.3, “Optimizing INFORMATION_SCHEMA Queries”.

• init_file

  Command-Line Format	--init-file=file_name
  System Variable	init_file
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	File name

  If specified, this variable names a file containing SQL statements to be read and executed during the startup process. Prior to MySQL 8.0.18, each statement must be on a single line and should not include comments. As of MySQL 8.0.18, the acceptable format for statements in the file is expanded to support these constructs:

  • delimiter ;, to set the statement delimiter to the; character.

  • delimiter $$, to set the statement delimiter to the$$ character sequence.

  • Multiple statements on the same line, delimited by the current delimiter.

  • Multiple-line statements.

  • Comments from a# character to the end of the line.

  • Comments from a--  sequence to the end of the line.

  • C-style comments from a/* sequence to the following*/ sequence, including over multiple lines.

  • Multiple-line string literals enclosed within either single quote (') or double quote (") characters.

  If the server is started with the--initialize or--initialize-insecure option, it operates in bootstrap 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 19.1.3, “Replication with Global Transaction Identifiers”.

  As of MySQL 8.0.17, threads created during server startup are used for tasks such as creating the data dictionary, running upgrade procedures, and creating system tables. To ensure a stable and predictable environment, these threads are executed with the server built-in defaults for some system variables, such assql_mode,character_set_server,collation_server,completion_type,explicit_defaults_for_timestamp, anddefault_table_encryption.

  These threads are also used to execute the statements in any file specified withinit_file when starting the server, so such statements execute with the server's built-in default values for those system variables.

• innodb_xxx

  InnoDB system variables are listed inSection 17.14, “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
  SET_VAR Hint Applies	No
  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=#
  Removed	8.0.16
  System Variable	internal_tmp_disk_storage_engine
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Enumeration
  Default Value	INNODB
  Valid Values	MYISAM INNODB

  Important

  In MySQL 8.0.16 and later, on-disk internal temporary tables always use theInnoDB storage engine; as of MySQL 8.0.16, this variable has been removed and is thus no longer supported.

  Prior to MySQL 8.0.16, this variable determines the storage engine used for on-disk internal temporary tables (seeStorage Engine for On-Disk Internal Temporary Tables). Permitted values areMYISAM andINNODB (the default).

• internal_tmp_mem_storage_engine

  Command-Line Format	--internal-tmp-mem-storage-engine=#
  System Variable	internal_tmp_mem_storage_engine
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	Yes
  Type	Enumeration
  Default Value	TempTable
  Valid Values	MEMORY TempTable

  The storage engine for in-memory internal temporary tables (seeSection 10.4.4, “Internal Temporary Table Use in MySQL”). Permitted values areTempTable (the default) andMEMORY.

  Theoptimizer uses the storage engine defined byinternal_tmp_mem_storage_engine for in-memory internal temporary tables.

  From MySQL 8.0.27, configuring a session setting forinternal_tmp_mem_storage_engine requires theSESSION_VARIABLES_ADMIN orSYSTEM_VARIABLES_ADMIN privilege.

• join_buffer_size

  Command-Line Format	--join-buffer-size=#
  System Variable	join_buffer_size
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	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. In MySQL 8.0.18 and later, this variable also controls the amount of memory used for hash joins. 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, or change the setting on a per-query basis by using aSET_VAR optimizer hint (seeSection 10.9.3, “Optimizer Hints”). 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 10.2.1.7, “Nested-Loop Join Algorithms”. For information about Batched Key Access, seeSection 10.2.1.12, “Block Nested-Loop and Batched Key Access Joins”. For information about hash joins, seeSection 10.2.1.4, “Hash Join Optimization”.

• keep_files_on_create

  Command-Line Format	--keep-files-on-create[={OFF|ON}]
  System Variable	keep_files_on_create
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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
  SET_VAR Hint Applies	No
  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 10.2.5.1, “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 15.7.7, “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 10.10.2, “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
  SET_VAR Hint Applies	No
  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 10.10.2, “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
  SET_VAR Hint Applies	No
  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 10.10.2, “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
  SET_VAR Hint Applies	No
  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 10.10.2, “The MyISAM Key Cache”.

• large_files_support

  System Variable	large_files_support
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	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
  SET_VAR Hint Applies	No
  Platform Specific	Linux
  Type	Boolean
  Default Value	OFF

  Whether large page support is enabled (via the--large-pages option). SeeSection 10.12.3.3, “Enabling Large Page Support”.

• large_page_size

  System Variable	large_page_size
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	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 10.12.3.3, “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
  SET_VAR Hint Applies	No
  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 12.12, “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
  SET_VAR Hint Applies	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 12.12, “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
  SET_VAR Hint Applies	No
  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 12.16, “MySQL Server Locale Support”.

• license

  System Variable	license
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	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
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  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 8.1.6, “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
  SET_VAR Hint Applies	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 also defines the amount of time that aLOCK INSTANCE FOR BACKUP statement waits for a lock before giving up.

• locked_in_memory

  System Variable	locked_in_memory
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	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
  SET_VAR Hint Applies	No
  Type	File name

  The default error log 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 7.4.2, “The Error Log”.

• log_error_services

  Command-Line Format	--log-error-services=value
  System Variable	log_error_services
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	String
  Default Value	log_filter_internal; log_sink_internal

  The components to enable for error logging. The variable may contain a list with 0, 1, or many elements. In the latter case, elements may be delimited by semicolon or (as of MySQL 8.0.12) comma, optionally followed by space. A given setting cannot use both semicolon and comma separators. Component order is significant because the server executes components in the order listed.

  From MySQL 8.0.30, any loadable (not built in) component named in thelog_error_services is implicitly loaded if it is not already loaded. Before MySQL 8.0.30, any loadable (not built in) component named in thelog_error_services value must first be installed withINSTALL COMPONENT. For more information, seeSection 7.4.2.1, “Error Log Configuration”.

• log_error_suppression_list

  Command-Line Format	--log-error-suppression-list=value
  Introduced	8.0.13
  System Variable	log_error_suppression_list
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	String
  Default Value	empty string

  Thelog_error_suppression_list system variable applies to events intended for the error log and specifies which events to suppress when they occur with a priority ofWARNING orINFORMATION. For example, if a particular type of warning is considered undesirable“noise” in the error log because it occurs frequently but is not of interest, it can be suppressed. This variable affects filtering performed by thelog_filter_internal error log filter component, which is enabled by default (seeSection 7.5.3, “Error Log Components”). Iflog_filter_internal is disabled,log_error_suppression_list has no effect.

  Thelog_error_suppression_list value may be the empty string for no suppression, or a list of one or more comma-separated values indicating the error codes to suppress. Error codes may be specified in symbolic or numeric form. A numeric code may be specified with or without theMY- prefix. Leading zeros in the numeric part are not significant. Examples of permitted code formats:

  ER_SERVER_SHUTDOWN_COMPLETEMY-000031000031MY-3131

  Symbolic values are preferable to numeric values for readability and portability. For information about the permitted error symbols and numbers, seeMySQL 8.0 Error Message Reference.

  The effect oflog_error_suppression_list combines with that oflog_error_verbosity. For additional information, seeSection 7.4.2.5, “Priority-Based Error Log Filtering (log_filter_internal)”.

• log_error_verbosity

  Command-Line Format	--log-error-verbosity=#
  System Variable	log_error_verbosity
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	2
  Minimum Value	1
  Maximum Value	3

  Thelog_error_verbosity system variable specifies the verbosity for handling events intended for the error log. This variable affects filtering performed by thelog_filter_internal error log filter component, which is enabled by default (seeSection 7.5.3, “Error Log Components”). Iflog_filter_internal is disabled,log_error_verbosity has no effect.

  Events intended for the error log have a priority ofERROR,WARNING, orINFORMATION.log_error_verbosity controls verbosity based on which priorities to permit for messages written to the log, as shown in the following table.

  log_error_verbosity Value	Permitted Message Priorities
  1	ERROR
  2	ERROR,WARNING
  3	ERROR,WARNING,INFORMATION

  There is also a priority ofSYSTEM. System messages about non-error situations are printed to the error log regardless of thelog_error_verbosity value. These messages include startup and shutdown messages, and some significant changes to settings.

  The effect oflog_error_verbosity combines with that oflog_error_suppression_list. For additional information, seeSection 7.4.2.5, “Priority-Based Error Log Filtering (log_filter_internal)”.

• log_output

  Command-Line Format	--log-output=name
  System Variable	log_output
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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 schema.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 7.4.1, “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
  SET_VAR Hint Applies	No
  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 7.4.5, “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_raw

  Command-Line Format	--log-raw[={OFF|ON}]
  System Variable (≥ 8.0.19)	log_raw
  Scope (≥ 8.0.19)	Global
  Dynamic (≥ 8.0.19)	Yes
  SET_VAR Hint Applies (≥ 8.0.19)	No
  Type	Boolean
  Default Value	OFF

  Thelog_raw system variable is initially set to the value of the--log-raw option. See the description of that option for more information. The system variable may also be set at runtime to change password masking behavior.

• log_slow_admin_statements

  Command-Line Format	--log-slow-admin-statements[={OFF|ON}]
  System Variable	log_slow_admin_statements
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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_slow_extra

  Command-Line Format	--log-slow-extra[={OFF|ON}]
  Introduced	8.0.14
  System Variable	log_slow_extra
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  If the slow query log is enabled and the output destination includesFILE, the server writes additional fields to log file lines that provide information about slow statements. SeeSection 7.4.5, “The Slow Query Log”.TABLE output is unaffected.

• log_syslog

  Command-Line Format	--log-syslog[={OFF|ON}]
  Deprecated	Yes (removed in 8.0.13)
  System Variable	log_syslog
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON (when error logging to system log is enabled)

  Prior to MySQL 8.0, this variable controlled whether to perform error logging to the system log (the Event Log on Windows, andsyslog on Unix and Unix-like systems).

  In MySQL 8.0, thelog_sink_syseventlog log component implements error logging to the system log (seeSection 7.4.2.8, “Error Logging to the System Log”), so this type of logging can be enabled by adding that component to thelog_error_services system variable.log_syslog is removed. (Prior to MySQL 8.0.13,log_syslog exists but is deprecated and has no effect.)

• log_syslog_facility

  Command-Line Format	--log-syslog-facility=value
  Removed	8.0.13
  System Variable	log_syslog_facility
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	String
  Default Value	daemon

  This variable was removed in MySQL 8.0.13 and replaced bysyseventlog.facility.

• log_syslog_include_pid

  Command-Line Format	--log-syslog-include-pid[={OFF|ON}]
  Removed	8.0.13
  System Variable	log_syslog_include_pid
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  This variable was removed in MySQL 8.0.13 and replaced bysyseventlog.include_pid.

• log_syslog_tag

  Command-Line Format	--log-syslog-tag=tag
  Removed	8.0.13
  System Variable	log_syslog_tag
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	String
  Default Value	empty string

  This variable was removed in MySQL 8.0.13 and replaced bysyseventlog.tag.

• log_timestamps

  Command-Line Format	--log-timestamps=#
  System Variable	log_timestamps
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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 (the 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
  SET_VAR Hint Applies	No
  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 7.4.5, “The Slow Query Log”.

