要查看服务器根据其编译默认值和读取的任何选项文件使用的值，请使用此命令：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

要查看服务器仅根据其编译默认值使用的值，忽略任何选项文件中的设置，请使用此命令：To see the values that a server uses based only on its compiled-in defaults, ignoring the settings in any option files, use this command:

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

要查看正在运行的服务器使用的当前值，请使用SHOW VARIABLES语句或性能模式系统变量表。请参阅第 29.12.14 节，“Performance Schema 系统变量表”。To see the current values used by a running server, use the SHOW VARIABLES statement or the Performance Schema system variable tables. See Section 29.12.14, “Performance Schema System Variable Tables”.

第 7.1.9 节，“使用系统变量”，讨论了设置和显示系统变量值的语法。Section 7.1.9, “Using System Variables”, discusses the syntax for setting and displaying system variable values.

第 7.1.9.2 节，“动态系统变量”，列出了可以在运行时设置的变量。Section 7.1.9.2, “Dynamic System Variables”, lists the variables that can be set at runtime.

有关调整系统变量的信息，请参阅 第 7.1.1 节，“配置服务器”。Information on tuning system variables can be found in Section 7.1.1, “Configuring the Server”.

第 17.14 节，“InnoDB 启动选项和系统变量”，列出了 InnoDB 系统变量。Section 17.14, “InnoDB Startup Options and System Variables”, lists InnoDB system variables.

第 25.4.3.9.2 节，“NDB Cluster 系统变量”，列出了特定于 NDB Cluster 的系统变量。Section 25.4.3.9.2, “NDB Cluster System Variables”, lists system variables which are specific to NDB Cluster.

有关特定于复制的服务器系统变量的信息，请参阅 第 19.1.6 节，“复制和二进制日志选项及变量”。For information on server system variables specific to replication, see Section 19.1.6, “Replication and Binary Logging Options and Variables”.

activate_all_roles_on_login

是否在用户登录服务器时启用所有授予角色的自动激活：Whether to enable automatic activation of all granted roles when users log in to the server:

授予的角色包括显式授予用户的角色以及在mandatory_roles系统变量值中列出的角色。Granted roles include those granted explicitly to the user and those named in the mandatory_roles system variable value.

activate_all_roles_on_login仅在登录时以及在以定义者上下文执行的存储程序和视图开始执行时生效。要在会话中更改活动角色，请使用SET ROLE。要更改存储程序的活动角色，程序主体应执行SET ROLE。activate_all_roles_on_login applies only at login time, and at the beginning of execution for stored programs and views that execute in definer context. To change the active roles within a session, use SET ROLE. To change the active roles for a stored program, the program body should execute SET ROLE.

admin_address

用于在管理网络接口上监听 TCP/IP 连接的 IP 地址（参见第 7.1.12.1 节，“连接接口”）。没有默认的admin_address值。如果在启动时未指定此变量，服务器将不维护管理接口。服务器还具有一个bind_address系统变量，用于配置常规（非管理）客户端 TCP/IP 连接。参见第 7.1.12.1 节，“连接接口”。The IP address on which to listen for TCP/IP connections on the administrative network interface (see Section 7.1.12.1, “Connection Interfaces”). There is no default admin_address value. If this variable is not specified at startup, the server maintains no administrative interface. The server also has a bind_address system variable for configuring regular (nonadministrative) client TCP/IP connections. See Section 7.1.12.1, “Connection Interfaces”.

如果指定了 admin_address，其值必须满足以下要求：If admin_address is specified, its value must satisfy these requirements:

可以将 IP 地址指定为 IPv4 或 IPv6 地址。如果该值是主机名，服务器会将其解析为 IP 地址并绑定到该地址。如果一个主机名解析为多个 IP 地址，服务器将使用第一个 IPv4 地址（如果有），否则使用第一个 IPv6 地址。An IP address can be specified as an IPv4 or IPv6 address. If the value is a host name, the server resolves the name to an IP address and binds to that address. If a host name resolves to multiple IP addresses, the server uses the first IPv4 address if there are any, or the first IPv6 address otherwise.

服务器对不同类型的地址的处理如下：The server treats different types of addresses as follows:

这些规则适用于为地址指定网络命名空间：These rules apply to specifying a network namespace for an address:

有关网络命名空间的更多信息，请参见第 7.1.14 节，“网络命名空间支持”。For additional information about network namespaces, see Section 7.1.14, “Network Namespace Support”.

如果绑定到地址失败，服务器会产生错误并且不会启动。If binding to the address fails, the server produces an error and does not start.

admin_address 系统变量类似于 bind_address 系统变量，它将服务器绑定到用于普通客户端连接的地址，但有以下区别：The admin_address system variable is similar to the bind_address system variable that binds the server to an address for ordinary client connections, but with these differences:

admin_port

用于管理网络接口连接的 TCP/IP 端口号（参见 第 7.1.12.1 节，“连接接口”）。将此变量设置为 0 会使用默认值。The TCP/IP port number to use for connections on the administrative network interface (see Section 7.1.12.1, “Connection Interfaces”). Setting this variable to 0 causes the default value to be used.

如果未指定 admin_address，则设置 admin_port 无效，因为在这种情况下，服务器不会维护任何管理网络接口。Setting admin_port has no effect if admin_address is not specified because in that case the server maintains no administrative network interface.

admin_ssl_ca

admin_ssl_ca 系统变量类似于 ssl_ca，只是它适用于管理连接接口，而不是主连接接口。有关配置管理接口加密支持的信息，请参阅 管理接口加密连接支持。The admin_ssl_ca system variable is like ssl_ca, except that it applies to the administrative connection interface rather than the main connection interface. For information about configuring encryption support for the administrative interface, see Administrative Interface Support for Encrypted Connections.

admin_ssl_capath

admin_ssl_capath 系统变量类似于 ssl_capath，只是它适用于管理连接接口，而不是主连接接口。有关为管理接口配置加密支持的信息，请参阅 管理接口加密连接支持。The admin_ssl_capath system variable is like ssl_capath, except that it applies to the administrative connection interface rather than the main connection interface. For information about configuring encryption support for the administrative interface, see Administrative Interface Support for Encrypted Connections.

admin_ssl_cert

admin_ssl_cert 系统变量类似于 ssl_cert，区别在于它适用于管理连接接口，而不是主连接接口。有关为管理接口配置加密支持的信息，请参阅 管理接口加密连接支持。The admin_ssl_cert system variable is like ssl_cert, except that it applies to the administrative connection interface rather than the main connection interface. For information about configuring encryption support for the administrative interface, see Administrative Interface Support for Encrypted Connections.

admin_ssl_cipher

admin_ssl_cipher 系统变量类似于 ssl_cipher，只是它适用于管理连接接口，而不是主连接接口。有关配置管理接口加密支持的信息，请参阅 管理接口加密连接支持。The admin_ssl_cipher system variable is like ssl_cipher, except that it applies to the administrative connection interface rather than the main connection interface. For information about configuring encryption support for the administrative interface, see Administrative Interface Support for Encrypted Connections.

