5.1.8 Server System Variables

The MySQL server maintains many system variables that configure its operation. Each system variable has a default value. System variables can be set at server startup using options on the command line or in an option file. Most of them can be changed dynamically at runtime using the SET statement, which enables you to modify operation of the server without having to stop and restart it. You can also use system variable values in expressions.

Setting a global system variable runtime value normally requires the SYSTEM_VARIABLES_ADMIN privilege (or the deprecated SUPER privilege). Setting a session system runtime variable value normally requires no special privileges and can be done by any user, although there are exceptions. For more information, see Section 5.1.9.1, “System Variable Privileges”

There are several ways to see the names and values of system variables:

• To see the values that a server will use based on its compiled-in defaults and any option files that it reads, use this command:

  mysqld --verbose --help

• To see the values that a server will use based only on its compiled-in defaults, ignoring the settings in any option files, use this command:

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

• To see the current values used by a running server, use the SHOW VARIABLES statement or the Performance Schema system variable tables. See Section 26.12.14, “Performance Schema System Variable Tables”.

This section provides a description of each system variable. For a system variable summary table, see Section 5.1.5, “Server System Variable Reference”. For more information about manipulation of system variables, see Section 5.1.9, “Using System Variables”.

For additional system variable information, see these sections:

• Section 5.1.9, “Using System Variables”, discusses the syntax for setting and displaying system variable values.

• Section 5.1.9.2, “Dynamic System Variables”, lists the variables that can be set at runtime.

• Information on tuning system variables can be found in Section 5.1.1, “Configuring the Server”.

• Section 15.14, “InnoDB Startup Options and System Variables”, lists InnoDB system variables.

• Section 22.3.3.9.2, “NDB Cluster System Variables”, lists system variables which are specific to NDB Cluster.

• For information on server system variables specific to replication, see Section 17.1.6, “Replication and Binary Logging Options and Variables”.

Note

Some of the following variable descriptions refer to “enabling” or “disabling” a variable. These variables can be enabled with the SET statement by setting them to ON or 1, or disabled by setting them to OFF or 0. Boolean variables can be set at startup to the values ON, TRUE, OFF, and FALSE (not case sensitive), as well as 1 and 0. See Section 4.2.2.4, “Program Option Modifiers”.

Some system variables control the size of buffers or caches. For a given buffer, the server might need to allocate internal data structures. These structures typically are allocated from the total memory allocated to the buffer, and the amount of space required might be platform dependent. This means that when you assign a value to a system variable that controls a buffer size, the amount of space actually available might differ from the value assigned. In some cases, the amount might be less than the value assigned. It is also possible that the server will adjust a value upward. For example, if you assign a value of 0 to a variable for which the minimal value is 1024, the server will set the value to 1024.

Values for buffer sizes, lengths, and stack sizes are given in bytes unless otherwise specified.

Some system variables take file name values. Unless otherwise specified, the default file location is the data directory if the value is a relative path name. To specify the location explicitly, use an absolute path name. Suppose that the data directory is /var/mysql/data. If a file-valued variable is given as a relative path name, it will be located under /var/mysql/data. If the value is an absolute path name, its location is as given by the path name.

• activate_all_roles_on_login

  Property	Value
  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:

  • If activate_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 with SET DEFAULT ROLE.

  • If activate_all_roles_on_login is disabled, the server activates the default roles specified with SET DEFAULT ROLE, if any, at login time.

  Granted roles include those granted explicitly to the user and those named in the mandatory_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, use SET ROLE. To change the active roles for a stored program, the program body should execute SET ROLE.

• admin_address

  Property	Value
  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 (see Section 5.1.12.1, “Connection Interfaces”). There is no default admin_address value. If this variable is not specified at startup, the server maintains no administrative interface. The server also has a bind_address system variable for configuring regular (nonadministrative) client TCP/IP connections. See Section 5.1.12.1, “Connection Interfaces”.

  If admin_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 ::).

  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 as 127.0.0.1 or ::1), the server accepts TCP/IP connections only for that IPv4 or IPv6 address.

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

  The admin_address system variable is similar to the bind_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

  Property	Value
  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 (see Section 5.1.12.1, “Connection Interfaces”). Setting this variable to 0 causes the default value to be used.

  Setting admin_port has no effect if admin_address is not specified because in that case the server maintains no administrative network interface.

• admin_ssl_ca

  Property	Value
  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

  The admin_ssl_ca system variable is like ssl_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, see Administrative Interface Support for Encrypted Connections.

• admin_ssl_capath

  Property	Value
  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

  The admin_ssl_capath system variable is like ssl_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, see Administrative Interface Support for Encrypted Connections.

• admin_ssl_cert

  Property	Value
  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

  The admin_ssl_cert system variable is like ssl_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, see Administrative Interface Support for Encrypted Connections.

• admin_ssl_cipher

  Property	Value
  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

  The admin_ssl_cipher system variable is like ssl_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, see Administrative Interface Support for Encrypted Connections.

• admin_ssl_crl

  Property	Value
  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

  The admin_ssl_crl system variable is like ssl_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, see Administrative Interface Support for Encrypted Connections.

• admin_ssl_crlpath

  Property	Value
  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

  The admin_ssl_crlpath system variable is like ssl_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, see Administrative Interface Support for Encrypted Connections.

• admin_ssl_key

  Property	Value
  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

  The admin_ssl_key system variable is like ssl_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, see Administrative Interface Support for Encrypted Connections.

• admin_tls_ciphersuites

  Property	Value
  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

  The admin_tls_ciphersuites system variable is like tls_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, see Administrative Interface Support for Encrypted Connections.

• admin_tls_version

  Property	Value
  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	TLSv1,TLSv1.1,TLSv1.2,TLSv1.3 (OpenSSL 1.1.1 and higher) TLSv1,TLSv1.1,TLSv1.2 (otherwise)

  The admin_tls_version system variable is like tls_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, see Administrative Interface Support for Encrypted Connections.

• authentication_windows_log_level

  Property	Value
  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 the authentication_windows Windows authentication plugin is enabled and debugging code is enabled. See Section 6.4.1.6, “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

  Property	Value
  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 the authentication_windows Windows authentication plugin is enabled. See Section 6.4.1.6, “Windows Pluggable Authentication”.

  A client that authenticates using the InitSecurityContext() function should provide a string identifying the service to which it connects (targetName). MySQL uses the principal name (UPN) of the account under which the server is running. The UPN has the form user_id@computer_name 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 a 0x00 byte in the first challenge, the client does not specify targetName, and as a result, NTLM authentication is used.

  If the server fails to obtain its UPN (which will happen primarily in environments that do not support Kerberos authentication), the UPN is not sent by the server and NTLM authentication is used.

• autocommit

  Property	Value
  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 use COMMIT to accept a transaction or ROLLBACK to cancel it. If autocommit is 0 and you change it to 1, MySQL performs an automatic COMMIT of any open transaction. Another way to begin a transaction is to use a START TRANSACTION or BEGIN statement. See Section 13.3.1, “START TRANSACTION, COMMIT, and ROLLBACK Statements”.

  By default, client connections begin with autocommit set to 1. To cause clients to begin with a default of 0, set the global autocommit value by starting the server with the --autocommit=0 option. To set the variable using an option file, include these lines:

  [mysqld]
  autocommit=0

• automatic_sp_privileges

  Property	Value
  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 the EXECUTE and ALTER ROUTINE privileges to the creator of a stored routine, if the user cannot already execute and alter or drop the routine. (The ALTER ROUTINE privilege is required to drop the routine.) The server also automatically drops those privileges from the creator when the routine is dropped. If automatic_sp_privileges is 0, the server does not automatically add or drop these privileges.

  The creator of a routine is the account used to execute the CREATE statement for it. This might not be the same as the account named as the DEFINER in the routine definition.

  If you start mysqld with --skip-new, automatic_sp_privileges is set to OFF.

  See also Section 24.2.2, “Stored Routines and MySQL Privileges”.

• auto_generate_certs

  Property	Value
  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 the auto_generate_certs system variable is enabled, no SSL options other than --ssl are specified, and the server-side SSL files are missing from the data directory. These files enable secure client connections using SSL; see Section 6.3.1, “Configuring MySQL to Use Encrypted Connections”.

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

  The sha256_password_auto_generate_rsa_keys and caching_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 unencypted connections.

• avoid_temporal_upgrade

  Property	Value
  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 whether ALTER TABLE implicitly upgrades temporal columns found to be in pre-5.6.4 format (TIME, DATETIME, and TIMESTAMP columns without support for fractional seconds precision). Upgrading such columns requires a table rebuild, which prevents any use of fast alterations that might otherwise apply to the operation to be performed.

  This variable is disabled by default. Enabling it causes ALTER TABLE not to rebuild temporal columns and thereby be able to take advantage of possible fast alterations.

  This variable is deprecated and will be removed in a future MySQL release.

• back_log

  Property	Value
  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. The back_log value indicates how many requests can be stacked during this short time before MySQL momentarily stops answering new requests. You need to increase this only if you expect a large number of connections in a short period of time.

  In other words, this value is the size of the listen queue for incoming TCP/IP connections. Your operating system has its own limit on the size of this queue. The manual page for the Unix listen() system call should have more details. Check your OS documentation for the maximum value for this variable. back_log cannot be set higher than your operating system limit.

  The default value is the value of max_connections, which enables the permitted backlog to adjust to the maximum permitted number of connections.

• basedir

  Property	Value
  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

  Property	Value
  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 most The table tbl_name is full errors for SELECT operations that require a large temporary table, but also slows down queries for which in-memory tables would suffice.

  The default value for new connection is OFF (use in-memory temporary tables). Normally, it should never be necessary to enable this variable. When in-memory internal temporary tables are managed by the TempTable storage engine (the default), and the maximum amount of memory that can be occupied by the TempTable storage engine is exceeded, the TempTable storage engine starts storing data to temporary files on disk. When in-memory temporary tables are managed by the MEMORY storage engine, in-memory tables are automatically converted to disk-based tables as required. For more information, see Section 8.4.4, “Internal Temporary Table Use in MySQL”.

• bind_address

  Property	Value
  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 the bind_address system variable at server startup. The server also has an admin_address system variable that enables administrative connections on a dedicated interface. See Section 5.1.12.1, “Connection Interfaces”.

  If bind_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 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 or host name; none can specify a wildcard address format (*, 0.0.0.0, or ::).

  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 option specifies a list of multiple values, this value is not permitted.

  • If the address is 0.0.0.0, the server accepts TCP/IP connections on all server host IPv4 interfaces. If the option 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 option 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 as 127.0.0.1 or ::1), the server accepts TCP/IP connections only for that IPv4 or IPv6 address.

  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 the 198.51.100.20 IPv4 address.

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

    The server listens on the 198.51.100.20 IPv4 address and the 2001:db8:0:f101::1 IPv6 address.

  • bind_address=198.51.100.20,*

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

  When bind_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. When bind_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, it may be necessary to increase the open_files_limit system variable.

  If you intend to bind the server to a specific address, be sure that the mysql.user system table contains an account with administrative privileges that you can use to connect to that address. Otherwise, you will not be able to shut down the server. For example, if you bind the server to *, you can connect to it using all existing accounts. But if you bind the server to ::1, it accepts connections only on that address. In that case, first make sure that the 'root'@'::1' account is present in the mysql.user table so you can still connect to the server to shut it down.

• block_encryption_mode

  Property	Value
  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 for AES_ENCRYPT() and AES_DECRYPT().

  block_encryption_mode takes a value in aes-keylen-mode format, where keylen is the key length in bits and mode is the encryption mode. The value is not case-sensitive. Permitted keylen values are 128, 192, and 256. Permitted mode values are ECB, CBC, CFB1, CFB8, CFB128, and OFB.

  For example, this statement causes the AES encryption functions to use a key length of 256 bits and the CBC mode:

  SET block_encryption_mode = 'aes-256-cbc';

  An error occurs for attempts to set block_encryption_mode to a value containing an unsupported key length or a mode that the SSL library does not support.

• bulk_insert_buffer_size

  Property	Value
  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

  MyISAM uses a special tree-like cache to make bulk inserts faster for INSERT ... SELECT, INSERT ... VALUES (...), (...), ..., and LOAD DATA when adding data to nonempty tables. This variable limits the size of the cache tree in bytes per thread. Setting it to 0 disables this optimization. The default value is 8MB.

  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. See Section 5.1.9.1, “System Variable Privileges”.

• caching_sha2_password_auto_generate_rsa_keys

  Property	Value
  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: The sha256_password_auto_generate_rsa_keys or caching_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 the sha256_password or caching_sha2_password plugin; see Section 6.4.1.3, “SHA-256 Pluggable Authentication”, and Section 6.4.1.2, “Caching SHA-2 Pluggable Authentication”.

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

  The auto_generate_certs system variable is related but controls autogeneration of SSL certificate and key files needed for secure connections using SSL.

• caching_sha2_password_private_key_path

  Property	Value
  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 the caching_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 about caching_sha2_password, see Section 6.4.1.2, “Caching SHA-2 Pluggable Authentication”.

• caching_sha2_password_public_key_path

  Property	Value
  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 the caching_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 about caching_sha2_password, including information about how clients request the RSA public key, see Section 6.4.1.2, “Caching SHA-2 Pluggable Authentication”.

• character_set_client

  Property	Value
  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 also Section 10.4, “Connection Character Sets and Collations”.) The global value of the variable is used to set the session value in cases when the client-requested value is unknown or not available, or the server is configured to ignore client requests:

  • The client requests a character set not known to the server. For example, a Japanese-enabled client requests sjis when connecting to a server not configured with sjis support.

  • The client is from a version of MySQL older than MySQL 4.1, and thus does not request a character set.

  • mysqld was started with the --skip-character-set-client-handshake option, which causes it to ignore client character set configuration. This reproduces MySQL 4.0 behavior and is useful should you wish to upgrade the server without upgrading all the clients.

  Some character sets cannot be used as the client character set. Attempting to use them as the character_set_client value produces an error. See Impermissible Client Character Sets.

• character_set_connection

  Property	Value
  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, see Section 10.3.8, “Character Set Introducers”.

• character_set_database

  Property	Value
  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 only the server should set this information. You should not set the value of this variable manually.

  The character set used by the default database. The server sets this variable whenever the default database changes. If there is no default database, the variable has the same value as character_set_server.

  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. See Section 5.1.9.1, “System Variable Privileges”.

  The global character_set_database and collation_database system variables are deprecated and will be removed in a future version of MySQL.

  Assigning a value to the session character_set_database and collation_database system variables is deprecated and assignments produce a warning. The session variables will become read only in a future version of MySQL and assignments will produce an error. It will remain possible to access the session variables to determine the database character set and collation for the default database.

• character_set_filesystem

  Property	Value
  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 the LOAD DATA and SELECT ... INTO OUTFILE statements and the LOAD_FILE() function. Such file names are converted from character_set_client to character_set_filesystem before the file opening attempt occurs. The default value is binary, which means that no conversion occurs. For systems on which multibyte file names are permitted, a different value may be more appropriate. For example, if the system represents file names using UTF-8, set character_set_filesystem to 'utf8mb4'.

  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. See Section 5.1.9.1, “System Variable Privileges”.

• character_set_results

  Property	Value
  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

  Property	Value
  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. See Section 10.15, “Character Set Configuration”. If you set this variable, you should also set collation_server to specify the collation for the character set.

• character_set_system

  Property	Value
  System Variable	character_set_system
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	String
  Default Value	utf8

  The character set used by the server for storing identifiers. The value is always utf8.

• character_sets_dir

  Property	Value
  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. See Section 10.15, “Character Set Configuration”.

• check_proxy_users

  Property	Value
  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 the check_proxy_users system variable is enabled, the server performs proxy user mapping for any authentication plugins that make such a request. However, it may also be necessary to enable plugin-specific system variables to take advantage of server proxy user mapping support:

  • For the mysql_native_password plugin, enable mysql_native_password_proxy_users.

  • For the sha256_password plugin, enable sha256_password_proxy_users.

  For information about user proxying, see Section 6.2.18, “Proxy Users”.

• collation_connection

  Property	Value
  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 (see Section 10.8.4, “Collation Coercibility in Expressions”).

• collation_database

  Property	Value
  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 only the server should set this information. You should not set the value of this variable manually.