• long_query_time

  Command-Line Format	--long-query-time=#
  System Variable	long_query_time
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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 7.4.5, “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.

  mysqldump performs a full table scan, which means its queries can often exceed along_query_time setting that is useful for regular queries. From MySQL 8.0.30, if you want to exclude most or all ofmysqldump’s queries from the slow query log, you can setmysqldump’s--mysqld-long-query-time command line option to change the session value of the system variable to a higher value.

• low_priority_updates

  Command-Line Format	--low-priority-updates[={OFF|ON}]
  System Variable	low_priority_updates
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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 10.11.2, “Table Locking Issues”.

  As of MySQL 8.0.27, 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 7.1.9.1, “System Variable Privileges”.

• lower_case_file_system

  System Variable	lower_case_file_system
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	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
  SET_VAR Hint Applies	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 11.2.3, “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 19.2.5, “How Servers Evaluate Replication Filtering Rules”.

  It is prohibited to start the server with alower_case_table_names setting that is different from the setting used when the server was initialized. The restriction is necessary because collations used by various data dictionary table fields are determined by the setting defined when the server is initialized, and restarting the server with a different setting would introduce inconsistencies with respect to how identifiers are ordered and compared.

  It is therefore necessary to configurelower_case_table_names to the desired setting before initializing the server. In most cases, this requires configuringlower_case_table_names in a MySQL option file before starting the MySQL server for the first time. For APT installations on Debian and Ubuntu, however, the server is initialized for you, and there is no opportunity to configure the setting in an option file beforehand. You must therefore use thedebconf-set-selection utility prior to installing MySQL using APT to enablelower_case_table_names. To do so, run this command before installing MySQL using APT:

  $> sudo debconf-set-selections <<< "mysql-server mysql-server/lowercase-table-names select Enabled"

  Note

  The ability to enablelower_case_table_names usingdebconf-set-selections was added in MySQL 8.0.17. Enablinglower_case_table_names sets the value to 1.

• mandatory_roles

  Command-Line Format	--mandatory-roles=value
  System Variable	mandatory_roles
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	String
  Default Value	empty string

  Roles the server should treat as mandatory. In effect, these roles are automatically granted to every user, although settingmandatory_roles does not actually change any user accounts, and the granted roles are not visible in themysql.role_edges system table.

  The variable value is a comma-separated list of role names. Example:

  SET PERSIST mandatory_roles = '`role1`@`%`,`role2`,role3,role4@localhost';

  Setting the runtime value ofmandatory_roles requires theROLE_ADMIN privilege, in addition to theSYSTEM_VARIABLES_ADMIN privilege (or the deprecatedSUPER privilege) normally required to set a global system variable runtime value.

  Role names consist of a user part and host part inuser_name@host_name format. The host part, if omitted, defaults to%. For additional information, seeSection 8.2.5, “Specifying Role Names”.

  Themandatory_roles value is a string, so user names and host names, if quoted, must be written in a fashion permitted for quoting within quoted strings.

  Roles named in the value ofmandatory_roles cannot be revoked withREVOKE or dropped withDROP ROLE orDROP USER.

  To prevent sessions from being made system sessions by default, a role that has theSYSTEM_USER privilege cannot be listed in the value of themandatory_roles system variable:

  • Ifmandatory_roles is assigned a role at startup that has theSYSTEM_USER privilege, the server writes a message to the error log and exits.

  • Ifmandatory_roles is assigned a role at runtime that has theSYSTEM_USER privilege, an error occurs and themandatory_roles value remains unchanged.

  Mandatory roles, like explicitly granted roles, do not take effect until activated (seeActivating Roles). At login time, role activation occurs for all granted roles if theactivate_all_roles_on_login system variable is enabled; otherwise, or for roles that are set as default roles otherwise. At runtime,SET ROLE activates roles.

  Roles that do not exist when assigned tomandatory_roles but are created later may require special treatment to be considered mandatory. For details, seeDefining Mandatory Roles.

  SHOW GRANTS displays mandatory roles according to the rules described inSection 15.7.7.21, “SHOW GRANTS Statement”.

• max_allowed_packet

  Command-Line Format	--max-allowed-packet=#
  System Variable	max_allowed_packet
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	67108864
  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 64MB.

  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 does not 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
  SET_VAR Hint Applies	No
  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
  SET_VAR Hint Applies	No
  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 7.1.12.1, “Connection Interfaces”.

• max_delayed_threads

  Command-Line Format	--max-delayed-threads=#
  Deprecated	Yes
  System Variable	max_delayed_threads
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	20
  Minimum Value	0
  Maximum Value	16384

  This system variable is deprecated (becauseDELAYED inserts are not supported) and subject to removal in a future MySQL release.

  As of MySQL 8.0.27, 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 7.1.9.1, “System Variable Privileges”.

• max_digest_length

  Command-Line Format	--max-digest-length=#
  System Variable	max_digest_length
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	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, this is equivalent toLENGTH(STATEMENT_DIGEST_TEXT(statement) ) + 64. This means that, when the value ofmax_digest_length is 1024 (the default), the maximum length for a normalized SQL statement before truncation occurs is in effect 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 29.10, “Performance Schema Statement Digests and Sampling”.

• max_error_count

  Command-Line Format	--max-error-count=#
  System Variable	max_error_count
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	Yes
  Type	Integer
  Default Value	1024
  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.

  As of MySQL 8.0.27, 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 7.1.9.1, “System Variable Privileges”.

• max_execution_time

  Command-Line Format	--max-execution-time=#
  System Variable	max_execution_time
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	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
  SET_VAR Hint Applies	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 10.4.4, “Internal Temporary Table Use in MySQL”.

  max_heap_table_size is not replicated. SeeSection 19.5.1.21, “Replication and MEMORY Tables”, andSection 19.5.1.39, “Replication and Variables”, for more information.

• max_insert_delayed_threads

  Deprecated	Yes
  System Variable	max_insert_delayed_threads
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	0
  Minimum Value	20
  Maximum Value	16384

  This variable is a synonym formax_delayed_threads. Likemax_delayed_threads, it is deprecated (becauseDELAYED inserts are not supported) and subject to removal in a future MySQL release.

  As of MySQL 8.0.27, 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 7.1.9.1, “System Variable Privileges”.

• max_join_size

  Command-Line Format	--max-join-size=#
  System Variable	max_join_size
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	Yes
  Type	Integer
  Default Value	18446744073709551615
  Minimum Value	1
  Maximum Value	18446744073709551615

  As of MySQL 8.0.31, this represents a limit on the maximum number of row accesses in base tables made by a join. If the server's estimate indicates that a greater number of rows thanmax_join_size must be read from the base tables, the statement is rejected with an error.

  MySQL 8.0.30 and earlier: 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).

  Regardless of MySQL release version, 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.

• max_length_for_sort_data

  Command-Line Format	--max-length-for-sort-data=#
  Deprecated	8.0.20
  System Variable	max_length_for_sort_data
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	Yes
  Type	Integer
  Default Value	4096
  Minimum Value	4
  Maximum Value	8388608
  Unit	bytes

  This variable is deprecated as of MySQL 8.0.20 due to optimizer changes that make it obsolete and of no effect. Previously, it acted as the cutoff on the size of index values that determines whichfilesort algorithm to use. SeeSection 10.2.1.16, “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
  SET_VAR Hint Applies	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
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	16382
  Minimum Value	0
  Maximum Value (≥ 8.0.18)	4194304
  Maximum Value (≤ 8.0.17)	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
  SET_VAR Hint Applies	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 15.7.7.22, “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
  SET_VAR Hint Applies	Yes
  Type	Integer
  Default Value	1024
  Minimum Value	4
  Maximum Value	8388608
  Unit	bytes

  The number of bytes to use when sorting string values which usePAD SPACE collations. The server uses only the firstmax_sort_length bytes of any such value and ignores the rest. Consequently, such values that differ only after the firstmax_sort_length bytes compare as equal forGROUP BY,ORDER BY, andDISTINCT operations. (This behavior differs from previous versions of MySQL, where this setting was applied to all values used in comparisons.)

  Increasing the value ofmax_sort_length may require increasing the value ofsort_buffer_size as well. For details, seeSection 10.2.1.16, “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
  SET_VAR Hint Applies	No
  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_user_connections

  Command-Line Format	--max-user-connections=#
  System Variable	max_user_connections
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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 8.2.21, “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
  SET_VAR Hint Applies	No
  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
  SET_VAR Hint Applies	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 14.9.9, “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 (removed in 8.0.13)
  System Variable	metadata_locks_cache_size
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	1024
  Minimum Value	1
  Maximum Value	1048576
  Unit	bytes

  This system variable was removed in MySQL 8.0.13.

• metadata_locks_hash_instances

  Command-Line Format	--metadata-locks-hash-instances=#
  Deprecated	Yes (removed in 8.0.13)
  System Variable	metadata_locks_hash_instances
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	8
  Minimum Value	1
  Maximum Value	1024

  This system variable was removed in MySQL 8.0.13.

• min_examined_row_limit

  Command-Line Format	--min-examined-row-limit=#
  System Variable	min_examined_row_limit
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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.

  As of MySQL 8.0.27, 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 7.1.9.1, “System Variable Privileges”.

• myisam_data_pointer_size

  Command-Line Format	--myisam-data-pointer-size=#
  System Variable	myisam_data_pointer_size
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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
  SET_VAR Hint Applies	No
  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
  SET_VAR Hint Applies	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
  SET_VAR Hint Applies	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 18.2.1, “MyISAM Startup Options”.

• myisam_repair_threads

  Command-Line Format	--myisam-repair-threads=#
  Deprecated	8.0.29 (removed in 8.0.30)
  System Variable	myisam_repair_threads
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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 8.0.29 and removed in MySQL 8.0.30.

  From MySQL 8.0.29, 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
  SET_VAR Hint Applies	No
  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
  SET_VAR Hint Applies	No
  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 10.3.8, “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
  SET_VAR Hint Applies	No
  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}]
  Deprecated	8.0.16
  System Variable	mysql_native_password_proxy_users
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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 8.2.19, “Proxy Users”.

• named_pipe

  Command-Line Format	--named-pipe[={OFF|ON}]
  System Variable	named_pipe
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	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	8.0.14
  System Variable	named_pipe_full_access_group
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	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 8.0.24, 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
  SET_VAR Hint Applies	No
  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
  SET_VAR Hint Applies	No
  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 alsoreplica_net_timeout andslave_net_timeout.

• net_retry_count

  Command-Line Format	--net-retry-count=#
  System Variable	net_retry_count
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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
  SET_VAR Hint Applies	No
  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}]
  Deprecated	8.0.35
  System Variable	new
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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.

  This variable is deprecated as of MySQL 8.0.35, and is subject to removal in a future release.

  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
  SET_VAR Hint Applies	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 14.9.8, “ngram Full-Text Parser”.

• offline_mode

  Command-Line Format	--offline-mode[={OFF|ON}]
  System Variable	offline_mode
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  In offline mode, the MySQL instance disconnects client users unless they have relevant privileges, and does not allow them to initiate new connections. Clients that are refused access receive anER_SERVER_OFFLINE_MODE error.

  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. To control offline mode, an administrator account must have theSYSTEM_VARIABLES_ADMIN privilege and theCONNECTION_ADMIN privilege (or the deprecatedSUPER privilege, which covers both these privileges).CONNECTION_ADMIN is required from MySQL 8.0.31 and recommended in all releases to prevent accidental lockout.

