Mysql Server System Variables [官网资料]

5.1.7 Server System Variables

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.

At runtime, setting a global system variable value requires the SUPER privilege. Setting a session system variable value normally requires no special privileges and can be done by any user, although there are exceptions. For more information, see Section 5.1.8.1, “System Variable Privileges”

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

To see the values that a server uses based on its compiled-in defaults and any option files that it reads, use this command:
```
mysqld --verbose --help
```
To see the values that a server uses based on only its compiled-in defaults, ignoring the settings in any option files, use this command:
```
mysqld --no-defaults --verbose --help
```
To see the current values used by a running server, use the SHOW VARIABLES statement or the Performance Schema system variable tables. See Section 25.12.13, “Performance Schema System Variable Tables”.

This section provides a description of each system variable. For a system variable summary table, see Section 5.1.4, “Server System Variable Reference”. For more information about manipulation of system variables, see Section 5.1.8, “Using System Variables”.

For additional system variable information, see these sections:

Section 5.1.8, “Using System Variables”, discusses the syntax for setting and displaying system variable values.
Section 5.1.8.2, “Dynamic System Variables”, lists the variables that can be set at runtime.
Information on tuning system variables can be found in Section 5.1.1, “Configuring the Server”.
Section 14.15, “InnoDB Startup Options and System Variables”, lists InnoDB system variables.
Section 21.4.3.9.2, “NDB Cluster System Variables”, lists system variables which are specific to NDB Cluster.
For information on server system variables specific to replication, see Section 16.1.6, “Replication and Binary Logging Options and Variables”.

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 for the server to adjust a value upward. For example, if you assign a value of 0 to a variable for which the minimal value is 1024, the server sets the value to 1024.

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

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

authentication_windows_log_level

authentication_windows_log_level Scope Global Dynamic No Type Integer Default Value 2 Minimum Value 0 Maximum Value 4

This variable is available only if the authentication_windows Windows authentication plugin is enabled and debugging code is enabled. See Section 6.4.1.8, “Windows Pluggable Authentication”.

This variable sets the logging level for the Windows authentication plugin. The following table shows the permitted values.

Value	Description
0	No logging
1	Log only error messages
2	Log level 1 messages and warning messages
3	Log level 2 messages and information notes
4	Log level 3 messages and debug messages

authentication_windows_use_principal_name
authentication_windows_use_principal_name Scope Global Dynamic No Type Boolean Default Value ON
This variable is available only if the authentication_windows Windows authentication plugin is enabled. See Section 6.4.1.8, “Windows Pluggable Authentication”.

A client that authenticates using the InitSecurityContext() function should provide a string identifying the service to which it connects (targetName). MySQL uses the principal name (UPN) of the account under which the server is running. The UPN has the form 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 happens primarily in environments that do not support Kerberos authentication), the UPN is not sent by the server and NTLM authentication is used.
autocommit
autocommit Scope Global, Session Dynamic Yes Type Boolean Default Value ON
The autocommit mode. If set to 1, all changes to a table take effect immediately. If set to 0, you must use COMMIT to accept a transaction 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
automatic_sp_privileges Scope Global Dynamic Yes Type Boolean Default Value ON
When this variable has a value of 1 (the default), the server automatically grants the EXECUTE 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 23.2.2, “Stored Routines and MySQL Privileges”.
auto_generate_certs
auto_generate_certs Scope Global Dynamic No Type Boolean Default Value ON
This variable is available if the server was compiled using OpenSSL (see Section 6.3.4, “SSL Library-Dependent Capabilities”). It controls whether the server autogenerates SSL key and certificate files in the data directory, if they do not already exist.

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

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

The sha256_password_auto_generate_rsa_keys system variable is related but controls autogeneration of RSA key-pair files needed for secure password exchange using RSA over unencypted connections.
avoid_temporal_upgrade
avoid_temporal_upgrade Scope Global Dynamic Yes Type Boolean Default Value OFF
This variable controls whether ALTER TABLE implicitly upgrades temporal columns found to be in pre-5.6.4 format (TIME, DATETIME, 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; expect it to be removed in a future release of MySQL.
back_log
back_log Scope Global Dynamic No Type Integer Default Value -1 (signifies autosizing; do not assign this literal value) Minimum Value 1 Maximum Value 65535
The number of outstanding connection requests MySQL can have. This comes into play when the main MySQL thread gets very many connection requests in a very short time. It then takes some time (although very little) for the main thread to check the connection and start a new thread. The back_log value indicates how many requests can be stacked during this short time before MySQL momentarily stops answering new requests. You need to increase this only if you expect a large number of connections in a short period of time.

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

The default value is based on the following formula, capped to a limit of 900:
```
50 + (max_connections / 5)
```
basedir
basedir Scope Global Dynamic No Type Directory name Default Value configuration-dependent default
The path to the MySQL installation base directory.
big_tables
big_tables Scope Global, Session Dynamic Yes Type Boolean Default Value OFF 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 connections is OFF (use in-memory temporary tables). Normally, it should never be necessary to enable this variable because the server is able to handle large result sets automatically by using memory for small temporary tables and switching to disk-based tables as required.
bind_address
bind_address Scope Global Dynamic No Type String Default Value *
The MySQL server listens on a single network socket for TCP/IP connections. This socket is bound to a single address, but it is possible for an address to map onto multiple network interfaces. To specify an address, set bind_address=addr at server startup, where addr is an IPv4 or IPv6 address or a host name. If addr is a host name, the server resolves the name to an IP address and binds to that address. If a host name resolves to multiple IP addresses, the server uses the first IPv4 address if there are any, or the first IPv6 address otherwise.

The server treats different types of addresses as follows:
- If the address is *, the server accepts TCP/IP connections on all server host IPv4 interfaces, and, if the server host supports IPv6, on all IPv6 interfaces. Use this address to permit both IPv4 and IPv6 connections on all server interfaces. This value is the default.
- If the address is 0.0.0.0, the server accepts TCP/IP connections on all server host IPv4 interfaces.
- If the address is ::, the server accepts TCP/IP connections on all server host IPv4 and IPv6 interfaces.
- If the address is an IPv4-mapped address, the server accepts TCP/IP connections for that address, in either IPv4 or IPv6 format. For example, if the server is bound to ::ffff:127.0.0.1, clients can connect using --host=127.0.0.1 or --host=::ffff:127.0.0.1.
- If the address is a “regular” IPv4 or IPv6 address (such as 127.0.0.1 or ::1), the server accepts TCP/IP connections only for that IPv4 or IPv6 address.
If binding to the address fails, the server produces an error and does not start.

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

This variable has no effect for the embedded server (libmysqld) and is not visible within the embedded server.
block_encryption_mode
block_encryption_mode Scope Global, Session Dynamic Yes Type String Default Value aes-128-ecb
This variable controls the block encryption mode for block-based algorithms such as AES. It affects encryption for AES_ENCRYPT() 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 encryption modes depend on whether MySQL was compiled using OpenSSL or yaSSL:
- For OpenSSL, permitted mode values are: ECB, CBC, CFB1, CFB8, CFB128, OFB
- For yaSSL, permitted mode values are: ECB, CBC
For example, this statement causes the AES encryption functions to use a key length of 256 bits and the CBC mode:
```
SET block_encryption_mode = 'aes-256-cbc';
```
An error occurs for attempts to set block_encryption_mode to a value containing an unsupported key length or a mode that the SSL library does not support.
bulk_insert_buffer_size
bulk_insert_buffer_size Scope Global, Session Dynamic Yes Type Integer Default Value 8388608 Minimum Value 0 Maximum Value (64-bit platforms) 18446744073709551615 Maximum Value (32-bit platforms) 4294967295 Unit bytes/thread
MyISAM uses a special tree-like cache to make bulk inserts faster 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.
character_set_client
character_set_client Scope Global, Session Dynamic Yes Type String Default Value utf8
The character set for statements that arrive from the client. The session value of this variable is set using the character set requested by the client when the client connects to the server. (Many clients support a --default-character-set option to enable this character set to be specified explicitly. See also Section 10.4, “Connection Character Sets and Collations”.) The global value of the variable is used to set the session value in cases when the client-requested value is unknown or not available, or the server is configured to ignore client requests:
- The client requests a character set not known to the server. For example, a Japanese-enabled client requests sjis when connecting to a server not configured 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
character_set_connection Scope Global, Session Dynamic Yes Type String Default Value utf8
The character set used for literals specified without a character set introducer and for number-to-string conversion. For information about introducers, see Section 10.3.8, “Character Set Introducers”.
character_set_database
character_set_database Scope Global, Session Dynamic Yes Type String Default Value latin1 Footnote This option is dynamic, but should be set only by server. You should not set this variable manually.
The character set used by the default database. The server sets this variable whenever the default database changes. If there is no default database, the variable has the same value as character_set_server.

The global character_set_database and collation_database system variables are deprecated in MySQL 5.7; expect them to be removed in a future version of MySQL.

Assigning a value to the session character_set_database and collation_database system variables is deprecated in MySQL 5.7 and assignments produce a warning. You should expect the session variables to become read only in a future version of MySQL and assignments to produce an error, while remaining possible to access the session variables to determine the database character set and collation for the default database.
character_set_filesystem
character_set_filesystem Scope Global, Session Dynamic Yes Type String Default Value binary
The file system character set. This variable is used to interpret string literals that refer to file names, such as in the LOAD DATA 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'.
character_set_results
character_set_results Scope Global, Session Dynamic Yes Type String Default Value utf8
The character set used for returning query results to the client. This includes result data such as column values, result metadata such as column names, and error messages.
character_set_server
character_set_server Scope Global, Session Dynamic Yes Type String Default Value latin1
The servers default character set. See Section 10.15, “Character Set Configuration”. If you set this variable, you should also set collation_server to specify the collation for the character set.
character_set_system
character_set_system Scope Global Dynamic No Type String Default Value utf8
The character set used by the server for storing identifiers. The value is always utf8.
character_sets_dir
character_sets_dir Scope Global Dynamic No Type Directory name
The directory where character sets are installed. See Section 10.15, “Character Set Configuration”.
check_proxy_users
check_proxy_users Scope Global Dynamic Yes Type Boolean Default Value OFF
Some authentication plugins implement proxy user mapping for themselves (for example, the PAM and Windows authentication plugins). Other authentication plugins do not support proxy users by default. Of these, some can request that the MySQL server itself map proxy users according to granted proxy privileges: mysql_native_password, sha256_password.

If the check_proxy_users system variable is enabled, the server performs proxy user mapping for any authentication plugins that make such a request. However, it may also be necessary to enable plugin-specific system variables to take advantage of server proxy user mapping support:
- For the mysql_native_password plugin, enable mysql_native_password_proxy_users.
- For the sha256_password plugin, enable sha256_password_proxy_users.
For information about user proxying, see Section 6.2.14, “Proxy Users”.
collation_connection
collation_connection Scope Global, Session Dynamic Yes Type String
The collation of the connection character set. collation_connection is important for comparisons of literal strings. For comparisons of strings with column values, collation_connection does not matter because columns have their own collation, which has a higher collation precedence (see Section 10.8.4, “Collation Coercibility in Expressions”).
collation_database
collation_database Scope Global, Session Dynamic Yes Type String Default Value latin1_swedish_ci Footnote This option is dynamic, but should be set only by server. You should not set this variable manually.
The collation used by the default database. The server sets this variable whenever the default database changes. If there is no default database, the variable has the same value as collation_server.

The global character_set_database and collation_database system variables are deprecated in MySQL 5.7; expect them to be removed in a future version of MySQL.

Assigning a value to the session character_set_database and collation_database system variables is deprecated in MySQL 5.7 and assignments produce a warning. Expect the session variables to become read only in a future version of MySQL and assignments to produce an error, while remaining possible to access the session variables to determine the database character set and collation for the default database.
collation_server
collation_server Scope Global, Session Dynamic Yes Type String Default Value latin1_swedish_ci
The server's default collation. See Section 10.15, “Character Set Configuration”.

completion_type

completion_type Scope Global, Session Dynamic Yes Type Enumeration Default Value NO_CHAIN Valid Values

NO_CHAIN

CHAIN

RELEASE

0

1

2

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

Value	Description
`NO_CHAIN` (or 0)	`COMMIT` 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

concurrent_insert Scope Global Dynamic Yes 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
connect_timeout Scope Global Dynamic Yes Type Integer Default Value 10 Minimum Value 2 Maximum Value 31536000 Unit seconds
The number of seconds that the mysqld server waits for a connect packet before responding with Bad handshake. The default value is 10 seconds.

Increasing the connect_timeout value might help if clients frequently encounter errors of the form Lost connection to MySQL server at 'XXX', system error: errno.
core_file
core_file Scope Global Dynamic No Type Boolean Default Value OFF
Whether to write a core file if the server unexpectedly exits. This variable is set by the --core-file option.
datadir
datadir Scope Global Dynamic No Type Directory name
The path to the MySQL server data directory. Relative paths are resolved with respect to the current directory. If you expect the server to be started automatically (that is, in contexts for which you cannot assume what the current directory is), it is best to specify the datadir value as an absolute path.
date_format
datetime_format
debug
debug Scope Global, Session Dynamic Yes Type String Default Value (Unix) d:t:i:o,/tmp/mysqld.trace Default Value (Windows) d:t:i:O,\mysqld.trace
This variable indicates the current debugging settings. It is available only for servers built with debugging support. The initial value comes from the value of instances of the --debug option given at server startup. The global and session values may be set at runtime.

Setting the session value of this system variable is a restricted operation. The session user must have privileges sufficient to set restricted session variables. See Section 5.1.8.1, “System Variable Privileges”.

Assigning a value that begins with + or - cause the value to added to or subtracted from the current value:
```
mysql> SET debug = 'T';
mysql> SELECT @@debug;
+---------+
| @@debug |
+---------+
| T       |
+---------+

mysql> SET debug = '+P';
mysql> SELECT @@debug;
+---------+
| @@debug |
+---------+
| P:T     |
+---------+

mysql> SET debug = '-P';
mysql> SELECT @@debug;
+---------+
| @@debug |
+---------+
| T       |
+---------+
```
For more information, see Section 5.8.3, “The DBUG Package”.
debug_sync
debug_sync Scope Session Dynamic Yes Type String
This variable is the user interface to the Debug Sync facility. Use of Debug Sync requires that MySQL be configured with the -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 has the same value as the global variable. The session value can be set to control synchronization points.

Setting the session value of this system variable is a restricted operation. The session user must have privileges sufficient to set restricted session variables. See Section 5.1.8.1, “System Variable Privileges”.

For a description of the Debug Sync facility and how to use synchronization points, see MySQL Internals: Test Synchronization.
default_authentication_plugin
default_authentication_plugin Scope Global Dynamic No Type Enumeration Default Value mysql_native_password Valid Values
mysql_native_password

sha256_password

The default authentication plugin. These values are permitted:
- mysql_native_password: Use MySQL native passwords; see Section 6.4.1.1, “Native Pluggable Authentication”.
- sha256_password: Use SHA-256 passwords; see Section 6.4.1.5, “SHA-256 Pluggable Authentication”.
Note
If this variable has a value other than mysql_native_password, clients older than MySQL 5.5.7 cannot connect because, of the permitted default authentication plugins, they understand only the mysql_native_password authentication protocol.