  The collation used by the default database. The server sets this variable whenever the default database changes. If there is no default database, the variable has the same value as collation_server.

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

  The global character_set_database and collation_database system variables are deprecated and will be removed in a future version of MySQL.

  Assigning a value to the session character_set_database and collation_database system variables is deprecated and assignments produce a warning. The session variables will become read only in a future version of MySQL and assignments will produce an error. It will remain possible to access the session variables to determine the database character set and collation for the default database.

• collation_server

  Property	Value
  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. See Section 10.15, “Character Set Configuration”.

• completion_type

  Property	Value
  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 and ROLLBACK are unaffected. This is the default value.
  CHAIN (or 1)	COMMIT and ROLLBACK are equivalent to COMMIT AND CHAIN and ROLLBACK AND CHAIN, respectively. (A new transaction starts immediately with the same isolation level as the just-terminated transaction.)
  RELEASE (or 2)	COMMIT and ROLLBACK are equivalent to COMMIT RELEASE and ROLLBACK RELEASE, respectively. (The server disconnects after terminating the transaction.)

  completion_type affects transactions that begin with START TRANSACTION or BEGIN and end with COMMIT or ROLLBACK. It does not apply to implicit commits resulting from execution of the statements listed in Section 13.3.3, “Statements That Cause an Implicit Commit”. It also does not apply for XA COMMIT, XA ROLLBACK, or when autocommit=1.

• concurrent_insert

  Property	Value
  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

  If AUTO (the default), MySQL permits INSERT and SELECT statements to run concurrently for MyISAM tables that have no free blocks in the middle of the data file.

  This variable can take the values shown in the following table. The variable can be assigned using either the name values or corresponding integer values.

  Value	Description
  NEVER (or 0)	Disables concurrent inserts
  AUTO (or 1)	(Default) Enables concurrent insert for MyISAM tables that do not have holes
  ALWAYS (or 2)	Enables concurrent inserts for all MyISAM tables, even those that have holes. For a table with a hole, new rows are inserted at the end of the table if it is in use by another thread. Otherwise, MySQL acquires a normal write lock and inserts the row into the hole.

  If you start mysqld with --skip-new, concurrent_insert is set to NEVER.

  See also Section 8.11.3, “Concurrent Inserts”.

• connect_timeout

  Property	Value
  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

  The number of seconds that the mysqld server waits for a connect packet before responding with Bad handshake. The default value is 10 seconds.

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

• core_file

  Property	Value
  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 crashes. This variable is set by the --core-file option.

• create_admin_listener_thread

  Property	Value
  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 (see Section 5.1.12.1, “Connection Interfaces”). The default is OFF; 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.

  Setting create_admin_listener_thread has no effect if admin_address is not specified because in that case the server maintains no administrative network interface.

• cte_max_recursion_depth

  Property	Value
  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, see Limiting Common Table Expression Recursion.

• datadir

  Property	Value
  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 the server will be started automatically (that is, in contexts for which you cannot assume what the current directory will be), it is best to specify the datadir value as an absolute path.

• debug

  Property	Value
  Command-Line Format	--debug[=debug_options]
  System Variable	debug
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	String
  Default Value (Windows)	d:t:i:O,\mysqld.trace
  Default Value (Unix)	d:t:i:o,/tmp/mysqld.trace

  This variable indicates the current debugging settings. It is available only for servers built with debugging support. The initial value comes from the value of instances of the --debug option given at server startup. The global and session values may be set at runtime.

  Setting the session value of this system variable is a restricted operation. The session user must have privileges sufficient to set restricted session variables. See Section 5.1.9.1, “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, see Section 29.5.4, “The DBUG Package”.

• debug_sync

  Property	Value
  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 -DENABLE_DEBUG_SYNC=1 CMake option (see Section 2.9.7, “MySQL Source-Configuration Options”). If Debug Sync is not compiled in, this system variable is not available.

  The global variable value is read only and indicates whether the facility is enabled. By default, Debug Sync is disabled and the value of debug_sync is OFF. If the server is started with --debug-sync-timeout=N, where N is a timeout value greater than 0, Debug Sync is enabled and the value of debug_sync is ON - current signal followed by the signal name. Also, N becomes the default timeout for individual synchronization points.

  The session value can be read by any user and will have the same value as the global variable. The session value can be set to control synchronization points.

  Setting the session value of this system variable is a restricted operation. The session user must have privileges sufficient to set restricted session variables. See Section 5.1.9.1, “System Variable Privileges”.

  For a description of the Debug Sync facility and how to use synchronization points, see MySQL Internals: Test Synchronization.

• default_authentication_plugin

  Property	Value
  Command-Line Format	--default-authentication-plugin=plugin_name
  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. These values are permitted:

  • mysql_native_password: Use MySQL native passwords; see Section 6.4.1.1, “Native Pluggable Authentication”.

  • sha256_password: Use SHA-256 passwords; see Section 6.4.1.3, “SHA-256 Pluggable Authentication”.

  • caching_sha2_password: Use SHA-256 passwords; see Section 6.4.1.2, “Caching SHA-2 Pluggable Authentication”.

  Note

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

  The default_authentication_plugin value affects these aspects of server operation:

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

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

• default_collation_for_utf8mb4

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

  For internal use by replication. This system variable is set to the default collation for the utf8mb4 character set. The value of the variable is replicated from a master to a slave so that the slave can correctly process data originating from a master with a different default collation for utf8mb4. This variable is primarily intended to support replication from a MySQL 5.7 or older master server to a MySQL 8.0 slave server, or group replication with a MySQL 5.7 primary node and one or more MySQL 8.0 secondaries. The default collation for utf8mb4 in MySQL 5.7 is utf8mb4_general_ci, but utf8mb4_0900_ai_ci in MySQL 8.0. The variable is not present in releases earlier than MySQL 8.0, so if the slave does not receive a value for the variable, it assumes the master is from an earlier release and sets the value to the previous default collation utf8mb4_general_ci.

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

  The default utf8mb4 collation is used in the following statements:

  • SHOW COLLATION and SHOW CHARACTER SET.

  • CREATE TABLE and ALTER TABLE having a CHARACTER SET utf8mb4 clause without a COLLATION clause, either for the table character set or for a column character set.

  • CREATE DATABASE and ALTER DATABASE having a CHARACTER SET utf8mb4 clause without a COLLATION clause.

  • Any statement containing a string literal of the form _utf8mb4'some text' without a COLLATE clause.

• default_password_lifetime

  Property	Value
  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

  This variable defines the global automatic password expiration policy. The default default_password_lifetime value is 0, which disables automatic password expiration. If the value of default_password_lifetime is a positive integer N, it indicates the permitted password lifetime; passwords must be changed every N days.

  The global password expiration policy can be overridden as desired for individual accounts using the password expiration option of the CREATE USER and ALTER USER statements. See Section 6.2.15, “Password Management”.

• default_storage_engine

  Property	Value
  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. See Chapter 16, Alternative Storage Engines. This variable sets the storage engine for permanent tables only. To set the storage engine for TEMPORARY tables, set the default_tmp_storage_engine system variable.

  To see which storage engines are available and enabled, use the SHOW ENGINES statement or query the INFORMATION_SCHEMA ENGINES table.

  If you disable the default storage engine at server startup, you must set the default engine for both permanent and TEMPORARY tables to a different engine or the server will not start.

• default_table_encryption

  Property	Value
  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 an ENCRYPTION clause.

  The default_table_encryption variable is only applicable to user-created schemas and general tablespaces. It does not govern encryption of the mysql system tablespace.

  Setting the runtime value of default_table_encryption requires the SYSTEM_VARIABLES_ADMIN and TABLE_ENCRYPTION_ADMIN privileges, or the deprecated SUPER privilege.

  default_table_encryption supports SET PERSIST and SET PERSIST_ONLY syntax. See Section 5.1.9.3, “Persisted System Variables”.

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

• default_tmp_storage_engine

  Property	Value
  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 for TEMPORARY tables (created with CREATE TEMPORARY TABLE). To set the storage engine for permanent tables, set the default_storage_engine system variable. Also see the discussion of that variable regarding possible values.

  If you disable the default storage engine at server startup, you must set the default engine for both permanent and TEMPORARY tables to a different engine or the server will not start.

• default_week_format

  Property	Value
  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 the WEEK() function. See Section 12.6, “Date and Time Functions”.

• delay_key_write

  Property	Value
  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	ON OFF ALL

  This variable specifies how to use delayed key writes. It applies only to MyISAM tables. Delayed key writing causes key buffers not to be flushed between writes. See also Section 16.2.1, “MyISAM Startup Options”.

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

  Option	Description
  OFF	DELAY_KEY_WRITE is ignored.
  ON	MySQL honors any DELAY_KEY_WRITE option specified in CREATE TABLE statements. This is the default value.
  ALL	All new opened tables are treated as if they were created with the DELAY_KEY_WRITE option enabled.

  Note

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

  If DELAY_KEY_WRITE is enabled for a table, the key buffer is not flushed for the table on every index update, but only when the table is closed. This speeds up writes on keys a lot, but if you use this feature, you should add automatic checking of all MyISAM tables by starting the server with the myisam_recover_options system variable set (for example, myisam_recover_options='BACKUP,FORCE'). See Section 5.1.8, “Server System Variables”, and Section 16.2.1, “MyISAM Startup Options”.

  If you start mysqld with --skip-new, delay_key_write is set to OFF.

  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

  Property	Value
  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 (because DELAYED inserts are not supported), and will be removed in a future release.

• delayed_insert_timeout

  Property	Value
  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

  This system variable is deprecated (because DELAYED inserts are not supported), and will be removed in a future release.

• delayed_queue_size

  Property	Value
  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 (because DELAYED inserts are not supported), and will be removed in a future release.

• disabled_storage_engines

  Property	Value
  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 new MyISAM or FEDERATED tables from being created, start the server with these lines in the server option file:

  [mysqld]
  disabled_storage_engines="MyISAM,FEDERATED"

  By default, disabled_storage_engines is empty (no engines disabled), but it can be set to a comma-separated list of one or more engines (not case sensitive). Any engine named in the value cannot be used to create tables or tablespaces with CREATE TABLE or CREATE TABLESPACE, and cannot be used with ALTER TABLE ... ENGINE or ALTER TABLESPACE ... ENGINE to change the storage engine of existing tables or tablespaces. Attempts to do so result in an ER_DISABLED_STORAGE_ENGINE error.

  disabled_storage_engines does not restrict other DDL statements for existing tables, such as CREATE INDEX, TRUNCATE TABLE, ANALYZE TABLE, DROP TABLE, or DROP TABLESPACE. This permits a smooth transition so that existing tables or tablespaces that use a disabled engine can be migrated to a permitted engine by means such as ALTER TABLE ... ENGINE permitted_engine.

  It is permitted to set the default_storage_engine or default_tmp_storage_engine system variable to a storage engine that is disabled. This could cause applications to behave erratically or fail, although that might be a useful technique in a development environment for identifying applications that use disabled engines, so that they can be modified.

  disabled_storage_engines is disabled and has no effect if the server is started with any of these options: --initialize, --initialize-insecure, --skip-grant-tables.

  Note

  Setting disabled_storage_engines might cause an issue with mysql_upgrade. For details, see Section 4.4.5, “mysql_upgrade — Check and Upgrade MySQL Tables”.

• disconnect_on_expired_password

  Property	Value
  Command-Line Format	--disconnect-on-expired-password[={OFF|ON}]
  System Variable	disconnect_on_expired_password
  Scope	Global
  Dynamic	No
  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 of disconnect_on_expired_password is irrelevant. The server permits the client to connect but puts it in sandbox mode.

  • If the client does not indicate that it can handle expired passwords, the server handles the client according to the value of disconnect_on_expired_password:

    • If disconnect_on_expired_password: is enabled, the server disconnects the client.

    • If disconnect_on_expired_password: is disabled, the server permits the client to connect but puts it in sandbox mode.

  For more information about the interaction of client and server settings relating to expired-password handling, see Section 6.2.16, “Server Handling of Expired Passwords”.

• div_precision_increment

  Property	Value
  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

  Property	Value
  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 the log_filter_dragnet error log filter component. If log_filter_dragnet is not installed, dragnet.log_error_filter_rules is unavailable. If log_filter_dragnet is installed but not enabled, changes to dragnet.log_error_filter_rules have no effect.

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

  Prior to MySQL 8.0.12, successful assignments to dragnet.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: 4569
  Message: filter configuration accepted:
           SET @@GLOBAL.dragnet.log_error_filter_rules=
           'IF prio!=ERROR THEN unset prio.';

  The value displayed by SHOW 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 to dragnet.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 symbol ERROR.

  • Optional spaces are removed.

  For additional information, see Section 5.4.2.3, “Types of Error Log Filtering”, and Section 5.5.3, “Error Log Components”.

• end_markers_in_json

  Property	Value
  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. See MySQL Internals: The end_markers_in_json System Variable.

• eq_range_index_dive_limit

  Property	Value
  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 up col_name values:

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

  In both cases, the expression contains N equality ranges. The optimizer can make row estimates using index dives or index statistics. If eq_range_index_dive_limit is greater than 0, the optimizer uses existing index statistics instead of index dives if there are eq_range_index_dive_limit or more equality ranges. Thus, to permit use of index dives for up to N equality ranges, set eq_range_index_dive_limit to N + 1. To disable use of index statistics and always use index dives regardless of N, set eq_range_index_dive_limit to 0.

  For more information, see Equality Range Optimization of Many-Valued Comparisons.

  To update table index statistics for best estimates, use ANALYZE TABLE.

• error_count

  The number of errors that resulted from the last statement that generated messages. This variable is read only. See Section 13.7.7.17, “SHOW ERRORS Statement”.

• event_scheduler

  Property	Value
  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 are ON, OFF, and DISABLED, with the default being OFF. Turning the Event Scheduler OFF is not the same as disabling the Event Scheduler, which requires setting the status to DISABLED. This variable and its effects on the Event Scheduler's operation are discussed in greater detail in Section 24.4.2, “Event Scheduler Configuration”

• explicit_defaults_for_timestamp

  Property	Value
  Command-Line Format	--explicit-defaults-for-timestamp[={OFF|ON}]
  Deprecated	Yes
  System Variable	explicit_defaults_for_timestamp
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  This system variable determines whether the server enables certain nonstandard behaviors for default values and NULL-value handling in TIMESTAMP columns. By default, explicit_defaults_for_timestamp is enabled, which disables the nonstandard behaviors. Disabling explicit_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.

  If explicit_defaults_for_timestamp is disabled, the server enables the nonstandard behaviors and handles TIMESTAMP columns as follows:

  • TIMESTAMP columns not explicitly declared with the NULL attribute are automatically declared with the NOT NULL attribute. Assigning such a column a value of NULL is permitted and sets the column to the current timestamp.

  • The first TIMESTAMP column in a table, if not explicitly declared with the NULL attribute or an explicit DEFAULT or ON UPDATE attribute, is automatically declared with the DEFAULT CURRENT_TIMESTAMP and ON UPDATE CURRENT_TIMESTAMP attributes.

  • TIMESTAMP columns following the first one, if not explicitly declared with the NULL attribute or an explicit DEFAULT attribute, are automatically declared as DEFAULT '0000-00-00 00:00:00' (the “zero” timestamp). For inserted rows that specify no explicit value for such a column, the column is assigned '0000-00-00 00:00:00' and no warning occurs.

    Depending on whether strict SQL mode or the NO_ZERO_DATE SQL mode is enabled, a default value of '0000-00-00 00:00:00' may be invalid. Be aware that the TRADITIONAL SQL mode includes strict mode and NO_ZERO_DATE. See Section 5.1.11, “Server SQL Modes”.

  The nonstandard behaviors just described are deprecated and will be removed in a future MySQL release.

  If explicit_defaults_for_timestamp is enabled, the server disables the nonstandard behaviors and handles TIMESTAMP columns as follows:

  • It is not possible to assign a TIMESTAMP column a value of NULL to set it to the current timestamp. To assign the current timestamp, set the column to CURRENT_TIMESTAMP or a synonym such as NOW().

  • TIMESTAMP columns not explicitly declared with the NOT NULL attribute are automatically declared with the NULL attribute and permit NULL values. Assigning such a column a value of NULL sets it to NULL, not the current timestamp.