  Offline mode has these characteristics:

  • Connected client users who do not have theCONNECTION_ADMIN privilege (or the deprecatedSUPER 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 theCONNECTION_ADMIN orSUPER privilege are not disconnected, and can initiate new connections to manage the server.

  • From MySQL 8.0.30, if the user that puts a server in offline mode does not have theSYSTEM_USER privilege, connected client users who have theSYSTEM_USER privilege are also not disconnected. However, these users cannot initiate new connections to the server while it is in offline mode, unless they have theCONNECTION_ADMIN orSUPER privilege as well. It is only their existing connection that cannot be terminated, because theSYSTEM_USER privilege is required to kill a session or statement that is executing with theSYSTEM_USER privilege.

  • Replication threads are permitted to keep applying data to the server.

• old

  Command-Line Format	--old[={OFF|ON}]
  Deprecated	8.0.35
  System Variable	old
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	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 10.9.4, “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.

  This variable is deprecated as of MySQL 8.0.35, and is subject to removal in a future release.

• old_alter_table

  Command-Line Format	--old-alter-table[={OFF|ON}]
  System Variable	old_alter_table
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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 15.1.9, “ALTER TABLE Statement”.

  ALTER TABLE ... DROP PARTITION withold_alter_table=ON rebuilds the partitioned table and attempts to move data from the dropped partition to another partition with a compatiblePARTITION ... VALUES definition. Data that cannot be moved to another partition is deleted. In earlier releases,ALTER TABLE ... DROP PARTITION withold_alter_table=ON deletes data stored in the partition and drops the partition.

• open_files_limit

  Command-Line Format	--open-files-limit=#
  System Variable	open_files_limit
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	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). Using the defaults for these variables yields 8161.

    On Windows only, 2048 (the value of the C Run-Time Library file descriptor maximum) is added to this number. This totals 10209, again using the default values for the indicated system variables.

  • max_connections * 5

  • MySQL 8.0.19 and higher: The operating system limit.

  • Prior to MySQL 8.0.19:

    • 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, capped to the maximum unsigned integer value. 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
  SET_VAR Hint Applies	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
  SET_VAR Hint Applies	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
  SET_VAR Hint Applies	Yes
  Type	Set
  Valid Values (≥ 8.0.22)	batched_key_access={on|off} block_nested_loop={on|off} condition_fanout_filter={on|off} derived_condition_pushdown={on|off} derived_merge={on|off} duplicateweedout={on|off} engine_condition_pushdown={on|off} firstmatch={on|off} hash_join={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} skip_scan={on|off} subquery_materialization_cost_based={on|off} subquery_to_derived={on|off} use_index_extensions={on|off} use_invisible_indexes={on|off}
  Valid Values (≥ 8.0.21, ≤ 8.0.22)	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} hash_join={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} skip_scan={on|off} subquery_materialization_cost_based={on|off} subquery_to_derived={on|off} use_index_extensions={on|off} use_invisible_indexes={on|off}
  Valid Values (≥ 8.0.18, ≤ 8.0.20)	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} hash_join={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} skip_scan={on|off} subquery_materialization_cost_based={on|off} use_index_extensions={on|off} use_invisible_indexes={on|off}
  Valid Values (≥ 8.0.13, ≤ 8.0.17)	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} skip_scan={on|off} subquery_materialization_cost_based={on|off} use_index_extensions={on|off} use_invisible_indexes={on|off}
  Valid Values (≤ 8.0.12)	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} use_invisible_indexes={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,use_invisible_indexes=off,skip_scan=on,                    hash_join=on,subquery_to_derived=off,                    prefer_ordering_index=on,hypergraph_optimizer=off,                    derived_condition_pushdown=on

  For more information about the syntax of this variable and the optimizer behaviors that it controls, seeSection 10.9.2, “Switchable Optimizations”.

• optimizer_trace

  Command-Line Format	--optimizer-trace=value
  System Variable	optimizer_trace
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	String

  This variable controls optimizer tracing. For details, seeSection 10.15, “Tracing the Optimizer”.

• optimizer_trace_features

  Command-Line Format	--optimizer-trace-features=value
  System Variable	optimizer_trace_features
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	String

  This variable enables or disables selected optimizer tracing features. For details, seeSection 10.15, “Tracing the Optimizer”.

• optimizer_trace_limit

  Command-Line Format	--optimizer-trace-limit=#
  System Variable	optimizer_trace_limit
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	1
  Minimum Value	0
  Maximum Value	2147483647

  The maximum number of optimizer traces to display. For details, seeSection 10.15, “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
  SET_VAR Hint Applies	Yes
  Type	Integer
  Default Value	1048576
  Minimum Value	0
  Maximum Value	4294967295
  Unit	bytes

  The maximum cumulative size of stored optimizer traces. For details, seeSection 10.15, “Tracing the Optimizer”.

• optimizer_trace_offset

  Command-Line Format	--optimizer-trace-offset=#
  System Variable	optimizer_trace_offset
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	-1
  Minimum Value	-2147483647
  Maximum Value	2147483647

  The offset of optimizer traces to display. For details, seeSection 10.15, “Tracing the Optimizer”.

• performance_schema_xxx

  Performance Schema system variables are listed inSection 29.15, “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=#
  System Variable	parser_max_mem_size
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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.

• partial_revokes

  Command-Line Format	--partial-revokes[={OFF|ON}]
  Introduced	8.0.16
  System Variable	partial_revokes
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF (if partial revokes do not exist) ON (if partial revokes exist)

  Enabling this variable makes it possible to revoke privileges partially. Specifically, for users who have privileges at the global level,partial_revokes enables privileges for specific schemas to be revoked while leaving the privileges in place for other schemas. For example, a user who has the globalUPDATE privilege can be restricted from exercising this privilege on themysql system schema. (Or, stated another way, the user is enabled to exercise theUPDATE privilege on all schemas except themysql schema.) In this sense, the user's globalUPDATE privilege is partially revoked.

  Once enabled,partial_revokes cannot be disabled if any account has privilege restrictions. If any such account exists, disablingpartial_revokes fails:

  • For attempts to disablepartial_revokes at startup, the server logs an error message and enablespartial_revokes.

  • For attempts to disablepartial_revokes at runtime, an error occurs and thepartial_revokes value remains unchanged.

  To disablepartial_revokes in this case, first modify each account that has partially revoked privileges, either by re-granting the privileges or by removing the account.

  Note

  In privilege assignments, enablingpartial_revokes causes MySQL to interpret occurrences of unescaped_ and% SQL wildcard characters in schema names as literal characters, just as if they had been escaped as\_ and\%. Because this changes how MySQL interprets privileges, it may be advisable to avoid unescaped wildcard characters in privilege assignments for installations wherepartial_revokes may be enabled.

  In addition, use of_ and% as wildcard characters in grants is deprecated as of MySQL 8.0.35, and you should expect support for them to be removed in a future version of MySQL.

  For more information, including instructions for removing partial revokes, seeSection 8.2.12, “Privilege Restriction Using Partial Revokes”.

• password_history

  Command-Line Format	--password-history=#
  System Variable	password_history
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	0
  Minimum Value	0
  Maximum Value	4294967295

  This variable defines the global policy for controlling reuse of previous passwords based on required minimum number of password changes. For an account password used previously, this variable indicates the number of subsequent account password changes that must occur before the password can be reused. If the value is 0 (the default), there is no reuse restriction based on number of password changes.

  Changes to this variable apply immediately to all accounts defined with thePASSWORD HISTORY DEFAULT option.

  The global number-of-changes password reuse policy can be overridden as desired for individual accounts using thePASSWORD HISTORY option of theCREATE USER andALTER USER statements. SeeSection 8.2.15, “Password Management”.

• password_require_current

  Command-Line Format	--password-require-current[={OFF|ON}]
  Introduced	8.0.13
  System Variable	password_require_current
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  This variable defines the global policy for controlling whether attempts to change an account password must specify the current password to be replaced.

  Changes to this variable apply immediately to all accounts defined with thePASSWORD REQUIRE CURRENT DEFAULT option.

  The global verification-required policy can be overridden as desired for individual accounts using thePASSWORD REQUIRE option of theCREATE USER andALTER USER statements. SeeSection 8.2.15, “Password Management”.

• password_reuse_interval

  Command-Line Format	--password-reuse-interval=#
  System Variable	password_reuse_interval
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	0
  Minimum Value	0
  Maximum Value	4294967295
  Unit	days

  This variable defines the global policy for controlling reuse of previous passwords based on time elapsed. For an account password used previously, this variable indicates the number of days that must pass before the password can be reused. If the value is 0 (the default), there is no reuse restriction based on time elapsed.

  Changes to this variable apply immediately to all accounts defined with thePASSWORD REUSE INTERVAL DEFAULT option.

  The global time-elapsed password reuse policy can be overridden as desired for individual accounts using thePASSWORD REUSE INTERVAL option of theCREATE USER andALTER USER statements. SeeSection 8.2.15, “Password Management”.

• persisted_globals_load

  Command-Line Format	--persisted-globals-load[={OFF|ON}]
  System Variable	persisted_globals_load
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  Whether to load persisted configuration settings from themysqld-auto.cnf file in the data directory. The server normally processes this file at startup after all other option files (seeSection 6.2.2.2, “Using Option Files”). Disablingpersisted_globals_load causes the server startup sequence to skipmysqld-auto.cnf.

  To modify the contents ofmysqld-auto.cnf, use theSET PERSIST,SET PERSIST_ONLY, andRESET PERSIST statements. SeeSection 7.1.9.3, “Persisted System Variables”.

• persist_only_admin_x509_subject

  Command-Line Format	--persist-only-admin-x509-subject=string
  Introduced	8.0.14
  System Variable	persist_only_admin_x509_subject
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	String
  Default Value	empty string

  SET PERSIST andSET PERSIST_ONLY enable system variables to be persisted to themysqld-auto.cnf option file in the data directory (seeSection 15.7.6.1, “SET Syntax for Variable Assignment”). Persisting system variables enables runtime configuration changes that affect subsequent server restarts, which is convenient for remote administration not requiring direct access to MySQL server host option files. However, some system variables are nonpersistible or can be persisted only under certain restrictive conditions.

  Thepersist_only_admin_x509_subject system variable specifies the SSL certificate X.509 Subject value that users must have to be able to persist system variables that are persist-restricted. The default value is the empty string, which disables the Subject check so that persist-restricted system variables cannot be persisted by any user.

  Ifpersist_only_admin_x509_subject is nonempty, users who connect to the server using an encrypted connection and supply an SSL certificate with the designated Subject value then can useSET PERSIST_ONLY to persist persist-restricted system variables. For information about persist-restricted system variables and instructions for configuring MySQL to enablepersist_only_admin_x509_subject, seeSection 7.1.9.4, “Nonpersistible and Persist-Restricted System Variables”.

• persist_sensitive_variables_in_plaintext

  Command-Line Format	--persist_sensitive_variables_in_plaintext[={OFF|ON}]
  Introduced	8.0.29
  System Variable	persist_sensitive_variables_in_plaintext
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  persist_sensitive_variables_in_plaintext controls whether the server is permitted to store the values of sensitive system variables in an unencrypted format, if keyring component support is not available at the time whenSET PERSIST is used to set the value of the system variable. It also controls whether or not the server can start if the encrypted values cannot be decrypted. Note that keyring plugins do not support secure storage of sensitive system variables; a keyring component (seeSection 8.4.4, “The MySQL Keyring”) must be enabled on the MySQL Server instance to support secure storage.