The default_authentication_plugin value affects these aspects of server operation:
- It determines which authentication plugin the server assigns to new accounts created by CREATE USER and GRANT statements that do not explicitly specify an authentication plugin.
- The old_passwords system variable affects password hashing for accounts that use the mysql_native_password or sha256_password authentication plugin. If the default authentication plugin is one of those plugins, the server sets old_passwords at startup to the value required by the plugin password hashing method.
- For an account created with either of the following statements, the server associates the account with the default authentication plugin and assigns the account the given password, hashed as required by that plugin:
```
CREATE USER ... IDENTIFIED BY 'cleartext password';
GRANT ...  IDENTIFIED BY 'cleartext password';
```
- For an account created with either of the following statements, the server associates the account with the default authentication plugin and assigns the account the given password hash, if the password hash has the format required by the plugin:
```
CREATE USER ... IDENTIFIED BY PASSWORD 'encrypted password';
GRANT ...  IDENTIFIED BY PASSWORD 'encrypted password';
```
  If the password hash is not in the format required by the default authentication plugin, the statement fails.
default_password_lifetime
default_password_lifetime Scope Global Dynamic Yes Type Integer Default Value (≥ 5.7.11) 0 Default Value (≤ 5.7.10) 360 Minimum Value 0 Maximum Value 65535 Unit days
This variable defines the global automatic password expiration policy. The default default_password_lifetime value is 0, which disables automatic password expiration. If the value 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 options of the ALTER USER statement. See Section 6.2.11, “Password Management”.
Note
Prior to MySQL 5.7.11, the default default_password_lifetime value is 360 (passwords must be changed approximately once per year). For those versions, be aware that, if you make no changes to the default_password_lifetime variable or to individual user accounts, all user passwords expire after 360 days, and all user accounts start running in restricted mode when this happens. Clients (which are effectively users) connecting to the server then get an error indicating that the password must be changed: ERROR 1820 (HY000): You must reset your password using ALTER USER statement before executing this statement.

However, this is easy to miss for clients that automatically connect to the server, such as connections made from scripts. To avoid having such clients suddenly stop working due to a password expiring, make sure to change the password expiration settings for those clients, like this:
```
ALTER USER 'script'@'localhost' PASSWORD EXPIRE NEVER;
```
Alternatively, set the default_password_lifetime variable to 0, thus disabling automatic password expiration for all users.
default_storage_engine
default_storage_engine Scope Global, Session Dynamic Yes Type Enumeration Default Value InnoDB
The default storage engine for tables. See Chapter 15, Alternative Storage Engines. This variable sets the storage engine for permanent tables only. To set the storage engine for TEMPORARY tables, set 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 cannot start.
default_tmp_storage_engine
default_tmp_storage_engine Scope Global, Session Dynamic 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 cannot start.
default_week_format
default_week_format Scope Global, Session Dynamic Yes Type Integer Default Value 0 Minimum Value 0 Maximum Value 7
The default mode value to use for the WEEK() function. See Section 12.7, “Date and Time Functions”.

delay_key_write

delay_key_write Scope Global Dynamic Yes Type Enumeration Default Value ON Valid Values

OFF

ON

ALL

This variable specifies how to use delayed key writes. It applies only to MyISAM tables. Delayed key writing causes key buffers not to be flushed between writes. See also Section 15.2.1, “MyISAM Startup Options”.

This variable can have one of the following values to affect handling of the DELAY_KEY_WRITE table option that can be used 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 5.1.7, “Server System Variables”, and Section 15.2.1, “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
delayed_insert_limit Scope Global Dynamic Yes Type Integer Default Value 100 Minimum Value 1 Maximum Value (64-bit platforms) 18446744073709551615 Maximum Value (32-bit platforms) 4294967295
This system variable is deprecated (because DELAYED inserts are not supported); expect it to be removed in a future release.
delayed_insert_timeout
delayed_insert_timeout Scope Global Dynamic Yes Type Integer Default Value 300 Minimum Value 1 Maximum Value 31536000 Unit seconds
This system variable is deprecated (because DELAYED inserts are not supported); expect it to be removed in a future release.
delayed_queue_size
delayed_queue_size Scope Global Dynamic Yes Type Integer Default Value 1000 Minimum Value 1 Maximum Value (64-bit platforms) 18446744073709551615 Maximum Value (32-bit platforms) 4294967295
This system variable is deprecated (because DELAYED inserts are not supported); expect it to be removed in a future release.
disabled_storage_engines
disabled_storage_engines Scope Global Dynamic No Type String Default Value empty string
This variable indicates which storage engines cannot be used to create tables or tablespaces. For example, to prevent new MyISAM 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: --bootstrap, --initialize, --initialize-insecure, --skip-grant-tables.
Note
Setting disabled_storage_engines might cause an issue with mysql_upgrade. For details, see Section 4.4.7, “mysql_upgrade — Check and Upgrade MySQL Tables”.
disconnect_on_expired_password
disconnect_on_expired_password Scope Global Dynamic No Type Boolean Default Value ON
This variable controls how the server handles clients with expired passwords:
- If the client indicates that it can handle expired passwords, the value of disconnect_on_expired_password is irrelevant. The server permits the client to connect but puts it in sandbox mode.
- If the client does not indicate that it can handle expired passwords, the server handles the client according to the value of disconnect_on_expired_password:
  - If disconnect_on_expired_password: is enabled, the server disconnects the client.
  - If disconnect_on_expired_password: is disabled, the server permits the client to connect but puts it in sandbox mode.
For more information about the interaction of client and server settings relating to expired-password handling, see Section 6.2.12, “Server Handling of Expired Passwords”.
div_precision_increment
div_precision_increment Scope Global, Session Dynamic Yes Type Integer Default Value 4 Minimum Value 0 Maximum Value 30
This variable indicates the number of digits by which to increase the scale of the result of division operations performed with the / operator. The default value is 4. The minimum and maximum values are 0 and 30, respectively. The following example illustrates the effect of increasing the default value.
```
mysql> SELECT 1/7;
+--------+
| 1/7    |
+--------+
| 0.1429 |
+--------+
mysql> SET div_precision_increment = 12;
mysql> SELECT 1/7;
+----------------+
| 1/7            |
+----------------+
| 0.142857142857 |
+----------------+
```
end_markers_in_json
end_markers_in_json Scope Global, Session Dynamic Yes Type Boolean Default Value OFF
Whether optimizer JSON output should add end markers. See MySQL Internals: The end_markers_in_json System Variable.

eq_range_index_dive_limit

Command-Line Format	`--eq-range-index-dive-limit=#`
System Variable	`eq_range_index_dive_limit`
Scope	Global, Session
Dynamic	Yes
Type	Integer
Default Value	`200`
Minimum Value	`0`
Maximum Value	`4294967295`

This variable indicates the number of equality ranges in an equality comparison condition when the optimizer should switch from using index dives to index statistics in estimating the number of qualifying rows. It applies to evaluation of expressions that have either of these equivalent forms, where the optimizer uses a nonunique index to look 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
Section 13.7.5.17, “SHOW ERRORS Statement”.
event_scheduler
event_scheduler Scope Global Dynamic Yes Type Enumeration Default Value OFF Valid Values
OFF

ON

DISABLED

This variable enables or disables, and starts or stops, the Event Scheduler. The possible status values are ON, OFF, and DISABLED. 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 23.4.2, “Event Scheduler Configuration”
explicit_defaults_for_timestamp
explicit_defaults_for_timestamp Scope Global, Session Dynamic Yes Type Boolean Default Value OFF
This system variable determines whether the server enables certain nonstandard behaviors for default values and NULL-value handling in TIMESTAMP columns. By default, explicit_defaults_for_timestamp is disabled, which enables the nonstandard behaviors.

If explicit_defaults_for_timestamp is disabled, the server enables the nonstandard behaviors and 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 5.1.10, “Server SQL Modes”.
The nonstandard behaviors just described are deprecated; expect them to be removed in a future release of MySQL.

If explicit_defaults_for_timestamp is enabled, the server disables the nonstandard behaviors and 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 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 release of MySQL. When removal of those behaviors occurs, explicit_defaults_for_timestamp no longer has any purpose, and you can expect it to be removed as well.

For additional information, see Section 11.2.6, “Automatic Initialization and Updating for TIMESTAMP and DATETIME”.
external_user
external_user Scope Session Dynamic No Type String
The external user name used during the authentication process, as set by the plugin used to authenticate the client. With native (built-in) MySQL authentication, or if the plugin does not set the value, this variable is NULL. See Section 6.2.14, “Proxy Users”.
flush
flush Scope Global Dynamic Yes Type Boolean Default Value OFF
If ON, the server flushes (synchronizes) all changes to disk after each SQL statement. Normally, MySQL does a write of all changes to disk only after each SQL statement and lets the operating system handle the synchronizing to disk. See Section B.3.3.3, “What to Do If MySQL Keeps Crashing”. This variable is set 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
flush_time Scope Global Dynamic Yes Type Integer Default Value 0 Minimum Value 0 Maximum Value 31536000 Unit seconds
If this is set to a nonzero value, all tables are closed every flush_time seconds to free up resources and synchronize unflushed data to disk. This option is best used only on systems with minimal resources.
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
foreign_key_checks Scope Global, Session Dynamic Yes Type Boolean Default Value ON
If set to 1 (the default), foreign key constraints are checked. If set to 0, foreign key constraints are ignored, with a couple of exceptions. When re-creating a table that was dropped, an error is returned if the table definition does not conform to the foreign key constraints referencing the table. Likewise, an ALTER TABLE operation returns an error if a foreign key definition is incorrectly formed. For more information, see Section 13.1.18.5, “FOREIGN KEY Constraints”.

Setting this variable has the same effect on NDB tables as it does 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 13.1.18.5, “FOREIGN KEY Constraints”.

Setting foreign_key_checks to 0 also affects data definition statements: DROP SCHEMA drops a schema even if it contains tables that have foreign keys that are referred to by tables outside the schema, 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 are not verified for consistency.

Dropping an index required by a foreign key constraint is not permitted, even with foreign_key_checks=0. The foreign key constraint must be removed before dropping the index (Bug #70260).
ft_boolean_syntax
ft_boolean_syntax Scope Global Dynamic Yes Type String Default Value + -><()~*:""&|
The list of operators supported by boolean full-text searches performed using IN BOOLEAN MODE. See Section 12.10.2, “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
ft_max_word_len Scope Global Dynamic No Type Integer Default Value 82 Minimum Value 10 Maximum Value 82
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
ft_min_word_len Scope Global Dynamic No Type Integer Default Value 4 Minimum Value 1 Maximum Value 82
The minimum length of the word to be included in a MyISAM FULLTEXT index.
Note
FULLTEXT indexes on MyISAM tables must be rebuilt after changing this variable. Use REPAIR TABLE tbl_name QUICK.
ft_query_expansion_limit
ft_query_expansion_limit Scope Global Dynamic No Type Integer Default Value 20 Minimum Value 0 Maximum Value 1000
The number of top matches to use for full-text searches performed using WITH QUERY EXPANSION.
ft_stopword_file
ft_stopword_file Scope Global Dynamic No Type File name
The file from which to read the list of stopwords for full-text searches on MyISAM tables. The server looks for the file in the data directory unless an absolute path name is given to specify a different directory. All the words from the file are used; comments are not honored. By default, a built-in list of stopwords is used (as defined in the storage/myisam/ft_static.c file). Setting this variable to the empty string ('') disables stopword filtering. See also Section 12.10.4, “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
general_log Scope Global Dynamic Yes Type Boolean Default Value OFF
Whether the general query log is enabled. The value can be 0 (or OFF) to disable the log or 1 (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
general_log_file Scope Global Dynamic Yes Type File name Default Value host_name.log
The name of the general query log file. The default value is host_name.log, but the initial value can be changed with the --general_log_file option.
group_concat_max_len
group_concat_max_len Scope Global, Session Dynamic Yes Type Integer Default Value 1024 Minimum Value 4 Maximum Value (64-bit platforms) 18446744073709551615 Maximum Value (32-bit platforms) 4294967295
The maximum permitted result length in bytes for the GROUP_CONCAT() function. The default is 1024.
have_compress
COMPRESS() and UNCOMPRESS() functions cannot be used.
have_crypt
ENCRYPT() function cannot be used.
Note
The ENCRYPT() function is deprecated in MySQL 5.7, will be removed in a future release of MySQL, and should no longer be used. (For one-way hashing, consider using SHA2() instead.) Consequently, have_crypt also is deprecated; expect it to be removed in a future release.
have_dynamic_loading
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
have_openssl
have_ssl.
have_profiling
Section 13.7.5.31, “SHOW PROFILES Statement”.

This variable is deprecated; expect it to be removed in a future release of MySQL.
have_query_cache
mysqld supports the query cache, NO if not.
Note
The query cache is deprecated as of MySQL 5.7.20, and is removed in MySQL 8.0. Deprecation includes have_query_cache.
have_rtree_keys
have_ssl
have_ssl Scope Global Dynamic No Type String Valid Values
YES (SSL support available)

DISABLED (SSL support was compiled into server, but server was not started with necessary options to enable it)

YES if mysqld supports SSL connections, DISABLED if the server was compiled with SSL support, but was not started with the appropriate connection-encryption options. For more information, see Section 2.9.6, “Configuring SSL Library Support”.
have_statement_timeout
have_statement_timeout Scope Global Dynamic No Type Boolean
Whether the statement execution timeout feature is available (see Statement Execution Time Optimizer Hints). The value can be NO if the background thread used by this feature could not be initialized.
have_symlink
--skip-symbolic-links option, the value is DISABLED.

This variable has no meaning on Windows.

host_cache_size

Command-Line Format	`--host-cache-size=#`
System Variable	`host_cache_size`
Scope	Global
Dynamic	Yes
Type	Integer
Default Value	`-1` (signifies autosizing; do not assign this literal value)
Minimum Value	`0`
Maximum Value	`65536`

The MySQL server maintains an in-memory host cache that contains client host name and IP address information and is used to avoid Domain Name System (DNS) lookups; see Section 5.1.11.2, “DNS Lookups and the Host Cache”.

The host_cache_size variable controls the size of the host cache, as well as the size of the Performance Schema host_cache table that exposes the cache contents. Setting host_cache_size has these effects:

Setting the size to 0 disables the host cache. With the cache disabled, the server performs a DNS lookup every time a client connects.
Changing the size at runtime causes an implicit host cache flushing operation that clears the host cache, truncates the host_cache table, and unblocks any blocked hosts.

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

Setting the host_cache_size system variable rather than the --skip-host-cache option is preferred for the reasons given in the previous paragraph. In addition, the --skip-host-cache option is deprecated in MySQL 8.0, and its removal is expected in a future version of MySQL.

hostname
hostname Scope Global Dynamic No Type String
The server sets this variable to the server host name at startup.
identity
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.
ignore_db_dirs
ignore_db_dirs Scope Global Dynamic No Type String
A comma-separated list of names that are not considered as database directories in the data directory. The value is set from any instances of --ignore-db-dir given at server startup.