  • TIMESTAMP columns declared with the NOT NULL attribute do not permit NULL values. For inserts that specify NULL for such a column, the result is either an error for a single-row insert or if strict SQL mode is enabled, or '0000-00-00 00:00:00' is inserted for multiple-row inserts with strict SQL mode disabled. In no case does assigning the column a value of NULL set it to the current timestamp.

  • TIMESTAMP columns explicitly declared with the NOT NULL attribute and without an explicit DEFAULT attribute are treated as having no default value. For inserted rows that specify no explicit value for such a column, the result depends on the SQL mode. If strict SQL mode is enabled, an error occurs. If strict SQL mode is not enabled, the column is declared with the implicit default of '0000-00-00 00:00:00' and a warning occurs. This is similar to how MySQL treats other temporal types such as DATETIME.

  • No TIMESTAMP column is automatically declared with the DEFAULT CURRENT_TIMESTAMP or ON UPDATE CURRENT_TIMESTAMP attributes. Those attributes must be explicitly specified.

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

  If explicit_defaults_for_timestamp is disabled at server startup, this warning appears in the error log:

  [Warning] TIMESTAMP with implicit DEFAULT value is deprecated.
  Please use --explicit_defaults_for_timestamp server option (see
  documentation for more details).

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

  Note

  explicit_defaults_for_timestamp is itself deprecated because its only purpose is to permit control over deprecated TIMESTAMP behaviors that are to be removed in a future MySQL release. When removal of those behaviors occurs, explicit_defaults_for_timestamp will have no purpose and will be removed as well.

  For additional information, see Section 11.2.5, “Automatic Initialization and Updating for TIMESTAMP and DATETIME”.

• external_user

  Property	Value
  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 is NULL. See Section 6.2.18, “Proxy Users”.

• flush

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

  If ON, the server flushes (synchronizes) all changes to disk after each SQL statement. Normally, MySQL does a write of all changes to disk only after each SQL statement and lets the operating system handle the synchronizing to disk. See Section B.4.3.3, “What to Do If MySQL Keeps Crashing”. This variable is set to ON if you start mysqld with the --flush option.

  Note

  If flush is enabled, the value of flush_time does not matter and changes to flush_time have no effect on flush behavior.

• flush_time

  Property	Value
  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

  If this is set to a nonzero value, all tables are closed every flush_time seconds to free up resources and synchronize unflushed data to disk. This option is best used only on systems with minimal resources.

  Note

  If flush is enabled, the value of flush_time does not matter and changes to flush_time have no effect on flush behavior.

• foreign_key_checks

  Property	Value
  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, an ALTER TABLE operation returns an error if a foreign key definition is incorrectly formed. For more information, see Section 13.1.20.5, “FOREIGN KEY Constraints”.

  Setting this variable has the same effect on NDB tables as it does for InnoDB tables. Typically you leave this setting enabled during normal operation, to enforce referential integrity. Disabling foreign key checking can be useful for reloading InnoDB tables in an order different from that required by their parent/child relationships. See Section 13.1.20.5, “FOREIGN KEY Constraints”.

  Setting foreign_key_checks to 0 also affects data definition statements: DROP SCHEMA drops a schema even if it contains tables that have foreign keys that are referred to by tables outside the schema, and DROP TABLE drops tables that have foreign keys that are referred to by other tables.

  Note

  Setting foreign_key_checks to 1 does not trigger a scan of the existing table data. Therefore, rows added to the table while foreign_key_checks = 0 will not be verified for consistency.

  Dropping an index required by a foreign key constraint is not permitted, even with foreign_key_checks=0. The foreign key constraint must be removed before dropping the index.

• ft_boolean_syntax

  Property	Value
  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 using IN BOOLEAN MODE. See Section 12.9.2, “Boolean Full-Text Searches”.

  The default variable value is '+ -><()~*:""&|'. The rules for changing the value are as follows:

  • Operator function is determined by position within the string.

  • The replacement value must be 14 characters.

  • Each character must be an ASCII nonalphanumeric character.

  • Either the first or second character must be a space.

  • No duplicates are permitted except the phrase quoting operators in positions 11 and 12. These two characters are not required to be the same, but they are the only two that may be.

  • Positions 10, 13, and 14 (which by default are set to :, &, and |) are reserved for future extensions.

• ft_max_word_len

  Property	Value
  Command-Line Format	--ft-max-word-len=#
  System Variable	ft_max_word_len
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Integer
  Minimum Value	10

  The maximum length of the word to be included in a MyISAM FULLTEXT index.

  Note

  FULLTEXT indexes on MyISAM tables must be rebuilt after changing this variable. Use REPAIR TABLE tbl_name QUICK.

• ft_min_word_len

  Property	Value
  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

  The minimum length of the word to be included in a MyISAM FULLTEXT index.

  Note

  FULLTEXT indexes on MyISAM tables must be rebuilt after changing this variable. Use REPAIR TABLE tbl_name QUICK.

• ft_query_expansion_limit

  Property	Value
  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 using WITH QUERY EXPANSION.

• ft_stopword_file

  Property	Value
  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 on MyISAM tables. The server looks for the file in the data directory unless an absolute path name is given to specify a different directory. All the words from the file are used; comments are not honored. By default, a built-in list of stopwords is used (as defined in the storage/myisam/ft_static.c file). Setting this variable to the empty string ('') disables stopword filtering. See also Section 12.9.4, “Full-Text Stopwords”.

  Note

  FULLTEXT indexes on MyISAM tables must be rebuilt after changing this variable or the contents of the stopword file. Use REPAIR TABLE tbl_name QUICK.

• general_log

  Property	Value
  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 (or OFF) to disable the log or 1 (or ON) to enable the log. The destination for log output is controlled by the log_output system variable; if that value is NONE, no log entries are written even if the log is enabled.

• general_log_file

  Property	Value
  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 is host_name.log, but the initial value can be changed with the --general_log_file option.

• generated_random_password_length

  Property	Value
  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 for CREATE USER, ALTER USER, and SET PASSWORD statements. For more information, see Random Password Generation.

• group_concat_max_len

  Property	Value
  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 the GROUP_CONCAT() function. The default is 1024.

• have_compress

  YES if the zlib compression library is available to the server, NO if not. If not, the COMPRESS() and UNCOMPRESS() functions cannot be used.

• have_dynamic_loading

  YES if mysqld supports dynamic loading of plugins, NO if not. If the value is NO, you cannot use options such as --plugin-load to load plugins at server startup, or the INSTALL PLUGIN statement to load plugins at runtime.

• have_geometry

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

• have_openssl

  This variable is an alias for have_ssl.

• have_profiling

  YES if statement profiling capability is present, NO if not. If present, the profiling system variable controls whether this capability is enabled or disabled. See Section 13.7.7.31, “SHOW PROFILES Statement”.

  This variable is deprecated and will 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 of NO, and will be removed in a future MySQL release.

• have_rtree_keys

  YES if RTREE indexes are available, NO if not. (These are used for spatial indexes in MyISAM tables.)

• have_ssl

  Property	Value
  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 the server, but the server was not started with the necessary options to enable it)

  YES if mysqld supports SSL connections, DISABLED if the server was compiled with SSL support, but was not started with the appropriate connection-encryption options. For more information, see Section 2.9.6, “Configuring SSL Library Support”.

• have_statement_timeout

  Property	Value
  System Variable	have_statement_timeout
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Boolean

  Whether the statement execution timeout feature is available (see Statement Execution Time Optimizer Hints). The value can be NO if the background thread used by this feature could not be initialized.

• have_symlink

  YES if symbolic link support is enabled, NO if not. This is required on Unix for support of the DATA DIRECTORY and INDEX DIRECTORY table options. If the server is started with the --skip-symbolic-links option, the value is DISABLED.

  This variable has no meaning on Windows.

  Note

  Symbolic link support, along with the --symbolic-links option that controls it, is deprecated and will be removed in a future version of MySQL. In addition, the option is disabled by default. The related have_symlink system variable also is deprecated and will be removed in a future version of MySQL.

• histogram_generation_max_mem_size

  Property	Value
  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

  The maximum amount of memory available for generating histogram statistics. See Section 8.9.6, “Optimizer Statistics”, and Section 13.7.3.1, “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. See Section 5.1.9.1, “System Variable Privileges”.

• host_cache_size

  Property	Value
  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

  This variable controls the size of the host cache, as well as the size of the Performance Schema host_cache table that exposes the cache contents. Setting the size to 0 disables the host cache. Changing the cache size at runtime causes an implicit FLUSH HOSTS operation that clears the host cache, truncates the host_cache table, and unblocks any blocked hosts.

  The default value is autosized to 128, plus 1 for a value of max_connections up to 500, plus 1 for every increment of 20 over 500 in the max_connections value, capped to a limit of 2000.

  Using the --skip-host-cache option is similar to setting the host_cache_size system variable to 0, but host_cache_size is more flexible because it can also be used to resize, enable, and disable the host cache at runtime, not just at server startup. Starting the server with --skip-host-cache does not prevent changes to the value of host_cache_size, but such changes have no effect and the cache is not re-enabled even if host_cache_size is set larger than 0 at runtime.

  For more information about how the host cache works, see Section 5.1.12.3, “DNS Lookups and the Host Cache”.

• hostname

  Property	Value
  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 the last_insert_id variable. It exists for compatibility with other database systems. You can read its value with SELECT @@identity, and set it using SET identity.

• init_connect

  Property	Value
  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 the CONNECTION_ADMIN privilege (or the deprecated SUPER privilege), the content of init_connect is not executed. This is done so that an erroneous value for init_connect does not prevent all clients from connecting. For example, the value might contain a statement that has a syntax error, thus causing client connections to fail. Not executing init_connect for users that have the CONNECTION_ADMIN or SUPER privilege enables them to open a connection and fix the init_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 thus init_connect execution will fail, leaving the client unable to connect. Skipping init_connect execution enables the user to connect and change password.

  The server discards any result sets produced by statements in the value of init_connect.

• information_schema_stats_expiry

  Property	Value
  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

  Some INFORMATION_SCHEMA tables contain columns that provide table statistics:

  STATISTICS.CARDINALITY
  TABLES.AUTO_INCREMENT
  TABLES.AVG_ROW_LENGTH
  TABLES.CHECKSUM
  TABLES.CHECK_TIME
  TABLES.CREATE_TIME
  TABLES.DATA_FREE
  TABLES.DATA_LENGTH
  TABLES.INDEX_LENGTH
  TABLES.MAX_DATA_LENGTH
  TABLES.TABLE_ROWS
  TABLES.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 the mysql.index_stats and mysql.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 the mysql.index_stats and mysql.table_stats dictionary tables. Subsequent queries retrieve the cached statistics until the cached statistics expire.

  The information_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, use ANALYZE TABLE.

  To always retrieve the latest statistics directly from the storage engine and bypass cached values, set information_schema_stats_expiry to 0.

  Querying statistics columns does not store or update statistics in the mysql.index_stats and mysql.table_stats dictionary tables under these circumstances:

  • When cached statistics have not expired.

  • When information_schema_stats_expiry is set to 0.

  • When the server is started in read_only, super_read_only, transaction_read_only, or innodb_read_only mode.

  • When the query also fetches Performance Schema data.

  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, see Section 8.2.3, “Optimizing INFORMATION_SCHEMA Queries”.

• init_file

  Property	Value
  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 bootstap mode and some functionality is unavailable that limits the statements permitted in the file. These include statements that relate to account management (such as CREATE USER or GRANT), replication, and global transaction identifiers. See Section 17.1.3, “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 as sql_mode, character_set_server, collation_server, completion_type, explicit_defaults_for_timestamp, and default_table_encryption.

  These threads are also used to execute the statements in any file specified with init_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 in Section 15.14, “InnoDB Startup Options and System Variables”. These variables control many aspects of storage, memory use, and I/O patterns for InnoDB tables, and are especially important now that InnoDB is the default storage engine.

• insert_id

  The value to be used by the following INSERT or ALTER TABLE statement when inserting an AUTO_INCREMENT value. This is mainly used with the binary log.

• interactive_timeout

  Property	Value
  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

  The number of seconds the server waits for activity on an interactive connection before closing it. An interactive client is defined as a client that uses the CLIENT_INTERACTIVE option to mysql_real_connect(). See also wait_timeout.

• internal_tmp_disk_storage_engine

  Property	Value
  Command-Line Format	--internal-tmp-disk-storage-engine=#
  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 the InnoDB 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 (see Storage Engine for On-Disk Internal Temporary Tables). Permitted values are MYISAM and INNODB (the default).

• internal_tmp_mem_storage_engine

  Property	Value
  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	TempTable MEMORY

  The storage engine for in-memory internal temporary tables (see Section 8.4.4, “Internal Temporary Table Use in MySQL”). Permitted values are TempTable (the default) and MEMORY.

  The optimizer uses the storage engine defined by internal_tmp_mem_storage_engine for in-memory internal temporary tables.

• join_buffer_size

  Property	Value
  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 (Other, 64-bit platforms)	18446744073709547520
  Maximum Value (Other, 32-bit platforms)	4294967295
  Maximum Value (Windows)	4294967295

  The minimum size of the buffer that is used for plain index scans, range index scans, and joins that do not use indexes and thus perform full table scans. Normally, the best way to get fast joins is to add indexes. Increase the value of join_buffer_size to get a faster full join when adding indexes is not possible. One join buffer is allocated for each full join between two tables. For a complex join between several tables for which indexes are not used, multiple join buffers might be necessary.

  Unless a Block Nested-Loop or Batched Key Access algorithm is used, there is no gain from setting the buffer larger than required to hold each matching row, and all joins allocate at least the minimum size, so use caution in setting this variable to a large value globally. It is better to keep the global setting small and change the session setting to a larger value only in sessions that are doing large joins, or change the setting on a per-query basis by using a SET_VAR optimizer hint (see Section 8.9.3, “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 of join_buffer_size defines how large the batch of keys is in each request to the storage engine. The larger the buffer, the more sequential access will be to the right hand table of a join operation, which can significantly improve performance.

  The default is 256KB. The maximum permissible setting for join_buffer_size is 4GB−1. Larger values are permitted for 64-bit platforms (except 64-bit Windows, for which large values are truncated to 4GB−1 with a warning).

  For additional information about join buffering, see Section 8.2.1.7, “Nested-Loop Join Algorithms”. For information about Batched Key Access, see Section 8.2.1.12, “Block Nested-Loop and Batched Key Access Joins”.

• keep_files_on_create

  Property	Value
  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 a MyISAM table is created with no DATA DIRECTORY option, the .MYD file is created in the database directory. By default, if MyISAM finds an existing .MYD file in this case, it overwrites it. The same applies to .MYI files for tables created with no INDEX DIRECTORY option. To suppress this behavior, set the keep_files_on_create variable to ON (1), in which case MyISAM will not overwrite existing files and returns an error instead. The default value is OFF (0).

  If a MyISAM table is created with a DATA DIRECTORY or INDEX DIRECTORY option and an existing .MYD or .MYI file is found, MyISAM always returns an error. It will not overwrite a file in the specified directory.

• key_buffer_size

  Property	Value
  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	8
  Maximum Value (64-bit platforms)	OS_PER_PROCESS_LIMIT
  Maximum Value (32-bit platforms)	4294967295

  Index blocks for MyISAM tables are buffered and are shared by all threads. key_buffer_size is the size of the buffer used for index blocks. The key buffer is also known as the key cache.

  The maximum permissible setting for key_buffer_size is 4GB−1 on 32-bit platforms. Larger values are permitted for 64-bit platforms. The effective maximum size might be less, depending on your available physical RAM and per-process RAM limits imposed by your operating system or hardware platform. The value of this variable indicates the amount of memory requested. Internally, the server allocates as much memory as possible up to this amount, but the actual allocation might be less.

  You can increase the value to get better index handling for all reads and multiple writes; on a system whose primary function is to run MySQL using the MyISAM storage engine, 25% of the machine's total memory is an acceptable value for this variable. However, you should be aware that, if you make the value too large (for example, more than 50% of the machine's total memory), your system might start to page and become extremely slow. This is because MySQL relies on the operating system to perform file system caching for data reads, so you must leave some room for the file system cache. You should also consider the memory requirements of any other storage engines that you may be using in addition to MyISAM.

  For even more speed when writing many rows at the same time, use LOCK TABLES. See Section 8.2.5.1, “Optimizing INSERT Statements”.