此变量指定的列表可能包括以下任何值：The list specified by this variable may include any of the following values:

在设置此变量时，如果尝试在密码列表中包含此处未显示的任何值，将引发错误（ER_BLOCKED_CIPHER）。Trying to include any values in the cipher list that are not shown here when setting this variable raises an error (ER_BLOCKED_CIPHER).

admin_ssl_crl

admin_ssl_crl 系统变量类似于 ssl_crl，只是它适用于管理连接接口，而不是主连接接口。有关为管理接口配置加密支持的信息，请参见 管理接口加密连接支持。The admin_ssl_crl system variable is like ssl_crl, except that it applies to the administrative connection interface rather than the main connection interface. For information about configuring encryption support for the administrative interface, see Administrative Interface Support for Encrypted Connections.

admin_ssl_crlpath

admin_ssl_crlpath 系统变量类似于 ssl_crlpath，只是它适用于管理连接接口，而不是主连接接口。有关为管理接口配置加密支持的信息，请参阅 行政接口对加密连接的支持。The admin_ssl_crlpath system variable is like ssl_crlpath, except that it applies to the administrative connection interface rather than the main connection interface. For information about configuring encryption support for the administrative interface, see Administrative Interface Support for Encrypted Connections.

admin_ssl_key

admin_ssl_key 系统变量类似于 ssl_key，不同之处在于它适用于管理连接接口而非主连接接口。有关配置管理接口加密支持的信息，请参见 管理接口加密连接支持。The admin_ssl_key system variable is like ssl_key, except that it applies to the administrative connection interface rather than the main connection interface. For information about configuring encryption support for the administrative interface, see Administrative Interface Support for Encrypted Connections.

admin_tls_ciphersuites

admin_tls_ciphersuites 系统变量类似于 tls_ciphersuites，只是它适用于管理连接接口，而不是主连接接口。有关配置管理接口加密支持的信息，请参阅 管理接口加密连接支持。The admin_tls_ciphersuites system variable is like tls_ciphersuites, except that it applies to the administrative connection interface rather than the main connection interface. For information about configuring encryption support for the administrative interface, see Administrative Interface Support for Encrypted Connections.

该值是一个包含零个或多个冒号分隔的密码套件名称的列表，这些名称来自此处列出的选项：The value is a list of zero or more colon-separated ciphersuite names from among those listed here:

在设置此变量时，如果尝试在密码列表中包含此处未显示的任何值，将引发错误（ER_BLOCKED_CIPHER）。Trying to include any values in the cipher list that are not shown here when setting this variable raises an error (ER_BLOCKED_CIPHER).

admin_tls_version

admin_tls_version 系统变量类似于 tls_version，只是它适用于管理连接接口，而不是主连接接口。有关配置管理接口加密支持的信息，请参见 管理接口加密连接支持。The admin_tls_version system variable is like tls_version, except that it applies to the administrative connection interface rather than the main connection interface. For information about configuring encryption support for the administrative interface, see Administrative Interface Support for Encrypted Connections.

authentication_policy

此变量用于管理多因素认证（MFA）功能。对于用于管理 MySQL 账户定义的 CREATE USER 和 ALTER USER 语句，它决定了可以指定哪些认证因素，其中 “factor” 对应于与账户关联的认证方法或插件。authentication_policy 确定多因素认证的以下方面：This variable is used to administer multifactor authentication (MFA) capabilities. For CREATE USER and ALTER USER statements used to manage MySQL account definitions, it determines what authentication factor or factors may be specified, where “factor” corresponds to an authentication method or plugin associated with an account. authentication_policy determines the following aspects of multifactor authentication:

因为authentication_policy仅在创建或修改账户时适用，所以其值的更改不会影响现有用户账户。Because authentication_policy applies only when accounts are created or altered, changes to its value have no effect on existing user accounts.

authentication_policy 的值是由 1、2 或 3 个逗号分隔的元素组成的列表，每个元素对应一个身份验证因素，并且每个元素的形式为此处列出的之一，其含义如下：The value of authentication_policy is a list of 1, 2, or 3 comma-separated elements, each corresponding to an authentication factor and each being of one of the forms listed here, with their meanings:

在每种情况下，元素可能被空白字符包围。整个列表必须用单引号括起来。In each case, an element may be surrounded by whitespace characters. The entire list must be enclosed in single quotes.

authentication_policy 必须至少包含一个非空因子，且任何空因子必须出现在列表的末尾，位于所有非空因子之后。这意味着 ',,' 是不允许的，因为这表示所有因子都是可选的。每个账户必须至少有一个认证因子。authentication_policy must contain at least one nonempty factor, and any empty factors must come at the end of the list, following any nonempty factors. This means that ',,' is not permitted because this signifies that all factors are optional. Every account must have at least one authentication factor.

authentication_policy 的默认值是 '*,,'。这意味着在账户定义中，因子 1 是必需的，可以使用任何认证插件（默认为 caching_sha2_password），而因子 2 和 3 是可选的，每个都可以使用任何认证插件。The default value of authentication_policy is '*,,'. This means that factor 1 is required in account definitions and can use any authentication plugin (with caching_sha2_password being the default), and that factors 2 and 3 are optional and each can use any authentication plugin.

如果 authentication_policy 没有为第一因素指定默认插件，则该因素的默认插件是 caching_sha2_password，虽然也可以使用其他插件。If authentication_policy does not specify a default plugin for the first factor, the default plugin for this factor is caching_sha2_password, although another plugin may be used.

下表显示了一些 authentication_policy 的可能值以及每个值在创建或更改账户时所建立的策略。The following table shows some possible values for authentication_policy and the policy that each establishes for creating or altering accounts.

authentication_windows_log_level

仅当启用了 authentication_windows Windows 身份验证插件并启用了调试代码时，此变量才可用。请参阅 第 8.4.1.6 节，“Windows 可插拔身份验证”。This variable is available only if the authentication_windows Windows authentication plugin is enabled and debugging code is enabled. See Section 8.4.1.6, “Windows Pluggable Authentication”.

此变量设置 Windows 身份验证插件的日志记录级别。下表显示允许的值。This variable sets the logging level for the Windows authentication plugin. The following table shows the permitted values.

authentication_windows_use_principal_name

该变量仅在启用 authentication_windows Windows 身份验证插件时可用。参见 第 8.4.1.6 节，“Windows 插件式身份验证”。This variable is available only if the authentication_windows Windows authentication plugin is enabled. See Section 8.4.1.6, “Windows Pluggable Authentication”.