  The default setting,ON, encrypts the values if keyring component support is available, and persists them unencrypted (with a warning) if it is not. The next time any persisted system variable is set, if keyring support is available at that time, the server encrypts the values of any unencrypted sensitive system variables. TheON setting also allows the server to start if encrypted system variable values cannot be decrypted, in which case a warning is issued and the default values for the system variables are used. In that situation, their values cannot be changed until they can be decrypted.

  The most secure setting,OFF, means sensitive system variable values cannot be persisted if keyring component support is unavailable. TheOFF setting also means the server does not start if encrypted system variable values cannot be decrypted.

  For more information, seePersisting Sensitive System Variables.

• pid_file

  Command-Line Format	--pid-file=file_name
  System Variable	pid_file
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	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 7.4.2, “The Error Log”.

• plugin_dir

  Command-Line Format	--plugin-dir=dir_name
  System Variable	plugin_dir
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	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
  SET_VAR Hint Applies	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
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	32768
  Minimum Value	1024
  Maximum Value	1073741824
  Unit	bytes

  The size of the buffer that is allocated when preloading indexes.

  As of MySQL 8.0.27, 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 7.1.9.1, “System Variable Privileges”.

• print_identified_with_as_hex

  Command-Line Format	--print-identified-with-as-hex[={OFF|ON}]
  Introduced	8.0.17
  System Variable	print_identified_with_as_hex
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  Password hash values displayed in theIDENTIFIED WITH clause of output fromSHOW CREATE USER may contain unprintable characters that have adverse effects on terminal displays and in other environments. Enablingprint_identified_with_as_hex causesSHOW CREATE USER to display such hash values as hexadecimal strings rather than as regular string literals. Hash values that do not contain unprintable characters still display as regular string literals, even with this variable enabled.

• 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 15.7.7.31, “SHOW PROFILES Statement”.

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

• 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 15.7.7.31, “SHOW PROFILES Statement”.

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

• protocol_compression_algorithms

  Command-Line Format	--protocol-compression-algorithms=value
  Introduced	8.0.18
  System Variable	protocol_compression_algorithms
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Set
  Default Value	zlib,zstd,uncompressed
  Valid Values	zlib zstd uncompressed

  The compression algorithms that the server permits for incoming connections. These include connections by client programs and by servers participating in source/replica replication or Group Replication. Compression does not apply to connections forFEDERATED tables.

  protocol_compression_algorithms does not control connection compression for X Protocol. SeeSection 22.5.5, “Connection Compression with X Plugin” for information on how this operates.

  The variable value is a list of one or more comma-separated compression algorithm names, in any order, chosen from the following items (not case-sensitive):

  • zlib: Permit connections that use thezlib compression algorithm.

  • zstd: Permit connections that use thezstd compression algorithm.

  • uncompressed: Permit uncompressed connections. If this algorithm name is not included in theprotocol_compression_algorithms value, the server does not permit uncompressed connections. It permits only compressed connections that use whichever other algorithms are specified in the value, and there is no fallback to uncompressed connections.

  The default value ofzlib,zstd,uncompressed indicates that the server permits all compression algorithms.

  For more information, seeSection 6.2.8, “Connection Compression Control”.

• protocol_version

  System Variable	protocol_version
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	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
  SET_VAR Hint Applies	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 8.2.19, “Proxy Users”.

• pseudo_replica_mode

  Introduced	8.0.26
  System Variable	pseudo_replica_mode
  Scope	Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean

  From MySQL 8.0.26,pseudo_replica_mode is used in place ofpseudo_slave_mode, which is deprecated from that release. The operation and effects are the same, only the terminology has changed.

  pseudo_replica_mode is for internal server use. It 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_replica_mode to true before executing any SQL statements.

  Setting the session value ofpseudo_replica_mode is a restricted operation. The session user must have either theREPLICATION_APPLIER privilege (seeSection 19.3.3, “Replication Privilege Checks”), or privileges sufficient to set restricted session variables (seeSection 7.1.9.1, “System Variable Privileges”). However, note that the variable is not intended for users to set; it is set automatically by the replication infrastructure.

  pseudo_replica_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_replica_mode has the following effects on theoriginal_commit_timestamp replication delay timestamp and theoriginal_server_version system variable:

  • If true, transactions that do not explicitly setoriginal_commit_timestamp ororiginal_server_version are assumed to originate on another, unknown server, so the value 0, meaning unknown, is assigned to both the timestamp and the system variable.

  • If false, transactions that do not explicitly setoriginal_commit_timestamp ororiginal_server_version are assumed to originate on the current server, so the current timestamp and the current server's version are assigned to the timestamp and the system variable.

  In MySQL 8.0.14 and later,pseudo_replica_mode has the following effects on the handling of a statement that sets one or more unsupported (removed or unknown) SQL modes:

  • If true, the server ignores the unsupported mode and raises a warning.

  • If false, the server rejects the statement withER_UNSUPPORTED_SQL_MODE.

• pseudo_slave_mode

  Deprecated	8.0.26
  System Variable	pseudo_slave_mode
  Scope	Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean

  From MySQL 8.0.26,pseudo_slave_mode is deprecated and the aliaspseudo_replica_mode is used instead.pseudo_slave_mode is for internal server use. It 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.

  Setting the session value of this system variable is a restricted operation. The session user must have either theREPLICATION_APPLIER privilege (seeSection 19.3.3, “Replication Privilege Checks”), or privileges sufficient to set restricted session variables (seeSection 7.1.9.1, “System Variable Privileges”). However, note that the variable is not intended for users to set; it is set automatically by the replication infrastructure.

  See the description of thepseudo_replica_mode system variable for the effects ofpseudo_slave_mode.

• pseudo_thread_id

  System Variable	pseudo_thread_id
  Scope	Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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.

  As of MySQL 8.0.14, 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 7.1.9.1, “System Variable Privileges”.

• query_alloc_block_size

  Command-Line Format	--query-alloc-block-size=#
  System Variable	query_alloc_block_size
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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_prealloc_size

  Command-Line Format	--query-prealloc-size=#
  Deprecated	8.0.29
  System Variable	query_prealloc_size
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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

  MySQL 8.0.28 and earlier: This sets 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.

  As of MySQL 8.0.29,query_prealloc_size is deprecated, and setting it no longer has any effect; you should expect its removal in a future release of MySQL.

• rand_seed1

  System Variable	rand_seed1
  Scope	Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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
  SET_VAR Hint Applies	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
  SET_VAR Hint Applies	Yes
  Type	Integer
  Default Value	8388608
  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
  SET_VAR Hint Applies	No
  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;

  As of MySQL 8.0.18, setting the session value of this system variable is no longer a restricted operation.

• read_buffer_size

  Command-Line Format	--read-buffer-size=#
  System Variable	read_buffer_size
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	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 other storage engines with the exception ofInnoDB:

  • 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.

  Beginning with MySQL 8.0.22, the value ofselect_into_buffer_size is used in place of the value ofread_buffer_size for the I/O cache buffer used when executingSELECT INTO DUMPFILE andSELECT INTO OUTFILE statements. (read_buffer_size is used for the I/O cache buffer size in all other cases.)

  For more information about memory use during different operations, seeSection 10.12.3.1, “How MySQL Uses Memory”.

• read_only

  Command-Line Format	--read-only[={OFF|ON}]
  System Variable	read_only
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  If theread_only system variable is enabled, the server permits no client updates except from users who have theCONNECTION_ADMIN privilege (or the deprecatedSUPER 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 theCONNECTION_ADMIN orSUPER privilege.

  • Settingsuper_read_only toON implicitly forcesread_only toON.

  • Settingread_only toOFF implicitly forcessuper_read_only toOFF.

  Whenread_only is enabled and whensuper_read_only is enabled, the server still 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.

  • Writes to the system tablemysql.gtid_executed, which stores GTIDs for executed transactions that are not present in the current binary log file.

  • 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 7.4.1, “Selecting General Query Log and Slow Query Log Output Destinations”.

  • 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
  SET_VAR Hint Applies	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 10.2.1.16, “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 10.12.3.1, “How MySQL Uses Memory”. For information about Multi-Range Read optimization, seeSection 10.2.1.11, “Multi-Range Read Optimization”.

• regexp_stack_limit

  Command-Line Format	--regexp-stack-limit=#
  System Variable	regexp_stack_limit
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	8000000
  Minimum Value	0
  Maximum Value	2147483647
  Unit	bytes

  The maximum available memory in bytes for the internal stack used for regular expression matching operations performed byREGEXP_LIKE() and similar functions (seeSection 14.8.2, “Regular Expressions”).

• regexp_time_limit

  Command-Line Format	--regexp-time-limit=#
  System Variable	regexp_time_limit
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	32
  Minimum Value	0
  Maximum Value	2147483647

  The time limit for regular expression matching operations performed byREGEXP_LIKE() and similar functions (seeSection 14.8.2, “Regular Expressions”). This limit is expressed as the maximum permitted number of steps performed by the match engine, and thus affects execution time only indirectly. Typically, it is on the order of milliseconds.

• require_row_format

  Introduced	8.0.19
  System Variable	require_row_format
  Scope	Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  This variable is for internal server use by replication andmysqlbinlog. It restricts DML events executed in the session to events encoded in row-based binary logging format only, and temporary tables cannot be created. Queries that do not respect the restrictions fail.

  Setting the session value of this system variable toON requires no privileges. Setting the session value of this system variable toOFF is a restricted operation, and the session user must have privileges sufficient to set restricted session variables. SeeSection 7.1.9.1, “System Variable Privileges”.

• require_secure_transport

  Command-Line Format	--require-secure-transport[={OFF|ON}]
  System Variable	require_secure_transport
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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.

  All replication group members should have the same value for this variable; otherwise, some members may not be able to join.

  See alsoConfiguring Encrypted Connections as Mandatory.

• resultset_metadata

  System Variable	resultset_metadata
  Scope	Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Enumeration
  Default Value	FULL
  Valid Values	FULL NONE

  For connections for which metadata transfer is optional, the client sets theresultset_metadata system variable to control whether the server returns result set metadata. Permitted values areFULL (return all metadata; this is the default) andNONE (return no metadata).

  For connections that are not metadata-optional, settingresultset_metadata toNONE produces an error.

  For details about managing result set metadata transfer, seeOptional Result Set Metadata.

• secondary_engine_cost_threshold

  Introduced	8.0.16
  System Variable	secondary_engine_cost_threshold
  Scope	Session
  Dynamic	Yes
  SET_VAR Hint Applies	Yes
  Type	Numeric
  Default Value	100000.000000
  Minimum Value	0
  Maximum Value	DBL_MAX (maximum double value)

  The optimizer cost threshold for query offload to a secondary engine.

  For use with HeatWave. SeeHeatWave User Guide.

• schema_definition_cache

  Command-Line Format	--schema-definition-cache=#
  System Variable	schema_definition_cache
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	256
  Minimum Value	256
  Maximum Value	524288

  Defines a limit for the number of schema definition objects, both used and unused, that can be kept in the dictionary object cache.

  Unused schema definition objects are only kept in the dictionary object cache when the number in use is less than the capacity defined byschema_definition_cache.