  You can check the performance of the key buffer by issuing a SHOW STATUS statement and examining the Key_read_requests, Key_reads, Key_write_requests, and Key_writes status variables. (See Section 13.7.7, “SHOW Statements”.) The Key_reads/Key_read_requests ratio should normally be less than 0.01. The Key_writes/Key_write_requests ratio is usually near 1 if you are using mostly updates and deletes, but might be much smaller if you tend to do updates that affect many rows at the same time or if you are using the DELAY_KEY_WRITE table option.

  The fraction of the key buffer in use can be determined using key_buffer_size in conjunction with the Key_blocks_unused status variable and the buffer block size, which is available from the key_cache_block_size system variable:

  1 - ((Key_blocks_unused * key_cache_block_size) / key_buffer_size)

  This value is an approximation because some space in the key buffer is allocated internally for administrative structures. Factors that influence the amount of overhead for these structures include block size and pointer size. As block size increases, the percentage of the key buffer lost to overhead tends to decrease. Larger blocks results in a smaller number of read operations (because more keys are obtained per read), but conversely an increase in reads of keys that are not examined (if not all keys in a block are relevant to a query).

  It is possible to create multiple MyISAM key caches. The size limit of 4GB applies to each cache individually, not as a group. See Section 8.10.2, “The MyISAM Key Cache”.

• key_cache_age_threshold

  Property	Value
  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)	18446744073709551615
  Maximum Value (32-bit platforms)	4294967295

  This value controls the demotion of buffers from the hot sublist of a key cache to the warm sublist. Lower values cause demotion to happen more quickly. The minimum value is 100. The default value is 300. See Section 8.10.2, “The MyISAM Key Cache”.

• key_cache_block_size

  Property	Value
  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

  The size in bytes of blocks in the key cache. The default value is 1024. See Section 8.10.2, “The MyISAM Key Cache”.

• key_cache_division_limit

  Property	Value
  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. See Section 8.10.2, “The MyISAM Key Cache”.

• large_files_support

  Property	Value
  System Variable	large_files_support
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No

  Whether mysqld was compiled with options for large file support.

• large_pages

  Property	Value
  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). See Section 8.12.3.2, “Enabling Large Page Support”.

• large_page_size

  Property	Value
  System Variable	large_page_size
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	0

  If large page support is enabled, this shows the size of memory pages. Large memory pages are supported only on Linux; on other platforms, the value of this variable is always 0. See Section 8.12.3.2, “Enabling Large Page Support”.

• last_insert_id

  The value to be returned from LAST_INSERT_ID(). This is stored in the binary log when you use LAST_INSERT_ID() in a statement that updates a table. Setting this variable does not update the value returned by the mysql_insert_id() C API function.

• lc_messages

  Property	Value
  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 is en_US. The server converts the argument to a language name and combines it with the value of lc_messages_dir to produce the location for the error message file. See Section 10.12, “Setting the Error Message Language”.

• lc_messages_dir

  Property	Value
  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 of lc_messages to produce the location for the error message file. See Section 10.12, “Setting the Error Message Language”.

• lc_time_names

  Property	Value
  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 the DATE_FORMAT(), DAYNAME() and MONTHNAME() functions. Locale names are POSIX-style values such as 'ja_JP' or 'pt_BR'. The default value is 'en_US' regardless of your system's locale setting. For further information, see Section 10.16, “MySQL Server Locale Support”.

• license

  Property	Value
  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

  Property	Value
  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-side LOCAL capability for LOAD DATA statements. Depending on the local_infile setting, the server refuses or permits local data loading by clients that have LOCAL enabled on the client side.

  To explicitly cause the server to refuse or permit LOAD DATA LOCAL statements (regardless of how client programs and libraries are configured at build time or runtime), start mysqld with local_infile disabled or enabled, respectively. local_infile can also be set at runtime. For more information, see Section 6.1.6, “Security Considerations for LOAD DATA LOCAL”.

• lock_wait_timeout

  Property	Value
  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

  This variable specifies the timeout in seconds for attempts to acquire metadata locks. The permissible values range from 1 to 31536000 (1 year). The default is 31536000.

  This timeout applies to all statements that use metadata locks. These include DML and DDL operations on tables, views, stored procedures, and stored functions, as well as LOCK TABLES, FLUSH TABLES WITH READ LOCK, and HANDLER statements.

  This timeout does not apply to implicit accesses to system tables in the mysql database, such as grant tables modified by GRANT or REVOKE statements or table logging statements. The timeout does apply to system tables accessed directly, such as with SELECT or UPDATE.

  The timeout value applies separately for each metadata lock attempt. A given statement can require more than one lock, so it is possible for the statement to block for longer than the lock_wait_timeout value before reporting a timeout error. When lock timeout occurs, ER_LOCK_WAIT_TIMEOUT is reported.

  lock_wait_timeout also defines the amount of time that a LOCK INSTANCE FOR BACKUP statement waits for a lock before giving up.

• locked_in_memory

  Property	Value
  System Variable	locked_in_memory
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No

  Whether mysqld was locked in memory with --memlock.

• log_error

  Property	Value
  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 is stderr. Otherwise, the destination is a file and the log_error value is the file name. See Section 5.4.2, “The Error Log”.

• log_error_services

  Property	Value
  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. Any loadable (not built in) component named in the log_error_services value must first be installed with INSTALL COMPONENT. For more information, see Section 5.4.2.1, “Error Log Component Configuration”.

• log_error_suppression_list

  Property	Value
  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

  The log_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 of WARNING or INFORMATION. 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 the log_filter_internal error log filter component, which is enabled by default (see Section 5.5.3, “Error Log Components”). If log_filter_internal is disabled, log_error_suppression_list has no effect.

  The log_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 the MY- prefix. Leading zeros in the numeric part are not significant. Examples of permitted code formats:

  ER_SERVER_SHUTDOWN_COMPLETE
  MY-000031
  000031
  MY-31
  31

  Symbolic values are preferable to numeric values for readability and portability. For information about the permitted error symbols and numbers, see Section B.3, “Error Message Reference”.

  The effect of log_error_suppression_list combines with that of log_error_verbosity. For additional information, see Section 5.4.2.4, “Priority-Based Error Log Filtering (log_filter_internal)”.

• log_error_verbosity

  Property	Value
  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

  The log_error_verbosity system variable specifies the verbosity for handling events intended for the error log. This variable affects filtering performed by the log_filter_internal error log filter component, which is enabled by default (see Section 5.5.3, “Error Log Components”). If log_filter_internal is disabled, log_error_verbosity has no effect.

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

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

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

  The effect of log_error_verbosity combines with that of log_error_suppression_list. For additional information, see Section 5.4.2.4, “Priority-Based Error Log Filtering (log_filter_internal)”.

• log_output

  Property	Value
  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 from TABLE, FILE, and NONE. TABLE selects logging to the general_log and slow_log tables in the mysql system schema. FILE selects logging to log files. NONE disables logging. If NONE is present in the value, it takes precedence over any other words that are present. TABLE and FILE can both be given to select both log output destinations.

  This variable selects log output destinations, but does not enable log output. To do that, enable the general_log and slow_query_log system variables. For FILE logging, the general_log_file and slow_query_log_file system variables determine the log file locations. For more information, see Section 5.4.1, “Selecting General Query Log and Slow Query Log Output Destinations”.

• log_queries_not_using_indexes

  Property	Value
  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. See Section 5.4.5, “The Slow Query Log”. This option does not necessarily mean that no index is used. For example, a query that uses a full index scan uses an index but would be logged because the index would not limit the number of rows.

• log_raw

  Property	Value
  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

  The log_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

  Property	Value
  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 include ALTER TABLE, ANALYZE TABLE, CHECK TABLE, CREATE INDEX, DROP INDEX, OPTIMIZE TABLE, and REPAIR TABLE.

• log_slow_extra

  Property	Value
  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 includes FILE, the server writes additional fields to log file lines that provide information about slow statements. See Section 5.4.5, “The Slow Query Log”. TABLE output is unaffected.

• log_syslog

  Property	Value
  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, and syslog on Unix and Unix-like systems).

  In MySQL 8.0, the log_sink_syseventlog log component implements error logging to the system log (see Section 5.4.2.7, “Error Logging to the System Log”), so this type of logging can be enabled by adding that component to the log_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

  Property	Value
  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 by syseventlog.facility.

• log_syslog_include_pid

  Property	Value
  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 by syseventlog.include_pid.

• log_syslog_tag

  Property	Value
  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 by syseventlog.tag.

• log_timestamps

  Property	Value
  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 with CONVERT_TZ() or by setting the session time_zone system variable.

  Permitted log_timestamps values are UTC (the default) and SYSTEM (the local system time zone).

  Timestamps are written using ISO 8601 / RFC 3339 format: YYYY-MM-DDThh:mm:ss.uuuuuu plus a tail value of Z signifying Zulu time (UTC) or ±hh:mm (an offset from UTC).

• log_throttle_queries_not_using_indexes

  Property	Value
  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

  If log_queries_not_using_indexes is enabled, the log_throttle_queries_not_using_indexes variable limits the number of such queries per minute that can be written to the slow query log. A value of 0 (the default) means “no limit”. For more information, see Section 5.4.5, “The Slow Query Log”.

• long_query_time

  Property	Value
  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

  If a query takes longer than this many seconds, the server increments the Slow_queries status variable. If the slow query log is enabled, the query is logged to the slow query log file. This value is measured in real time, not CPU time, so a query that is under the threshold on a lightly loaded system might be above the threshold on a heavily loaded one. The minimum and default values of long_query_time are 0 and 10, respectively. The value can be specified to a resolution of microseconds. See Section 5.4.5, “The Slow Query Log”.

  Smaller values of this variable result in more statements being considered long-running, with the result that more space is required for the slow query log. For very small values (less than one second), the log may grow quite large in a small time. Increasing the number of statements considered long-running may also result in false positives for the “excessive Number of Long Running Processes” alert in MySQL Enterprise Monitor, especially if Group Replication is enabled. For these reasons, very small values should be used in test environments only, or, in production environments, only for a short period.

• low_priority_updates

  Property	Value
  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 to 1, all INSERT, UPDATE, DELETE, and LOCK TABLE WRITE statements wait until there is no pending SELECT or LOCK TABLE READ on the affected table. 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 as MyISAM, MEMORY, and MERGE). See Section 8.11.2, “Table Locking Issues”.

• lower_case_file_system

  Property	Value
  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

  Property	Value
  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	0
  Minimum Value	0
  Maximum Value	2

  If set to 0, table names are stored as specified and comparisons are case-sensitive. If set to 1, table names are stored in lowercase on disk and comparisons are not case sensitive. If set to 2, table names are stored as given but compared in lowercase. This option also applies to database names and table aliases. For additional details, see Section 9.2.3, “Identifier Case Sensitivity”.

  On Windows the default value is 1. On macOS, the default value is 2. On Linux, a value of 2 is not supported; the server forces the value to 0 instead.

  You should not set lower_case_table_names to 0 if you are running MySQL on a system where the data directory resides on a case-insensitive file system (such as on Windows or macOS). It is an unsupported combination that could result in a hang condition when running an INSERT INTO ... SELECT ... FROM tbl_name operation with the wrong tbl_name lettercase. With MyISAM, 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.

  If you are using InnoDB tables, you should set this variable to 1 on all platforms to force names to be converted to lowercase.

  The setting of this variable affects the behavior of replication filtering options with regard to case sensitivity. For more information, see Section 17.2.5, “How Servers Evaluate Replication Filtering Rules”.

  It is prohibited to start the server with a lower_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 configure lower_case_table_names to the desired setting before initializing the server. In most cases, this requires configuring lower_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 the debconf-set-selection utility prior to installing MySQL using APT to enable lower_case_table_names. To do so, run this command before installing MySQL using APT:

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

  Note

  The ability to enable lower_case_table_names using debconf-set-selections was added in MySQL 8.0.17. Enabling lower_case_table_names sets the value to 1.

• mandatory_roles

  Property	Value
  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 setting mandatory_roles does not actually change any user accounts, and the granted roles are not visible in the mysql.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 of mandatory_roles requires the ROLE_ADMIN privilege, in addition to the SYSTEM_VARIABLES_ADMIN privilege (or the deprecated SUPER privilege) normally required to set a global system variable runtime value.

  Role names consist of a user part and host part in user_name@host_name format. The host part, if omitted, defaults to %. For additional information, see Section 6.2.5, “Specifying Role Names”.

  The mandatory_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 of mandatory_roles cannot be revoked with REVOKE or dropped with DROP ROLE or DROP USER.

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

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

  • If mandatory_roles is assigned a role at runtime that has the SYSTEM_USER privilege, an error occurs and the mandatory_roles value remains unchanged.

  Mandatory roles, like explicitly granted roles, do not take effect until activated (see Activating Roles). At login time, role activation occurs for all granted roles if the activate_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 to mandatory_roles but are created later may require special treatment to be considered mandatory. For details, see Defining Mandatory Roles.

  SHOW GRANTS displays mandatory roles according to the rules described in Section 13.7.7.21, “SHOW GRANTS Statement”.

• max_allowed_packet

  Property	Value
  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

  The maximum size of one packet or any generated/intermediate string, or any parameter sent by the mysql_stmt_send_long_data() C API function. The default is 64MB.

  The packet message buffer is initialized to net_buffer_length bytes, but can grow up to max_allowed_packet bytes when needed. This value by default is small, to catch large (possibly incorrect) packets.

  You must increase this value if you are using large BLOB columns or long strings. It should be as big as the largest BLOB you want to use. The protocol limit for max_allowed_packet is 1GB. The value should be a multiple of 1024; nonmultiples are rounded down to the nearest multiple.

  When you change the message buffer size by changing the value of the max_allowed_packet variable, you should also change the buffer size on the client side if your client program permits it. The default max_allowed_packet value built in to the client library is 1GB, but individual client programs might override this. For example, mysql and mysqldump have defaults of 16MB and 24MB, respectively. They also enable you to change the client-side value by setting max_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 will not send to the client more bytes than the current global max_allowed_packet value. (The global value could be less than the session value if the global value is changed after the client connects.)

• max_connect_errors

  Property	Value
  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

  After max_connect_errors successive connection requests from a host are interrupted without a successful connection, the server blocks that host from further connections. If a connection from a host is established successfully within fewer than max_connect_errors attempts after a previous connection was interrupted, the error count for the host is cleared to zero. However, once a host is blocked, flushing the host cache is the only way to unblock it. To flush the host cache, execute a FLUSH HOSTS statement, a TRUNCATE TABLE statement that truncates the Performance Schema host_cache table, or a mysqladmin flush-hosts command.

  For more information about how the host cache works, see Section 5.1.12.3, “DNS Lookups and the Host Cache”.

• max_connections

  Property	Value
  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. For more information, see Section 5.1.12.1, “Connection Interfaces”.

• max_delayed_threads

  Property	Value
  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 (because DELAYED inserts are not supported), and will be removed in a future release.

• max_digest_length

  Property	Value
  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

  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.

  Decreasing the max_digest_length value reduces memory use but causes the digest value of more statements to become indistinguishable if they differ only at the end. Increasing the value permits longer statements to be distinguished but increases memory use, particularly for workloads that involve large numbers of simultaneous sessions (the server allocates max_digest_length bytes per session).

  The parser uses this system variable as a limit on the maximum length of normalized statement digests that it computes. The Performance Schema, if it tracks statement digests, makes a copy of the digest value, using the performance_schema_max_digest_length. system variable as a limit on the maximum length of digests that it stores. Consequently, if performance_schema_max_digest_length is less than max_digest_length, digest values stored in the Performance Schema are truncated relative to the original digest values.

  For more information about statement digesting, see Section 26.10, “Performance Schema Statement Digests and Sampling”.

• max_error_count

  Property	Value
  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 the SHOW ERRORS and SHOW 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 by GET DIAGNOSTICS.

• max_execution_time

  Property	Value
  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

  The execution timeout for SELECT statements, in milliseconds. If the value is 0, timeouts are not enabled.

  max_execution_time applies as follows:

  • The global max_execution_time value provides the default for the session value for new connections. The session value applies to SELECT executions executed within the session that include no MAX_EXECUTION_TIME(N) optimizer hint or for which N is 0.

  • max_execution_time applies to read-only SELECT 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 for SELECT statements in stored programs.