使用 InitSecurityContext() 函数进行身份验证的客户端应提供一个标识其连接的服务的字符串 (targetName)。MySQL 使用服务器运行帐户的主体名称 (UPN)。UPN 的形式为 user_id@computer_name，无需在任何地方注册即可使用。该 UPN 会在身份验证握手开始时由服务器发送。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.

此变量用于控制服务器是否在初始挑战中发送 UPN。默认情况下，该变量为启用状态。出于安全原因，可以将其禁用，以避免将服务器的帐户名称以明文形式发送给客户端。如果该变量被禁用，服务器在第一次挑战中总是发送一个 0x00 字节，客户端不会指定 targetName，因此会使用 NTLM 身份验证。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.

如果服务器无法获取其 UPN（这主要发生在不支持 Kerberos 身份验证的环境中），服务器将不会发送 UPN，并使用 NTLM 身份验证。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

自动提交模式。如果设置为 1，对表的所有更改会立即生效。如果设置为 0，您必须使用COMMIT 来接受事务，或者使用ROLLBACK 来取消事务。如果autocommit 为 0 并且您将其更改为 1，MySQL 会对任何未提交的事务执行自动COMMIT。另一种开始事务的方法是使用START TRANSACTION 或BEGIN 语句。参见第 15.3.1 节，“START TRANSACTION、COMMIT 和 ROLLBACK 语句”。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 15.3.1, “START TRANSACTION, COMMIT, and ROLLBACK Statements”.

默认情况下，客户端连接的 autocommit 设置为 1。若要使客户端以默认 0 开始，请通过使用 --autocommit=0 选项启动服务器来设置全局 autocommit 值。要使用选项文件设置该变量，请包含以下行：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

当此变量的值为 1（默认值）时，如果用户尚不能执行、修改或删除该存储例程，服务器会自动授予存储例程的创建者 EXECUTE 和 ALTER ROUTINE 权限。（删除例程需要 ALTER ROUTINE 权限。）当例程被删除时，服务器还会自动从创建者处移除这些权限。如果 automatic_sp_privileges 为 0，服务器不会自动添加或移除这些权限。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.

例程的创建者是用于执行 CREATE 语句的账户。这可能与例程定义中作为 DEFINER 指定的账户不同。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.

如果你用 mysqld 并加上 --skip-new 启动，automatic_sp_privileges 将被设置为 OFF。If you start mysqld with --skip-new, automatic_sp_privileges is set to OFF.

另请参见 第 27.2.2 节，“存储例程与 MySQL 权限”。See also Section 27.2.2, “Stored Routines and MySQL Privileges”.

auto_generate_certs

此变量控制服务器是否在数据目录中自动生成 SSL 密钥和证书文件，如果它们尚不存在。This variable controls whether the server autogenerates SSL key and certificate files in the data directory, if they do not already exist.

在启动时，如果启用了auto_generate_certs 系统变量，并且数据目录中缺少服务器端 SSL 文件，服务器会自动在数据目录中生成服务器端和客户端的 SSL 证书及密钥文件。在这种情况下，无论其他 TLS 选项的值如何，这些证书都会被生成。证书和密钥文件使客户端能够使用 SSL 进行安全连接；参见 第 8.3.1 节，“配置 MySQL 使用加密连接”。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 and the server-side SSL files are missing from the data directory. These certificates are always generated in such cases, regardless of the values of any other TLS options. The certificate and key files enable secure client connections using SSL; see Section 8.3.1, “Configuring MySQL to Use Encrypted Connections”.

关于 SSL 文件自动生成的更多信息，包括文件名和特性，请参见 第 8.3.3.1 节，“使用 MySQL 创建 SSL 和 RSA 证书及密钥”For more information about SSL file autogeneration, including file names and characteristics, see Section 8.3.3.1, “Creating SSL and RSA Certificates and Keys using MySQL”

sha256_password_auto_generate_rsa_keys 和 caching_sha2_password_auto_generate_rsa_keys 系统变量相关，但它们控制的是在未加密连接中使用 RSA 进行安全密码交换所需的 RSA 密钥对文件的自动生成。The sha256_password_auto_generate_rsa_keys and caching_sha2_password_auto_generate_rsa_keys system variables are related but control autogeneration of RSA key-pair files needed for secure password exchange using RSA over unencrypted connections.

back_log

MySQL 可以处理的未完成连接请求的数量。当主 MySQL 线程在非常短的时间内收到很多连接请求时，这一参数就会起作用。然后主线程需要一些时间（虽然很短）来检查连接并启动新线程。back_log 值表示在 MySQL 暂时停止响应新请求之前，这段短时间内可以积压的请求数量。只有在您预计会在短时间内有大量连接时，才需要增加此值。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.

换句话说，这个值是用于传入 TCP/IP 连接的侦听队列的大小。您的操作系统对该队列的大小有自己的限制。Unix listen() 系统调用的手册页应该有更多细节。请查阅您的操作系统文档以获取该变量的最大值。back_log 不能设置高于操作系统限制的值。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.

默认值是 max_connections 的值，这允许允许的队列根据允许的最大连接数自动调整。The default value is the value of max_connections, which enables the permitted backlog to adjust to the maximum permitted number of connections.

basedir

MySQL 安装基础目录的路径。The path to the MySQL installation base directory.

big_tables

如果启用，服务器会将所有临时表存储在磁盘上，而不是内存中。这可以防止大多数需要大临时表的 SELECT 操作中出现 The table tbl_name is full 错误，但也会降低那些内存表就足够的查询的速度。If enabled, the server stores all temporary tables on disk rather than in memory. This prevents most The table tbl_name is full errors for SELECT operations that require a large temporary table, but also slows down queries for which in-memory tables would suffice.

新连接的默认值是 OFF（使用内存临时表）。通常情况下，启用此变量是不必要的。当内存中的 内部 临时表由 TempTable 存储引擎（默认引擎）管理，并且 TempTable 存储引擎可以占用的最大内存量被超过时，TempTable 存储引擎会开始将数据存储到磁盘上的临时文件中。当内存中的临时表由 MEMORY 存储引擎管理时，内存表会根据需要自动转换为基于磁盘的表。更多信息请参见 第 10.4.4 节，“MySQL 中内部临时表的使用”。The default value for new connections is OFF (use in-memory temporary tables). Normally, it should never be necessary to enable this variable. When in-memory internal temporary tables are managed by the TempTable storage engine (the default), and the maximum amount of memory that can be occupied by the TempTable storage engine is exceeded, the TempTable storage engine starts storing data to temporary files on disk. When in-memory temporary tables are managed by the MEMORY storage engine, in-memory tables are automatically converted to disk-based tables as required. For more information, see Section 10.4.4, “Internal Temporary Table Use in MySQL”.

bind_address bind_address

MySQL 服务器在一个或多个网络套接字上监听 TCP/IP 连接。每个套接字绑定到一个地址，但一个地址可能映射到多个网络接口。要指定服务器应如何监听 TCP/IP 连接，请在服务器启动时设置 bind_address 系统变量。服务器还有一个 admin_address 系统变量，允许在专用接口上进行管理连接。参见 第 7.1.12.1 节，“连接接口”。The MySQL server listens on one or more network sockets for TCP/IP connections. Each socket is bound to one address, but it is possible for an address to map onto multiple network interfaces. To specify how the server should listen for TCP/IP connections, set the bind_address system variable at server startup. The server also has an admin_address system variable that enables administrative connections on a dedicated interface. See Section 7.1.12.1, “Connection Interfaces”.