  A setting of0 means that schema definition objects are only kept in the dictionary object cache while they are in use.

  For more information, seeSection 16.4, “Dictionary Object Cache”.

• secure_file_priv

  Command-Line Format	--secure-file-priv=dir_name
  System Variable	secure_file_priv
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	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	empty
  DEB,RPM,SVR4	/var/lib/mysql-files
  Otherwise	mysql-files under theCMAKE_INSTALL_PREFIX value

  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.

• select_into_buffer_size

  Command-Line Format	--select-into-buffer-size=#
  Introduced	8.0.22
  System Variable	select_into_buffer_size
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	Yes
  Type	Integer
  Default Value	131072
  Minimum Value	8192
  Maximum Value	2147479552
  Unit	bytes
  Block Size	4096

  When usingSELECT INTO OUTFILE orSELECT INTO DUMPFILE to dump data into one or more files for backup creation, data migration, or other purposes, writes can often be buffered and then trigger a large burst of write I/O activity to the disk or other storage device and stall other queries that are more sensitive to latency. You can use this variable to control the size of the buffer used to write data to the storage device to determine when buffer synchronization should occur, and thus to prevent write stalls of the kind just described from occurring.

  select_into_buffer_size overrides any value set forread_buffer_size. (select_into_buffer_size andread_buffer_size have the same default, maximum, and minimum values.) You can also useselect_into_disk_sync_delay to set a timeout to be observed afterwards, each time synchronization takes place.

  As of MySQL 8.0.27, 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 7.1.9.1, “System Variable Privileges”.

• select_into_disk_sync

  Command-Line Format	--select-into-disk-sync={ON|OFF}
  Introduced	8.0.22
  System Variable	select_into_disk_sync
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	Yes
  Type	Boolean
  Default Value	OFF
  Valid Values	OFF ON

  When set onON, enables buffer synchronization of writes to an output file by a long-runningSELECT INTO OUTFILE orSELECT INTO DUMPFILE statement usingselect_into_buffer_size.

• select_into_disk_sync_delay

  Command-Line Format	--select-into-disk-sync-delay=#
  Introduced	8.0.22
  System Variable	select_into_disk_sync_delay
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	Yes
  Type	Integer
  Default Value	0
  Minimum Value	0
  Maximum Value	31536000
  Unit	milliseconds

  When buffer synchronization of writes to an output file by a long-runningSELECT INTO OUTFILE orSELECT INTO DUMPFILE statement is enabled byselect_into_disk_sync, this variable sets an optional delay (in milliseconds) following synchronization.0 (the default) means no delay.

  As of MySQL 8.0.27, 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 7.1.9.1, “System Variable Privileges”.

• session_track_gtids

  Command-Line Format	--session-track-gtids=value
  System Variable	session_track_gtids
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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 7.1.18, “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
  SET_VAR Hint Applies	No
  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 7.1.18, “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
  SET_VAR Hint Applies	No
  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 7.1.18, “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
  SET_VAR Hint Applies	No
  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.)

  To enable display of the Statement ID for each statement processed, use thestatement_id variable. For example:

  mysql>  SET @@SESSION.session_track_system_variables='statement_id'mysql>  SELECT 1;+---+| 1 |+---+| 1 |+---+1 row in set (0.0006 sec)Statement ID: 603835

  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. This value also enables display of the Statement ID for each successful statement processed.

  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 7.1.18, “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
  SET_VAR Hint Applies	No
  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 7.1.18, “Server Tracking of Client Session State”.

• sha256_password_auto_generate_rsa_keys

  Command-Line Format	--sha256-password-auto-generate-rsa-keys[={OFF|ON}]
  Deprecated	8.0.16
  System Variable	sha256_password_auto_generate_rsa_keys
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  The server uses this variable to determine whether to autogenerate 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 all of these conditions are true: Thesha256_password_auto_generate_rsa_keys orcaching_sha2_password_auto_generate_rsa_keys system variable is enabled; no RSA options are specified; the RSA files are missing from the data directory. These key-pair files enable secure password exchange using RSA over unencrypted connections for accounts authenticated by thesha256_password orcaching_sha2_password plugin; seeSection 8.4.1.3, “SHA-256 Pluggable Authentication”, andSection 8.4.1.2, “Caching SHA-2 Pluggable Authentication”.

  For more information about RSA file autogeneration, including file names and characteristics, seeSection 8.3.3.1, “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
  Deprecated	8.0.16
  System Variable	sha256_password_private_key_path
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	File name
  Default Value	private_key.pem

  The value of this variable 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 8.4.1.3, “SHA-256 Pluggable Authentication”.

• sha256_password_proxy_users

  Command-Line Format	--sha256-password-proxy-users[={OFF|ON}]
  Deprecated	8.0.16
  System Variable	sha256_password_proxy_users
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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 8.2.19, “Proxy Users”.

• sha256_password_public_key_path

  Command-Line Format	--sha256-password-public-key-path=file_name
  Deprecated	8.0.16
  System Variable	sha256_password_public_key_path
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	File name
  Default Value	public_key.pem

  The value of this variable 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 8.4.1.3, “SHA-256 Pluggable Authentication”.

• shared_memory

  Command-Line Format	--shared-memory[={OFF|ON}]
  System Variable	shared_memory
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	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
  SET_VAR Hint Applies	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_create_table_skip_secondary_engine

  Command-Line Format	--show-create-table-skip-secondary-engine[={OFF|ON}]
  Introduced	8.0.18
  System Variable	show_create_table_skip_secondary_engine
  Scope	Session
  Dynamic	Yes
  SET_VAR Hint Applies	Yes
  Type	Boolean
  Default Value	OFF

  Enablingshow_create_table_skip_secondary_engine causes theSECONDARY ENGINE clause to be excluded fromSHOW CREATE TABLE output, and fromCREATE TABLE statements dumped by themysqldump utility.

  mysqldump provides the--show-create-skip-secondary-engine option. When specified, it enables theshow_create_table_skip_secondary_engine system variable for the duration of the dump operation.

  Attempting amysqldump operation with the--show-create-skip-secondary-engine option on a release prior to MySQL 8.0.18 that does not support theshow_create_table_skip_secondary_engine variable causes an error.

  For use with HeatWave. SeeHeatWave User Guide.

• show_create_table_verbosity

  Command-Line Format	--show-create-table-verbosity[={OFF|ON}]
  System Variable	show_create_table_verbosity
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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_gipk_in_create_table_and_information_schema

  Command-Line Format	--show-gipk-in-create-table-and-information-schema[={OFF|ON}]
  Introduced	8.0.30
  System Variable	show_gipk_in_create_table_and_information_schema
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  Whether generated invisible primary keys are visible in the output ofSHOW statements and in Information Schema tables. When this variable is set toOFF, such keys are not shown.

  This variable is not replicated.

  For more information, seeSection 15.1.20.11, “Generated Invisible Primary Keys”.

• show_old_temporals

  Command-Line Format	--show-old-temporals[={OFF|ON}]
  Deprecated	Yes
  System Variable	show_old_temporals
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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=utf8mb4 COLLATE=utf8mb4_0900_ai_ci

  Output for theCOLUMN_TYPE column of the Information SchemaCOLUMNS table is affected similarly.

  This variable is deprecated and subject to removal in a future MySQL release.

  As of MySQL 8.0.27, 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 7.1.9.1, “System Variable Privileges”.

• skip_external_locking

  Command-Line Format	--skip-external-locking[={OFF|ON}]
  System Variable	skip_external_locking
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	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 10.11.5, “External Locking”.

• skip_name_resolve

  Command-Line Format	--skip-name-resolve[={OFF|ON}]
  System Variable	skip_name_resolve
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	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 7.1.12.3, “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
  SET_VAR Hint Applies	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 7.1.12.3, “DNS Lookups and the Host Cache”.

  Because starting the server with--skip-grant-tables disables authentication checks, the server also disables remote connections in that case by enablingskip_networking.

• skip_show_database

  Command-Line Format	--skip-show-database
  System Variable	skip_show_database
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	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 any static global privilege is considered a privilege for all databases, any static global privilege enables a user to see all database names withSHOW DATABASES or by examining theSCHEMATA table ofINFORMATION_SCHEMA, except databases that have been restricted at the database level by partial revokes.

• slow_launch_time

  Command-Line Format	--slow-launch-time=#
  System Variable	slow_launch_time
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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
  SET_VAR Hint Applies	No
  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 7.4.5, “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
  SET_VAR Hint Applies	No
  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
  SET_VAR Hint Applies	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
  SET_VAR Hint Applies	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 10.2.1.16, “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 perform sorts. 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
  SET_VAR Hint Applies	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 14.15, “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.

  Prior to MySQL 8.0.16, the transformation ofWHEREauto_col IS NULL toWHEREauto_col = LAST_INSERT_ID() was performed only when the statement was executed, so that the value ofsql_auto_is_null during execution determined whether the query was transformed. In MySQL 8.0.16 and later, the transformation is performed during statement preparation.

  The default value ofsql_auto_is_null isOFF.

• sql_big_selects

  System Variable	sql_big_selects
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	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
  SET_VAR Hint Applies	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_generate_invisible_primary_key

  Command-Line Format	--sql-generate-invisible-primary-key[={OFF|ON}]
  Introduced	8.0.30
  System Variable	sql_generate_invisible_primary_key
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  Whether this server adds a generated invisible primary key to anyInnoDB table that is created without one.

  This variable is not replicated. In addition, even if set on the replica, it is ignored by replication applier threads; this means that, by default, a replica does not generate a primary key for any replicated table which, on the source, was created without one. In MySQL 8.0.32 and later, you can cause the replica to generate invisible primary keys for such tables by settingREQUIRE_TABLE_PRIMARY_KEY_CHECK = GENERATE as part of aCHANGE REPLICATION SOURCE TO statement, optionally specifying a replication channel.

  For more information and examples, seeSection 15.1.20.11, “Generated Invisible Primary Keys”.

• sql_log_off

  System Variable	sql_log_off
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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 7.1.9.1, “System Variable Privileges”.

• sql_mode

  Command-Line Format	--sql-mode=name
  System Variable	sql_mode
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	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_ENGINE_SUBSTITUTION
  Valid Values	ALLOW_INVALID_DATES ANSI_QUOTES ERROR_FOR_DIVISION_BY_ZERO HIGH_NOT_PRECEDENCE IGNORE_SPACE NO_AUTO_VALUE_ON_ZERO NO_BACKSLASH_ESCAPES NO_DIR_IN_CREATE NO_ENGINE_SUBSTITUTION 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 TIME_TRUNCATE_FRACTIONAL

  The current server SQL mode, which can be set dynamically. For details, seeSection 7.1.11, “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
  SET_VAR Hint Applies	No
  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
  SET_VAR Hint Applies	No
  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 15.7.7.10, “SHOW CREATE TABLE Statement”, andSection 15.7.7.6, “SHOW CREATE DATABASE Statement”.

• sql_require_primary_key

  Command-Line Format	--sql-require-primary-key[={OFF|ON}]
  Introduced	8.0.13
  System Variable	sql_require_primary_key
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	Yes
  Type	Boolean
  Default Value	OFF

  Whether statements that create new tables or alter the structure of existing tables enforce the requirement that tables have a primary key.

  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 7.1.9.1, “System Variable Privileges”.