• max_heap_table_size

  Property	Value
  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)	1844674407370954752
  Maximum Value (32-bit platforms)	4294967295

  This variable sets the maximum size to which user-created MEMORY tables are permitted to grow. The value of the variable is used to calculate MEMORY table MAX_ROWS values. Setting this variable has no effect on any existing MEMORY table, unless the table is re-created with a statement such as CREATE TABLE or altered with ALTER TABLE or TRUNCATE TABLE. A server restart also sets the maximum size of existing MEMORY tables to the global max_heap_table_size value.

  This variable is also used in conjunction with tmp_table_size to limit the size of internal in-memory tables. See Section 8.4.4, “Internal Temporary Table Use in MySQL”.

  max_heap_table_size is not replicated. See Section 17.5.1.21, “Replication and MEMORY Tables”, and Section 17.5.1.38, “Replication and Variables”, for more information.

• max_insert_delayed_threads

  Property	Value
  Deprecated	Yes
  System Variable	max_insert_delayed_threads
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer

  This variable is a synonym for max_delayed_threads.

  This system variable is deprecated (because DELAYED inserts are not supported), and will be removed in a future release.

• max_join_size

  Property	Value
  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

  Do not permit statements that probably need to examine more than max_join_size rows (for single-table statements) or row combinations (for multiple-table statements) or that are likely to do more than max_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 a WHERE clause, that take a long time, or that return millions of rows. For more information, see Using Safe-Updates Mode (--safe-updates).

  Setting this variable to a value other than DEFAULT resets the value of sql_big_selects to 0. If you set the sql_big_selects value again, the max_join_size variable is ignored.

• max_length_for_sort_data

  Property	Value
  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

  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 which filesort algorithm to use. See Section 8.2.1.16, “ORDER BY Optimization”.

• max_points_in_geometry

  Property	Value
  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 the points_per_circle argument to the ST_Buffer_Strategy() function.

• max_prepared_stmt_count

  Property	Value
  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

  Property	Value
  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 (64-bit platforms)	18446744073709551615
  Default Value (32-bit platforms)	4294967295
  Minimum Value	1
  Maximum Value (64-bit platforms)	18446744073709551615
  Maximum Value (32-bit platforms)	4294967295

  Limit the assumed maximum number of seeks when looking up rows based on a key. The MySQL optimizer assumes that no more than this number of key seeks are required when searching for matching rows in a table by scanning an index, regardless of the actual cardinality of the index (see Section 13.7.7.22, “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

  Property	Value
  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

  The number of bytes to use when sorting data values. The server uses only the first max_sort_length bytes of each value and ignores the rest. Consequently, values that differ only after the first max_sort_length bytes compare as equal for GROUP BY, ORDER BY, and DISTINCT operations.

  Increasing the value of max_sort_length may require increasing the value of sort_buffer_size as well. For details, see Section 8.2.1.16, “ORDER BY Optimization”

• max_sp_recursion_depth

  Property	Value
  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
  Maximum Value	255

  The number of times that any given stored procedure may be called recursively. The default value for this option is 0, which completely disables recursion in stored procedures. The maximum value is 255.

  Stored procedure recursion increases the demand on thread stack space. If you increase the value of max_sp_recursion_depth, it may be necessary to increase thread stack size by increasing the value of thread_stack at server startup.

• max_user_connections

  Property	Value
  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 nonzero MAX_USER_CONNECTIONS resource limit, the session max_user_connections value is set to that limit.

  • Otherwise, the session max_user_connections value is set to the global value.

  Account resource limits are specified using the CREATE USER or ALTER USER statement. See Section 6.2.20, “Setting Account Resource Limits”.

• max_write_lock_count

  Property	Value
  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 (64-bit platforms)	18446744073709551615
  Default Value (32-bit platforms)	4294967295
  Minimum Value	1
  Maximum Value (64-bit platforms)	18446744073709551615
  Maximum Value (32-bit platforms)	4294967295

  After this many write locks, permit some pending read lock requests to be processed in between. Write lock requests have higher priority than read lock requests. However, if max_write_lock_count is set to some low value (say, 10), read lock requests may be preferred over pending write lock requests if the read lock requests have already been passed over in favor of 10 write lock requests. Normally this behavior does not occur because max_write_lock_count by default has a very large value.

• mecab_rc_file

  Property	Value
  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

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

  The mecab_rc_file option defines the path to the mecabrc configuration file, which is the configuration file for MeCab. The option is read-only and can only be set at startup. The mecabrc configuration file is required to initialize MeCab.

  For information about the MeCab full-text parser, see Section 12.9.9, “MeCab Full-Text Parser Plugin”.

  For information about options that can be specified in the MeCab mecabrc configuration file, refer to the MeCab Documentation on the Google Developers site.

• metadata_locks_cache_size

  Property	Value
  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

  This system variable was removed in MySQL 8.0.13.

• metadata_locks_hash_instances

  Property	Value
  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

  Property	Value
  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.

• myisam_data_pointer_size

  Property	Value
  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

  The default pointer size in bytes, to be used by CREATE TABLE for MyISAM tables when no MAX_ROWS option is specified. This variable cannot be less than 2 or larger than 7. The default value is 6. See Section B.4.2.11, “The table is full”.

• myisam_max_sort_file_size

  Property	Value
  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 (64-bit platforms)	9223372036854775807
  Default Value (32-bit platforms)	2147483648

  The maximum size of the temporary file that MySQL is permitted to use while re-creating a MyISAM index (during REPAIR TABLE, ALTER TABLE, or LOAD DATA). If the file size would be larger than this value, the index is created using the key cache instead, which is slower. The value is given in bytes.

  If MyISAM index files exceed this size and disk space is available, increasing the value may help performance. The space must be available in the file system containing the directory where the original index file is located.

• myisam_mmap_size

  Property	Value
  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

  The maximum amount of memory to use for memory mapping compressed MyISAM files. If many compressed MyISAM tables are used, the value can be decreased to reduce the likelihood of memory-swapping problems.

• myisam_recover_options

  Property	Value
  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 the MyISAM storage engine recovery mode. The variable value is any combination of the values of OFF, DEFAULT, BACKUP, FORCE, or QUICK. If you specify multiple values, separate them by commas. Specifying the variable with no value at server startup is the same as specifying DEFAULT, and specifying with an explicit value of "" disables recovery (same as a value of OFF). If recovery is enabled, each time mysqld opens a MyISAM table, it checks whether the table is marked as crashed or was not closed properly. (The last option works only if you are running with external locking disabled.) If this is the case, mysqld runs a check on the table. If the table was corrupted, mysqld attempts to repair it.

  The following options affect how the repair works.

  Option	Description
  OFF	No recovery.
  DEFAULT	Recovery without backup, forcing, or quick checking.
  BACKUP	If the data file was changed during recovery, save a backup of the tbl_name.MYD file as tbl_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 options BACKUP,FORCE. This forces a repair of a table even if some rows would be deleted, but it keeps the old data file as a backup so that you can later examine what happened.

  See Section 16.2.1, “MyISAM Startup Options”.

• myisam_repair_threads

  Property	Value
  Command-Line Format	--myisam-repair-threads=#
  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

  If this value is greater than 1, MyISAM table indexes are created in parallel (each index in its own thread) during the Repair by sorting process. The default value is 1.

  Note

  Multithreaded repair is still beta-quality code.

• myisam_sort_buffer_size

  Property	Value
  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 (Other, 64-bit platforms)	18446744073709551615
  Maximum Value (Other, 32-bit platforms)	4294967295
  Maximum Value (Windows, 64-bit platforms)	18446744073709551615
  Maximum Value (Windows, 32-bit platforms)	4294967295

  The size of the buffer that is allocated when sorting MyISAM indexes during a REPAIR TABLE or when creating indexes with CREATE INDEX or ALTER TABLE.

• myisam_stats_method

  Property	Value
  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_equal nulls_unequal nulls_ignored

  How the server treats NULL values when collecting statistics about the distribution of index values for MyISAM tables. This variable has three possible values, nulls_equal, nulls_unequal, and nulls_ignored. For nulls_equal, all NULL index values are considered equal and form a single value group that has a size equal to the number of NULL values. For nulls_unequal, NULL values are considered unequal, and each NULL forms a distinct value group of size 1. For nulls_ignored, NULL values are ignored.

  The method that is used for generating table statistics influences how the optimizer chooses indexes for query execution, as described in Section 8.3.8, “InnoDB and MyISAM Index Statistics Collection”.

• myisam_use_mmap

  Property	Value
  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 writing MyISAM tables.

• mysql_native_password_proxy_users

  Property	Value
  Command-Line Format	--mysql-native-password-proxy-users[={OFF|ON}]
  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 the mysql_native_password built-in authentication plugin supports proxy users. It has no effect unless the check_proxy_users system variable is enabled. For information about user proxying, see Section 6.2.18, “Proxy Users”.

• named_pipe

  Property	Value
  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

  Property	Value
  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	*everyone*
  Valid Values	*everyone* empty string

  (Windows only.) The access control granted to clients on the named pipe created by the MySQL server is set to the minimum necessary for successful communication when the named_pipe system variable is enabled to support named-pipe connections. Newer MySQL client software can open named pipe connections without any additional configuration, however, older 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 older named-pipe clients. Initially, the value is set to '*everyone*' by default, which permits users of the Everyone group on Windows to continue using older clients until the older clients are upgraded. In contrast, setting the value to an empty string means that no Windows user will be granted full access to the named pipe. The default value '*everyone*' provides a language-independent way of referring to the Everyone group on Windows.

  Ideally, a new Windows local group name (for example, mysql_old_client_users) should be created in Windows and then used to replace the default value for this variable when access to older client software 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 older named-pipe client is denied access until the user is added to the group by a Windows administrator, and then the user logs out and logs in (required by Windows).

• net_buffer_length

  Property	Value
  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

  Each client thread is associated with a connection buffer and result buffer. Both begin with a size given by net_buffer_length but are dynamically enlarged up to max_allowed_packet bytes as needed. The result buffer shrinks to net_buffer_length after each SQL statement.

  This variable should not normally be changed, but if you have very little memory, you can set it to the expected length of statements sent by clients. If statements exceed this length, the connection buffer is automatically enlarged. The maximum value to which net_buffer_length can be set is 1MB.

  The session value of this variable is read only.

• net_read_timeout

  Property	Value
  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

  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 also slave_net_timeout.

• net_retry_count

  Property	Value
  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

  Property	Value
  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

  The number of seconds to wait for a block to be written to a connection before aborting the write. See also net_read_timeout.

• new

  Property	Value
  Command-Line Format	--new[={OFF|ON}]
  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 always OFF.

  In NDB Cluster, setting this variable to ON makes it possible to employ partitioning types other than KEY or LINEAR KEY with NDB tables. This feature is experimental only, and not supported in production. For additional information, see User-defined partitioning and the NDB storage engine (NDB Cluster).

• ngram_token_size

  Property	Value
  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. The ngram_token_size option is read-only and can only be modified at startup. The default value is 2 (bigram). The maximum value is 10.

  For more information about how to configure this variable, see Section 12.9.8, “ngram Full-Text Parser”.

• offline_mode

  Property	Value
  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

  Whether the server is in “offline mode”, which has these characteristics:

  • Connected client users who do not have the CONNECTION_ADMIN privilege (or the deprecated SUPER privilege) are disconnected on the next request, with an appropriate error. Disconnection includes terminating running statements and releasing locks. Such clients also cannot initiate new connections, and receive an appropriate error.

  • Connected client users who have the CONNECTION_ADMIN or SUPER privilege are not disconnected, and can initiate new connections to manage the server.

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

  Only users who have the SYSTEM_VARIABLES_ADMIN or SUPER privilege can control offline mode. To put a server in offline mode, change the value of the offline_mode system variable from OFF to ON. To resume normal operations, change offline_mode from ON to OFF. In offline mode, clients that are refused access receive an ER_SERVER_OFFLINE_MODE error.

• old

  Property	Value
  Command-Line Format	--old[={OFF|ON}]
  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.

  When old is enabled, it changes the default scope of index hints to that used prior to MySQL 5.1.17. That is, index hints with no FOR clause apply only to how indexes are used for row retrieval and not to resolution of ORDER BY or GROUP BY clauses. (See Section 8.9.4, “Index Hints”.) Take care about enabling this in a replication setup. With statement-based binary logging, having different modes for the master and slaves might lead to replication errors.

• old_alter_table

  Property	Value
  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 an ALTER TABLE operation. It reverts to using a temporary table, copying over the data, and then renaming the temporary table to the original, as used by MySQL 5.0 and earlier. For more information on the operation of ALTER TABLE, see Section 13.1.9, “ALTER TABLE Statement”.

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

• open_files_limit

  Property	Value
  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 to mysqld from the operating system. mysqld reserves descriptors with setrlimit(), using the value requested at startup by setting this variable directly or by using the --open-files-limit option to mysqld_safe. If mysqld produces the error Too many open files, try increasing the open_files_limit value. Internally, the maximum value for this variable is the maximum unsigned integer value, but the actual maximum is platform dependent.

  The value of open_files_limit at runtime indicates the number of file descriptors actually permitted to mysqld by the operating system, which might differ from the value requested at startup. If the number of file descriptors requested during startup cannot be allocated, mysqld writes a warning to the error log.

  The effective open_files_limit value is based on the value specified at system startup (if any) and the values of max_connections and table_open_cache, using these formulas:

  • 10 + max_connections + (table_open_cache * 2)

  • max_connections * 5

  • Operating system limit if that limit is positive but not Infinity

  • If 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 will permit.

  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 ulimit -n.

• optimizer_prune_level

  Property	Value
  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

  Property	Value
  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

  Property	Value
  Command-Line Format	--optimizer-switch=value
  System Variable	optimizer_switch
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	Yes
  Type	Set
  Valid Values (≥ 8.0.21)	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} use_index_extensions={on|off} use_invisible_indexes={on|off}
  Valid Values (≥ 8.0.18)	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)	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}

  The optimizer_switch system variable enables control over optimizer behavior. The value of this variable is a set of flags, each of which has a value of on or off 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

  For more information about the syntax of this variable and the optimizer behaviors that it controls, see Section 8.9.2, “Switchable Optimizations”.

• optimizer_trace

  Property	Value
  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, see MySQL Internals: Tracing the Optimizer.

• optimizer_trace_features

  Property	Value
  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, see MySQL Internals: Tracing the Optimizer.

• optimizer_trace_limit

  Property	Value
  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

  The maximum number of optimizer traces to display. For details, see MySQL Internals: Tracing the Optimizer.

• optimizer_trace_max_mem_size

  Property	Value
  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

  The maximum cumulative size of stored optimizer traces. For details, see MySQL Internals: Tracing the Optimizer.

• optimizer_trace_offset

  Property	Value
  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

  The offset of optimizer traces to display. For details, see MySQL Internals: Tracing the Optimizer.

• performance_schema_xxx

  Performance Schema system variables are listed in Section 26.15, “Performance Schema System Variables”. These variables may be used to configure Performance Schema operation.

• parser_max_mem_size

  Property	Value
  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

  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

  Property	Value
  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 global UPDATE privilege can be restricted from exercising this privilege on the mysql system schema. (Or, stated another way, the user is enabled to exercise the UPDATE privilege on all schemas except the mysql schema.) In this sense, the user's global UPDATE privilege is partially revoked.

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

  • For attempts to disable partial_revokes at startup, the server logs an error message and enables partial_revokes.

  • For attempts to disable partial_revokes at runtime, an error occurs and the partial_revokes value remains unchanged.

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

  For more information, including instructions for removing partial revokes, see Section 6.2.12, “Privilege Restriction Using Partial Revokes”.

• password_history

  Property	Value
  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 the PASSWORD HISTORY DEFAULT option.

  The global number-of-changes password reuse policy can be overridden as desired for individual accounts using the PASSWORD HISTORY option of the CREATE USER and ALTER USER statements. See Section 6.2.15, “Password Management”.

• password_require_current

  Property	Value
  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 the PASSWORD REQUIRE CURRENT DEFAULT option.

  The global verification-required policy can be overridden as desired for individual accounts using the PASSWORD REQUIRE option of the CREATE USER and ALTER USER statements. See Section 6.2.15, “Password Management”.

• password_reuse_interval

  Property	Value
  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

  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 the PASSWORD REUSE INTERVAL DEFAULT option.