As of MySQL 5.7.11, --ignore-db-dir can be used at data directory initialization time with mysqld --initialize to specify directories that the server should ignore for purposes of assessing whether an existing data directory is considered empty. See Section 2.10.1, “Initializing the Data Directory”.

This system variable is deprecated in MySQL 5.7. With the introduction of the data dictionary in MySQL 8.0, it became superfluous and was removed in that version.
init_connect
init_connect Scope Global Dynamic Yes Type String
A string to be executed by the server for each client that connects. The string consists of one or more SQL statements, separated by semicolon characters.

For users that have the SUPER privilege, the content 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 SUPER privilege enables them to open a connection and fix the init_connect value.

As of MySQL 5.7.22, init_connect execution is skipped for any client user with an expired password. This is done because such a user cannot execute arbitrary statements, and thus init_connect execution fails, 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 of init_connect.
init_file
init_file Scope Global Dynamic No Type File name
If specified, this variable names a file containing SQL statements to be read and executed during the startup process. Each statement must be on a single line and should not include comments.

If the server is started with any of the --bootstrap, --initialize, or --initialize-insecure options, it operates in bootstap mode and some functionality is unavailable that limits the statements permitted in the file. These include statements that relate to account management (such as CREATE USER or GRANT), replication, and global transaction identifiers. See Section 16.1.3, “Replication with Global Transaction Identifiers”.
innodb_xxx

InnoDB system variables are listed in Section 14.15, “InnoDB Startup Options and System Variables”. These variables control many aspects of storage, memory use, and I/O patterns for InnoDB tables, and are especially important now that InnoDB is the default storage engine.
insert_id
INSERT or ALTER TABLE statement when inserting an AUTO_INCREMENT value. This is mainly used with the binary log.
interactive_timeout
interactive_timeout Scope Global, Session Dynamic Yes Type Integer Default Value 28800 Minimum Value 1 Maximum Value 31536000 Unit seconds
The number of seconds the server waits for activity on an interactive connection before closing it. An interactive client is defined as a client that uses the CLIENT_INTERACTIVE option to mysql_real_connect(). See also wait_timeout.
internal_tmp_disk_storage_engine
internal_tmp_disk_storage_engine Scope Global Dynamic Yes Type Enumeration Default Value INNODB Valid Values
MYISAM

INNODB

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

The optimizer uses the storage engine defined by internal_tmp_disk_storage_engine for on-disk internal temporary tables.

When using internal_tmp_disk_storage_engine=INNODB (the default), queries that generate on-disk internal temporary tables that exceed InnoDB row or column limits return Row size too large or Too many columns errors. The workaround is to set internal_tmp_disk_storage_engine to MYISAM.
join_buffer_size
join_buffer_size Scope Global, Session Dynamic Yes Type Integer Default Value 262144 Minimum Value 128 Maximum Value (Windows) 4294967168 Maximum Value (Other, 64-bit platforms) 18446744073709551488 Maximum Value (Other, 32-bit platforms) 4294967168 Unit bytes Block Size 128
The minimum size of the buffer that is used for plain index scans, range index scans, and joins that do not use indexes and thus perform full table scans. Normally, the best way to get fast joins is to add indexes. Increase the value of join_buffer_size to get a faster full join when adding indexes is not possible. One join buffer is allocated for each full join between two tables. For a complex join between several tables for which indexes are not used, multiple join buffers might be necessary.

The default is 256KB. The maximum permissible setting for join_buffer_size is 4GB?1. Larger values are permitted for 64-bit platforms (except 64-bit Windows, for which large values are truncated to 4GB?1 with a warning). The block size is 128, and a value that is not an exact multiple of the block size is rounded down to the next lower multiple of the block size by MySQL Server before storing the value for the system variable. The parser allows values up to the maximum unsigned integer value for the platform (4294967295 or 2³²?1 for a 32-bit system, 18446744073709551615 or 2⁶⁴?1 for a 64-bit system) but the actual maximum is a block size lower.

Unless a Block Nested-Loop or Batched Key Access algorithm is used, there is no gain from setting the buffer larger than required to hold each matching row, and all joins allocate at least the minimum size, so use caution in setting this variable to a large value globally. It is better to keep the global setting small and change the session setting to a larger value only in sessions that are doing large joins. Memory allocation time can cause substantial performance drops if the global size is larger than needed by most queries that use it.

When Block Nested-Loop is used, a larger join buffer can be beneficial up to the point where all required columns from all rows in the first table are stored in the join buffer. This depends on the query; the optimal size may be smaller than holding all rows from the first tables.

When Batched Key Access is used, the value of join_buffer_size defines how large the batch of keys is in each request to the storage engine. The larger the buffer, the more sequential access is made to the right hand table of a join operation, which can significantly improve performance.

For additional information about join buffering, see Section 8.2.1.6, “Nested-Loop Join Algorithms”. For information about Batched Key Access, see Section 8.2.1.11, “Block Nested-Loop and Batched Key Access Joins”.
keep_files_on_create
keep_files_on_create Scope Global, Session Dynamic Yes 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 does 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 does not overwrite a file in the specified directory.
key_buffer_size
key_buffer_size Scope Global Dynamic Yes Type Integer Default Value 8388608 Minimum Value 0 Maximum Value (64-bit platforms) OS_PER_PROCESS_LIMIT Maximum Value (32-bit platforms) 4294967295 Unit bytes
Index blocks for MyISAM tables are buffered and are shared by all threads. key_buffer_size is the size of the buffer used for index blocks. The key buffer is also known as the key cache.

The minimum permissible setting is 0, but you cannot set key_buffer_size to 0 dynamically. A setting of 0 drops the key cache, which is not permitted at runtime. Setting key_buffer_size to 0 is permitted only at startup, in which case the key cache is not initialized. Changing the key_buffer_size setting at runtime from a value of 0 to a permitted non-zero value initializes the key cache.

key_buffer_size can be increased or decreased only in increments or multiples of 4096 bytes. Increasing or decreasing the setting by a nonconforming value produces a warning and truncates the setting to a conforming value.

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

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

For even more speed when writing many rows at the same time, use LOCK TABLES. See Section 8.2.4.1, “Optimizing INSERT Statements”.

You can check the performance of the key buffer by issuing a SHOW STATUS statement and examining the Key_read_requests, Key_reads, Key_write_requests, and Key_writes status variables. (See Section 13.7.5, “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
key_cache_age_threshold Scope Global Dynamic Yes Type Integer Default Value 300 Minimum Value 100 Maximum Value (64-bit platforms) 18446744073709551516 Maximum Value (32-bit platforms) 4294967196 Block Size 100
This value controls the demotion of buffers from the hot sublist of a key cache to the warm sublist. Lower values cause demotion to happen more quickly. The minimum value is 100. The default value is 300. See Section 8.10.2, “The MyISAM Key Cache”.

The block size is 100. A value that is not an exact multiple of the block size is rounded down to the next lower multiple of the block size by MySQL Server before storing the value for the system variable. The parser allows values up to the maximum unsigned integer value for the platform (4294967295 or 2³²?1 for a 32-bit system, 18446744073709551615 or 2⁶⁴?1 for a 64-bit system) but the actual maximum is a block size lower.
key_cache_block_size
key_cache_block_size Scope Global Dynamic Yes Type Integer Default Value 1024 Minimum Value 512 Maximum Value 16384 Unit bytes Block Size 512
The size in bytes of blocks in the key cache. The default value is 1024. See Section 8.10.2, “The MyISAM Key Cache”.
key_cache_division_limit
key_cache_division_limit Scope Global Dynamic Yes Type Integer Default Value 100 Minimum Value 1 Maximum Value 100
The division point between the hot and warm sublists of the key cache buffer list. The value is the percentage of the buffer list to use for the warm sublist. Permissible values range from 1 to 100. The default value is 100. See Section 8.10.2, “The MyISAM Key Cache”.
large_files_support
large_files_support Scope Global Dynamic No Type Boolean
Whether mysqld was compiled with options for large file support.
large_pages
large_pages Scope Global Dynamic No Platform Specific Linux Type Boolean Default Value OFF
Whether large page support is enabled (via the --large-pages option). See Section 8.12.4.2, “Enabling Large Page Support”.
large_page_size
large_page_size Scope Global Dynamic No Type Integer Default Value 0 Minimum Value 0 Maximum Value 65535 Unit bytes
If large page support is enabled, this shows the size of memory pages. Large memory pages are supported only on Linux; on other platforms, the value of this variable is always 0. See Section 8.12.4.2, “Enabling Large Page Support”.
last_insert_id
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
lc_messages Scope Global, Session Dynamic Yes Type String Default Value en_US
The locale to use for error messages. The default is en_US. The server converts the argument to a language name and combines it with the value 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
lc_messages_dir Scope Global Dynamic No Type Directory name
The directory where error messages are located. The server uses the value together with the value of lc_messages to produce the location for the error message file. See Section 10.12, “Setting the Error Message Language”.
lc_time_names
lc_time_names Scope Global, Session Dynamic Yes Type String
This variable specifies the locale that controls the language used to display day and month names and abbreviations. This variable affects the output from the DATE_FORMAT(), DAYNAME() 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
license Scope Global Dynamic No Type String Default Value GPL
The type of license the server has.
local_infile
local_infile Scope Global Dynamic Yes Type Boolean Default Value ON
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
lock_wait_timeout Scope Global, Session Dynamic Yes Type Integer Default Value 31536000 Minimum Value 1 Maximum Value 31536000 Unit seconds
This variable specifies the timeout in seconds for attempts to acquire metadata locks. The permissible values range from 1 to 31536000 (1 year). The default is 31536000.

This timeout applies to all statements that use metadata locks. These include DML and DDL operations on tables, views, stored procedures, and stored functions, as well as LOCK TABLES, FLUSH TABLES WITH READ LOCK, 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 does not apply to delayed inserts, which always execute with a timeout of 1 year. This is done to avoid unnecessary timeouts because a session that issues a delayed insert receives no notification of delayed insert timeouts.
locked_in_memory
locked_in_memory Scope Global Dynamic No Type Boolean Default Value OFF
Whether mysqld was locked in memory with --memlock.
log_error
log_error Scope Global Dynamic No Type File name
The error log output destination. If the destination is the console, the value is stderr. Otherwise, the destination is a file and the log_error value is the file name. See Section 5.4.2, “The Error Log”.
log_error_verbosity
log_error_verbosity Scope Global Dynamic Yes Type Integer Default Value 3 Minimum Value 1 Maximum Value 3
The verbosity of the server in writing error, warning, and note messages to the error log. The following table shows the permitted values. The default is 3.

log_error_verbosity Value Permitted Messages

1 Error messages

2 Error and warning messages

3 Error, warning, and information messages

log_error_verbosity was added in MySQL 5.7.2. It is preferred over, and should be used instead of, the older log_warnings system variable. See the description of log_warnings for information about how that variable relates to log_error_verbosity. In particular, assigning a value to log_warnings assigns a value to log_error_verbosity and vice versa.
log_output
log_output Scope Global Dynamic Yes Type Set Default Value FILE Valid Values
TABLE

FILE

NONE

The destination or destinations for general query log and slow query log output. The value is a list one or more comma-separated words chosen from TABLE, FILE, and NONE. TABLE selects logging to the general_log and slow_log tables in the mysql system database. 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
log_queries_not_using_indexes Scope Global Dynamic Yes Type Boolean Default Value OFF
If you enable this variable with the slow query log enabled, queries that are expected to retrieve all rows are logged. See Section 5.4.5, “The Slow Query Log”. This option does not necessarily mean that no index is used. For example, a query that uses a full index scan uses an index but would be logged because the index would not limit the number of rows.
log_slow_admin_statements
log_slow_admin_statements Scope Global Dynamic Yes Type Boolean Default Value OFF
Include slow administrative statements in the statements written to the slow query log. Administrative statements include ALTER TABLE, ANALYZE TABLE, CHECK TABLE, CREATE INDEX, DROP INDEX, OPTIMIZE TABLE, and REPAIR TABLE.
log_syslog
log_syslog Scope Global Dynamic Yes Type Boolean Default Value (Unix) OFF Default Value (Windows) ON
Whether to write error log output to the system log. This is the Event Log on Windows, and syslog on Unix and Unix-like systems. The default value is platform specific:
- On Windows, Event Log output is enabled by default.
- On Unix and Unix-like systems, syslog output is disabled by default.
Regardless of the default, log_syslog can be set explicitly to control output on any supported platform.

System log output control is distinct from sending error output to a file or the console. Error output can be directed to a file or the console in addition to or instead of the system log as desired. See Section 5.4.2, “The Error Log”.
log_syslog_facility
log_syslog_facility Scope Global Dynamic Yes Type String Default Value daemon
The facility for error log output written to syslog (what type of program is sending the message). This variable has no effect unless the log_syslog system variable is enabled. See Section 5.4.2.3, “Error Logging to the System Log”.

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

This variable does not exist on Windows.
log_syslog_include_pid
log_syslog_include_pid Scope Global Dynamic Yes Type Boolean Default Value ON
Whether to include the server process ID in each line of error log output written to syslog. This variable has no effect unless the log_syslog system variable is enabled. See Section 5.4.2.3, “Error Logging to the System Log”.

This variable does not exist on Windows.
log_syslog_tag
log_syslog_tag Scope Global Dynamic Yes Type String Default Value empty string
The tag to be added to the server identifier in error log output written to syslog. This variable has no effect unless the log_syslog system variable is enabled. See Section 5.4.2.3, “Error Logging to the System Log”.

By default, the server identifier is mysqld with no tag. If a tag value of tag is specified, it is appended to the server identifier with a leading hyphen, resulting in an identifier of mysqld-tag.

On Windows, to use a tag that does not already exist, the server must be run from an account with Administrator privileges, to permit creation of a registry entry for the tag. Elevated privileges are not required if the tag already exists.
log_timestamps
log_timestamps Scope Global Dynamic Yes Type Enumeration Default Value UTC Valid Values
UTC

SYSTEM

This variable controls the time zone of timestamps in messages written to the error log, and in general query log and slow query log messages written to files. It does not affect the time zone of general query log and slow query log messages written to tables (mysql.general_log, mysql.slow_log). Rows retrieved from those tables can be converted from the local system time zone to any desired time zone with CONVERT_TZ() or by setting the session time_zone system variable.

Permitted log_timestamps values are UTC (the default) and SYSTEM (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
log_throttle_queries_not_using_indexes Scope Global Dynamic Yes Type Integer Default Value 0 Minimum Value 0 Maximum Value 4294967295
If log_queries_not_using_indexes is enabled, 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”.
log_warnings
log_warnings Scope Global Dynamic Yes Type Integer Default Value 2 Minimum Value 0 Maximum Value (64-bit platforms) 18446744073709551615 Maximum Value (32-bit platforms) 4294967295
Whether to produce additional warning messages to the error log. As of MySQL 5.7.2, information items previously governed by log_warnings are governed by log_error_verbosity, which is preferred over, and should be used instead of, the older log_warnings system variable. (The log_warnings system variable and --log-warnings command-line option are deprecated; expect them to be removed in a future release of MySQL.)

log_warnings is enabled by default (the default is 1 before MySQL 5.7.2, 2 as of 5.7.2). To disable it, set it to 0. If the value is greater than 0, the server logs messages about statements that are unsafe for statement-based logging. If the value is greater than 1, the server logs aborted connections and access-denied errors for new connection attempts. See Section B.3.2.9, “Communication Errors and Aborted Connections”.