  Enabling this variable helps avoid performance problems in row-based replication that can occur when tables have no primary key. Suppose that a table has no primary key and an update or delete modifies multiple rows. On the replication source server, this operation can be performed using a single table scan but, when replicated using row-based replication, results in a table scan for each row to be modified on the replica. With a primary key, these table scans do not occur.

  sql_require_primary_key applies to both base tables andTEMPORARY tables, and changes to its value are replicated to replica servers. As of MySQL 8.0.18, it applies only to storage engines that can participate in replication.

  When enabled,sql_require_primary_key has these effects:

  • Attempts to create a new table with no primary key fail with an error. This includesCREATE TABLE ... LIKE. It also includesCREATE TABLE ... SELECT, unless theCREATE TABLE part includes a primary key definition.

  • Attempts to drop the primary key from an existing table fail with an error, with the exception that dropping the primary key and adding a primary key in the sameALTER TABLE statement is permitted.

    Dropping the primary key fails even if the table also contains aUNIQUE NOT NULL index.

  • Attempts to import a table with no primary key fail with an error.

  TheREQUIRE_TABLE_PRIMARY_KEY_CHECK option of theCHANGE REPLICATION SOURCE TO statement (MySQL 8.0.23 and later) orCHANGE MASTER TO statement (before MySQL 8.0.23) enables a replica to select its own policy for primary key checks. When the option is set toON for a replication channel, the replica always uses the valueON for thesql_require_primary_key system variable in replication operations, requiring a primary key. When the option is set toOFF, the replica always uses the valueOFF for thesql_require_primary_key system variable in replication operations, so that a primary key is never required, even if the source required one. When theREQUIRE_TABLE_PRIMARY_KEY_CHECK option is set toSTREAM, which is the default, the replica uses whatever value is replicated from the source for each transaction. With theSTREAM setting for theREQUIRE_TABLE_PRIMARY_KEY_CHECK option, if privilege checks are in use for the replication channel, thePRIVILEGE_CHECKS_USER account needs privileges sufficient to set restricted session variables, so that it can set the session value for thesql_require_primary_key system variable. With theON orOFF settings, the account does not need these privileges. For more information, seeSection 19.3.3, “Replication Privilege Checks”.

• sql_safe_updates

  System Variable	sql_safe_updates
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	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
  SET_VAR Hint Applies	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
  SET_VAR Hint Applies	No
  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 (≥ 8.0.16)	Yes
  Dynamic (≤ 8.0.15)	No
  SET_VAR Hint Applies	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.

  As of MySQL 8.0.16, this variable is dynamic and can be modified at runtime to affect the TLS context the server uses for new connections established after the execution ofALTER INSTANCE RELOAD TLS or after a restart if the variable value was persisted. SeeServer-Side Runtime Configuration and Monitoring for Encrypted Connections. Prior to MySQL 8.0.16, this variable can be set only at server startup.

• ssl_capath

  Command-Line Format	--ssl-capath=dir_name
  System Variable	ssl_capath
  Scope	Global
  Dynamic (≥ 8.0.16)	Yes
  Dynamic (≤ 8.0.15)	No
  SET_VAR Hint Applies	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.

  As of MySQL 8.0.16, this variable is dynamic and can be modified at runtime to affect the TLS context the server uses for new connections established after the execution ofALTER INSTANCE RELOAD TLS or after a restart if the variable value was persisted. SeeServer-Side Runtime Configuration and Monitoring for Encrypted Connections. Prior to MySQL 8.0.16, this variable can be set only at server startup.

• ssl_cert

  Command-Line Format	--ssl-cert=file_name
  System Variable	ssl_cert
  Scope	Global
  Dynamic (≥ 8.0.16)	Yes
  Dynamic (≤ 8.0.15)	No
  SET_VAR Hint Applies	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.

  As of MySQL 8.0.16, this variable is dynamic and can be modified at runtime to affect the TLS context the server uses for new connections established after the execution ofALTER INSTANCE RELOAD TLS or after a restart if the variable value was persisted. SeeServer-Side Runtime Configuration and Monitoring for Encrypted Connections. Prior to MySQL 8.0.16, this variable can be set only at server startup.

  Note

  Chained SSL certificate support was added in v8.0.30; previously only the first certificate was read.

• ssl_cipher

  Command-Line Format	--ssl-cipher=name
  System Variable	ssl_cipher
  Scope	Global
  Dynamic (≥ 8.0.16)	Yes
  Dynamic (≤ 8.0.15)	No
  SET_VAR Hint Applies	No
  Type	String
  Default Value	NULL

  The list of permissible encryption ciphers for connections that use TLS protocols up through TLSv1.2. If no cipher in the list is supported, encrypted connections that use these TLS protocols do not work.

  For greatest portability, the cipher list should be a list of one or more cipher names, separated by colons. The following example shows two cipher names separated by a colon:

  [mysqld]ssl_cipher="DHE-RSA-AES128-GCM-SHA256:AES128-SHA"

  OpenSSL supports the syntax for specifying ciphers described in the OpenSSL documentation athttps://www.openssl.org/docs/manmaster/man1/ciphers.html.

  For information about which encryption ciphers MySQL supports, seeSection 8.3.2, “Encrypted Connection TLS Protocols and Ciphers”.

  As of MySQL 8.0.16, this variable is dynamic and can be modified at runtime to affect the TLS context the server uses for new connections established after the execution ofALTER INSTANCE RELOAD TLS or after a restart if the variable value was persisted. SeeServer-Side Runtime Configuration and Monitoring for Encrypted Connections. Prior to MySQL 8.0.16, this variable can be set only at server startup.

• ssl_crl

  Command-Line Format	--ssl-crl=file_name
  System Variable	ssl_crl
  Scope	Global
  Dynamic (≥ 8.0.16)	Yes
  Dynamic (≤ 8.0.15)	No
  SET_VAR Hint Applies	No
  Type	File name
  Default Value	NULL

  The path name of the file containing certificate revocation lists in PEM format.

  As of MySQL 8.0.16, this variable is dynamic and can be modified at runtime to affect the TLS context the server uses for new connections established after the execution ofALTER INSTANCE RELOAD TLS or after a restart if the variable value was persisted. SeeServer-Side Runtime Configuration and Monitoring for Encrypted Connections. Prior to MySQL 8.0.16, this variable can be set only at server startup.

• ssl_crlpath

  Command-Line Format	--ssl-crlpath=dir_name
  System Variable	ssl_crlpath
  Scope	Global
  Dynamic (≥ 8.0.16)	Yes
  Dynamic (≤ 8.0.15)	No
  SET_VAR Hint Applies	No
  Type	Directory name
  Default Value	NULL

  The path of the directory that contains certificate revocation-list files in PEM format.

  As of MySQL 8.0.16, this variable is dynamic and can be modified at runtime to affect the TLS context the server uses for new connections established after the execution ofALTER INSTANCE RELOAD TLS or after a restart if the variable value was persisted. SeeServer-Side Runtime Configuration and Monitoring for Encrypted Connections. Prior to MySQL 8.0.16, this variable can be set only at server startup.

• ssl_fips_mode

  Command-Line Format	--ssl-fips-mode={OFF|ON|STRICT}
  Deprecated	8.0.34
  System Variable	ssl_fips_mode
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Enumeration
  Default Value	OFF
  Valid Values	OFF (or 0) ON (or 1) STRICT (or 2)

  Controls whether to enable FIPS mode on the server side. Thessl_fips_mode system variable differs from otherssl_xxx system variables in that it is not used to control whether the server permits encrypted connections, but rather to affect which cryptographic operations are permitted. SeeSection 8.8, “FIPS Support”.

  Thesessl_fips_mode values are permitted:

  • OFF (or 0): Disable FIPS mode.

  • ON (or 1): Enable FIPS mode.

  • STRICT (or 2): Enable“strict” FIPS mode.

  Note

  If the OpenSSL FIPS Object Module is not available, the only permitted value forssl_fips_mode isOFF. In this case, settingssl_fips_mode toON orSTRICT at startup causes the server to produce an error message and exit.

  As of MySQL 8.0.34, this option is deprecated and made read-only. Expect it to be removed in a future version of MySQL.

• ssl_key

  Command-Line Format	--ssl-key=file_name
  System Variable	ssl_key
  Scope	Global
  Dynamic (≥ 8.0.16)	Yes
  Dynamic (≤ 8.0.15)	No
  SET_VAR Hint Applies	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.

  As of MySQL 8.0.16, this variable is dynamic and can be modified at runtime to affect the TLS context the server uses for new connections established after the execution ofALTER INSTANCE RELOAD TLS or after a restart if the variable value was persisted. SeeServer-Side Runtime Configuration and Monitoring for Encrypted Connections. Prior to MySQL 8.0.16, this variable can be set only at server startup.

• ssl_session_cache_mode

  Command-Line Format	--ssl_session_cache_mode={ON|OFF}
  Introduced	8.0.29
  System Variable	ssl_session_cache_mode
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON
  Valid Values	ON OFF

  Controls whether to enable the session cache in memory on the server side and session-ticket generation by the server. The default mode isON (enable session cache mode). A change to thessl_session_cache_mode system variable has an effect only after theALTER INSTANCE RELOAD TLS statement has been executed, or after a restart if the variable value was persisted.

  Thesessl_session_cache_mode values are permitted:

  • ON: Enable session cache mode.

  • OFF: Disable session cache mode.

  The server does not advertise its support for session resumption if the value of this system variable isOFF. When running on OpenSSL 1.0.x the session tickets are always generated, but the tickets are not usable whenssl_session_cache_mode is enabled.

  The current value in effect forssl_session_cache_mode can be observed with theSsl_session_cache_mode status variable.

• ssl_session_cache_timeout

  Command-Line Format	--ssl_session_cache_timeout
  Introduced	8.0.29
  System Variable	ssl_session_cache_timeout
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	300
  Minimum Value	0
  Maximum Value	84600
  Unit	seconds

  Sets a period of time during which prior session reuse is permitted when establishing a new encrypted connection to the server, provided thessl_session_cache_mode system variable is enabled and prior session data is available. If the session timeout expires, a session can no longer be reused.

  The default value is 300 seconds and the maximum value is 84600 (or one day in seconds). A change to thessl_session_cache_timeout system variable has an effect only after theALTER INSTANCE RELOAD TLS statement has been executed, or after a restart if the variable value was persisted. The current value in effect forssl_session_cache_timeout can be observed with theSsl_session_cache_timeout status variable.

• statement_id

  System Variable	statement_id
  Scope	Session
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Integer

  Each statement executed in the current session is assigned a sequence number. This can be used together with thesession_track_system_variables system variable to identify this statement in Performance Schema tables such as theevents_statements_history table.

• stored_program_cache

  Command-Line Format	--stored-program-cache=#
  System Variable	stored_program_cache
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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.

  The stored procedure and stored function caches exists in parallel with the stored program definition cache partition of thedictionary object cache. The stored procedure and stored function caches are per connection, while the stored program definition cache is shared. The existence of objects in the stored procedure and stored function caches have no dependence on the existence of objects in the stored program definition cache, and vice versa. For more information, seeSection 16.4, “Dictionary Object Cache”.

• stored_program_definition_cache

  Command-Line Format	--stored-program-definition-cache=#
  System Variable	stored_program_definition_cache
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	256
  Minimum Value	256
  Maximum Value	524288

  Defines a limit for the number of stored program definition objects, both used and unused, that can be kept in the dictionary object cache.