如果指定了bind_address，它接受一个或多个地址值的列表，每个地址值可以指定单个非通配符的 IP 地址或主机名。每个地址可能包含网络命名空间说明符。如果只指定一个地址，可以使用允许在多个网络接口上监听的通配符地址格式之一（*、0.0.0.0 或 ::）。多个地址用逗号分隔。列出多个值时，每个值必须指定单个非通配符 IP 地址（IPv4 或 IPv6）或主机名，并且不允许使用通配符地址格式（*、0.0.0.0 或 ::）。If bind_address is specified, it accepts a list of one or more address values, each of which may specify a single non-wildcard IP address or host name. Each address may include a network namespace specifier. If only one address is specified, it may make use of one of the wildcard address formats that permit listening on multiple network interfaces (*, 0.0.0.0, or ::). Multiple addresses are separated by commas. When multiple values are listed, each value must specify a single non-wildcard IP address (either IPv4 or IPv6) or a host name, and wildcard address formats (*, 0.0.0.0, or ::) are not allowed.

IP 地址可以指定为 IPv4 或 IPv6 地址。对于任何作为主机名的值，服务器会将该名称解析为 IP 地址并绑定到该地址。如果主机名解析为多个 IP 地址，服务器会使用第一个 IPv4 地址（如果有的话），否则使用第一个 IPv6 地址。IP addresses can be specified as IPv4 or IPv6 addresses. For any value that is a host name, the server resolves the name to an IP address and binds to that address. If a host name resolves to multiple IP addresses, the server uses the first IPv4 address if there are any, or the first IPv6 address otherwise.

服务器对不同类型的地址的处理如下：The server treats different types of addresses as follows:

这些规则适用于为地址指定网络命名空间：These rules apply to specifying a network namespace for an address:

有关网络命名空间的更多信息，请参见第 7.1.14 节，“网络命名空间支持”。For additional information about network namespaces, see Section 7.1.14, “Network Namespace Support”.

如果绑定任意地址失败，服务器会报错并无法启动。If binding to any address fails, the server produces an error and does not start.

示例：Examples:

当 bind_address 指定单个值（通配符或非通配符）时，服务器在单个套接字上监听，对于通配符地址，该套接字可能绑定到多个网络接口。当 bind_address 指定多个值的列表时，服务器为每个值监听一个套接字，每个套接字绑定到单个网络接口。套接字数量与指定值的数量成线性关系。根据操作系统接受连接的效率，较长的值列表可能会对接受 TCP/IP 连接的性能产生影响。When bind_address names a single value (wildcard or non-wildcard), the server listens on a single socket, which for a wildcard address may be bound to multiple network interfaces. When bind_address names a list of multiple values, the server listens on one socket per value, with each socket bound to a single network interface. The number of sockets is linear with the number of values specified. Depending on operating system connection-acceptance efficiency, long value lists might incur a performance penalty for accepting TCP/IP connections.

由于文件描述符会分配给监听套接字和网络命名空间文件，因此可能需要增加 open_files_limit 系统变量。 Because file descriptors are allocated for listening sockets and network namespace files, it may be necessary to increase the open_files_limit system variable.

如果您打算将服务器绑定到特定地址，请确保 mysql.user 系统表中包含一个具有管理权限的账户，以便您可以使用该账户连接到该地址。否则，您将无法关闭服务器。例如，如果您将服务器绑定到 *，您可以使用所有现有账户进行连接。但如果您将服务器绑定到 ::1，它只接受该地址的连接。在这种情况下，首先确保 'root'@'::1' 账户存在于 mysql.user 表中，以便您仍然可以连接到服务器并关闭它。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.

block_encryption_mode

该变量控制块加密算法（例如 AES）的块加密模式。它影响 AES_ENCRYPT() 和 AES_DECRYPT() 的加密。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 的值采用 aes-keylen-mode 格式，其中 keylen 是密钥长度（以位为单位），mode 是加密模式。该值不区分大小写。允许的 keylen 值为 128、192 和 256。允许的 mode 值为 ECB、CBC、CFB1、CFB8、CFB128 和 OFB。block_encryption_mode takes a value in aes-keylen-mode format, where keylen is the key length in bits and mode is the encryption mode. The value is not case-sensitive. Permitted keylen values are 128, 192, and 256. Permitted mode values are ECB, CBC, CFB1, CFB8, CFB128, and OFB.

例如，这条语句使 AES 加密函数使用 256 位的密钥长度和 CBC 模式：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';

尝试将 block_encryption_mode 设置为包含不支持的密钥长度或 SSL 库不支持的模式的值时，会发生错误。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.

build_id

这是一个 160 位的SHA1签名，由链接器在 Linux 系统上使用-DWITH_BUILD_ID=ON（默认启用）编译服务器时生成，并转换为十六进制字符串。这个只读值作为唯一的构建 ID，并在启动时写入服务器日志。This is a 160-bit SHA1 signature which is generated by the linker when compiling the server on Linux systems with -DWITH_BUILD_ID=ON (enabled by default), and converted to a hexadecimal string. This read-only value serves as a unique build ID, and is written into the server log at startup.

build_id在 Linux 以外的平台上不受支持。build_id is not supported on platforms other than Linux.

bulk_insert_buffer_size bulk_insert_buffer_size

MyISAM 使用一种特殊的树状缓存来加快在非空表中进行批量插入的速度，例如 INSERT ... SELECT、INSERT ... VALUES (...), (...), ... 以及 LOAD DATA。此变量限制每个线程缓存树的字节大小。将其设置为 0 将禁用此优化。默认值为 8MB。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.

设置此系统变量的会话值是一项受限操作。会话用户必须具有足够的权限来设置受限会话变量。请参见第 7.1.9.1 节，“系统变量权限”。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 7.1.9.1, “System Variable Privileges”.

caching_sha2_password_digest_rounds

caching_sha2_password 认证插件用于密码存储的哈希轮数。The number of hash rounds used by the caching_sha2_password authentication plugin for password storage.