If you use replication, enabling this variable by setting it greater than 0 is recommended, to get more information about what is happening, such as messages about network failures and reconnections.

If a replica server is started with log_warnings enabled, the replica prints messages to the error log to provide information about its status, such as the binary log and relay log coordinates where it starts its job, when it is switching to another relay log, when it reconnects after a disconnect, and so forth.

Assigning a value to log_warnings assigns a value to log_error_verbosity and vice versa. The variables are related as follows:
- Suppression of all log_warnings items, achieved with log_warnings=0, is achieved with log_error_verbosity=1 (errors only).
- Items printed for log_warnings=1 or higher count as warnings and are printed for log_error_verbosity=2 or higher.
- Items printed for log_warnings=2 count as notes and are printed for log_error_verbosity=3.
As of MySQL 5.7.2, the default log level is controlled by log_error_verbosity, which has a default of 3. In addition, the default for log_warnings changes from 1 to 2, which corresponds to log_error_verbosity=3. To achieve a logging level similar to the previous default, set log_error_verbosity=2.

In MySQL 5.7.2 and higher, use of log_warnings is still permitted but maps onto use of log_error_verbosity as follows:
- Setting log_warnings=0 is equivalent to log_error_verbosity=1 (errors only).
- Setting log_warnings=1 is equivalent to log_error_verbosity=2 (errors, warnings).
- Setting log_warnings=2 (or higher) is equivalent to log_error_verbosity=3 (errors, warnings, notes), and the server sets log_warnings to 2 if a larger value is specified.
long_query_time
long_query_time Scope Global, Session Dynamic Yes Type Numeric Default Value 10 Minimum Value 0 Maximum Value 31536000 Unit seconds
If a query takes longer than this many seconds, the server increments the Slow_queries status variable. If the slow query log is enabled, the query is logged to the slow query log file. This value is measured in real time, not CPU time, so a query that is under the threshold on a lightly loaded system might be above the threshold on a heavily loaded one. The minimum and default values of long_query_time are 0 and 10, respectively. The maximum is 31536000, which is 365 days in seconds. The value can be specified to a resolution of microseconds. See Section 5.4.5, “The Slow Query Log”.

Smaller values of this variable result in more statements being considered long-running, with the result that more space is required for the slow query log. For very small values (less than one second), the log may grow quite large in a small time. Increasing the number of statements considered long-running may also result in false positives for the “excessive Number of Long Running Processes” alert in MySQL Enterprise Monitor, especially if Group Replication is enabled. For these reasons, very small values should be used in test environments only, or, in production environments, only for a short period.
low_priority_updates
low_priority_updates Scope Global, Session Dynamic Yes 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
lower_case_file_system Scope Global Dynamic No Type Boolean
This variable describes the case sensitivity of file names on the file system where the data directory is located. OFF means file names are case-sensitive, ON means they are not case-sensitive. This variable is read only because it reflects a file system attribute and setting it would have no effect on the file system.
lower_case_table_names
lower_case_table_names Scope Global Dynamic No Type Integer Default Value (macOS) 2 Default Value (Unix) 0 Default Value (Windows) 1 Minimum Value 0 Maximum Value 2
If set to 0, table names are stored as specified and comparisons are case-sensitive. If set to 1, table names are stored in lowercase on disk and comparisons are not case-sensitive. If set to 2, table names are stored as given but compared in lowercase. This option also applies to database names and table aliases. For additional details, see Section 9.2.3, “Identifier Case Sensitivity”.

The default value of this variable is platform-dependent (see lower_case_file_system). On Linux and other Unix-like systems, the default is 0. On Windows the default value is 1. On macOS, the default value is 2. On Linux (and other Unix-like systems), setting the value to 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.

The setting of this variable affects the behavior of replication filtering options with regard to case sensitivity. For more information, see Section 16.2.5, “How Servers Evaluate Replication Filtering Rules”.
max_allowed_packet
max_allowed_packet Scope Global, Session Dynamic Yes Type Integer Default Value 4194304 Minimum Value 1024 Maximum Value 1073741824 Unit bytes Block Size 1024
The maximum size of one packet or any generated/intermediate string, or any parameter sent by the mysql_stmt_send_long_data() C API function. The default is 4MB.

The packet message buffer is initialized to net_buffer_length bytes, but can grow up 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 cannot send to the client more bytes than the current global max_allowed_packet value. (The global value could be less than the session value if the global value is changed after the client connects.)
max_connect_errors
max_connect_errors Scope Global Dynamic Yes Type Integer Default Value 100 Minimum Value 1 Maximum Value (64-bit platforms) 18446744073709551615 Maximum Value (32-bit platforms) 4294967295
After max_connect_errors successive connection requests from a host are interrupted without a successful connection, the server blocks that host from further connections. If a connection from a host is established successfully within fewer than max_connect_errors attempts after a previous connection was interrupted, the error count for the host is cleared to zero. To unblock blocked hosts, flush the host cache; see Flushing the Host Cache.
max_connections
max_connections Scope Global Dynamic Yes Type Integer Default Value 151 Minimum Value 1 Maximum Value 100000
The maximum permitted number of simultaneous client connections. The maximum effective value is the lesser of the effective value of open_files_limit - 810, and the value actually set for max_connections.

For more information, see Section 5.1.11.1, “Connection Interfaces”.
max_delayed_threads
max_delayed_threads Scope Global, Session Dynamic Yes Type Integer Default Value 20 Minimum Value 0 Maximum Value 16384
This system variable is deprecated (because DELAYED inserts are not supported); expect it to be removed in a future release.
max_digest_length
max_digest_length Scope Global Dynamic No Type Integer Default Value 1024 Minimum Value 0 Maximum Value 1048576 Unit bytes
The maximum number of bytes of memory reserved per session for computation of normalized statement digests. Once that amount of space is used during digest computation, truncation occurs: no further tokens from a parsed statement are collected or figure into its digest value. Statements that differ only after that many bytes of parsed tokens produce the same normalized statement digest and are considered identical if compared or if aggregated for digest statistics.
Warning
Setting max_digest_length to zero disables digest production, which also disables server functionality that requires digests, such as MySQL Enterprise Firewall.

Decreasing the max_digest_length value reduces memory use but causes the digest value of more statements to become indistinguishable if they differ only at the end. Increasing the value permits longer statements to be distinguished but increases memory use, particularly for workloads that involve large numbers of simultaneous sessions (the server 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 25.10, “Performance Schema Statement Digests”.
max_error_count
max_error_count Scope Global, Session Dynamic Yes Type Integer Default Value 64 Minimum Value 0 Maximum Value 65535
The maximum number of error, warning, and information messages to be stored for display by the SHOW ERRORS 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
max_execution_time Scope Global, Session Dynamic Yes Type Integer Default Value 0 Minimum Value 0 Maximum Value 4294967295 Unit milliseconds
The execution timeout for SELECT statements, in milliseconds. If the value is 0, timeouts are not enabled.

max_execution_time applies as follows:
- The global max_execution_time value provides the default for the session value for new connections. The session value applies 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
max_heap_table_size Scope Global, Session Dynamic Yes Type Integer Default Value 16777216 Minimum Value 16384 Maximum Value (64-bit platforms) 18446744073709550592 Maximum Value (32-bit platforms) 4294966272 Unit bytes Block Size 1024
This variable sets the maximum size to which user-created MEMORY tables are permitted to grow. The value of the variable is used to calculate MEMORY table MAX_ROWS values.

The block size is 1024. A value that is not an exact multiple of the block size is rounded down to the next lower multiple of the block size by MySQL Server before storing the value for the system variable. The parser allows values up to the maximum unsigned integer value for the platform (4294967295 or 2³²?1 for a 32-bit system, 18446744073709551615 or 2⁶⁴?1 for a 64-bit system) but the actual maximum is a block size lower.

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 16.4.1.20, “Replication and MEMORY Tables”, and Section 16.4.1.37, “Replication and Variables”, for more information.
max_insert_delayed_threads
max_insert_delayed_threads Scope Global, Session Dynamic Yes Type Integer Default Value 0 Minimum Value 20 Maximum Value 16384
This variable is a synonym for max_delayed_threads.

This system variable is deprecated (because DELAYED inserts are not supported); expect it to be removed in a future release.
max_join_size
max_join_size Scope Global, Session Dynamic Yes Type Integer Default Value 18446744073709551615 Minimum Value 1 Maximum Value 18446744073709551615
Do not permit statements that probably need to examine more than max_join_size rows (for single-table statements) or row combinations (for multiple-table statements) or that are likely to do more 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.

If a query result is in the query cache, no result size check is performed, because the result has previously been computed and it does not burden the server to send it to the client.
max_length_for_sort_data
max_length_for_sort_data Scope Global, Session Dynamic Yes Type Integer Default Value 1024 Minimum Value 4 Maximum Value 8388608 Unit bytes
The cutoff on the size of index values that determines which filesort algorithm to use. See Section 8.2.1.14, “ORDER BY Optimization”.
max_points_in_geometry
max_points_in_geometry Scope Global, Session Dynamic Yes Type Integer Default Value 65536 Minimum Value 3 Maximum Value 1048576
The maximum value of the points_per_circle argument to the ST_Buffer_Strategy() function.
max_prepared_stmt_count
max_prepared_stmt_count Scope Global Dynamic Yes Type Integer Default Value 16382 Minimum Value 0 Maximum Value 1048576
This variable limits the total number of prepared statements in the server. It can be used in environments where there is the potential for denial-of-service attacks based on running the server out of memory by preparing huge numbers of statements. If the value is set lower than the current number of prepared statements, existing statements are not affected and can be used, but no new statements can be prepared until the current number drops below the limit. Setting the value to 0 disables prepared statements.
max_seeks_for_key
max_seeks_for_key Scope Global, Session Dynamic Yes Type Integer Default Value (Windows) 4294967295 Default Value (Other, 64-bit platforms) 18446744073709551615 Default Value (Other, 32-bit platforms) 4294967295 Minimum Value 1 Maximum Value (Windows) 4294967295 Maximum Value (Other, 64-bit platforms) 18446744073709551615 Maximum Value (Other, 32-bit platforms) 4294967295
Limit the assumed maximum number of seeks when looking up rows based on a key. The MySQL optimizer assumes that no more than this number of key seeks are required when searching for matching rows in a table by scanning an index, regardless of the actual cardinality of the index (see Section 13.7.5.22, “SHOW INDEX Statement”). By setting this to a low value (say, 100), you can force MySQL to prefer indexes instead of table scans.
max_sort_length
max_sort_length Scope Global, Session Dynamic Yes Type Integer Default Value 1024 Minimum Value 4 Maximum Value 8388608 Unit bytes
The number of bytes to use when sorting data values. The server uses only the first max_sort_length bytes of each value and ignores the rest. Consequently, values that differ only after the 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 8.2.1.14, “ORDER BY Optimization”
max_sp_recursion_depth
max_sp_recursion_depth Scope Global, Session Dynamic Yes Type Integer Default Value 0 Minimum Value 0 Maximum Value 255
The number of times that any given stored procedure may be called recursively. The default value for this option is 0, which completely disables recursion in stored procedures. The maximum value is 255.

Stored procedure recursion increases the demand on thread stack space. If you increase the value of max_sp_recursion_depth, it may be necessary to increase thread stack size by increasing the value of thread_stack at server startup.
max_tmp_tables
max_user_connections
max_user_connections Scope Global, Session Dynamic Yes Type Integer Default Value 0 Minimum Value 0 Maximum Value 4294967295
The maximum number of simultaneous connections permitted to any given MySQL user account. A value of 0 (the default) means “no limit.”

This variable has a global value that can be set at server startup or runtime. It also has a read-only session value that indicates the effective simultaneous-connection limit that applies to the account associated with the current session. The session value is initialized as follows:
- If the user account has a nonzero MAX_USER_CONNECTIONS resource limit, the 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 6.2.16, “Setting Account Resource Limits”.
max_write_lock_count
max_write_lock_count Scope Global Dynamic Yes Type Integer Default Value (Windows) 4294967295 Default Value (Other, 64-bit platforms) 18446744073709551615 Default Value (Other, 32-bit platforms) 4294967295 Minimum Value 1 Maximum Value (Windows) 4294967295 Maximum Value (Other, 64-bit platforms) 18446744073709551615 Maximum Value (Other, 32-bit platforms) 4294967295
After this many write locks, permit some pending read lock requests to be processed in between. Write lock requests have higher priority than read lock requests. However, if max_write_lock_count is set to some low value (say, 10), read lock requests may be preferred over pending write lock requests if the read lock requests have already been passed over in favor of 10 write lock requests. Normally this behavior does not occur because max_write_lock_count by default has a very large value.
mecab_rc_file Scope Global Dynamic No Type File name
The mecab_rc_file option is used when setting up the MeCab full-text parser.

The mecab_rc_file option defines the path to 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 12.10.9, “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
metadata_locks_cache_size Scope Global Dynamic No Type Integer Default Value 1024 Minimum Value 1 Maximum Value 1048576 Unit bytes
The size of the metadata locks cache. The server uses this cache to avoid creation and destruction of synchronization objects. This is particularly helpful on systems where such operations are expensive, such as Windows XP.

In MySQL 5.7.4, metadata locking implementation changes make this variable unnecessary, and so it is deprecated; expect it to be removed in a future release of MySQL.
metadata_locks_hash_instances
metadata_locks_hash_instances Scope Global Dynamic No Type Integer Default Value 8 Minimum Value 1 Maximum Value 1024
The set of metadata locks can be partitioned into separate hashes to permit connections accessing different objects to use different locking hashes and reduce contention. The metadata_locks_hash_instances system variable specifies the number of hashes (default 8).