  Unused stored program definition objects are only kept in the dictionary object cache when the number in use is less than the capacity defined bystored_program_definition_cache.

  A setting of 0 means that stored program definition objects are only kept in the dictionary object cache while they are in use.

  The stored program definition cache partition exists in parallel with the stored procedure and stored function caches that are configured using thestored_program_cache option.

  Thestored_program_cache option sets a soft upper limit for the number of cached stored procedures or functions per connection, and the limit is checked each time a connection executes a stored procedure or function. The stored program definition cache partition, on the other hand, is a shared cache that stores stored program definition objects for other purposes. The existence of objects in the stored program definition cache partition has no dependence on the existence of objects in the stored procedure cache or stored function cache, and vice versa.

  For related information, seeSection 16.4, “Dictionary Object Cache”.

• super_read_only

  Command-Line Format	--super-read-only[={OFF|ON}]
  System Variable	super_read_only
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  If theread_only system variable is enabled, the server permits no client updates except from users who have theCONNECTION_ADMIN privilege (or the deprecatedSUPER privilege). If thesuper_read_only system variable is also enabled, the server prohibits client updates even from users who haveCONNECTION_ADMIN orSUPER. 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),INSTALL PLUGIN, andINSTALL COMPONENT. These operations are prohibited because they involve changes to tables in themysql system schema.

  Similarly, if the Event Scheduler is enabled, enabling thesuper_read_only system variable prevents it from updating event“last executed” timestamps in theevents data dictionary table. This causes the Event Scheduler to stop the next time it tries to execute a scheduled event, after writing a message to the server error log. (In this situation theevent_scheduler system variable does not change fromON toOFF. An implication is that this variable rejects the DBAintent that the Event Scheduler be enabled or disabled, where its actual status of started or stopped may be distinct.). Ifsuper_read_only is subsequently disabled after being enabled, the server automatically restarts the Event Scheduler as needed, as of MySQL 8.0.26. Prior to MySQL 8.0.26, it is necessary to manually restart the Event Scheduler by enabling it again.

  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.

• syseventlog.facility

  Command-Line Format	--syseventlog.facility=value
  Introduced	8.0.13
  System Variable	syseventlog.facility
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	String
  Default Value	daemon

  The facility for error log output written tosyslog (what type of program is sending the message). This variable is unavailable unless thelog_sink_syseventlog error log component is installed. SeeSection 7.4.2.8, “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.

• syseventlog.include_pid

  Command-Line Format	--syseventlog.include-pid[={OFF|ON}]
  Introduced	8.0.13
  System Variable	syseventlog.include_pid
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  Whether to include the server process ID in each line of error log output written tosyslog. This variable is unavailable unless thelog_sink_syseventlog error log component is installed. SeeSection 7.4.2.8, “Error Logging to the System Log”.

  This variable does not exist on Windows.

• syseventlog.tag

  Command-Line Format	--syseventlog.tag=tag
  Introduced	8.0.13
  System Variable	syseventlog.tag
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	String
  Default Value	empty string

  The tag to be added to the server identifier in error log output written tosyslog or the Windows Event Log. This variable is unavailable unless thelog_sink_syseventlog error log component is installed. SeeSection 7.4.2.8, “Error Logging to the System Log”.

  By default, no tag is set, so the server identifier is simplyMySQL on Windows, andmysqld on other platforms. If a tag value oftag is specified, it is appended to the server identifier with a leading hyphen, resulting in asyslog identifier ofmysqld-tag (orMySQL-tag on Windows).

  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.

• system_time_zone

  System Variable	system_time_zone
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	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.

  As of MySQL 8.0.26, in addition to startup time initialization, if the server host time zone changes (for example, due to daylight saving time),system_time_zone reflects that change, which has these implications for applications:

  • Queries that referencesystem_time_zone will get one value before a daylight saving change and a different value after the change.

  • For queries that begin executing before a daylight saving change and end after the change, thesystem_time_zone remains constant within the query because the value is usually cached at the beginning of execution.

  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 7.1.15, “MySQL Server Time Zone Support”.

• table_definition_cache

  Command-Line Format	--table-definition-cache=#
  System Variable	table_definition_cache
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	-1 (signifies autosizing; do not assign this literal value)
  Minimum Value	400
  Maximum Value	524288

  The number of table definitions 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:

  MIN(400 + table_open_cache / 2, 2000)

  ForInnoDB, thetable_definition_cache setting acts as a soft limit for the number of table instances in the dictionary object cache and the number file-per-table tablespaces that can be open at one time.

  If the number of table instances in the dictionary object cache exceeds thetable_definition_cache limit, an LRU mechanism begins marking table instances for eviction and eventually removes them from the dictionary object 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.

  The table definition cache exists in parallel with the table definition cache partition of thedictionary object cache. Both caches store table definitions but serve different parts of the MySQL server. Objects in one cache have no dependence on the existence of objects in the other. For more information, seeSection 16.4, “Dictionary Object Cache”.

• table_encryption_privilege_check

  Command-Line Format	--table-encryption-privilege-check[={OFF|ON}]
  Introduced	8.0.16
  System Variable	table_encryption_privilege_check
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  Controls theTABLE_ENCRYPTION_ADMIN privilege check that occurs when creating or altering a schema or general tablespace with encryption that differs from thedefault_table_encryption setting, or when creating or altering a table with an encryption setting that differs from the default schema encryption. The check is disabled by default.

  Settingtable_encryption_privilege_check at runtime requires theSUPER privilege.

  table_encryption_privilege_check supportsSET PERSIST andSET PERSIST_ONLY syntax. SeeSection 7.1.9.3, “Persisted System Variables”.

  For more information, seeDefining an Encryption Default for Schemas and General Tablespaces.

• table_open_cache

  Command-Line Format	--table-open-cache=#
  System Variable	table_open_cache
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	4000
  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 10.4.3.1, “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
  SET_VAR Hint Applies	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.

• tablespace_definition_cache

  Command-Line Format	--tablespace-definition-cache=#
  System Variable	tablespace_definition_cache
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	256
  Minimum Value	256
  Maximum Value	524288

  Defines a limit for the number of tablespace definition objects, both used and unused, that can be kept in the dictionary object cache.

  Unused tablespace definition objects are only kept in the dictionary object cache when the number in use is less than the capacity defined bytablespace_definition_cache.

  A setting of0 means that tablespace definition objects are only kept in the dictionary object cache while they are in use.

  For more information, seeSection 16.4, “Dictionary Object Cache”.

• temptable_max_mmap

  Command-Line Format	--temptable-max-mmap=#
  Introduced	8.0.23
  System Variable	temptable_max_mmap
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	1073741824
  Minimum Value	0
  Maximum Value	2^64-1
  Unit	bytes

  Defines the maximum amount of memory (in bytes) the TempTable storage engine is permitted to allocate from memory-mapped temporary files before it starts storing data toInnoDB internal temporary tables on disk. A setting of 0 disables allocation of memory from memory-mapped temporary files. For more information, seeSection 10.4.4, “Internal Temporary Table Use in MySQL”.

• temptable_max_ram

  Command-Line Format	--temptable-max-ram=#
  System Variable	temptable_max_ram
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	1073741824
  Minimum Value	2097152
  Maximum Value	2^64-1
  Unit	bytes

  Defines the maximum amount of memory that can be occupied by theTempTable storage engine before it starts storing data on disk. The default value is 1073741824 bytes (1GiB). For more information, seeSection 10.4.4, “Internal Temporary Table Use in MySQL”.

• temptable_use_mmap

  Command-Line Format	--temptable-use-mmap[={OFF|ON}]
  Introduced	8.0.16
  Deprecated	8.0.26
  System Variable	temptable_use_mmap
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  Defines whether the TempTable storage engine allocates space for internal in-memory temporary tables as memory-mapped temporary files when the amount of memory occupied by the TempTable storage engine exceeds the limit defined by thetemptable_max_ram variable. Whentemptable_use_mmap is disabled, the TempTable storage engine usesInnoDB on-disk internal temporary tables instead. For more information, seeSection 10.4.4, “Internal Temporary Table Use in MySQL”.

• thread_cache_size

  Command-Line Format	--thread-cache-size=#
  System Variable	thread_cache_size
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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 7.1.10, “Server Status Variables”.

  The default value is based on the following formula, capped to a limit of 100:

  8 + (max_connections / 100)

• thread_handling

  Command-Line Format	--thread-handling=name
  System Variable	thread_handling
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	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 7.9, “Debugging MySQL”.

• thread_pool_algorithm

  Command-Line Format	--thread-pool-algorithm=#
  System Variable	thread_pool_algorithm
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	0
  Minimum Value	0
  Maximum Value	1

  This variable controls which algorithm the thread pool plugin uses:

  • 0: Use a conservative low-concurrency algorithm.

  • 1: Use an aggressive high-currency algorithm which performs better with optimal thread counts, but performance may be degraded if the number of connections reaches extremely high values.

  This variable is available only if the thread pool plugin is enabled. SeeSection 7.6.3, “MySQL Enterprise Thread Pool”.

• thread_pool_dedicated_listeners

  Command-Line Format	--thread-pool-dedicated-listeners
  Introduced	8.0.23
  System Variable	thread_pool_dedicated_listeners
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  Dedicates a listener thread in each thread group to listen for incoming statements from connections assigned to the group.

  • OFF: (Default) Disables dedicated listener threads.

  • ON: Dedicates a listener thread in each thread group to listen for incoming statements from connections assigned to the group. Dedicated listener threads do not execute queries.

  Enablingthread_pool_dedicated_listeners is only useful when a transaction limit is defined bythread_pool_max_transactions_limit. Otherwise,thread_pool_dedicated_listeners should not be enabled.

  HeatWave Service introduced this variable in MySQL 8.0.23. It is available with MySQL Enterprise Edition from MySQL 8.0.31.

• 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
  SET_VAR Hint Applies	No
  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 7.6.3, “MySQL Enterprise Thread Pool”.

• thread_pool_max_active_query_threads

  Command-Line Format	--thread-pool-max-active-query-threads
  Introduced	8.0.19
  System Variable	thread_pool_max_active_query_threads
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	0
  Minimum Value	0
  Maximum Value	512

  The maximum permissible number of active (running) query threads per group. If the value is 0, the thread pool plugin uses up to as many threads as are available.

  This variable is available only if the thread pool plugin is enabled. SeeSection 7.6.3, “MySQL Enterprise Thread Pool”.

• thread_pool_max_transactions_limit

  Command-Line Format	--thread-pool-max-transactions-limit
  Introduced	8.0.23
  System Variable	thread_pool_max_transactions_limit
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	0
  Minimum Value	0
  Maximum Value	1000000

  The maximum number of transactions permitted by the thread pool plugin. Defining a transaction limit binds a thread to a transaction until it commits, which helps stabilize throughput during high concurrency.

  The default value of 0 means that there is no transaction limit. The variable is dynamic but cannot be changed from 0 to a higher value at runtime and vice versa. A non-zero value at startup permits dynamic configuration at runtime. TheCONNECTION_ADMIN privilege is required to configurethread_pool_max_transactions_limit at runtime.