  The global time-elapsed password reuse policy can be overridden as desired for individual accounts using the PASSWORD REUSE INTERVAL option of the CREATE USER and ALTER USER statements. See Section 6.2.15, “Password Management”.

• persisted_globals_load

  Property	Value
  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 the mysqld-auto.cnf file in the data directory. The server normally processes this file at startup after all other option files (see Section 4.2.2.2, “Using Option Files”). Disabling persisted_globals_load causes the server startup sequence to skip mysqld-auto.cnf.

  To modify the contents of mysqld-auto.cnf, use the SET PERSIST, SET PERSIST_ONLY, and RESET PERSIST statements. See Section 5.1.9.3, “Persisted System Variables”.

• persist_only_admin_x509_subject

  Property	Value
  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 and SET PERSIST_ONLY enable system variables to be persisted to the mysqld-auto.cnf option file in the data directory (see Section 13.7.6.1, “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 acan be persisted only under certain restrictive conditions.

  The persist_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.

  If persist_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 use SET PERSIST_ONLY to persist persist-restricted system variables. For information about persist-restricted system variables and instructions for configuring MySQL to enable persist_only_admin_x509_subject, see Section 5.1.9.4, “Nonpersistible and Persist-Restricted System Variables”.

• pid_file

  Property	Value
  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 of host_name.pid, where host_name is the name of the host machine.

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

• plugin_dir

  Property	Value
  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 using SELECT ... INTO DUMPFILE. This can be prevented by making plugin_dir read only to the server or by setting secure_file_priv to a directory where SELECT writes can be made safely.

• port

  Property	Value
  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

  Property	Value
  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

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

• print_identified_with_as_hex

  Property	Value
  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 the IDENTIFIED WITH clause of output from SHOW CREATE USER may contain unprintable characters that have adverse effects on terminal displays and in other environments. Enabling print_identified_with_as_hex causes SHOW 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 or OFF (the default), statement profiling is disabled. If set to 1 or ON, statement profiling is enabled and the SHOW PROFILE and SHOW PROFILES statements provide access to profiling information. See Section 13.7.7.31, “SHOW PROFILES Statement”.

  This variable is deprecated and will be removed in a future MySQL release.

• profiling_history_size

  The number of statements for which to maintain profiling information if profiling is enabled. The default value is 15. The maximum value is 100. Setting the value to 0 effectively disables profiling. See Section 13.7.7.31, “SHOW PROFILES Statement”.

  This variable is deprecated and will be removed in a future MySQL release.

• protocol_compression_algorithms

  Property	Value
  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 master/slave replication or Group Replication. Compression does not apply to connections for FEDERATED tables.

  protocol_compression_algorithms does not control connection compression for X Protocol. See Section 20.5.5, “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 the zlib compression algorithm.

  • zstd: Permit connections that use the zstd compression algorithm (zstd 1.3).

  • uncompressed: Permit uncompressed connections. If this algorithm name is not included in the protocol_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 of zlib,zstd,uncompressed indicates that the server permits all compression algorithms.

  For more information, see Section 4.2.7, “Connection Compression Control”.

• protocol_version

  Property	Value
  System Variable	protocol_version
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Integer

  The version of the client/server protocol used by the MySQL server.

• proxy_user

  Property	Value
  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 is NULL. See Section 6.2.18, “Proxy Users”.

• pseudo_slave_mode

  Property	Value
  System Variable	pseudo_slave_mode
  Scope	Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer

  This system variable is for internal server use. pseudo_slave_mode assists with the correct handling of transactions that originated on older or newer servers than the server currently processing them. mysqlbinlog sets the value of pseudo_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 the REPLICATION_APPLIER privilege (see Section 17.3.3, “Replication Privilege Checks”), or privileges sufficient to set restricted session variables (see Section 5.1.9.1, “System Variable Privileges”). However, note that the variable is not intended for users to set; it is set automatically by the replication infrastructure.

  pseudo_slave_mode has the following effects on the handling of prepared XA transactions, which can be attached to or detached from the handling session (by default, the session that issues XA START):

  • If true, and the handling session has executed an internal-use BINLOG statement, XA transactions are automatically detached from the session as soon as the first part of the transaction up to XA PREPARE finishes, so they can be committed or rolled back by any session that has the XA_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_slave_mode has the following effects on the original_commit_timestamp replication delay timestamp and the original_server_version system variable:

  • If true, transactions that do not explicitly set original_commit_timestamp or original_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 set original_commit_timestamp or original_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_slave_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 with ER_UNSUPPORTED_SQL_MODE.

• pseudo_thread_id

  Property	Value
  System Variable	pseudo_thread_id
  Scope	Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer

  This variable is for internal server use.

  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. See Section 5.1.9.1, “System Variable Privileges”.

• query_alloc_block_size

  Property	Value
  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	4294967295
  Block Size	1024

  The allocation size of memory blocks that are allocated for objects created during statement parsing and execution. If you have problems with memory fragmentation, it might help to increase this parameter.

• query_prealloc_size

  Property	Value
  Command-Line Format	--query-prealloc-size=#
  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)	18446744073709551615
  Maximum Value (32-bit platforms)	4294967295
  Block Size	1024

  The size of the persistent buffer used for statement parsing and execution. This buffer is not freed between statements. If you are running complex queries, a larger query_prealloc_size value might be helpful in improving performance, because it can reduce the need for the server to perform memory allocation during query execution operations.

• rand_seed1

  Property	Value
  System Variable	rand_seed1
  Scope	Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer

  The rand_seed1 and rand_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 of SHOW VARIABLES.

  The purpose of these variables is to support replication of the RAND() function. For statements that invoke RAND(), the master passes two values to the slave, where they are used to seed the random number generator. The slave uses these values to set the session variables rand_seed1 and rand_seed2 so that RAND() on the slave generates the same value as on the master.

• rand_seed2

  See the description for rand_seed1.

• range_alloc_block_size

  Property	Value
  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)	18446744073709547520
  Maximum Value	4294967295
  Block Size	1024

  The size of blocks that are allocated when doing range optimization.

• range_optimizer_max_mem_size

  Property	Value
  Command-Line Format	--range-optimizer-max-mem-size=#
  System Variable	range_optimizer_max_mem_size
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	8388608
  Minimum Value	0
  Maximum Value	18446744073709551615

  The limit on memory consumption for the range optimizer. A value of 0 means “no limit.” If an execution plan considered by the optimizer uses the range access method but the optimizer estimates that the amount of memory needed for this method would exceed the limit, it abandons the plan and considers other plans. For more information, see Limiting Memory Use for Range Optimization.

• rbr_exec_mode

  Property	Value
  System Variable	rbr_exec_mode
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Enumeration
  Default Value	STRICT
  Valid Values	IDEMPOTENT STRICT

  For internal use by mysqlbinlog. This variable switches the server between IDEMPOTENT mode and STRICT mode. IDEMPOTENT mode causes suppression of duplicate-key and no-key-found errors in BINLOG statements generated by mysqlbinlog. This mode is useful when replaying a row-based binary log on a server that causes conflicts with existing data. mysqlbinlog sets this mode when you specify the --idempotent option by writing the following to the output:

  SET SESSION RBR_EXEC_MODE=IDEMPOTENT;

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

• read_buffer_size

  Property	Value
  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

  Each thread that does a sequential scan for a MyISAM table allocates a buffer of this size (in bytes) for each table it scans. If you do many sequential scans, you might want to increase this value, which defaults to 131072. The value of this variable should be a multiple of 4KB. If it is set to a value that is not a multiple of 4KB, its value will be rounded down to the nearest multiple of 4KB.

  This option is also used in the following context for all storage engines:

  • For caching the indexes in a temporary file (not a temporary table), when sorting rows for ORDER BY.

  • For bulk insert into partitions.

  • For caching results of nested queries.

  read_buffer_size is also used in one other storage engine-specific way: to determine the memory block size for MEMORY tables.

  For more information about memory use during different operations, see Section 8.12.3.1, “How MySQL Uses Memory”.

• read_only

  Property	Value
  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 the read_only system variable is enabled, the server permits no client updates except from users who have the CONNECTION_ADMIN privilege (or the deprecated SUPER privilege). This variable is disabled by default.

  The server also supports a super_read_only system variable (disabled by default), which has these effects:

  • If super_read_only is enabled, the server prohibits client updates, even from users who have the CONNECTION_ADMIN or SUPER privilege.

  • Setting super_read_only to ON implicitly forces read_only to ON.

  • Setting read_only to OFF implicitly forces super_read_only to OFF.

  Even with read_only enabled, the server permits these operations:

  • Updates performed by slave threads, if the server is a replication slave. In replication setups, it can be useful to enable read_only on slave servers to ensure that slaves accept updates only from the master server and not from clients.

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

  • Use of ANALYZE TABLE or OPTIMIZE 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 replication slaves can be performed with mysqlcheck --all-databases --analyze.

  • Operations on TEMPORARY tables.

  • Inserts into the log tables (mysql.general_log and mysql.slow_log); see Section 5.4.1, “Selecting General Query Log and Slow Query Log Output Destinations”.

  • Updates to Performance Schema tables, such as UPDATE or TRUNCATE TABLE operations.

  Changes to read_only on a master server are not replicated to slave servers. The value can be set on a slave server independent of the setting on the master.

  The following conditions apply to attempts to enable read_only (including implicit attempts resulting from enabling super_read_only):

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

  • The attempt blocks while other clients have any ongoing statement, active LOCK TABLES WRITE, or ongoing commit, until the locks are released and the statements and transactions end. While the attempt to enable read_only is pending, requests by other clients for table locks or to begin transactions also block until read_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 with FLUSH TABLES WITH READ LOCK) because that does not involve table locks.

• read_rnd_buffer_size

  Property	Value
  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

  This variable is used for reads from MyISAM tables, and, for any storage engine, for Multi-Range Read optimization.

  When reading rows from a MyISAM table in sorted order following a key-sorting operation, the rows are read through this buffer to avoid disk seeks. See Section 8.2.1.16, “ORDER BY Optimization”. Setting the variable to a large value can improve ORDER BY performance by a lot. However, this is a buffer allocated for each client, so you should not set the global variable to a large value. Instead, change the session variable only from within those clients that need to run large queries.

  For more information about memory use during different operations, see Section 8.12.3.1, “How MySQL Uses Memory”. For information about Multi-Range Read optimization, see Section 8.2.1.11, “Multi-Range Read Optimization”.

• regexp_stack_limit

  Property	Value
  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

  The maximum available memory in bytes for the internal stack used for regular expression matching operations performed by REGEXP_LIKE() and similar functions (see Section 12.7.2, “Regular Expressions”).

• regexp_time_limit

  Property	Value
  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 by REGEXP_LIKE() and similar functions (see Section 12.7.2, “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

  Property	Value
  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 and mysqlbinlog. 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 to ON requires no privileges. Setting the session value of this system variable to OFF is a restricted operation, and the session user must have privileges sufficient to set restricted session variables. See Section 5.1.9.1, “System Variable Privileges”.

• require_secure_transport

  Property	Value
  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 that use SSL, or connections that use a socket file (on Unix) or shared memory (on Windows). The server rejects nonsecure connection attempts, which fail with an ER_SECURE_TRANSPORT_REQUIRED error.

  This capability supplements per-account SSL requirements, which take precedence. For example, if an account is defined with REQUIRE SSL, enabling require_secure_transport does not make it possible to use the account to connect using a Unix socket file.

  It is possible for a server to have no secure transports available. For example, a server on Windows supports no secure transports if started without specifying any SSL certificate or key files and with the shared_memory system variable disabled. Under these conditions, attempts to enable require_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 an ER_NO_SECURE_TRANSPORTS_CONFIGURED error.

  See also Configuring Encrypted Connections as Mandatory.

• resultset_metadata

  Property	Value
  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 the resultset_metadata system variable to control whether the server returns result set metadata. Permitted values are FULL (return all metadata; this is the default) and NONE (return no metadata).

  For connections that are not metadata-optional, setting resultset_metadata to NONE produces an error.

  For details about managing result set metadata transfer, see Section 28.7.26, “C API Optional Result Set Metadata”.

• secondary_engine_cost_threshold

  Property	Value
  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)

  For future use.

• schema_definition_cache

  Property	Value
  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 by schema_definition_cache.

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

  For more information, see Section 14.4, “Dictionary Object Cache”.

• secure_file_priv

  Property	Value
  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 the LOAD DATA and SELECT ... INTO OUTFILE statements and the LOAD_FILE() function. These operations are permitted only to users who have the FILE 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 will not create it.

  • If set to NULL, the server disables import and export operations.

  The default value is platform specific and depends on the value of the INSTALL_LAYOUT CMake option, as shown in the following table. To specify the default secure_file_priv value explicitly if you are building from source, use the INSTALL_SECURE_FILE_PRIVDIR CMake option.

  INSTALL_LAYOUT Value	Default secure_file_priv Value
  STANDALONE	empty
  DEB, RPM, SVR4	/var/lib/mysql-files
  Otherwise	mysql-files under the CMAKE_INSTALL_PREFIX value

  The server checks the value of secure_file_priv at startup and writes a warning to the error log if the value is insecure. A non-NULL value is considered insecure if it is empty, or the value is the data directory or a subdirectory of it, or a directory that is accessible by all users. If secure_file_priv is set to a nonexistent path, the server writes an error message to the error log and exits.

• session_track_gtids

  Property	Value
  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 tracks GTIDs within the current session and returns them to the client. Depending on the variable value, at the end of executing each transaction, the server GTIDs are captured by the tracker and returned to the client. These session_track_gtids values are permitted:

  • OFF: The tracker collects no GTIDs. This is the default.

  • OWN_GTID: The tracker collects GTIDs generated by successfully committed read/write transactions.

  • ALL_GTIDS: The tracker collects all GTIDs in the gtid_executed system variable at the time the current transaction commits, regardless of whether the transaction is read/write or read only.

  session_track_gtids cannot be set within transactional context.

  For more information about session state tracking, see Section 5.1.17, “Server Tracking of Client Session State Changes”.

• session_track_schema

  Property	Value
  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, see Section 5.1.17, “Server Tracking of Client Session State Changes”.

• session_track_state_change

  Property	Value
  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.

  The session_track_state_change variable controls only notification of when changes occur, not what the changes are. For example, state-change notifications occur when the default schema is set or tracked session system variables are assigned, but the notification does not include the schema name or variable values. To receive notification of the schema name or session system variable values, use the session_track_schema or session_track_system_variables system variable, respectively.

  Note

  Assigning a value to session_track_state_change itself is not considered a state change and is not reported as such. However, if its name listed in the value of session_track_system_variables, any assignments to it do result in notification of the new value.

  For more information about session state tracking, see Section 5.1.17, “Server Tracking of Client Session State Changes”.

• session_track_system_variables

  Property	Value
  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 for time_zone, autocommit, character_set_client, character_set_results, and character_set_connection. (The latter three variables are those affected by SET NAMES.)

  The special value * causes the server to track assignments to all session variables. If given, this value must be specified by itself without specific system variable names.

  To disable notification of session variable assignments, set session_track_system_variables to the empty string.

  If session system variable tracking is enabled, notification occurs for all assignments to tracked session variables, even if the new values are the same as the old.

  For more information about session state tracking, see Section 5.1.17, “Server Tracking of Client Session State Changes”.

• session_track_transaction_info

  Property	Value
  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. These session_track_transaction_info values are permitted:

  • OFF: Disable transaction state tracking. This is the default.

  • STATE: Enable transaction state tracking without characteristics tracking. State tracking enables the client to determine whether a transaction is in progress and whether it could be moved to a different session without being rolled back.

  • CHARACTERISTICS: Enable transaction state tracking, including characteristics tracking. Characteristics tracking enables the client to determine how to restart a transaction in another session so that it has the same characteristics as in the original session. The following characteristics are relevant for this purpose:

    ISOLATION LEVEL
    READ ONLY
    READ WRITE
    WITH CONSISTENT SNAPSHOT

  For a client to safely relocate a transaction to another session, it must track not only transaction state but also transaction characteristics. In addition, the client must track the transaction_isolation and transaction_read_only system variables to correctly determine the session defaults. (To track these variables, list them in the value of the session_track_system_variables system variable.)

  For more information about session state tracking, see Section 5.1.17, “Server Tracking of Client Session State Changes”.