将哈希轮数增加到默认值以上会导致性能下降，这种下降与增加的数量成正比：Increasing the number of hashing rounds above the default value incurs a performance penalty that correlates with the amount of increase:

caching_sha2_password_auto_generate_rsa_keys

服务器使用此变量来确定是否在数据目录中自动生成 RSA 私钥/公钥对文件，如果它们尚不存在。The server uses this variable to determine whether to autogenerate RSA private/public key-pair files in the data directory if they do not already exist.

启动时，如果满足以下条件，服务器会自动在数据目录中生成 RSA 私钥/公钥对文件：sha256_password_auto_generate_rsa_keys 或 caching_sha2_password_auto_generate_rsa_keys系统变量被启用;未指定 RSA 选项;RSA 文件在数据目录中缺失。这些密钥对文件允许通过 RSA 通过未加密连接安全交换密码，用于由sha256_password（弃用）或caching_sha2_password;参见 第 8.4.1.3 节，“SHA-256 可插拔认证”，以及 第 8.4.1.2 节，“缓存 SHA-2 可插拔认证”。At startup, the server automatically generates RSA private/public key-pair files in the data directory if all of these conditions are true: The sha256_password_auto_generate_rsa_keys or caching_sha2_password_auto_generate_rsa_keys system variable is enabled; no RSA options are specified; the RSA files are missing from the data directory. These key-pair files enable secure password exchange using RSA over unencrypted connections for accounts authenticated by the sha256_password (deprecated) or caching_sha2_password plugin; see Section 8.4.1.3, “SHA-256 Pluggable Authentication”, and Section 8.4.1.2, “Caching SHA-2 Pluggable Authentication”.

有关 RSA 文件自动生成的更多信息，包括文件名称和特性，请参阅 第 8.3.3.1 节，“使用 MySQL 创建 SSL 和 RSA 证书及密钥”For more information about RSA file autogeneration, including file names and characteristics, see Section 8.3.3.1, “Creating SSL and RSA Certificates and Keys using MySQL”

auto_generate_certs 系统变量相关，但它控制的是使用 SSL 进行安全连接所需的 SSL 证书和密钥文件的自动生成。The auto_generate_certs system variable is related but controls autogeneration of SSL certificate and key files needed for secure connections using SSL.

caching_sha2_password_private_key_path

此变量指定用于 caching_sha2_password 身份验证插件的 RSA 私钥文件的路径名称。如果文件以相对路径命名，则相对于服务器数据目录进行解析。该文件必须为 PEM 格式。This variable specifies the path name of the RSA private key file for the caching_sha2_password authentication plugin. If the file is named as a relative path, it is interpreted relative to the server data directory. The file must be in PEM format.

有关 caching_sha2_password 的信息，请参见 第 8.4.1.2 节，“缓存 SHA-2 可插拔认证”。For information about caching_sha2_password, see Section 8.4.1.2, “Caching SHA-2 Pluggable Authentication”.

caching_sha2_password_public_key_path

该变量指定用于 caching_sha2_password 身份验证插件的 RSA 公钥文件的路径名。如果文件名是相对路径，它将相对于服务器数据目录进行解释。该文件必须为 PEM 格式。This variable specifies the path name of the RSA public key file for the caching_sha2_password authentication plugin. If the file is named as a relative path, it is interpreted relative to the server data directory. The file must be in PEM format.

有关 caching_sha2_password 的信息，包括客户端如何请求 RSA 公钥的信息，请参见 第 8.4.1.2 节，“缓存 SHA-2 可插拔身份验证”。For information about caching_sha2_password, including information about how clients request the RSA public key, see Section 8.4.1.2, “Caching SHA-2 Pluggable Authentication”.

character_set_client

来自客户端的语句的字符集。该变量的会话值是根据客户端连接到服务器时请求的字符集设置的。（许多客户端支持 --default-character-set 选项，以便显式指定此字符集。另请参见 第 12.4 节，“连接字符集和排序规则”。）当客户端请求的值未知或不可用，或者服务器配置为忽略客户端请求时，将使用该变量的全局值来设置会话值。当客户端请求服务器未知的字符集时，就会发生这种情况，例如，当一个支持日语的客户端在连接到未配置 sjis 支持的服务器时请求 sjis。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 12.4, “Connection Character Sets and Collations”.) The global value of the variable is used to set the session value in cases when the client-requested value is unknown or not available, or the server is configured to ignore client requests. This can happen when the client requests a character set not known to the server, such as when a Japanese-enabled client requests sjis when connecting to a server not configured with sjis support.

某些字符集不能用作客户端字符集。尝试将它们用作 character_set_client 值会产生错误。请参阅 不允许的客户端字符集。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

用于未指定字符集引入符的字符串字面量以及数字到字符串转换的字符集。有关引入符的信息，请参见 第 12.3.8 节，“字符集引入符”。The character set used for literals specified without a character set introducer and for number-to-string conversion. For information about introducers, see Section 12.3.8, “Character Set Introducers”.

character_set_database

默认数据库使用的字符集。每当默认数据库更改时，服务器会设置此变量。如果没有默认数据库，该变量的值与character_set_server相同。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.

设置此系统变量的会话值是一项受限操作。会话用户必须具有足够的权限来设置受限会话变量。请参见第 7.1.9.1 节，“系统变量权限”。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 7.1.9.1, “System Variable Privileges”.

全局 character_set_database 和 collation_database 系统变量已被弃用；预计将在未来的 MySQL 版本中移除。The global character_set_database and collation_database system variables are deprecated; expect them to be removed in a future version of MySQL.

为会话 character_set_database 和 collation_database 系统变量分配值已被弃用，分配操作会产生警告。预计在未来的 MySQL 版本中，这些会话变量将变为只读（对它们的分配将产生错误），但仍可以访问这些会话变量以确定默认数据库的字符集和排序规则。Assigning a value to the session character_set_database and collation_database system variables is deprecated and assignments produce a warning. Expect the session variables to become read-only (and assignments to them to produce an error) in a future version of MySQL in which it remains possible to access the session variables to determine the database character set and collation for the default database.

character_set_filesystem

文件系统字符集。该变量用于解释指向文件名的字符串字面值，例如在LOAD DATA和SELECT ... INTO OUTFILE语句以及LOAD_FILE()函数中。在尝试打开文件之前，这些文件名会从character_set_client转换为character_set_filesystem。默认值是binary，这意味着不会进行转换。对于允许多字节文件名的系统，可能需要设置不同的值。例如，如果系统使用 UTF-8 表示文件名，则将character_set_filesystem设置为'utf8mb4'。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'.