  When you define a transaction limit, enablingthread_pool_dedicated_listeners creates a dedicated listener thread in each thread group. The additional dedicated listener thread consumes more resources and affects thread pool performance.thread_pool_dedicated_listeners should therefore be used cautiously.

  When the limit defined bythread_pool_max_transactions_limit has been reached, new connections appear to hang until one or more existing transactions are completed. The same occurs when attempting to start a new transaction on an existing connection. If existing connections are blocked or long-running, a privileged connection may be required to access the server to increase the limit, remove the limit, or kill running transactions. SeePrivileged Connections.

  HeatWave Service introduced this variable in MySQL 8.0.23. It is available with MySQL Enterprise Edition in from MySQL 8.0.31.

• thread_pool_max_unused_threads

  Command-Line Format	--thread-pool-max-unused-threads=#
  System Variable	thread_pool_max_unused_threads
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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 7.6.3, “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
  SET_VAR Hint Applies	No
  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 7.6.3, “MySQL Enterprise Thread Pool”.

• thread_pool_query_threads_per_group

  Command-Line Format	--thread-pool-query-threads-per-group
  Introduced	8.0.31
  System Variable	thread_pool_query_threads_per_group
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	1
  Minimum Value	1
  Maximum Value	4096

  The maximum number of query threads permitted in a thread group. The maximum value is 4096, but ifthread_pool_max_transactions_limit is set,thread_pool_query_threads_per_group must not exceed that value.

  The default value of 1 means there is one active query thread in each thread group, which works well for many loads. When you are using the high concurrency thread pool algorithm (thread_pool_algorithm = 1), consider increasing the value if you experience slower response times due to long-running transactions.

  TheCONNECTION_ADMIN privilege is required to configurethread_pool_query_threads_per_group at runtime.

  If you decrease the value ofthread_pool_query_threads_per_group at runtime, threads that are currently running user queries are allowed to complete, then moved to the reserve pool or terminated. if you increment the value at runtime and the thread group needs more threads, these are taken from the reserve pool if possible, otherwise they are created.

  This variable is available from MySQL 8.0.31 in HeatWave Service and MySQL Enterprise Edition.

• thread_pool_size

  Command-Line Format	--thread-pool-size=#
  System Variable	thread_pool_size
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	16
  Minimum Value	1
  Maximum Value (≥ 8.0.19)	512
  Maximum Value (≤ 8.0.18)	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 7.6.3, “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
  SET_VAR Hint Applies	No
  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 7.6.3, “MySQL Enterprise Thread Pool”.

• thread_pool_transaction_delay

  Command-Line Format	--thread-pool-transaction-delay
  Introduced	8.0.31
  System Variable	thread_pool_transaction_delay
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	0
  Minimum Value	0
  Maximum Value	300000

  The delay period before executing a new transaction, in milliseconds. The maximum value is 300000 (5 minutes).

  A transaction delay can be used in cases where parallel transactions affect the performance of other operations due to resource contention. For example, if parallel transactions affect index creation or an online buffer pool resizing operation, you can configure a transaction delay to reduce resource contention while those operations are running.

  Worker threads sleep for the number of milliseconds specified bythread_pool_transaction_delay before executing a new transaction.

  Thethread_pool_transaction_delay setting does not affect queries issued from a privileged connection (a connection assigned to theAdmin thread group). These queries are not subject to a configured transaction delay.

• thread_stack

  Command-Line Format	--thread-stack=#
  System Variable	thread_stack
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value (64-bit platforms, ≥ 8.0.27)	1048576
  Default Value (64-bit platforms, ≤ 8.0.26)	286720
  Default Value (32-bit platforms, ≥ 8.0.27)	1048576
  Default Value (32-bit platforms, ≤ 8.0.26)	221184
  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_zone

  System Variable	time_zone
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies (≥ 8.0.17)	Yes
  SET_VAR Hint Applies (≤ 8.0.16)	No
  Type	String
  Default Value	SYSTEM
  Minimum Value (≥ 8.0.19)	-13:59
  Minimum Value (≤ 8.0.18)	-12:59
  Maximum Value (≥ 8.0.19)	+14:00
  Maximum Value (≤ 8.0.18)	+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 7.1.15, “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
  SET_VAR Hint Applies	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.

  timestamp is aDOUBLE rather thanBIGINT because its value includes a microseconds part. The maximum value corresponds to'2038-01-19 03:14:07' UTC, the same as for theTIMESTAMP data type.

  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_ciphersuites

  Command-Line Format	--tls-ciphersuites=ciphersuite_list
  Introduced	8.0.16
  System Variable	tls_ciphersuites
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	String
  Default Value	NULL

  Which ciphersuites the server permits for encrypted connections that use TLSv1.3. The value is a list of zero or more colon-separated ciphersuite names.

  The ciphersuites that can be named for this variable depend on the SSL library used to compile MySQL. If this variable is not set, its default value isNULL, which means that the server permits the default set of ciphersuites. If the variable is set to the empty string, no ciphersuites are enabled and encrypted connections cannot be established. For more information, seeSection 8.3.2, “Encrypted Connection TLS Protocols and Ciphers”.

• tls_version

  Command-Line Format	--tls-version=protocol_list
  System Variable	tls_version
  Scope	Global
  Dynamic (≥ 8.0.16)	Yes
  Dynamic (≤ 8.0.15)	No
  SET_VAR Hint Applies	No
  Type	String
  Default Value (≥ 8.0.28)	TLSv1.2,TLSv1.3
  Default Value (≥ 8.0.16, ≤ 8.0.27)	TLSv1,TLSv1.1,TLSv1.2,TLSv1.3
  Default Value (≤ 8.0.15)	TLSv1,TLSv1.1,TLSv1.2

  Which protocols the server permits for encrypted connections. The value is a list of one or more comma-separated protocol names, which are not case-sensitive. 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 8.3.2, “Encrypted Connection TLS Protocols and Ciphers”.

  As of MySQL 8.0.16, this variable is dynamic and can be modified at runtime to affect the TLS context the server uses for new connections. SeeServer-Side Runtime Configuration and Monitoring for Encrypted Connections. Prior to MySQL 8.0.16, this variable can be set only at server startup.

  Important

  • Support for the TLSv1 and TLSv1.1 connection protocols is removed from MySQL Server as of MySQL 8.0.28. The protocols were deprecated from MySQL 8.0.26. SeeRemoval of Support for the TLSv1 and TLSv1.1 Protocols for more information.

  • Support for the TLSv1.3 protocol is available in MySQL Server as of MySQL 8.0.16, provided that MySQL Server was compiled using OpenSSL 1.1.1 or higher. The server checks the version of OpenSSL at startup, and if it is lower than 1.1.1, TLSv1.3 is removed from the default value for the system variable. In that case, the defaults are“TLSv1,TLSv1.1,TLSv1.2” up to and including MySQL 8.0.27, and“TLSv1.2” from MySQL 8.0.28.

  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
  SET_VAR Hint Applies	Yes
  Type	Integer
  Default Value	16777216
  Minimum Value	1024
  Maximum Value	18446744073709551615
  Unit	bytes

  Defines the maximum size of internal in-memory temporary tables created by theMEMORY storage engine and, as of MySQL 8.0.28, theTempTable storage engine. If an internal in-memory temporary table exceeds this size, it is automatically converted to an on-disk internal temporary table.

  Thetmp_table_size variable does not apply to user-createdMEMORY tables. User-createdTempTable tables are not supported.

  When using theMEMORY storage engine for internal in-memory temporary tables, the actual size limit is the smaller oftmp_table_size andmax_heap_table_size. Themax_heap_table_size setting does not apply toTempTable tables.

  Increase the value oftmp_table_size (andmax_heap_table_size if necessary when using theMEMORY storage engine for internal in-memory temporary tables) 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 10.4.4, “Internal Temporary Table Use in MySQL”.

• tmpdir

  Command-Line Format	--tmpdir=dir_name
  System Variable	tmpdir
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	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 thereplica_load_tmpdir orslave_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
  SET_VAR Hint Applies	No
  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	transaction_isolation
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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 15.3.7, “SET TRANSACTION Statement”.

• transaction_prealloc_size

  Command-Line Format	--transaction-prealloc-size=#
  Deprecated	8.0.29
  System Variable	transaction_prealloc_size
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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.

  Beginning with MySQL 8.0.29,transaction_prealloc_size is deprecated; the initial size of the transaction memory pool is fixed, and setting this variable no longer has any effect. (The functioning oftransaction_alloc_block_size is unaffected by this change.) Expecttransaction_prealloc_size to be removed in a future release of MySQL.

• transaction_read_only

  Command-Line Format	--transaction-read-only[={OFF|ON}]
  System Variable	transaction_read_only
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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 15.3.7, “SET TRANSACTION Statement”.

• unique_checks

  System Variable	unique_checks
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	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
  SET_VAR Hint Applies	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.

• use_secondary_engine

  Introduced	8.0.13
  System Variable	use_secondary_engine
  Scope	Session
  Dynamic	Yes
  SET_VAR Hint Applies	Yes
  Type	Enumeration
  Default Value	ON
  Valid Values	OFF ON FORCED

  For future use.

  Whether to execute queries using a secondary engine.

  For use with HeatWave. SeeHeatWave User Guide.

• validate_password.xxx

  Thevalidate_password component implements a set of system variables having names of the formvalidate_password.xxx. These variables affect password testing by that component; seeSection 8.4.3.2, “Password Validation Options and Variables”.

• version

  The version number for the server. The value might also include a suffix indicating server build or configuration information.-debug indicates that the server was built with debugging support enabled.

• version_comment

  System Variable	version_comment
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	String

  TheCMake configuration program has aCOMPILATION_COMMENT_SERVER option that permits a comment to be specified when building MySQL. This variable contains the value of that comment. (Prior to MySQL 8.0.14,version_comment is set by theCOMPILATION_COMMENT option.) SeeSection 2.8.7, “MySQL Source-Configuration Options”.

• version_compile_machine

  System Variable	version_compile_machine
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	String

  The type of the server binary.

• version_compile_os

  System Variable	version_compile_os
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	String

  The type of operating system on which MySQL was built.

• version_compile_zlib

  System Variable	version_compile_zlib
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	String

  The version of the compiled-inzlib library.

• wait_timeout

  Command-Line Format	--wait-timeout=#
  System Variable	wait_timeout
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  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 15.7.7.42, “SHOW WARNINGS Statement”.

• windowing_use_high_precision

  Command-Line Format	--windowing-use-high-precision[={OFF|ON}]
  System Variable	windowing_use_high_precision
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	Yes
  Type	Boolean
  Default Value	ON

  Whether to compute window operations without loss of precision. SeeSection 10.2.1.21, “Window Function Optimization”.

• xa_detach_on_prepare

  Command-Line Format	--xa-detach-on-prepare[={OFF|ON}]
  Introduced	8.0.29
  System Variable	xa_detach_on_prepare
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  When set toON (enabled), all XA transactions are detached (disconnected) from the connection (session) as part ofXA PREPARE. This means that the XA transaction can be committed or rolled back by another connection, even if the originating connection has not terminated, and this connection can start new transactions.

  Temporary tables cannot be used inside detached XA transactions.

  When this isOFF (disabled), an XA transaction is strictly associated with the same connection until the session disconnects. It is recommended that you allow it to be enabled (the default behavior) for replication.

  For more information, seeSection 15.3.8.2, “XA Transaction States”.