In MySQL 5.7.4, metadata locking implementation changes make this variable unnecessary, and so it is deprecated; expect it to be removed in a future release of MySQL.
min_examined_row_limit
min_examined_row_limit Scope Global, Session Dynamic Yes Type Integer Default Value 0 Minimum Value 0 Maximum Value (64-bit platforms) 18446744073709551615 Maximum Value (32-bit platforms) 4294967295
Queries that examine fewer than this number of rows are not logged to the slow query log.

log_error_verbosity Value	Permitted Messages
1	Error messages
2	Error and warning messages
3	Error, warning, and information messages

multi_range_count

Command-Line Format	`--multi-range-count=#`
Deprecated	Yes
System Variable	`multi_range_count`
Scope	Global, Session
Dynamic	Yes
Type	Integer
Default Value	`256`
Minimum Value	`1`
Maximum Value	`4294967295`

This variable has no effect. It is deprecated and is removed in MySQL 8.0.

myisam_data_pointer_size
myisam_data_pointer_size Scope Global Dynamic Yes Type Integer Default Value 6 Minimum Value 2 Maximum Value 7 Unit bytes
The default pointer size in bytes, to be used by CREATE TABLE 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.3.2.10, “The table is full”.
myisam_max_sort_file_size
myisam_max_sort_file_size Scope Global Dynamic Yes Type Integer Default Value (Windows) 2146435072 Default Value (Other, 64-bit platforms) 9223372036853727232 Default Value (Other, 32-bit platforms) 2147483648 Minimum Value 0 Maximum Value (Windows) 2146435072 Maximum Value (Other, 64-bit platforms) 9223372036853727232 Maximum Value (Other, 32-bit platforms) 2147483648 Unit bytes
The maximum size of the temporary file that MySQL is permitted to use while re-creating a MyISAM index (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
myisam_mmap_size Scope Global Dynamic No Type Integer Default Value (64-bit platforms) 18446744073709551615 Default Value (32-bit platforms) 4294967295 Minimum Value 7 Maximum Value (64-bit platforms) 18446744073709551615 Maximum Value (32-bit platforms) 4294967295 Unit bytes
The maximum amount of memory to use for memory mapping compressed MyISAM files. If many compressed MyISAM tables are used, the value can be decreased to reduce the likelihood of memory-swapping problems.

myisam_recover_options

myisam_recover_options Scope Global Dynamic No Type Enumeration Default Value OFF Valid Values

OFF

DEFAULT

BACKUP

FORCE

QUICK

Set the MyISAM storage engine recovery mode. The variable value is any combination of the values 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 15.2.1, “MyISAM Startup Options”.

myisam_repair_threads
myisam_repair_threads Scope Global, Session Dynamic Yes Type Integer Default Value 1 Minimum Value 1 Maximum Value (64-bit platforms) 18446744073709551615 Maximum Value (32-bit platforms) 4294967295 Note
This system variable is deprecated in MySQL 5.7; expect it to be removed in a future release of MySQL.

From MySQL 5.7.38, values other than 1 produce a warning.

If this value is greater than 1, MyISAM table indexes are created in parallel (each index in its own thread) during the Repair by sorting process. The default value is 1.
Note
Multithreaded repair is beta-quality code.
myisam_sort_buffer_size
myisam_sort_buffer_size Scope Global, Session Dynamic Yes Type Integer Default Value 8388608 Minimum Value 4096 Maximum Value (64-bit platforms) 18446744073709551615 Maximum Value (32-bit platforms) 4294967295 Unit bytes
The size of the buffer that is allocated when sorting MyISAM indexes during a REPAIR TABLE or when creating indexes with CREATE INDEX or ALTER TABLE.
myisam_stats_method
myisam_stats_method Scope Global, Session Dynamic Yes Type Enumeration Default Value nulls_unequal Valid Values
nulls_unequal

nulls_equal

nulls_ignored

How the server treats NULL values when collecting statistics about the distribution of index values 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 8.3.7, “InnoDB and MyISAM Index Statistics Collection”.
myisam_use_mmap
myisam_use_mmap Scope Global Dynamic Yes Type Boolean Default Value OFF
Use memory mapping for reading and writing MyISAM tables.
mysql_native_password_proxy_users
mysql_native_password_proxy_users Scope Global Dynamic Yes Type Boolean Default Value OFF
This variable controls whether the mysql_native_password built-in authentication plugin supports proxy users. It has no effect unless the check_proxy_users system variable is enabled. For information about user proxying, see Section 6.2.14, “Proxy Users”.
named_pipe
named_pipe Scope Global Dynamic No Platform Specific Windows Type Boolean Default Value OFF
(Windows only.) Indicates whether the server supports connections over named pipes.
named_pipe_full_access_group
named_pipe_full_access_group Scope Global Dynamic No Platform Specific Windows Type String Default Value empty string Valid Values
empty string

valid Windows local group name

*everyone*

(Windows only.) The access control granted to clients on the named pipe created by the MySQL server is set to the minimum necessary for successful communication when the named_pipe system variable is enabled to support named-pipe connections. Some MySQL client software can open named pipe connections without any additional configuration; however, other client software may still require full access to open a named pipe connection.

This variable sets the name of a Windows local group whose members are granted sufficient access by the MySQL server to use named-pipe clients. As of MySQL 5.7.34, the default value is set to an empty string, which means that no Windows user is granted full access to the named pipe.

A new Windows local group name (for example, mysql_access_client_users) can be created in Windows and then used to replace the default value when access is absolutely necessary. In this case, limit the membership of the group to as few users as possible, removing users from the group when their client software is upgraded. A non-member of the group who attempts to open a connection to MySQL with the affected named-pipe client is denied access until a Windows administrator adds the user to the group. Newly added users must log out and log in again to join the group (required by Windows).

Setting the value to '*everyone*' provides a language-independent way of referring to the Everyone group on Windows. The Everyone group is not secure by default.
net_buffer_length
net_buffer_length Scope Global, Session Dynamic Yes Type Integer Default Value 16384 Minimum Value 1024 Maximum Value 1048576 Unit bytes Block Size 1024
Each client thread is associated with a connection buffer and result buffer. Both begin with a size given by net_buffer_length but are dynamically enlarged up 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
net_read_timeout Scope Global, Session Dynamic Yes Type Integer Default Value 30 Minimum Value 1 Maximum Value 31536000 Unit seconds
The number of seconds to wait for more data from a connection before aborting the read. When the server is reading from the client, net_read_timeout is the timeout value controlling when to abort. When the server is writing to the client, net_write_timeout is the timeout value controlling when to abort. See also slave_net_timeout.
net_retry_count
net_retry_count Scope Global, Session Dynamic Yes Type Integer Default Value 10 Minimum Value 1 Maximum Value (64-bit platforms) 18446744073709551615 Maximum Value (32-bit platforms) 4294967295
If a read or write on a communication port is interrupted, retry this many times before giving up. This value should be set quite high on FreeBSD because internal interrupts are sent to all threads.
net_write_timeout
net_write_timeout Scope Global, Session Dynamic Yes Type Integer Default Value 60 Minimum Value 1 Maximum Value 31536000 Unit seconds
The number of seconds to wait for a block to be written to a connection before aborting the write. See also net_read_timeout.
new
new Scope Global, Session Dynamic Yes Disabled by skip-new Type Boolean Default Value OFF
This variable was used in MySQL 4.0 to turn on some 4.1 behaviors, and is retained for backward compatibility. Its value is always OFF.

In NDB Cluster, setting this variable to ON makes it possible to employ partitioning types other 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 Scope Global Dynamic No Type Integer Default Value 2 Minimum Value 1 Maximum Value 10
Defines the n-gram token size for the n-gram full-text parser. The ngram_token_size option is read-only and can only be modified at startup. The default value is 2 (bigram). The maximum value is 10.

For more information about how to configure this variable, see Section 12.10.8, “ngram Full-Text Parser”.
offline_mode
offline_mode Scope Global Dynamic Yes Type Boolean Default Value OFF
Whether the server is in “offline mode”, which has these characteristics:
- Connected client users who do not have the SUPER privilege are disconnected on the next request, with an appropriate error. Disconnection includes terminating running statements and releasing locks. Such clients also cannot initiate new connections, and receive an appropriate error.
- Connected client users who have the SUPER privilege are not disconnected, and can initiate new connections to manage the server.
- Replica threads are permitted to keep applying data to the server.
Only users who have the SUPER privilege can control offline mode. To put a server in offline mode, change the value of 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
old Scope Global Dynamic No Type Boolean Default Value OFF
old is a compatibility variable. It is disabled by default, but can be enabled at startup to revert the server to behaviors present in older versions.

When old is enabled, it changes the default scope of index hints to that used prior to MySQL 5.1.17. That is, index hints with 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 source and replicas might lead to replication errors.
old_alter_table
old_alter_table Scope Global, Session Dynamic Yes Type Boolean Default Value OFF
When this variable is enabled, the server does not use the optimized method of processing an ALTER TABLE operation. It reverts to using a temporary table, copying over the data, and then renaming the temporary table to the original, as used by MySQL 5.0 and earlier. For more information on the operation of ALTER TABLE, see Section 13.1.8, “ALTER TABLE Statement”.
old_passwords
old_passwords Scope Global, Session Dynamic Yes Type Enumeration Default Value 0 Valid Values
0

2
Note
This system variable is deprecated in MySQL 5.7; expect it to be removed in a future release of MySQL.

This variable controls the password hashing method used by the PASSWORD() function. It also influences password hashing performed by CREATE USER and GRANT statements that specify a password using an IDENTIFIED BY clause.

The following table shows, for each password hashing method, the permitted value of old_passwords and which authentication plugins use the hashing method.

Password Hashing Method old_passwords Value Associated Authentication Plugin

MySQL 4.1 native hashing 0 mysql_native_password

SHA-256 hashing 2 sha256_password

If you set old_passwords=2, follow the instructions for using the sha256_password plugin at Section 6.4.1.5, “SHA-256 Pluggable Authentication”.

The server sets the global old_passwords value during startup to be consistent with the password hashing method required by the authentication plugin indicated by the default_authentication_plugin system variable.

When a client successfully connects to the server, the server sets the session old_passwords value appropriately for the account authentication method. For example, if the account uses the sha256_password authentication plugin, the server sets old_passwords=2.

For additional information about authentication plugins and hashing formats, see Section 6.2.13, “Pluggable Authentication”, and Section 6.1.2.4, “Password Hashing in MySQL”.
open_files_limit
open_files_limit Scope Global Dynamic No Type Integer Default Value 5000, with possible adjustment Minimum Value 0 Maximum Value platform dependent
The number of file descriptors available to mysqld from the operating system:
- At startup, mysqld reserves descriptors with setrlimit(), using the value requested at by setting this variable directly or by using the --open-files-limit option to mysqld_safe. If mysqld produces the 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.
- At runtime, the value of open_files_limit indicates the number of file descriptors actually permitted to mysqld by the operating system, which might differ from the value requested at startup. If the number of file descriptors requested during startup cannot be allocated, mysqld writes a warning to the error log.
The effective open_files_limit value is based on the value specified at system startup (if any) and the values of max_connections and table_open_cache, using these formulas:
- 10 + max_connections + (table_open_cache * 2)
- max_connections * 5
- The operating system limit if that limit is positive but not Infinity.
- If the operating system limit is Infinity: open_files_limit value if specified at startup, 5000 if not.
The server attempts to obtain the number of file descriptors using the maximum of those values. If that many descriptors cannot be obtained, the server attempts to obtain as many as the system permits.

The effective value is 0 on systems where MySQL cannot change the number of open files.

On Unix, the value cannot be set greater than the value displayed by the ulimit -n command. On Linux systems using systemd, the value cannot be set greater than LimitNOFile (this is DefaultLimitNOFILE, if LimitNOFile is not set); otherwise, on Linux, the value of open_files_limit cannot exceed ulimit -n.
optimizer_prune_level
optimizer_prune_level Scope Global, Session Dynamic Yes Type Integer Default Value 1 Minimum Value 0 Maximum Value 1
Controls the heuristics applied during query optimization to prune less-promising partial plans from the optimizer search space. A value of 0 disables heuristics so that the optimizer performs an exhaustive search. A value of 1 causes the optimizer to prune plans based on the number of rows retrieved by intermediate plans.
optimizer_search_depth
optimizer_search_depth Scope Global, Session Dynamic Yes Type Integer Default Value 62 Minimum Value 0 Maximum Value 62
The maximum depth of search performed by the query optimizer. Values larger than the number of relations in a query result in better query plans, but take longer to generate an execution plan for a query. Values smaller than the number of relations in a query return an execution plan quicker, but the resulting plan may be far from being optimal. If set to 0, the system automatically picks a reasonable value.
optimizer_switch
optimizer_switch Scope Global, Session Dynamic Yes Type Set Valid Values (≥ 5.7.33)
batched_key_access={on|off}

block_nested_loop={on|off}

condition_fanout_filter={on|off}

derived_merge={on|off}

duplicateweedout={on|off}

engine_condition_pushdown={on|off}

firstmatch={on|off}

index_condition_pushdown={on|off}

index_merge={on|off}

index_merge_intersection={on|off}

index_merge_sort_union={on|off}

index_merge_union={on|off}

loosescan={on|off}

materialization={on|off}

mrr={on|off}

mrr_cost_based={on|off}

prefer_ordering_index={on|off}

semijoin={on|off}

subquery_materialization_cost_based={on|off}

use_index_extensions={on|off}
Valid Values (≤ 5.7.32)
batched_key_access={on|off}

block_nested_loop={on|off}

condition_fanout_filter={on|off}

derived_merge={on|off}

duplicateweedout={on|off}

engine_condition_pushdown={on|off}

firstmatch={on|off}

index_condition_pushdown={on|off}

index_merge={on|off}

index_merge_intersection={on|off}

index_merge_sort_union={on|off}

index_merge_union={on|off}

loosescan={on|off}

materialization={on|off}

mrr={on|off}

mrr_cost_based={on|off}

semijoin={on|off}

subquery_materialization_cost_based={on|off}

use_index_extensions={on|off}

The optimizer_switch system variable enables control over optimizer behavior. The value of this variable is a set of flags, each of which has a value 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,
                    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
optimizer_trace Scope Global, Session Dynamic Yes Type String
This variable controls optimizer tracing. For details, see MySQL Internals: Tracing the Optimizer.
optimizer_trace_features
optimizer_trace_features Scope Global, Session Dynamic Yes Type String
This variable enables or disables selected optimizer tracing features. For details, see MySQL Internals: Tracing the Optimizer.
optimizer_trace_limit
optimizer_trace_limit Scope Global, Session Dynamic Yes Type Integer Default Value 1 Minimum Value 0 Maximum Value 2147483647
The maximum number of optimizer traces to display. For details, see MySQL Internals: Tracing the Optimizer.
optimizer_trace_max_mem_size
optimizer_trace_max_mem_size Scope Global, Session Dynamic Yes Type Integer Default Value 16384 Minimum Value 0 Maximum Value 4294967295 Unit bytes
The maximum cumulative size of stored optimizer traces. For details, see MySQL Internals: Tracing the Optimizer.
optimizer_trace_offset
optimizer_trace_offset Scope Global, Session Dynamic Yes Type Integer Default Value -1 Minimum Value -2147483647 Maximum Value 2147483647
The offset of optimizer traces to display. For details, see MySQL Internals: Tracing the Optimizer.
performance_schema_xxx

Performance Schema system variables are listed in Section 25.15, “Performance Schema System Variables”. These variables may be used to configure Performance Schema operation.
parser_max_mem_size
parser_max_mem_size Scope Global, Session Dynamic Yes Type Integer Default Value (64-bit platforms) 18446744073709551615 Default Value (32-bit platforms) 4294967295 Minimum Value 10000000 Maximum Value (64-bit platforms) 18446744073709551615 Maximum Value (32-bit platforms) 4294967295 Unit bytes
The maximum amount of memory available to the parser. The default value places no limit on memory available. The value can be reduced to protect against out-of-memory situations caused by parsing long or complex SQL statements.
pid_file
pid_file Scope Global Dynamic No Type File name
The path name of the file in which the server writes its process ID. The server creates the file in the data directory unless an absolute path name is given to specify a different directory. If you specify this variable, you must specify a value. If you do not specify this variable, MySQL uses a default value of 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
plugin_dir Scope Global Dynamic No Type Directory name Default Value BASEDIR/lib/plugin
The path name of the plugin directory.