• sha256_password_auto_generate_rsa_keys

  Property	Value
  Command-Line Format	--sha256-password-auto-generate-rsa-keys[={OFF|ON}]
  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: The sha256_password_auto_generate_rsa_keys or caching_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 the sha256_password or caching_sha2_password plugin; see Section 6.4.1.3, “SHA-256 Pluggable Authentication”, and Section 6.4.1.2, “Caching SHA-2 Pluggable Authentication”.

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

  The auto_generate_certs system variable is related but controls autogeneration of SSL certificate and key files needed for secure connections using SSL.

• sha256_password_private_key_path

  Property	Value
  Command-Line Format	--sha256-password-private-key-path=file_name
  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 the sha256_password authentication plugin. If the file is named as a relative path, it is interpreted relative to the server data directory. The file must be in PEM format.

  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 about sha256_password, see Section 6.4.1.3, “SHA-256 Pluggable Authentication”.

• sha256_password_proxy_users

  Property	Value
  Command-Line Format	--sha256-password-proxy-users[={OFF|ON}]
  System Variable	sha256_password_proxy_users
  Scope	Global
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  This variable controls whether the sha256_password built-in authentication plugin supports proxy users. It has no effect unless the check_proxy_users system variable is enabled. For information about user proxying, see Section 6.2.18, “Proxy Users”.

• sha256_password_public_key_path

  Property	Value
  Command-Line Format	--sha256-password-public-key-path=file_name
  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 the sha256_password authentication plugin. If the file is named as a relative path, it is interpreted relative to the server data directory. The file must be in PEM format. Because this file stores a public key, copies can be freely distributed to client users. (Clients that explicitly specify a public key when connecting to the server using RSA password encryption must use the same public key as that used by the server.)

  For information about sha256_password, including information about how clients specify the RSA public key, see Section 6.4.1.3, “SHA-256 Pluggable Authentication”.

• shared_memory

  Property	Value
  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

  Property	Value
  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 is MYSQL. The name is case-sensitive.

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

• show_create_table_skip_secondary_engine

  Property	Value
  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

  Enabling show_create_table_skip_secondary_engine causes the SECONDARY ENGINE clause to be excluded from SHOW CREATE TABLE output, and from CREATE TABLE statements dumped by the mysqldump utility.

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

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

• show_create_table_verbosity

  Property	Value
  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 the ROW_FORMAT table option if the row format is the default format. Enabling this variable causes SHOW CREATE TABLE to display ROW_FORMAT regardless of whether it is the default format.

• show_old_temporals

  Property	Value
  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

  Whether SHOW CREATE TABLE output includes comments to flag temporal columns found to be in pre-5.6.4 format (TIME, DATETIME, and TIMESTAMP 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

  Output for the COLUMN_TYPE column of the INFORMATION_SCHEMA.COLUMNS table is affected similarly.

  This variable is deprecated and will be removed in a future MySQL release.

• skip_external_locking

  Property	Value
  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 is OFF if mysqld uses external locking (system locking), ON if external locking is disabled. This affects only MyISAM table access.

  This variable is set by the --external-locking or --skip-external-locking option. External locking is disabled by default.

  External locking affects only MyISAM table access. For more information, including conditions under which it can and cannot be used, see Section 8.11.5, “External Locking”.

• skip_name_resolve

  Property	Value
  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 is OFF, mysqld resolves host names when checking client connections. If it is ON, mysqld uses only IP numbers; in this case, all Host column values in the grant tables must be IP addresses. See Section 5.1.12.3, “DNS Lookups and the Host Cache”.

  Depending on the network configuration of your system and the Host values for your accounts, clients may need to connect using an explicit --host option, such as --host=127.0.0.1 or --host=::1.

  An attempt to connect to the host 127.0.0.1 normally resolves to the localhost account. However, this fails if the server is run with skip_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 as root 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

  Property	Value
  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 with mysqld must be made using named pipes or shared memory (on Windows) or Unix socket files (on Unix). This option is highly recommended for systems where only local clients are permitted. See Section 5.1.12.3, “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 enabling skip_networking.

• skip_show_database

  Property	Value
  Command-Line Format	--skip-show-database
  System Variable	skip_show_database
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No

  This prevents people from using the SHOW DATABASES statement if they do not have the SHOW DATABASES privilege. This can improve security if you have concerns about users being able to see databases belonging to other users. Its effect depends on the SHOW DATABASES privilege: If the variable value is ON, the SHOW DATABASES statement is permitted only to users who have the SHOW DATABASES privilege, and the statement displays all database names. If the value is OFF, SHOW DATABASES is permitted to all users, but displays the names of only those databases for which the user has the SHOW 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 with SHOW DATABASES or by examining the SCHEMATA table of INFORMATION_SCHEMA, except databases that have been restricted at the database level by partial revokes.

• slow_launch_time

  Property	Value
  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

  If creating a thread takes longer than this many seconds, the server increments the Slow_launch_threads status variable.

• slow_query_log

  Property	Value
  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 (or OFF) to disable the log or 1 (or ON) to enable the log. The destination for log output is controlled by the log_output system variable; if that value is NONE, no log entries are written even if the log is enabled.

  “Slow” is determined by the value of the long_query_time variable. See Section 5.4.5, “The Slow Query Log”.

• slow_query_log_file

  Property	Value
  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 is host_name-slow.log, but the initial value can be changed with the --slow_query_log_file option.

• socket

  Property	Value
  Command-Line Format	--socket={file_name|pipe_name}
  System Variable	socket
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	String
  Default Value (Other)	/tmp/mysql.sock
  Default Value (Windows)	MySQL

  On Unix platforms, this variable is the name of the socket file that is used for local client connections. The default is /tmp/mysql.sock. (For some distribution formats, the directory might be different, such as /var/lib/mysql for RPMs.)

  On Windows, this variable is the name of the named pipe that is used for local client connections. The default value is MySQL (not case-sensitive).

• sort_buffer_size

  Property	Value
  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 (Other, 64-bit platforms)	18446744073709551615
  Maximum Value (Other, 32-bit platforms)	4294967295
  Maximum Value (Windows)	4294967295

  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 the sort_buffer_size value must be large enough to accommodate fifteen tuples in the sort buffer. Also, increasing the value of max_sort_length may require increasing the value of sort_buffer_size. For more information, see Section 8.2.1.16, “ORDER BY Optimization”

  If you see many Sort_merge_passes per second in SHOW GLOBAL STATUS output, you can consider increasing the sort_buffer_size value to speed up ORDER BY or GROUP 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 will slow down most queries that sort. It is best to increase it as a session setting, and only for the sessions that need a larger size. On Linux, there are thresholds of 256KB and 2MB where larger values may significantly slow down memory allocation, so you should consider staying below one of those values. Experiment to find the best value for your workload. See Section B.4.3.5, “Where MySQL Stores Temporary Files”.

  The maximum permissible setting for sort_buffer_size is 4GB−1. Larger values are permitted for 64-bit platforms (except 64-bit Windows, for which large values are truncated to 4GB−1 with a warning).

• sql_auto_is_null

  Property	Value
  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 generated AUTO_INCREMENT value, you can find that value by issuing a statement of the following form:

  SELECT * FROM tbl_name WHERE auto_col IS NULL

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

  The behavior of retrieving an AUTO_INCREMENT value by using an IS NULL comparison is used by some ODBC programs, such as Access. See Obtaining Auto-Increment Values. This behavior can be disabled by setting sql_auto_is_null to OFF.

  Prior to MySQL 8.0.16, the transformation of WHERE auto_col IS NULL to WHERE auto_col = LAST_INSERT_ID() was performed only when the statement was executed, so that the value of sql_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 of sql_auto_is_null is OFF.

• sql_big_selects

  Property	Value
  System Variable	sql_big_selects
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	Yes
  Type	Boolean
  Default Value	ON

  If set to OFF, MySQL aborts SELECT 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 of max_join_size). This is useful when an inadvisable WHERE statement has been issued. The default value for a new connection is ON, which permits all SELECT statements.

  If you set the max_join_size system variable to a value other than DEFAULT, sql_big_selects is set to OFF.

• sql_buffer_result

  Property	Value
  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 from SELECT 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 is OFF.

• sql_log_off

  Property	Value
  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 is OFF (that is, enable logging). To disable or enable general query logging for the current session, set the session sql_log_off variable to ON or OFF.

  Setting the session value of this system variable is a restricted operation. The session user must have privileges sufficient to set restricted session variables. See Section 5.1.9.1, “System Variable Privileges”.

• sql_mode

  Property	Value
  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, see Section 5.1.11, “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

  Property	Value
  System Variable	sql_notes
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  If enabled (the default), diagnostics of Note level increment warning_count and the server records them. If disabled, Note diagnostics do not increment warning_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

  Property	Value
  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 for SHOW CREATE TABLE and SHOW CREATE DATABASE statements. If disabled, quoting is disabled. This option is enabled by default so that replication works for identifiers that require quoting. See Section 13.7.7.10, “SHOW CREATE TABLE Statement”, and Section 13.7.7.6, “SHOW CREATE DATABASE Statement”.

• sql_require_primary_key

  Property	Value
  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. See Section 5.1.9.1, “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 master 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 slave. With a primary key, these table scans do not occur.

  sql_require_primary_key applies to both base tables and TEMPORARY tables, and changes to its value are replicated to slave 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 includes CREATE TABLE ... LIKE. It also includes CREATE TABLE ... SELECT, unless the CREATE 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 same ALTER TABLE statement is permitted.

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

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

  The REQUIRE_TABLE_PRIMARY_KEY_CHECK option of the CHANGE MASTER TO statement enables a replication slave to select its own policy for primary key checks. When the option is set to ON for a replication channel, the slave always uses the value ON for the sql_require_primary_key system variable in replication operations, requiring a primary key. When the option is set to OFF, the slave always uses the value OFF for the sql_require_primary_key system variable in replication operations, so that a primary key is never required, even if the master required one. When the REQUIRE_TABLE_PRIMARY_KEY_CHECK option is set to STREAM, which is the default, the slave uses whatever value is replicated from the master for each transaction. With the STREAM setting for the REQUIRE_TABLE_PRIMARY_KEY_CHECK option, if privilege checks are in use for the replication channel, the PRIVILEGE_CHECKS_USER account needs privileges sufficient to set restricted session variables, so that it can set the session value for the sql_require_primary_key system variable. With the ON or OFF settings, the account does not need these privileges. For more information, see Section 17.3.3, “Replication Privilege Checks”.

• sql_safe_updates

  Property	Value
  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 and DELETE statements that do not use a key in the WHERE clause or a LIMIT clause produce an error. This makes it possible to catch UPDATE and DELETE statements where keys are not used properly and that would probably change or delete a large number of rows. The default value is OFF.

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

• sql_select_limit

  Property	Value
  System Variable	sql_select_limit
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	Yes
  Type	Integer

  The maximum number of rows to return from SELECT statements. For more information, see Using Safe-Updates Mode (--safe-updates).

  The default value for a new connection is the maximum number of rows that the server permits per table. Typical default values are (2³²)−1 or (2⁶⁴)−1. If you have changed the limit, the default value can be restored by assigning a value of DEFAULT.

  If a SELECT has a LIMIT clause, the LIMIT takes precedence over the value of sql_select_limit.

• sql_warnings

  Property	Value
  System Variable	sql_warnings
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	OFF

  This variable controls whether single-row INSERT statements produce an information string if warnings occur. The default is OFF. Set the value to ON to produce an information string.

• ssl_ca

  Property	Value
  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 TSL context the server uses for new connections. See Server-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

  Property	Value
  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.

  As of MySQL 8.0.16, this variable is dynamic and can be modified at runtime to affect the TSL context the server uses for new connections. See Server-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

  Property	Value
  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 with ssl_cert set to a certificate that uses any restricted cipher or cipher category, the server starts with support for encrypted connections disabled. For information about cipher restrictions, see Connection Cipher Configuration.

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

• ssl_cipher

  Property	Value
  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 will not work.

  For greatest portability, the cipher list should be a list of one or more cipher names, separated by colons. Examples:

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

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

  For information about which encryption ciphers MySQL supports, see Section 6.3.2, “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 TSL context the server uses for new connections. See Server-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

  Property	Value
  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 TSL context the server uses for new connections. See Server-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

  Property	Value
  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 TSL context the server uses for new connections. See Server-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

  Property	Value
  Command-Line Format	--ssl-fips-mode={OFF|ON|STRICT}
  System Variable	ssl_fips_mode
  Scope	Global
  Dynamic	Yes
  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. The ssl_fips_mode system variable differs from other ssl_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. See Section 6.6, “FIPS Support”.

  These ssl_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 for ssl_fips_mode is OFF. In this case, setting ssl_fips_mode to ON or STRICT at startup causes the server to produce an error message and exit.

• ssl_key

  Property	Value
  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 TSL context the server uses for new connections. See Server-Side Runtime Configuration and Monitoring for Encrypted Connections. Prior to MySQL 8.0.16, this variable can be set only at server startup.

• stored_program_cache

  Property	Value
  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 the dictionary 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, see Section 14.4, “Dictionary Object Cache”.

• stored_program_definition_cache

  Property	Value
  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 by stored_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 the stored_program_cache option.

  The stored_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, see Section 14.4, “Dictionary Object Cache”.

• super_read_only

  Property	Value
  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 the read_only system variable is enabled, the server permits no client updates except from users who have the CONNECTION_ADMIN privilege (or the deprecated SUPER privilege). If the super_read_only system variable is also enabled, the server prohibits client updates even from users who have CONNECTION_ADMIN or SUPER. See the description of the read_only system variable for a description of read-only mode and information about how read_only and super_read_only interact.

  Client updates prevented when super_read_only is enabled include operations that do not necessarily appear to be updates, such as CREATE FUNCTION (to install a UDF), INSTALL PLUGIN, and INSTALL COMPONENT. These operations are prohibited because they involve changes to tables in the mysql system schema.

  Changes to super_read_only on a master server are not replicated to slave servers. The value can be set on a slave server independent of the setting on the master.

• syseventlog.facility

  Property	Value
  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 to syslog (what type of program is sending the message). This variable is unavailable unless the log_sink_syseventlog error log component is installed. See Section 5.4.2.7, “Error Logging to the System Log”.

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

  This variable does not exist on Windows.

• syseventlog.include_pid

  Property	Value
  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 to syslog. This variable is unavailable unless the log_sink_syseventlog error log component is installed. See Section 5.4.2.7, “Error Logging to the System Log”.

  This variable does not exist on Windows.

• syseventlog.tag

  Property	Value
  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 to syslog or the Windows Event Log. This variable is unavailable unless the log_sink_syseventlog error log component is installed. See Section 5.4.2.7, “Error Logging to the System Log”.

  By default, no tag is set, so the server identifier is simply MySQL on Windows, and mysqld on other platforms. If a tag value of tag is specified, it is appended to the server identifier with a leading hyphen, resulting in a syslog identifier of mysqld-tag (or MySQL-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

  Property	Value
  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 set system_time_zone. Typically the time zone is specified by the TZ environment variable. It also can be specified using the --timezone option of the mysqld_safe script.

  The system_time_zone variable differs from time_zone. Although they might have the same value, the latter variable is used to initialize the time zone for each client that connects. See Section 5.1.14, “MySQL Server Time Zone Support”.

• table_definition_cache

  Property	Value
  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 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)

  For InnoDB, table_definition_cache acts as a soft limit for the number of open table instances in the InnoDB data dictionary cache. If the number of open table instances exceeds the table_definition_cache setting, the LRU mechanism begins to mark table instances for eviction and eventually removes them from the data dictionary cache. The limit helps address situations in which significant amounts of memory would be used to cache rarely used table instances until the next server restart. The number of table instances with cached metadata could be higher than the limit defined by table_definition_cache, because parent and child table instances with foreign key relationships are not placed on the LRU list and are not subject to eviction from memory.

  Additionally, table_definition_cache defines a soft limit for the number of InnoDB file-per-table tablespaces that can be open at one time, which is also controlled by innodb_open_files. If both table_definition_cache and innodb_open_files are set, the highest setting is used. If neither variable is set, table_definition_cache, which has a higher default value, is used. If the number of open tablespace file handles exceeds the limit defined by table_definition_cache or innodb_open_files, the LRU mechanism searches the tablespace file LRU list for files that are fully flushed and are not currently being extended. This process is performed each time a new tablespace is opened. If there are no “inactive” tablespaces, no tablespace files are closed.