设置此系统变量的会话值是一项受限操作。会话用户必须具有足够的权限来设置受限会话变量。请参见第 7.1.9.1 节，“系统变量权限”。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 7.1.9.1, “System Variable Privileges”.

character_set_results

用于将查询结果返回给客户端的字符集。这包括结果数据，如列值，结果元数据，如列名，以及错误消息。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

服务器的默认字符集。参见 第 12.15 节，“字符集配置”。如果设置此变量，你也应该设置 collation_server 来指定字符集的校对规则。The servers default character set. See Section 12.15, “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

服务器用于存储标识符的字符集。该值始终为 utf8mb3。The character set used by the server for storing identifiers. The value is always utf8mb3.

character_sets_dir

安装字符集的目录。请参见第 12.15 节，“字符集配置”。The directory where character sets are installed. See Section 12.15, “Character Set Configuration”.

check_proxy_users

一些认证插件为自己实现了代理用户映射（例如，PAM 和 Windows 认证插件）。其他认证插件默认不支持代理用户。在这些插件中，有些可以请求 MySQL 服务器根据授予的代理权限映射代理用户：mysql_native_password（已弃用）、sha256_password（已弃用）。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 (deprecated), sha256_password (deprecated).

如果启用了 check_proxy_users 系统变量，服务器会为任何提出此类请求的认证插件执行代理用户映射。为了利用服务器的代理用户映射支持，可能还需要启用插件特定的系统变量：If the check_proxy_users system variable is enabled, the server performs proxy user mapping for any authentication plugins that make such a request. It may also be necessary to enable plugin-specific system variables to take advantage of server proxy user mapping support:

有关用户代理的信息，请参阅 第 8.2.19 节，“代理用户”。For information about user proxying, see Section 8.2.19, “Proxy Users”.

collation_connection

连接字符集的排序规则。collation_connection 对字面字符串的比较非常重要。对于与列值的字符串比较，collation_connection 并不重要，因为列有自己的排序规则，其排序优先级更高（参见 第 12.8.4 节，“表达式中的排序规则可强制性”）。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 12.8.4, “Collation Coercibility in Expressions”).

为此变量使用用户定义排序规则的名称会引发警告。Using the name of a user-defined collation for this variable raises a warning.

collation_database collation_database

默认数据库使用的排序规则。每当默认数据库更改时，服务器会设置此变量。如果没有默认数据库，该变量的值与 collation_server 相同。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.

全局 character_set_database 和 collation_database 系统变量已被弃用；预计将在未来的 MySQL 版本中移除。The global character_set_database and collation_database system variables are deprecated; expect them to be removed in a future version of MySQL.

为会话 character_set_database 和 collation_database 系统变量分配值已被弃用，分配操作会产生警告。预期在 MySQL 的未来版本中，这些会话变量将变为只读（分配操作会产生错误），但仍可以访问会话变量以确定默认数据库的字符集和排序规则。Assigning a value to the session character_set_database and collation_database system variables is deprecated and assignments produce a warning. Expect the session variables to become read-only (and assignments to produce an error) in a future version of MySQL in which it remains possible to access the session variables to determine the database character set and collation for the default database.

使用用户定义的排序规则名称为 collation_database 会触发警告。Using the name of a user-defined collation for collation_database raises a warning.

collation_server

服务器的默认校对规则。参见 第 12.15 节，“字符集配置”。The server's default collation. See Section 12.15, “Character Set Configuration”.

将此设置为用户定义的排序规则名称会引发警告。Setting this to the name of a user-defined collation raises a warning.

completion_type

事务完成类型。该变量可以采用下表所示的值。该变量可以使用名称值或相应的整数值进行赋值。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.

completion_type 影响以 START TRANSACTION 或 BEGIN并以COMMIT 或 ROLLBACK。它不适用于执行第 15.3.3 节，“导致隐式提交的语句”中列出的语句执行而产生的隐式提交。同样不适用于XA COMMIT XA ROLLBACK），或当 autocommit=1。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 15.3.3, “Statements That Cause an Implicit Commit”. It also does not apply for XA COMMIT, XA ROLLBACK, or when autocommit=1.

component_scheduler.enabled

在启动时设置为OFF时，后台线程不会启动。任务仍然可以被调度，但它们不会运行，直到component_scheduler被启用。在启动时设置为ON时，该组件完全可用。When set to OFF at startup, the background thread does not start. Tasks can still be scheduled, but they do not run until component_scheduler is enabled. When set to ON at startup, the component is fully operational.

也可以动态设置该值以获得以下效果：It is also possible to set the value dynamically to get the following effects:

concurrent_insert

如果是 AUTO（默认值），MySQL 允许在 MyISAM 表中同时运行 INSERT 和 SELECT 语句，这些表在数据文件的中间没有空闲块。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.

该变量可以取下表所示的值。变量可以使用名称值或相应的整数值进行赋值。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.

开始mysqld设置为--skip-new, concurrent_insert用于NEVER.If you start mysqld with --skip-new, concurrent_insert is set to NEVER.

另见 第 10.11.3 节，“并发插入”。See also Section 10.11.3, “Concurrent Inserts”.

connect_timeout

mysqld 服务器在响应 Bad handshake 之前等待连接数据包的秒数。默认值为 10 秒。The number of seconds that the mysqld server waits for a connect packet before responding with Bad handshake. The default value is 10 seconds.

如果客户端经常遇到类似 connect_timeout 的错误，增加 Lost connection to MySQL server at 'XXX', system error: errno 的值可能会有所帮助。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.

connection_memory_chunk_size

设置全局内存使用计数器 Global_connection_memory 更新的分块大小。只有当所有用户连接的总内存消耗变化超过此数值时，状态变量才会更新。通过设置 connection_memory_chunk_size = 0 来禁用更新。Set the chunking size for updates to the global memory usage counter Global_connection_memory. The status variable is updated only when total memory consumption by all user connections changes by more than this amount. Disable updates by setting connection_memory_chunk_size = 0.

内存计算不包括系统用户（如 MySQL root 用户）使用的内存。InnoDB 缓冲池使用的内存也不包括在内。The memory calculation is exclusive of any memory used by system users such as the MySQL root user. Memory used by the InnoDB buffer pool is also not included.

您必须拥有 SYSTEM_VARIABLES_ADMIN 或 SUPER 权限才能设置此变量。You must have the SYSTEM_VARIABLES_ADMIN or SUPER privilege to set this variable.

connection_memory_limit

设置单个用户连接可以使用的最大内存量。如果任何用户连接使用的内存超过此数量，该连接的所有查询将被拒绝，并返回 ER_CONN_LIMIT，包括当前正在运行的任何查询。Set the maximum amount of memory that can be used by a single user connection. If any user connection uses more than this amount, all queries from this connection are rejected with ER_CONN_LIMIT, including any queries currently running.