If the plugin directory is writable by the server, it may be possible for a user to write executable code to a file in the directory using SELECT ... INTO DUMPFILE. This can be prevented by 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
port Scope Global Dynamic No Type Integer Default Value 3306 Minimum Value 0 Maximum Value 65535
The number of the port on which the server listens for TCP/IP connections. This variable can be set with the --port option.
preload_buffer_size
preload_buffer_size Scope Global, Session Dynamic Yes Type Integer Default Value 32768 Minimum Value 1024 Maximum Value 1073741824 Unit bytes
The size of the buffer that is allocated when preloading indexes.
profiling
SHOW PROFILE and SHOW PROFILES statements provide access to profiling information. See Section 13.7.5.31, “SHOW PROFILES Statement”.

This variable is deprecated; expect it to be removed in a future release of MySQL.
profiling_history_size
profiling is enabled. The default value is 15. The maximum value is 100. Setting the value to 0 effectively disables profiling. See Section 13.7.5.31, “SHOW PROFILES Statement”.

This variable is deprecated; expect it to be removed in a future release of MySQL.
protocol_version
protocol_version Scope Global Dynamic No Type Integer Default Value 10 Minimum Value 0 Maximum Value 4294967295
The version of the client/server protocol used by the MySQL server.
proxy_user
proxy_user Scope Session Dynamic No Type String
If the current client is a proxy for another user, this variable is the proxy user account name. Otherwise, this variable is NULL. See Section 6.2.14, “Proxy Users”.
pseudo_slave_mode
pseudo_slave_mode Scope Session Dynamic Yes Type Boolean
This system variable is for internal server use. pseudo_slave_mode assists with the correct handling of transactions that originated on older or newer servers than the server currently processing them. mysqlbinlog sets the value of pseudo_slave_mode to true before executing any SQL statements.

pseudo_slave_mode has the following effects on the handling of prepared XA transactions, which can be attached to or detached from the handling session (by default, the session that 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_thread_id
pseudo_thread_id Scope Session Dynamic Yes Type Integer Default Value 2147483647 Minimum Value 0 Maximum Value 2147483647
This variable is for internal server use.
Warning
Changing the session value of the pseudo_thread_id system variable changes the value returned by the CONNECTION_ID() function.
query_alloc_block_size
query_alloc_block_size Scope Global, Session Dynamic Yes Type Integer Default Value 8192 Minimum Value 1024 Maximum Value 4294966272 Unit bytes Block Size 1024
The allocation size in bytes of memory blocks that are allocated for objects created during statement parsing and execution. If you have problems with memory fragmentation, it might help to increase this parameter.

The block size for the byte number is 1024. A value that is not an exact multiple of the block size is rounded down to the next lower multiple of the block size by MySQL Server before storing the value for the system variable. The parser allows values up to the maximum unsigned integer value for the platform (4294967295 or 2³²?1 for a 32-bit system, 18446744073709551615 or 2⁶⁴?1 for a 64-bit system) but the actual maximum is a block size lower.
query_cache_limit
query_cache_limit Scope Global Dynamic Yes Type Integer Default Value 1048576 Minimum Value 0 Maximum Value (64-bit platforms) 18446744073709551615 Maximum Value (32-bit platforms) 4294967295 Unit bytes
Do not cache results that are larger than this number of bytes. The default value is 1MB.
Note
The query cache is deprecated as of MySQL 5.7.20, and is removed in MySQL 8.0. Deprecation includes query_cache_limit.
query_cache_min_res_unit
query_cache_min_res_unit Scope Global Dynamic Yes Type Integer Default Value 4096 Minimum Value 512 Maximum Value (64-bit platforms) 18446744073709551615 Maximum Value (32-bit platforms) 4294967295 Unit bytes
The minimum size (in bytes) for blocks allocated by the query cache. The default value is 4096 (4KB). Tuning information for this variable is given in Section 8.10.3.3, “Query Cache Configuration”.
Note
The query cache is deprecated as of MySQL 5.7.20, and is removed in MySQL 8.0. Deprecation includes query_cache_min_res_unit.
query_cache_size
query_cache_size Scope Global Dynamic Yes Type Integer Default Value 1048576 Minimum Value 0 Maximum Value (64-bit platforms) 18446744073709551615 Maximum Value (32-bit platforms) 4294967295 Unit bytes
The amount of memory allocated for caching query results. By default, the query cache is disabled. This is achieved using a default value of 1M, with a default for query_cache_type of 0. (To reduce overhead significantly if you set the size to 0, you should also start the server with query_cache_type=0.

The permissible values are multiples of 1024; other values are rounded down to the nearest multiple. For nonzero values of query_cache_size, that many bytes of memory are allocated even if query_cache_type=0. See Section 8.10.3.3, “Query Cache Configuration”, for more information.

The query cache needs a minimum size of about 40KB to allocate its structures. (The exact size depends on system architecture.) If you set the value of query_cache_size too small, a warning occurs, as described in Section 8.10.3.3, “Query Cache Configuration”.
Note
The query cache is deprecated as of MySQL 5.7.20, and is removed in MySQL 8.0. Deprecation includes query_cache_size.

Password Hashing Method	old_passwords Value	Associated Authentication Plugin
MySQL 4.1 native hashing	0	`mysql_native_password`
SHA-256 hashing	2	`sha256_password`

query_cache_type

query_cache_type Scope Global, Session Dynamic Yes Type Enumeration Default Value 0 Valid Values

0

1

2

Set the query cache type. Setting the GLOBAL value sets the type for all clients that connect thereafter. Individual clients can set the SESSION value to affect their own use of the query cache. Possible values are shown in the following table.

Option	Description
`0` or `OFF`	Do not cache results in or retrieve results from the query cache. Note that this does not deallocate the query cache buffer. To do that, you should set `query_cache_size` to 0.
`1` or `ON`	Cache all cacheable query results except for those that begin with `SELECT SQL_NO_CACHE`.
`2` or `DEMAND`	Cache results only for cacheable queries that begin with `SELECT SQL_CACHE`.

This variable defaults to OFF.

If the server is started with query_cache_type set to 0, it does not acquire the query cache mutex at all, which means that the query cache cannot be enabled at runtime and there is reduced overhead in query execution.

Note

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

query_cache_wlock_invalidate
query_cache_wlock_invalidate Scope Global, Session Dynamic Yes Type Boolean Default Value OFF
Normally, when one client acquires a WRITE lock on a MyISAM table, other clients are not blocked from issuing statements that read from the table if the query results are present in the query cache. Setting this variable to 1 causes acquisition of a WRITE lock for a table to invalidate any queries in the query cache that refer to the table. This forces other clients that attempt to access the table to wait while the lock is in effect.
Note
The query cache is deprecated as of MySQL 5.7.20, and is removed in MySQL 8.0. Deprecation includes query_cache_wlock_invalidate.
query_prealloc_size
query_prealloc_size Scope Global, Session Dynamic Yes Type Integer Default Value 8192 Minimum Value 8192 Maximum Value (64-bit platforms) 18446744073709550592 Maximum Value (32-bit platforms) 4294966272 Unit bytes Block Size 1024
The size in bytes of the persistent buffer used for statement parsing and execution. This buffer is not freed between statements. If you are running complex queries, a larger query_prealloc_size value might be helpful in improving performance, because it can reduce the need for the server to perform memory allocation during query execution operations. You should be aware that doing this does not necessarily eliminate allocation completely; the server may still allocate memory in some situations, such as for operations relating to transactions, or to stored programs.

The block size is 1024. A value that is not an exact multiple of the block size is rounded down to the next lower multiple of the block size by MySQL Server before storing the value for the system variable. The parser allows values up to the maximum unsigned integer value for the platform (4294967295 or 2³²?1 for a 32-bit system, 18446744073709551615 or 2⁶⁴?1 for a 64-bit system) but the actual maximum is a block size lower.
rand_seed1
rand_seed1 Scope Session Dynamic Yes Type Integer Default Value N/A Minimum Value 0 Maximum Value 4294967295
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 source passes two values to the replica, where they are used to seed the random number generator. The replica uses these values to set the session variables rand_seed1 and rand_seed2 so that RAND() on the replica generates the same value as on the source.
rand_seed2
rand_seed1.
range_alloc_block_size
range_alloc_block_size Scope Global, Session Dynamic Yes Type Integer Default Value 4096 Minimum Value 4096 Maximum Value (64-bit platforms) 18446744073709550592 Maximum Value 4294966272 Unit bytes Block Size 1024
The size in bytes of blocks that are allocated when doing range optimization.

The block size for the byte number is 1024. A value that is not an exact multiple of the block size is rounded down to the next lower multiple of the block size by MySQL Server before storing the value for the system variable. The parser allows values up to the maximum unsigned integer value for the platform (4294967295 or 2³²?1 for a 32-bit system, 18446744073709551615 or 2⁶⁴?1 for a 64-bit system) but the actual maximum is a block size lower.
range_optimizer_max_mem_size
range_optimizer_max_mem_size Scope Global, Session Dynamic Yes Type Integer Default Value (≥ 5.7.12) 8388608 Default Value (≤ 5.7.11) 1536000 Minimum Value 0 Maximum Value 18446744073709551615 Unit bytes
The limit on memory consumption for the range optimizer. A value of 0 means “no limit.” If an execution plan considered by the optimizer uses the range access method but the optimizer estimates that the amount of memory needed for this method would exceed the limit, it abandons the plan and considers other plans. For more information, see Limiting Memory Use for Range Optimization.
rbr_exec_mode
rbr_exec_mode Scope Session Dynamic Yes Type Enumeration Default Value STRICT Valid Values
STRICT