  The table definition cache exists in parallel with the table definition cache partition of the dictionary 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 objects in the other. For more information, see Section 14.4, “Dictionary Object Cache”.

• table_encryption_privilege_check

  Property	Value
  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 the TABLE_ENCRYPTION_ADMIN privilege check that occurs when creating or altering a schema or general tablespace with encryption that differs from the default_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.

  Setting table_encryption_privilege_check at runtime requires the SUPER privilege.

  table_encryption_privilege_check supports SET PERSIST and SET PERSIST_ONLY syntax. See Section 5.1.9.3, “Persisted System Variables”.

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

• table_open_cache

  Property	Value
  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 that mysqld requires. You can check whether you need to increase the table cache by checking the Opened_tables status variable. See Section 5.1.10, “Server Status Variables”. If the value of Opened_tables is large and you do not use FLUSH TABLES often (which just forces all tables to be closed and reopened), then you should increase the value of the table_open_cache variable. For more information about the table cache, see Section 8.4.3.1, “How MySQL Opens and Closes Tables”.

• table_open_cache_instances

  Property	Value
  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 size table_open_cache / table_open_cache_instances . A session needs to lock only one instance to access it for DML statements. This segments cache access among instances, permitting higher performance for operations that use the cache when there are many sessions accessing tables. (DDL statements still require a lock on the entire cache, but such statements are much less frequent than DML statements.)

  A value of 8 or 16 is recommended on systems that routinely use 16 or more cores.

• tablespace_definition_cache

  Property	Value
  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 by tablespace_definition_cache.

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

  For more information, see Section 14.4, “Dictionary Object Cache”.

• temptable_max_ram

  Property	Value
  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

  Defines the maximum amount of memory that can be occupied by the TempTable storage engine before it starts storing data on disk. The default value is 1073741824 bytes (1GiB). For more information, see Section 8.4.4, “Internal Temporary Table Use in MySQL”.

• temptable_use_mmap

  Property	Value
  Command-Line Format	--temptable-use-mmap[={OFF|ON}]
  Introduced	8.0.16
  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 the temptable_max_ram variable. When temptable_use_mmap is disabled, the TempTable storage engine uses InnoDB on-disk internal temporary tables instead. For more information, see Section 8.4.4, “Internal Temporary Table Use in MySQL”.

• thread_cache_size

  Property	Value
  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 than thread_cache_size threads there. Requests for threads are satisfied by reusing threads taken from the cache if possible, and only when the cache is empty is a new thread created. This variable can be increased to improve performance if you have a lot of new connections. Normally, this does not provide a notable performance improvement if you have a good thread implementation. However, if your server sees hundreds of connections per second you should normally set thread_cache_size high enough so that most new connections use cached threads. By examining the difference between the Connections and Threads_created status variables, you can see how efficient the thread cache is. For details, see Section 5.1.10, “Server Status Variables”.

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

  8 + (max_connections / 100)

• thread_handling

  Property	Value
  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 are no-threads (the server uses a single thread to handle one connection) and one-thread-per-connection (the server uses one thread to handle each client connection). no-threads is useful for debugging under Linux; see Section 29.5, “Debugging and Porting MySQL”.

• thread_pool_algorithm

  Property	Value
  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:

  • A value of 0 (the default) uses a conservative low-concurrency algorithm which is most well tested and is known to produce very good results.

  • A value of 1 increases the concurrency and uses a more aggressive algorithm which at times has been known to perform 5–10% better on optimal thread counts, but has degrading performance as the number of connections increases. Its use should be considered as experimental and not supported.

  This variable is available only if the thread pool plugin is enabled. See Section 5.6.3, “MySQL Enterprise Thread Pool”

• thread_pool_high_priority_connection

  Property	Value
  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. See Section 5.6.3, “MySQL Enterprise Thread Pool”

• thread_pool_max_active_query_threads

  Property	Value
  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.

• thread_pool_max_unused_threads

  Property	Value
  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 of N where N is greater than 0 means 1 consumer thread and N−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 will sleep as a consumer thread. When a thread must be woken up, a consumer thread is selected if there is one. A reserve thread is selected only when there is no consumer thread to wake up.

  This variable is available only if the thread pool plugin is enabled. See Section 5.6.3, “MySQL Enterprise Thread Pool”

• thread_pool_prio_kickup_timer

  Property	Value
  Command-Line Format	--thread-pool-prio-kickup-timer=#
  System Variable	thread_pool_prio_kickup_timer
  Scope	Global, Session
  Dynamic	Yes
  SET_VAR Hint Applies	No
  Type	Integer
  Default Value	1000
  Minimum Value	0
  Maximum Value	4294967294

  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). The range of values is 0 to 2³² − 2.

  This variable is available only if the thread pool plugin is enabled. See Section 5.6.3, “MySQL Enterprise Thread Pool”

• thread_pool_size

  Property	Value
  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. The default value is 16, with a range from 1 to 64 of permissible values. If a value outside this range is specified, the thread pool plugin does not load and the server writes a message to the error log.

  This variable is available only if the thread pool plugin is enabled. See Section 5.6.3, “MySQL Enterprise Thread Pool”

• thread_pool_stall_limit

  Property	Value
  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

  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 a value of 6 (the default) means 60ms. The range of values is 4 to 600 (40ms to 6s). Short wait values permit threads to start more quickly. Short values are also better for avoiding deadlock situations. Long wait values are useful for workloads that include long-running statements, to avoid starting too many new statements while the current ones execute.

  This variable is available only if the thread pool plugin is enabled. See Section 5.6.3, “MySQL Enterprise Thread Pool”

• thread_stack

  Property	Value
  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)	286720
  Default Value (32-bit platforms)	221184
  Minimum Value	131072
  Maximum Value (64-bit platforms)	18446744073709551615
  Maximum Value (32-bit platforms)	4294967295
  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

  Property	Value
  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)	-14:00
  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 of system_time_zone”). The value can be specified explicitly at server startup with the --default-time-zone option. See Section 5.1.14, “MySQL Server Time Zone Support”.

  Note

  If set to SYSTEM, every MySQL function call that requires a time zone calculation makes a system library call to determine the current system time zone. This call may be protected by a global mutex, resulting in contention.

• timestamp

  Property	Value
  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 by UNIX_TIMESTAMP(), not a value in 'YYYY-MM-DD hh:mm:ss' format) or DEFAULT.

  Setting timestamp to a constant value causes it to retain that value until it is changed again. Setting timestamp to DEFAULT causes its value to be the current date and time as of the time it is accessed.

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

  SET timestamp affects the value returned by NOW() but not by SYSDATE(). This means that timestamp settings in the binary log have no effect on invocations of SYSDATE(). The server can be started with the --sysdate-is-now option to cause SYSDATE() to be an alias for NOW(), in which case SET timestamp affects both functions.

• tls_ciphersuites

  Property	Value
  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 is NULL, 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, see Section 6.3.2, “Encrypted Connection TLS Protocols and Ciphers”.

• tls_version

  Property	Value
  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 (≥ 8.0.16)	TLSv1,TLSv1.1,TLSv1.2,TLSv1.3 (OpenSSL 1.1.1 and higher) TLSv1,TLSv1.1,TLSv1.2 (otherwise)
  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. The protocols that can be named for this variable depend on the SSL library used to compile MySQL. Permitted protocols should be chosen such as not to leave “holes” in the list. For details, see Section 6.3.2, “Encrypted Connection TLS Protocols and Ciphers”.

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

• tmp_table_size

  Property	Value
  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

  The maximum size of internal in-memory temporary tables. This variable does not apply to user-created MEMORY tables.

  The actual limit is the smaller of tmp_table_size and max_heap_table_size. When an in-memory temporary table exceeds the limit, MySQL automatically converts it to an on-disk temporary table.

  Increase the value of tmp_table_size (and max_heap_table_size if necessary) if you do many advanced GROUP BY queries and you have lots of memory.

  You can compare the number of internal on-disk temporary tables created to the total number of internal temporary tables created by comparing Created_tmp_disk_tables and Created_tmp_tables values.

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

• tmpdir

  Property	Value
  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 replication slave, and you are using a non-permanent location for tmpdir, consider setting a different temporary directory for the slave using the slave_load_tmpdir variable. For a replication slave, the temporary files used to replicate LOAD DATA statements are stored in this directory, so with a permanent location they can survive machine restarts, although replication can now continue after a restart if the temporary files have been removed.

  For more information about the storage location of temporary files, see Section B.4.3.5, “Where MySQL Stores Temporary Files”.

• transaction_alloc_block_size

  Property	Value
  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
  Block Size	1024

  The amount in bytes by which to increase a per-transaction memory pool which needs memory. See the description of transaction_prealloc_size.

• transaction_isolation

  Property	Value
  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 is REPEATABLE-READ.

  The transaction isolation level has three scopes: global, session, and next transaction. This three-scope implementation leads to some nonstandard isolation-level assignment semantics, as described later.

  To set the global transaction isolation level at startup, use the --transaction-isolation server option.

  At runtime, the isolation level can be set directly using the SET statement to assign a value to the transaction_isolation system variable, or indirectly using the SET TRANSACTION statement. If you set transaction_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 this SET statement to set the global value:

  SET GLOBAL transaction_isolation = 'READ-COMMITTED';

  Setting the global transaction_isolation value sets the isolation level for all subsequent sessions. Existing sessions are unaffected.

  To set the session or next-level transaction_isolation value, use the SET statement. For most session system variables, these statements are equivalent ways to set the value:

  SET @@SESSION.var_name = value;
  SET SESSION var_name = value;
  SET var_name = value;
  SET @@var_name = value;

  As mentioned previously, the transaction isolation level has a next-transaction scope, in addition to the global and session scopes. To enable the next-transaction scope to be set, SET syntax for assigning session system variable values has nonstandard semantics for transaction_isolation:

  • To set the session isolation level, use any of these syntaxes:

    SET @@SESSION.transaction_isolation = value;
    SET SESSION transaction_isolation = value;
    SET transaction_isolation = value;

    For each of those syntaxes, these semantics apply:

    • Sets the isolation level for all subsequent transactions performed within the session.

    • Permitted within transactions, but does not affect the current ongoing transaction.

    • If executed between transactions, overrides any preceding statement that sets the next-transaction isolation level.

    • Corresponds to SET SESSION TRANSACTION ISOLATION LEVEL (with the SESSION keyword).

  • To set the next-transaction isolation level, use this syntax:

    SET @@transaction_isolation = value;

    For that syntax, these semantics apply:

    • Sets the isolation level only for the next single transaction performed within the session.

    • Subsequent transactions revert to the session isolation level.

    • Not permitted within transactions.

    • Corresponds to SET TRANSACTION ISOLATION LEVEL (without the SESSION keyword).

  For more information about SET TRANSACTION and its relationship to the transaction_isolation system variable, see Section 13.3.7, “SET TRANSACTION Statement”.

• transaction_prealloc_size

  Property	Value
  Command-Line Format	--transaction-prealloc-size=#
  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
  Block Size	1024

  There is a per-transaction memory pool from which various transaction-related allocations take memory. The initial size of the pool in bytes is transaction_prealloc_size. For every allocation that cannot be satisfied from the pool because it has insufficient memory available, the pool is increased by transaction_alloc_block_size bytes. When the transaction ends, the pool is truncated to transaction_prealloc_size bytes.

  By making transaction_prealloc_size sufficiently large to contain all statements within a single transaction, you can avoid many malloc() calls.

• transaction_read_only

  Property	Value
  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 be OFF (read/write; the default) or ON (read only).

  The transaction access mode has three scopes: global, session, and next transaction. This three-scope implementation leads to some nonstandard access-mode assignment semantics, as described later.

  To set the global transaction access mode at startup, use the --transaction-read-only server option.

  At runtime, the access mode can be set directly using the SET statement to assign a value to the transaction_read_only system variable, or indirectly using the SET TRANSACTION statement. For example, use this SET statement to set the global value:

  SET GLOBAL transaction_read_only = ON;

  Setting the global transaction_read_only value sets the access mode for all subsequent sessions. Existing sessions are unaffected.

  To set the session or next-level transaction_read_only value, use the SET statement. For most session system variables, these statements are equivalent ways to set the value:

  SET @@SESSION.var_name = value;
  SET SESSION var_name = value;
  SET var_name = value;
  SET @@var_name = value;

  As mentioned previously, the transaction access mode has a next-transaction scope, in addition to the global and session scopes. To enable the next-transaction scope to be set, SET syntax for assigning session system variable values has nonstandard semantics for transaction_read_only,

  • To set the session access mode, use any of these syntaxes:

    SET @@SESSION.transaction_read_only = value;
    SET SESSION transaction_read_only = value;
    SET transaction_read_only = value;

    For each of those syntaxes, these semantics apply:

    • Sets the access mode for all subsequent transactions performed within the session.

    • Permitted within transactions, but does not affect the current ongoing transaction.

    • If executed between transactions, overrides any preceding statement that sets the next-transaction access mode.

    • Corresponds to SET SESSION TRANSACTION {READ WRITE | READ ONLY} (with the SESSION keyword).

  • To set the next-transaction access mode, use this syntax:

    SET @@transaction_read_only = value;

    For that syntax, these semantics apply:

    • Sets the access mode only for the next single transaction performed within the session.

    • Subsequent transactions revert to the session access mode.

    • Not permitted within transactions.

    • Corresponds to SET TRANSACTION {READ WRITE | READ ONLY} (without the SESSION keyword).

  For more information about SET TRANSACTION and its relationship to the transaction_read_only system variable, see Section 13.3.7, “SET TRANSACTION Statement”.

• unique_checks

  Property	Value
  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 in InnoDB tables are performed. If set to 0, storage engines are permitted to assume that duplicate keys are not present in input data. If you know for certain that your data does not contain uniqueness violations, you can set this to 0 to speed up large table imports to InnoDB.

  Setting this variable to 0 does not require storage engines to ignore duplicate keys. An engine is still permitted to check for them and issue duplicate-key errors if it detects them.

• updatable_views_with_limit

  Property	Value
  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 a LIMIT clause. (Such updates often are generated by GUI tools.) An update is an UPDATE or DELETE statement. Primary key here means a PRIMARY KEY, or a UNIQUE index in which no column can contain NULL.

  The variable can have two values:

  • 1 or YES: Issue a warning only (not an error message). This is the default value.

  • 0 or NO: Prohibit the update.

• use_secondary_engine

  Property	Value
  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.

• validate_password.xxx

  The validate_password component implements a set of system variables having names of the form validate_password.xxx. These variables affect password testing by that component; see Section 6.4.3.2, “Password Validation Options and Variables”.

• validate_user_plugins

  Property	Value
  Command-Line Format	--validate-user-plugins[={OFF|ON}]
  System Variable	validate_user_plugins
  Scope	Global
  Dynamic	No
  SET_VAR Hint Applies	No
  Type	Boolean
  Default Value	ON

  If this variable is enabled (the default), the server checks each user account and produces a warning if conditions are found that would make the account unusable:

  • The account requires an authentication plugin that is not loaded.

  • The account requires the sha256_password or caching_sha2_password authentication plugin but the server was started with neither SSL nor RSA enabled as required by the plugin.

  Enabling validate_user_plugins slows down server initialization and FLUSH PRIVILEGES. If you do not require the additional checking, you can disable this variable at startup to avoid the performance decrement.

• 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

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

  The CMake configuration program has a COMPILATION_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 the COMPILATION_COMMENT option.) See Section 2.9.7, “MySQL Source-Configuration Options”.

• version_compile_machine

  Property	Value
  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

  Property	Value
  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

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

  The version of the compiled-in zlib library.

• wait_timeout

  Property	Value
  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 (Other)	31536000
  Maximum Value (Windows)	2147483

  The number of seconds the server waits for activity on a noninteractive connection before closing it.

  On thread startup, the session wait_timeout value is initialized from the global wait_timeout value or from the global interactive_timeout value, depending on the type of client (as defined by the CLIENT_INTERACTIVE connect option to mysql_real_connect()). See also interactive_timeout.

• warning_count

  The number of errors, warnings, and notes that resulted from the last statement that generated messages. This variable is read only. See Section 13.7.7.40, “SHOW WARNINGS Statement”.

• windowing_use_high_precision

  Property	Value
  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. See Section 8.2.1.21, “Window Function Optimization”.