此变量设置的限制不适用于系统用户或 MySQL root 账户。InnoDB 缓冲池使用的内存也不包含在内。The limit set by this variable does not apply to system users, or to the MySQL root account. Memory used by the InnoDB buffer pool is also not included.

您必须拥有 SYSTEM_VARIABLES_ADMIN 或 SUPER 权限才能设置此变量。You must have the SYSTEM_VARIABLES_ADMIN or SUPER privilege to set this variable.

core_file

当服务器意外退出时是否写入核心文件。此变量由 --core-file 选项设置。Whether to write a core file if the server unexpectedly exits. This variable is set by the --core-file option.

create_admin_listener_thread

是否为管理网络接口上的客户端连接使用专用监听线程（参见第 7.1.12.1 节，“连接接口”）。默认值为OFF；即主接口上的普通连接的管理线程也处理管理接口的连接。Whether to use a dedicated listening thread for client connections on the administrative network interface (see Section 7.1.12.1, “Connection Interfaces”). The default is OFF; that is, the manager thread for ordinary connections on the main interface also handles connections for the administrative interface.

根据平台类型和工作负载等因素，你可能会发现某个变量设置比另一个设置更能带来更好的性能。Depending on factors such as platform type and workload, you may find one setting for this variable yields better performance than the other setting.

如果未指定 admin_address，则设置 create_admin_listener_thread 将无效，因为在这种情况下，服务器不会维护任何管理网络接口。Setting create_admin_listener_thread has no effect if admin_address is not specified because in that case the server maintains no administrative network interface.

cte_max_recursion_depth

公共表表达式（CTE）的最大递归深度。服务器将终止执行任何递归层数超过该变量值的 CTE。有关更多信息，请参见 限制公共表表达式递归。The common table expression (CTE) maximum recursion depth. The server terminates execution of any CTE that recurses more levels than the value of this variable. For more information, see Limiting Common Table Expression Recursion.

datadir

MySQL 服务器数据目录的路径。相对路径相对于当前目录进行解析。如果您希望服务器自动启动（即在无法预先知道当前目录的环境中），最好将 datadir 值指定为绝对路径。The path to the MySQL server data directory. Relative paths are resolved with respect to the current directory. If you expect the server to be started automatically (that is, in contexts for which you cannot know the current directory in advance), it is best to specify the datadir value as an absolute path.

debug

此变量指示当前的调试设置。它仅适用于启用调试支持构建的服务器。初始值来自服务器启动时提供的 --debug 选项的值。全局值和会话值可以在运行时设置。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.

设置此系统变量的会话值是一项受限操作。会话用户必须具有足够的权限来设置受限会话变量。请参见第 7.1.9.1 节，“系统变量权限”。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 7.1.9.1, “System Variable Privileges”.

分配以 + 或 - 开头的值会导致该值被加到或从当前值中减去：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       |
+---------+

更多信息，请参阅 第 7.9.4 节，“DBUG 包”。For more information, see Section 7.9.4, “The DBUG Package”.

debug_sync

此变量是调试同步功能的用户界面。使用调试同步功能要求 MySQL 使用 -DWITH_DEBUG=ON CMake 选项进行配置（参见 第 2.8.7 节，“MySQL 源代码配置选项”）；否则，此系统变量不可用。This variable is the user interface to the Debug Sync facility. Use of Debug Sync requires that MySQL be configured with the -DWITH_DEBUG=ON CMake option (see Section 2.8.7, “MySQL Source-Configuration Options”); otherwise, this system variable is not available.

全局变量的值是只读的，用于指示该功能是否启用。默认情况下，调试同步（Debug Sync）是禁用的，debug_sync 的值为 OFF。如果服务器使用 --debug-sync-timeout=N 启动，其中 N 是大于 0 的超时时间值，则调试同步被启用，debug_sync 的值为 ON - current signal，后跟信号名称。同时，N 成为各个同步点的默认超时时间。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.

会话值可以被任何用户读取，并且与全局变量具有相同的值。可以设置会话值以控制同步点。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.

设置此系统变量的会话值是一项受限操作。会话用户必须具有足够的权限来设置受限会话变量。请参见第 7.1.9.1 节，“系统变量权限”。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 7.1.9.1, “System Variable Privileges”.

有关调试同步工具以及如何使用同步点的说明，请参阅 MySQL 内部结构：测试同步。For a description of the Debug Sync facility and how to use synchronization points, see MySQL Internals: Test Synchronization.

default_collation_for_utf8mb4

服务器将该变量设置为 utf8mb4 字符集的默认排序。变量的值会从源复制到副本，以便副本能够正确处理来自源的数据，而 utf8mb4不同。该变量主要用于支持从 MySQL 5.7 或更早的复制源服务器到较晚的 MySQL 副本服务器，或带有 MySQL 5.7 主节点和一个或多个 MySQL 8.0 或更新次级服务器的组复制。MySQL 5.7 中 utf8mb4是 utf8mb4_general_ci，但在后续版本系列中为 utf8mb4_0900_ai_ci。该变量不存在于 MySQL 8.0 之前的版本，因此如果副本没有收到该变量的值，它会假设源代码来自更早版本，并将该值设置为之前的默认排序utf8mb4_general_ci。This variable is set by the server to the default collation for the utf8mb4 character set. The value of the variable is replicated from a source to a replica so that the replica can correctly process data originating from a source with a different default collation for utf8mb4. This variable is primarily intended to support replication from a MySQL 5.7 or older replication source server to a later MySQL replica server, or group replication with a MySQL 5.7 primary node and one or more MySQL 8.0 or later secondaries. The default collation for utf8mb4 in MySQL 5.7 is utf8mb4_general_ci, but utf8mb4_0900_ai_ci in later release series. The variable is not present in releases earlier than MySQL 8.0, so if the replica does not receive a value for the variable, it assumes the source is from an earlier release and sets the value to the previous default collation utf8mb4_general_ci.

以下语句中使用默认的 utf8mb4 排序规则：The default utf8mb4 collation is used in the following statements:

另请参见 第 12.9 节，“Unicode 支持”。See also Section 12.9, “Unicode Support”.

default_password_lifetime

此变量定义了全局自动密码过期策略。默认的 default_password_lifetime 值为 0，这将禁用自动密码过期。如果 default_password_lifetime 的值为正整数 N，则表示允许的密码有效期；密码必须每 N 天更改一次。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.

可以使用 CREATE USER 和 ALTER USER 语句的密码过期选项，根据需要覆盖全局密码过期策略。请参阅 第 8.2.15 节，“密码管理”。The global password expiration policy can be overridden as desired for individual accounts using the password expiration option of the CREATE USER and ALTER USER statements. See Section 8.2.15, “Password Management”.

default_storage_engine

表的默认存储引擎。参见 第 18 章，其他存储引擎。此变量仅设置永久表的存储引擎。要设置TEMPORARY表的存储引擎，请设置default_tmp_storage_engine系统变量。The default storage engine for tables. See Chapter 18, 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.