IDEMPOTENT

For internal use by mysqlbinlog. This variable switches the server between IDEMPOTENT mode 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;
```
read_buffer_size
read_buffer_size Scope Global, Session Dynamic Yes Type Integer Default Value 131072 Minimum Value 8192 Maximum Value 2147479552 Unit bytes Block Size 4096
Each thread that does a sequential scan for a MyISAM table allocates a buffer of this size (in bytes) for each table it scans. If you do many sequential scans, you might want to increase this value, which defaults to 131072. The value of this variable should be a multiple of 4KB. If it is set to a value that is not a multiple of 4KB, its value is rounded down to the nearest multiple of 4KB.

This option is also used in the following context for all storage engines:
- For caching the indexes in a temporary file (not a temporary table), when sorting rows for ORDER BY.
- For bulk insert into partitions.
- For caching results of nested queries.
read_buffer_size is also used in one other storage engine-specific way: to determine the memory block size for MEMORY tables.

For more information about memory use during different operations, see Section 8.12.4.1, “How MySQL Uses Memory”.
read_only
read_only Scope Global Dynamic Yes Type Boolean Default Value OFF
If the read_only system variable is enabled, the server permits no client updates except from users who have the 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 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 replication threads, if the server is a replica. In replication setups, it can be useful to enable read_only on replica servers to ensure that replicas accept updates only from the source server and not from clients.
- Use of ANALYZE TABLE 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 replicas 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”.
- As of MySQL 5.7.16, updates to Performance Schema tables, such as UPDATE or TRUNCATE TABLE operations.
Changes to read_only on a replication source server are not replicated to replica servers. The value can be set on a replica independent of the setting on the source.

The following conditions apply to attempts to enable read_only (including implicit attempts resulting from 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
read_rnd_buffer_size Scope Global, Session Dynamic Yes Type Integer Default Value 262144 Minimum Value 1 Maximum Value 2147483647 Unit bytes
This variable is used for reads from MyISAM tables, and, for any storage engine, for Multi-Range Read optimization.

When reading rows from a MyISAM table in sorted order following a key-sorting operation, the rows are read through this buffer to avoid disk seeks. See Section 8.2.1.14, “ORDER BY Optimization”. Setting the variable to a large value can 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 8.12.4.1, “How MySQL Uses Memory”. For information about Multi-Range Read optimization, see Section 8.2.1.10, “Multi-Range Read Optimization”.
require_secure_transport
require_secure_transport Scope Global Dynamic Yes Type Boolean Default Value OFF
Whether client connections to the server are required to use some form of secure transport. When this variable is enabled, the server permits only TCP/IP connections encrypted using TLS/SSL, or connections that use a socket file (on Unix) or shared memory (on Windows). The server rejects nonsecure connection attempts, which fail with an ER_SECURE_TRANSPORT_REQUIRED error.

This capability supplements per-account SSL requirements, which take precedence. For example, if an account is defined with REQUIRE SSL, 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.
secure_auth
secure_auth Scope Global Dynamic Yes Type Boolean Default Value ON Valid Values ON
If this variable is enabled, the server blocks connections by clients that attempt to use accounts that have passwords stored in the old (pre-4.1) format. Enable this variable to prevent all use of passwords employing the old format (and hence insecure communication over the network).

This variable is deprecated; expect it to be removed in a future release of MySQL. It is always enabled and attempting to disable it produces an error.

Server startup fails with an error if this variable is enabled and the privilege tables are in pre-4.1 format. See Section 6.4.1.3, “Migrating Away from Pre-4.1 Password Hashing and the mysql_old_password Plugin”.
Note
Passwords that use the pre-4.1 hashing method are less secure than passwords that use the native password hashing method and should be avoided. Pre-4.1 passwords are deprecated and support for them is removed in MySQL 5.7.5. For account upgrade instructions, see Section 6.4.1.3, “Migrating Away from Pre-4.1 Password Hashing and the mysql_old_password Plugin”.

secure_file_priv

secure_file_priv Scope Global Dynamic No Type String Default Value platform specific Valid Values

empty string

dirname

NULL

This variable is used to limit the effect of data import and export operations, such as those performed by the LOAD DATA 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 does not create it.
If set to NULL, the server disables import and export operations.

The default value is platform specific and depends on the value of the INSTALL_LAYOUT CMake option, as shown in the following table. To specify the 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`, `WIN`	`NULL` (>= MySQL 5.7.16), empty (< MySQL 5.7.16)
`DEB`, `RPM`, `SLES`, `SVR4`	`/var/lib/mysql-files`
Otherwise	`mysql-files` under the `CMAKE_INSTALL_PREFIX` value

To set the default secure_file_priv value for the libmysqld embedded server, use the INSTALL_SECURE_FILE_PRIV_EMBEDDEDDIR CMake option. The default value for this option is NULL.

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
session_track_gtids Scope Global, Session Dynamic Yes Type Enumeration Default Value OFF Valid Values
OFF

OWN_GTID

ALL_GTIDS

Controls whether the server returns GTIDs to the client, enabling the client to use them to track the server state. Depending on the variable value, at the end of executing each transaction, the server’s GTIDs are captured and returned to the client as part of the acknowledgement. The possible values for session_track_gtids are as follows:
- OFF: The server does not return GTIDs to the client. This is the default.
- OWN_GTID: The server returns the GTIDs for all transactions that were successfully committed by this client in its current session since the last acknowledgement. Typically, this is the single GTID for the last transaction committed, but if a single client request resulted in multiple transactions, the server returns a GTID set containing all the relevant GTIDs.
- ALL_GTIDS: The server returns the global value of its gtid_executed system variable, which it reads at a point after the transaction is successfully committed. As well as the GTID for the transaction just committed, this GTID set includes all transactions committed on the server by any client, and can include transactions committed after the point when the transaction currently being acknowledged was committed.
session_track_gtids cannot be set within transactional context.

For more information about session state tracking, see Section 5.1.15, “Server Tracking of Client Session State”.
session_track_schema
session_track_schema Scope Global, Session Dynamic Yes Type Boolean Default Value ON
Controls whether the server tracks when the default schema (database) is set within the current session and notifies the client to make the schema name available.

If the schema name tracker is enabled, name notification occurs each time the default schema is set, even if the new schema name is the same as the old.

For more information about session state tracking, see Section 5.1.15, “Server Tracking of Client Session State”.
session_track_state_change
session_track_state_change Scope Global, Session Dynamic Yes Type Boolean Default Value OFF
Controls whether the server tracks changes to the state of the current session and notifies the client when state changes occur. Changes can be reported for these attributes of client session state:
- The default schema (database).
- Session-specific values for system variables.
- User-defined variables.
- Temporary tables.
- Prepared statements.
If the session state tracker is enabled, notification occurs for each change that involves tracked session attributes, even if the new attribute values are the same as the old. For example, setting a user-defined variable to its current value results in a notification.

The session_track_state_change variable controls only notification of when changes occur, not what the changes are. For example, state-change notifications occur when the default schema is set or tracked session system variables are assigned, but the notification does not include the schema name or variable values. To receive notification of the schema name or session system variable values, use 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 5.1.15, “Server Tracking of Client Session State”.
session_track_system_variables
session_track_system_variables Scope Global, Session Dynamic Yes Type String Default Value time_zone, autocommit, character_set_client, character_set_results, character_set_connection
Controls whether the server tracks assignments to session system variables and notifies the client of the name and value of each assigned variable. The variable value is a comma-separated list of variables for which to track assignments. By default, notification is enabled for time_zone, autocommit, character_set_client, character_set_results, 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 5.1.15, “Server Tracking of Client Session State”.
session_track_transaction_info
session_track_transaction_info Scope Global, Session Dynamic Yes Type Enumeration Default Value OFF Valid Values
OFF

STATE

CHARACTERISTICS

Controls whether the server tracks the state and characteristics of transactions within the current session and notifies the client to make this information available. These session_track_transaction_info values are permitted:
- OFF: Disable transaction state tracking. This is the default.
- STATE: Enable transaction state tracking without characteristics tracking. State tracking enables the client to determine whether a transaction is in progress and whether it could be moved to a different session without being rolled back.
- CHARACTERISTICS: Enable transaction state tracking, including characteristics tracking. Characteristics tracking enables the client to determine how to restart a transaction in another session so that it has the same characteristics as in the original session. The following characteristics are relevant for this purpose:
```
ISOLATION LEVEL
READ ONLY
READ WRITE
WITH CONSISTENT SNAPSHOT
```
For a client to safely relocate a transaction to another session, it must track not only transaction state but also transaction characteristics. In addition, the client must track the transaction_isolation 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 5.1.15, “Server Tracking of Client Session State”.
sha256_password_auto_generate_rsa_keys
sha256_password_auto_generate_rsa_keys Scope Global Dynamic No Type Boolean Default Value ON
This variable is available if the server was compiled using OpenSSL (see Section 6.3.4, “SSL Library-Dependent Capabilities”). It controls whether the server autogenerates RSA private/public key-pair files in the data directory, if they do not already exist.

At startup, the server automatically generates RSA private/public key-pair files in the data directory if the sha256_password_auto_generate_rsa_keys system variable is enabled, no RSA options are specified, and the RSA files are missing from the data directory. These files enable secure password exchange using RSA over unencrypted connections for accounts authenticated by the sha256_password plugin; see Section 6.4.1.5, “SHA-256 Pluggable Authentication”.

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

The auto_generate_certs system variable is related but controls autogeneration of SSL certificate and key files needed for secure connections using SSL.
sha256_password_private_key_path
sha256_password_private_key_path Scope Global Dynamic No Type File name Default Value private_key.pem
This variable is available if MySQL was compiled using OpenSSL (see Section 6.3.4, “SSL Library-Dependent Capabilities”). Its value is the path name of the RSA private key file for the sha256_password authentication plugin. If the file is named as a relative path, it is interpreted relative to the server data directory. The file must be in PEM format.
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 6.4.1.5, “SHA-256 Pluggable Authentication”.
sha256_password_proxy_users
sha256_password_proxy_users Scope Global Dynamic Yes Type Boolean Default Value OFF
This variable controls whether the sha256_password built-in authentication plugin supports proxy users. It has no effect unless the check_proxy_users system variable is enabled. For information about user proxying, see Section 6.2.14, “Proxy Users”.
sha256_password_public_key_path
sha256_password_public_key_path Scope Global Dynamic No Type File name Default Value public_key.pem
This variable is available if MySQL was compiled using OpenSSL (see Section 6.3.4, “SSL Library-Dependent Capabilities”). Its value is the path name of the RSA public key file for the sha256_password authentication plugin. If the file is named as a relative path, it is interpreted relative to the server data directory. The file must be in PEM format. Because this file stores a public key, copies can be freely distributed to client users. (Clients that explicitly specify a public key when connecting to the server using RSA password encryption must use the same public key as that used by the server.)

For information about sha256_password, including information about how clients specify the RSA public key, see Section 6.4.1.5, “SHA-256 Pluggable Authentication”.
shared_memory
shared_memory Scope Global Dynamic No Platform Specific Windows Type Boolean Default Value OFF
(Windows only.) Whether the server permits shared-memory connections.
shared_memory_base_name
shared_memory_base_name Scope Global Dynamic No Platform Specific Windows Type String Default Value MYSQL
(Windows only.) The name of shared memory to use for shared-memory connections. This is useful when running multiple MySQL instances on a single physical machine. The default name is MYSQL. The name is case-sensitive.

This variable applies only if the server is started with the shared_memory system variable enabled to support shared-memory connections.
show_compatibility_56
show_compatibility_56 Scope Global Dynamic Yes Type Boolean Default Value OFF
The INFORMATION_SCHEMA has tables that contain system and status variable information (see Section 24.3.11, “The INFORMATION_SCHEMA GLOBAL_VARIABLES and SESSION_VARIABLES Tables”, and Section 24.3.10, “The INFORMATION_SCHEMA GLOBAL_STATUS and SESSION_STATUS Tables”). As of MySQL 5.7.6, the Performance Schema also contains system and status variable tables (see Section 25.12.13, “Performance Schema System Variable Tables”, and Section 25.12.14, “Performance Schema Status Variable Tables”). The Performance Schema tables are intended to replace the INFORMATION_SCHEMA tables, which are deprecated as of MySQL 5.7.6 and are removed in MySQL 8.0.

For advice on migrating away from the INFORMATION_SCHEMA tables to the Performance Schema tables, see Section 25.20, “Migrating to Performance Schema System and Status Variable Tables”. To assist in the migration, you can use the show_compatibility_56 system variable, which affects whether MySQL 5.6 compatibility is enabled with respect to how system and status variable information is provided by the INFORMATION_SCHEMA and Performance Schema tables, and also by the SHOW VARIABLES and SHOW STATUS statements.
Note
show_compatibility_56 is deprecated because its only purpose is to permit control over deprecated system and status variable information sources which you can expect to be removed in a future release of MySQL. When those sources are removed, show_compatibility_56 no longer has any purpose, and you can expect it be removed as well.

The following discussion describes the effects of show_compatibility_56:
- Overview of show_compatibility_56 Effects
- Effect of show_compatibility_56 on SHOW Statements
- Effect of show_compatibility_56 on INFORMATION_SCHEMA Tables
- Effect of show_compatibility_56 on Performance Schema Tables
- Effect of show_compatibility_56 on Slave Status Variables
- Effect of show_compatibility_56 on FLUSH STATUS
For better understanding, it is strongly recommended that you also read these sections:
- Section 25.12.13, “Performance Schema System Variable Tables”
- Section 25.12.14, “Performance Schema Status Variable Tables”
- Section 25.12.15.10, “Status Variable Summary Tables”
show_compatibility_56 system variable affects these aspects of server operation regarding system and status variables:
- Information available from the SHOW VARIABLES and SHOW STATUS statements
- Information available from the INFORMATION_SCHEMA tables that provide system and status variable information
- Information available from the Performance Schema tables that provide system and status variable information
- The effect of the FLUSH STATUS statement on status variables
This list summarizes the effects of show_compatibility_56, with additional details given later:
- When show_compatibility_56 is ON, compatibility with MySQL 5.6 is enabled. Older variable information sources (SHOW statements, INFORMATION_SCHEMA tables) produce the same output as in MySQL 5.6.
- When show_compatibility_56 is OFF, compatibility with MySQL 5.6 is disabled. Selecting from the INFORMATION_SCHEMA tables produces an error because the Performance Schema tables are intended to replace them. The INFORMATION_SCHEMA tables are deprecated as of MySQL 5.7.6 and are removed in MySQL 8.0.
  
  To obtain system and status variable information When show_compatibility_56=OFF, use the Performance Schema tables or the SHOW statements.
  Note
  When show_compatibility_56=OFF, the SHOW VARIABLES and SHOW STATUS statements display rows from the Performance Schema global_variables, session_variables, global_status, and session_status tables.
  
  As of MySQL 5.7.9, those tables are world readable and accessible without the SELECT privilege, which means that SELECT is not needed to use the SHOW statements, either. Before MySQL 5.7.9, the SELECT privilege is required to access those Performance Schema tables, either directly, or indirectly through the SHOW statements.
- Several Slave_xxx status variables are available from SHOW STATUS when show_compatibility_56 is ON. When show_compatibility_56 is OFF, some of those variables are not exposed to SHOW STATUS. The information they provide is available in replication-related Performance Schema tables, as described later.
- show_compatibility_56 has no effect on system variable access using @@ notation: @@GLOBAL.var_name, @@SESSION.var_name, @@var_name.
- show_compatibility_56 has no effect for the embedded server, which produces 5.6-compatible output in all cases.
The following descriptions detail the effect of setting show_compatibility_56 to ON or OFF in the contexts in which this variable applies.
SHOW GLOBAL VARIABLES statement:
- ON: MySQL 5.6 output.
- OFF: Output displays rows from the Performance Schema global_variables table.
SHOW [SESSION | LOCAL] VARIABLES statement:
- ON: MySQL 5.6 output.
- OFF: Output displays rows from the Performance Schema session_variables table. (In MySQL 5.7.6 and 5.7.7, OFF output does not fully reflect all system variable values in effect for the current session; it includes no rows for global variables that have no session counterpart. This is corrected in MySQL 5.7.8.)
SHOW GLOBAL STATUS statement:
- ON: MySQL 5.6 output.
- OFF: Output displays rows from the Performance Schema global_status table, plus the Com_xxx statement execution counters.
  
  OFF output includes no rows for session variables that have no global counterpart, unlike ON output.
SHOW [SESSION | LOCAL] STATUS statement:
- ON: MySQL 5.6 output.
- OFF: Output displays rows from the Performance Schema session_status table, plus the Com_xxx statement execution counters. (In MySQL 5.7.6 and 5.7.7, OFF output does not fully reflect all status variable values in effect for the current session; it includes no rows for global variables that have no session counterpart. This is corrected in MySQL 5.7.8.)
In MySQL 5.7.6 and 5.7.7, for each of the SHOW statements just described, use of a WHERE clause produces a warning when show_compatibility_56=ON and an error when show_compatibility_56=OFF. (This applies to WHERE clauses that are not optimized away. For example, WHERE 1 is trivially true, is optimized away, and thus produces no warning or error.) This behavior does not occur as of MySQL 5.7.8; WHERE is supported as before 5.7.6.
GLOBAL_VARIABLES, SESSION_VARIABLES, GLOBAL_STATUS, and SESSION_STATUS):
- ON: MySQL 5.6 output, with a deprecation warning.
- OFF: Selecting from these tables produces an error. (Before 5.7.9, selecting from these tables produces no output, with a deprecation warning.)
global_variables: Global system variables only.
session_variables: System variables in effect for the current session: A row for each session variable, and a row for each global variable that has no session counterpart.
variables_by_thread: Session system variables only, for each active session.

ON: Same output as for OFF. (Before 5.7.8, these tables produce no output.)

Performance Schema status variable tables:

OFF:
- global_status: Global status variables only.
- session_status: Status variables in effect the current session: A row for each session variable, and a row for each global variable that has no session counterpart.
- status_by_account Session status variables only, aggregated per account.
- status_by_host: Session status variables only, aggregated per host name.
- status_by_thread: Session status variables only, for each active session.
- status_by_user: Session status variables only, aggregated per user name.
The Performance Schema does not collect statistics for Com_xxx status variables in the status variable tables. To obtain global and per-session statement execution counts, use the events_statements_summary_global_by_event_name and events_statements_summary_by_thread_by_event_name tables, respectively.
ON: Same output as for OFF. (Before 5.7.9, these tables produce no output.)

`SHOW STATUS`.

`OFF`: Some of those replica variables are not exposed to `SHOW STATUS` or the Performance Schema status variable tables. The information they provide is available in replication-related Performance Schema tables. The following table shows which `Slave_xxx` status variables become unavailable in `SHOW STATUS` and their locations in Performance Schema replication tables.

Status Variable Performance Schema Location

`Slave_heartbeat_period` `replication_connection_configuration` table, `HEARTBEAT_INTERVAL` column

`Slave_last_heartbeat` `replication_connection_status` table, `LAST_HEARTBEAT_TIMESTAMP` column

`Slave_received_heartbeats` `replication_connection_status` table, `COUNT_RECEIVED_HEARTBEATS` column

`Slave_retried_transactions` `replication_applier_status` table, `COUNT_TRANSACTIONS_RETRIES` column

`Slave_running` `replication_connection_status` and `replication_applier_status` tables, `SERVICE_STATE` column

Status Variable	Performance Schema Location
`Slave_heartbeat_period`	`replication_connection_configuration` table, `HEARTBEAT_INTERVAL` column
`Slave_last_heartbeat`	`replication_connection_status` table, `LAST_HEARTBEAT_TIMESTAMP` column
`Slave_received_heartbeats`	`replication_connection_status` table, `COUNT_RECEIVED_HEARTBEATS` column
`Slave_retried_transactions`	`replication_applier_status` table, `COUNT_TRANSACTIONS_RETRIES` column
`Slave_running`	`replication_connection_status` and `replication_applier_status` tables, `SERVICE_STATE` column

FLUSH STATUS statement:

ON: This statement produces MySQL 5.6 behavior. It adds the current thread's session status variable values to the global values and resets the session values to zero. Some global variables may be reset to zero as well. It also resets the counters for key caches (default and named) to zero and sets Max_used_connections to the current number of open connections.
OFF: This statement adds the session status from all active sessions to the global status variables, resets the status of all active sessions, and resets account, host, and user status values aggregated from disconnected sessions.

show_create_table_verbosity

show_create_table_verbosity Scope Global, Session Dynamic Yes 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

show_old_temporals Scope Global, Session Dynamic Yes Type Boolean Default Value OFF

Whether SHOW CREATE TABLE output includes comments to flag temporal columns found to be in pre-5.6.4 format (TIME, DATETIME, 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=latin1

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

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

skip_external_locking

skip_external_locking Scope Global Dynamic No Type Boolean Default Value ON

This is OFF if mysqld uses external locking (system locking), ON if external locking is disabled. This affects 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

skip_name_resolve Scope Global Dynamic No Type Boolean Default Value OFF

Whether to resolve host names when checking client connections. If this variable is OFF, mysqld resolves host names when checking client connections. If it is ON, mysqld uses only IP numbers; in this case, all Host column values in the grant tables must be IP addresses. See Section 5.1.11.2, “DNS Lookups and the Host Cache”.

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

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

skip_networking Scope Global Dynamic No Type Boolean Default Value OFF

This variable controls whether the server permits TCP/IP connections. By default, it is disabled (permit TCP connections). If enabled, the server permits only local (non-TCP/IP) connections and all interaction with mysqld must be made using named pipes or shared memory (on Windows) or Unix socket files (on Unix). This option is highly recommended for systems where only local clients are permitted. See Section 5.1.11.2, “DNS Lookups and the Host Cache”.

skip_show_database

skip_show_database Scope Global Dynamic No Type Boolean Default Value OFF

This prevents people from using the SHOW DATABASES statement if they do not have 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 a global privilege is considered a privilege for all databases, any global privilege enables a user to see all database names with SHOW DATABASES or by examining the INFORMATION_SCHEMA SCHEMATA table.

slow_launch_time

slow_launch_time Scope Global Dynamic Yes Type Integer Default Value 2 Minimum Value 0 Maximum Value 31536000 Unit seconds

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

slow_query_log

slow_query_log Scope Global Dynamic Yes Type Boolean Default Value OFF

Whether the slow query log is enabled. The value can be 0 (or OFF) to disable the log or 1 (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

slow_query_log_file Scope Global Dynamic Yes Type File name Default Value host_name-slow.log

The name of the slow query log file. The default value is host_name-slow.log, but the initial value can be changed with the --slow_query_log_file option.

socket

socket Scope Global Dynamic No Type String Default Value (Windows) MySQL Default Value (Other) /tmp/mysql.sock

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

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

sort_buffer_size

sort_buffer_size Scope Global, Session Dynamic Yes Type Integer Default Value 262144 Minimum Value 32768 Maximum Value (Windows) 4294967295 Maximum Value (Other, 64-bit platforms) 18446744073709551615 Maximum Value (Other, 32-bit platforms) 4294967295 Unit bytes

Each session that must perform a sort allocates a buffer of this size. sort_buffer_size is not specific to any storage engine and applies in a general manner for optimization. At minimum 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 8.2.1.14, “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 slows down most queries that sort. It is best to increase it as a session setting, and only for the sessions that need a larger size. On Linux, there are thresholds of 256KB and 2MB where larger values may significantly slow down memory allocation, so you should consider staying below one of those values. Experiment to find the best value for your workload. See Section B.3.3.5, “Where MySQL Stores Temporary Files”.

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

sql_auto_is_null

sql_auto_is_null Scope Global, Session Dynamic Yes Type Boolean Default Value OFF

If this variable is enabled, then after a statement that successfully inserts an automatically generated AUTO_INCREMENT value, you can find that value by issuing a statement of the following form:

SELECT * FROM tbl_name WHERE auto_col IS NULL

If the statement returns a row, the value returned is the same as if you invoked the LAST_INSERT_ID() function. For details, including the return value after a multiple-row insert, see Section 12.16, “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.

The default value of sql_auto_is_null is OFF.

sql_big_selects

sql_big_selects Scope Global, Session Dynamic 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

sql_buffer_result Scope Global, Session Dynamic 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

sql_log_off Scope Global, Session Dynamic Yes Type Boolean Default Value OFF Valid Values

OFF (enable logging)

ON (disable logging)

This variable controls whether logging to the general query log is disabled for the current session (assuming that the general query log itself is enabled). The default value is OFF (that is, enable logging). To disable or enable general query logging for the current session, set the 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 5.1.8.1, “System Variable Privileges”.

sql_mode

sql_mode Scope Global, Session Dynamic Yes Type Set Default Value

ONLY_FULL_GROUP_BY STRICT_TRANS_TABLES NO_ZERO_IN_DATE NO_ZERO_DATE ERROR_FOR_DIVISION_BY_ZERO NO_AUTO_CREATE_USER NO_ENGINE_SUBSTITUTION

Valid Values

ALLOW_INVALID_DATES

ANSI_QUOTES

ERROR_FOR_DIVISION_BY_ZERO

HIGH_NOT_PRECEDENCE

IGNORE_SPACE

NO_AUTO_CREATE_USER

NO_AUTO_VALUE_ON_ZERO

NO_BACKSLASH_ESCAPES

NO_DIR_IN_CREATE

NO_ENGINE_SUBSTITUTION

NO_FIELD_OPTIONS

NO_KEY_OPTIONS

NO_TABLE_OPTIONS

NO_UNSIGNED_SUBTRACTION

NO_ZERO_DATE

NO_ZERO_IN_DATE

ONLY_FULL_GROUP_BY

PAD_CHAR_TO_FULL_LENGTH

PIPES_AS_CONCAT

REAL_AS_FLOAT

STRICT_ALL_TABLES

STRICT_TRANS_TABLES

The current server SQL mode, which can be set dynamically. For details, see Section 5.1.10, “Server SQL Modes”.

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

sql_notes Scope Global, Session Dynamic Yes 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

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

If enabled (the default), the server quotes identifiers for SHOW CREATE TABLE 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 13.7.5.10, “SHOW CREATE TABLE Statement”, and Section 13.7.5.6, “SHOW CREATE DATABASE Statement”.

sql_safe_updates

sql_safe_updates Scope Global, Session Dynamic 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

sql_select_limit Scope Global, Session Dynamic Yes Type Integer Default Value 18446744073709551615 Minimum Value 0 Maximum Value 18446744073709551615

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

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

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

sql_warnings

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

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

ssl_ca

ssl_ca Scope Global Dynamic No Type File name Default Value NULL

The path name of the Certificate Authority (CA) certificate file in PEM format. The file contains a list of trusted SSL Certificate Authorities.

ssl_capath

ssl_capath Scope Global Dynamic No Type Directory name Default Value NULL

The path name of the directory that contains trusted SSL Certificate Authority (CA) certificate files in PEM format. Support for this capability depends on the SSL library used to compile MySQL; see Section 6.3.4, “SSL Library-Dependent Capabilities”.

ssl_cert

ssl_cert Scope Global Dynamic No Type File name Default Value NULL

The path name of the server SSL public key certificate file in PEM format.

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

ssl_cipher

ssl_cipher Scope Global Dynamic No Type String Default Value NULL

The list of permissible ciphers for connection encryption. If no cipher in the list is supported, encrypted connections do not work.

For greatest portability, the cipher list should be a list of one or more cipher names, separated by colons. This format is understood both by OpenSSL and yaSSL. The following example shows two cipher names separated by a colon:

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

OpenSSL supports a more flexible syntax for specifying ciphers, as described in the OpenSSL documentation at https://www.openssl.org/docs/manmaster/man1/openssl-ciphers.html. yaSSL does not, so attempts to use that extended syntax fail for a MySQL distribution compiled using yaSSL.

For information about which encryption ciphers MySQL supports, see Section 6.3.2, “Encrypted Connection TLS Protocols and Ciphers”.

ssl_crl

ssl_crl Scope Global Dynamic No Type File name Default Value NULL

The path name of the file containing certificate revocation lists in PEM format. Support for revocation-list capability depends on the SSL library used to compile MySQL. See Section 6.3.4, “SSL Library-Dependent Capabilities”.

ssl_crlpath

ssl_crlpath Scope Global Dynamic No Type Directory name Default Value NULL

The path of the directory that contains certificate revocation-list files in PEM format. Support for revocation-list capability depends on the SSL library used to compile MySQL. See Section 6.3.4, “SSL Library-Dependent Capabilities”.

ssl_key

ssl_key Scope Global Dynamic No Type File name Default Value NULL

The path name of the server SSL private key file in PEM format. For better security, use a certificate with an RSA key size of at least 2048 bits.

If the key file is protected by a passphrase, the server prompts the user for the passphrase. The password must be given interactively; it cannot be stored in a file. If the passphrase is incorrect, the program continues as if it could not read the key.

stored_program_cache

stored_program_cache Scope Global Dynamic Yes Type Integer Default Value 256 Minimum Value 16 Maximum Value 524288

Sets a soft upper limit for the number of cached stored routines per connection. The value of this variable is specified in terms of the number of stored routines held in each of the two caches maintained by the MySQL Server for, respectively, stored procedures and stored functions.

Whenever a stored routine is executed this cache size is checked before the first or top-level statement in the routine is parsed; if the number of routines of the same type (stored procedures or stored functions according to which is being executed) exceeds the limit specified by this variable, the corresponding cache is flushed and memory previously allocated for cached objects is freed. This allows the cache to be flushed safely, even when there are dependencies between stored routines.

super_read_only

super_read_only Scope Global Dynamic Yes Type Boolean Default Value OFF

If the read_only system variable is enabled, the server permits no client updates except from users who have the SUPER privilege. If the super_read_only system variable is also enabled, the server prohibits client updates even from users who have 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 loadable function) and INSTALL PLUGIN. These operations are prohibited because they involve changes to tables in the mysql system database.

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

sync_frm

sync_frm Scope Global Dynamic Yes Type Boolean Default Value ON

If this variable is set to 1, when any nontemporary table is created its .frm file is synchronized to disk (using fdatasync()). This is slower but safer in case of a crash. The default is 1.

This variable is deprecated in MySQL 5.7 and is removed in MySQL 8.0 (when .frm files become obsolete).

system_time_zone

system_time_zone Scope Global Dynamic No Type String

The server system time zone. When the server begins executing, it inherits a time zone setting from the machine defaults, possibly modified by the environment of the account used for running the server or the startup script. The value is used to set system_time_zone. To explicitly specify the system time zone, set the TZ environment variable or use the --timezone option of the mysqld_safe script.

The system_time_zone variable differs from the time_zone variable. Although they might have the same value, the latter variable is used to initialize the time zone for each client that connects. See Section 5.1.13, “MySQL Server Time Zone Support”.

table_definition_cache

table_definition_cache Scope Global Dynamic Yes Type Integer Default Value -1 (signifies autosizing; do not assign this literal value) Minimum Value 400 Maximum Value 524288

The number of table definitions (from .frm files) that can be stored in the table definition cache. If you use a large number of tables, you can create a large table definition cache to speed up opening of tables. The table definition cache takes less space and does not use file descriptors, unlike the normal table cache. The minimum value is 400. The default value is based on the following formula, capped to a limit of 2000:

400 + (table_open_cache / 2)

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

If the number of table instances in the InnoDB data dictionary cache exceeds the table_definition_cache limit, an LRU mechanism begins marking table instances for eviction and eventually removes them from the InnoDB data dictionary cache. The number of open tables with cached metadata can be higher than the table_definition_cache limit due to table instances with foreign key relationships, which are not placed on the LRU list.

The number of file-per-table tablespaces that can be open at one time is limited by both the table_definition_cache and innodb_open_files settings. If both variables are set, the highest setting is used. If neither variable is set, the table_definition_cache setting, which has a higher default value, is used. If the number of open tablespaces exceeds the limit defined by table_definition_cache or innodb_open_files, an LRU mechanism searches the LRU list for tablespace files that are fully flushed and not currently being extended. This process is performed each time a new tablespace is opened. Only inactive tablespaces are closed.

table_open_cache

table_open_cache Scope Global Dynamic Yes Type Integer Default Value 2000 Minimum Value 1 Maximum Value 524288

The number of open tables for all threads. Increasing this value increases the number of file descriptors that mysqld requires. The effective value of this variable is the greater of the effective value of open_files_limit - 10 - the effective value of max_connections / 2, and 400; that is

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

You can check whether you need to increase the table cache by checking the Opened_tables status variable. 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

table_open_cache_instances Scope Global Dynamic No Type Integer Default Value 16 Minimum Value 1 Maximum Value 64

The number of open tables cache instances. To improve scalability by reducing contention among sessions, the open tables cache can be partitioned into several smaller cache instances of size table_open_cache / table_open_cache_instances . A session needs to lock only one instance to access it for DML statements. This segments cache access among instances, permitting higher performance for operations that use the cache when there are many sessions accessing tables. (DDL statements still require a lock on the entire cache, but such statements are much less frequent than DML statements.)

A value of 8 or 16 is recommended on systems that routinely use 16 or more cores. However, if you have many large triggers on your tables that cause a high memory load, the default setting for table_open_cache_instances might lead to excessive memory usage. In that situation, it can be helpful to set table_open_cache_instances to 1 in order to restrict memory usage.

thread_cache_size

thread_cache_size Scope Global Dynamic Yes Type Integer Default Value -1 (signifies autosizing; do not assign this literal value) Minimum Value 0 Maximum Value 16384

How many threads the server should cache for reuse. When a client disconnects, the client's threads are put in the cache if there are fewer than thread_cache_size threads there. Requests for threads are satisfied by reusing threads taken from the cache if possible, and only when the cache is empty is a new thread created. This variable can be increased to improve performance if you have a lot of new connections. Normally, this does not provide a notable performance improvement if you have a good thread implementation. However, if your server sees hundreds of connections per second you should normally 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 5.1.9, “Server Status Variables”.

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

8 + (max_connections / 100)

This variable has no effect for the embedded server (libmysqld) and as of MySQL 5.7.2 is no longer visible within the embedded server.

thread_handling

thread_handling Scope Global Dynamic No Type Enumeration Default Value one-thread-per-connection Valid Values

no-threads

one-thread-per-connection

loaded-dynamically

The thread-handling model used by the server for connection threads. The permissible values are no-threads (the server uses a single thread to handle one connection), one-thread-per-connection (the server uses one thread to handle each client connection), and loaded-dynamically (set by the thread pool plugin when it initializes). no-threads is useful for debugging under Linux; see Section 5.8, “Debugging MySQL”.

This variable has no effect for the embedded server (libmysqld) and as of MySQL 5.7.2 is no longer visible within the embedded server.

thread_pool_algorithm

thread_pool_algorithm Scope Global Dynamic No Type Integer Default Value 0 Minimum Value 0 Maximum Value 1

This variable controls which algorithm the thread pool plugin uses:

A value of 0 (the default) uses a conservative low-concurrency algorithm which is most well tested and is known to produce very good results.
A value of 1 increases the concurrency and uses a more aggressive algorithm which at times has been known to perform 5–10% better on optimal thread counts, but has degrading performance as the number of connections increases. Its use should be considered as experimental and not supported.