要查看哪些存储引擎可用和启用，请使用 SHOW ENGINES 语句或查询 INFORMATION_SCHEMA ENGINES 表。To see which storage engines are available and enabled, use the SHOW ENGINES statement or query the INFORMATION_SCHEMA ENGINES table.

如果在服务器启动时禁用默认存储引擎，必须为永久表和 TEMPORARY 表设置不同的默认引擎，否则服务器无法启动。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 else the server does not start.

default_table_encryption

定义在创建模式和通用表空间时，如果未指定ENCRYPTION子句，所应用的默认加密设置。Defines the default encryption setting applied to schemas and general tablespaces when they are created without specifying an ENCRYPTION clause.

default_table_encryption变量仅适用于用户创建的模式和通用表空间。它不管理mysql系统表空间的加密。The default_table_encryption variable is only applicable to user-created schemas and general tablespaces. It does not govern encryption of the mysql system tablespace.

设置 default_table_encryption 的运行时值需要 SYSTEM_VARIABLES_ADMIN 和 TABLE_ENCRYPTION_ADMIN 权限，或者已弃用的 SUPER 权限。Setting the runtime value of default_table_encryption requires the SYSTEM_VARIABLES_ADMIN and TABLE_ENCRYPTION_ADMIN privileges, or the deprecated SUPER privilege.

在 Group Replication 运行时，default_table_encryption 的值无法更改。The value of default_table_encryption cannot be changed while Group Replication is running.

default_table_encryption 支持 SET PERSIST 和 SET PERSIST_ONLY 语法。参见 第 7.1.9.3 节，“持久化系统变量”。default_table_encryption supports SET PERSIST and SET PERSIST_ONLY syntax. See Section 7.1.9.3, “Persisted System Variables”.

更多信息，请参见 为模式和通用表空间定义加密默认值。For more information, see Defining an Encryption Default for Schemas and General Tablespaces.

default_tmp_storage_engine

TEMPORARY 表（使用 CREATE TEMPORARY TABLE 创建）的默认存储引擎。要设置永久表的存储引擎，请设置 default_storage_engine 系统变量。另请参阅该变量的讨论以了解可能的取值。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.

如果在服务器启动时禁用默认存储引擎，必须为永久表和 TEMPORARY 表设置不同的默认引擎，否则服务器无法启动。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 else the server does not start.

default_week_format

的默认模式值WEEK()函数。请参见第 14.7 节，“日期和时间函数”.The default mode value to use for the WEEK() function. See Section 14.7, “Date and Time Functions”.

delay_key_write

该变量指定如何使用延迟键写入。它仅适用于MyISAM表。延迟键写入会导致键缓冲区在写入之间不被刷新。另请参阅18.2.1 节，“MyISAM 启动选项”。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 18.2.1, “MyISAM Startup Options”.

此变量可以取以下值之一，以影响可在DELAY_KEY_WRITE语句中使用的CREATE TABLE表选项的处理方式。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.

如果为某个表启用了 DELAY_KEY_WRITE，则在每次索引更新时不会刷新该表的键缓冲区，而仅在表关闭时刷新。这大大加快了键的写入速度，但如果使用此功能，应该通过在启动服务器时设置 myisam_recover_options 系统变量来自动检查所有 MyISAM 表（例如，myisam_recover_options='BACKUP,FORCE'）。参见 第 7.1.8 节，“服务器系统变量”，以及 第 18.2.1 节，“MyISAM 启动选项”。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 7.1.8, “Server System Variables”, and Section 18.2.1, “MyISAM Startup Options”.

如果你使用 mysqld 并带上 --skip-new 启动，则 delay_key_write 的值将被设置为 OFF。If you start mysqld with --skip-new, delay_key_write is set to OFF.

delayed_insert_limit

该系统变量已被弃用（因为不支持DELAYED 插入），您应该预期它将在未来的版本中被移除。This system variable is deprecated (because DELAYED inserts are not supported), and you should expect it to be removed in a future release.

delayed_insert_timeout

该系统变量已被弃用（因为不支持DELAYED 插入），您应该预期它将在未来的版本中被移除。This system variable is deprecated (because DELAYED inserts are not supported), and you should expect it to be removed in a future release.

delayed_queue_size

该系统变量已被弃用（因为不支持DELAYED 插入），您应该预期它将在未来的版本中被移除。This system variable is deprecated (because DELAYED inserts are not supported), and you should expect it to be removed in a future release.

disabled_storage_engines

该变量指示哪些存储引擎不能用于创建表或表空间。例如，要防止创建新的 MyISAM 或 FEDERATED 表，可以在服务器选项文件中使用以下几行启动服务器：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"

默认情况下，disabled_storage_engines为空（未禁用引擎），但可设置为一个或多个引擎的逗号分隔列表（不区分大小写）。值中命名的任何引擎都不能用于创建具有 CREATE TABLE 或 CREATE TABLESPACE，且不能与 ALTER TABLE ... ENGINE 或 ALTER TABLESPACE ... ENGINE 用于更改现有表或表空间的存储引擎。尝试更改时会出现 ER_DISABLED_STORAGE_ENGINE 错误。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不限制现有表的其他 DDL 语句，例如CREATE INDEX, TRUNCATE TABLE, ANALYZE TABLE, DROP TABLE，或DROP TABLESPACE。这允许平稳过渡，使使用禁用引擎的现有表或表空间可以通过例如ALTER TABLE ... ENGINE permitted_engine.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.

允许将 default_storage_engine 或 default_tmp_storage_engine 系统变量设置为已禁用的存储引擎。这可能导致应用程序行为异常或失败，尽管在开发环境中这可能是一个有用的技术，用于识别使用已禁用引擎的应用程序，以便对其进行修改。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 如果服务器是使用以下任何选项启动的，将被禁用且无效：--initialize、--initialize-insecure、--skip-grant-tables。disabled_storage_engines is disabled and has no effect if the server is started with any of these options: --initialize, --initialize-insecure, --skip-grant-tables.

disconnect_on_expired_password

此变量控制服务器如何处理密码已过期的客户端：This variable controls how the server handles clients with expired passwords:

有关客户端和服务器设置在处理过期密码方面的交互的更多信息，请参见 第 8.2.16 节，“服务器处理过期密码”。For more information about the interaction of client and server settings relating to expired-password handling, see Section 8.2.16, “Server Handling of Expired Passwords”.

div_precision_increment

此变量表示使用 / 运算符进行除法运算时，结果的小数位数增加的位数。默认值为 4。最小值和最大值分别为 0 和 30。以下示例说明增加默认值的效果。This variable indicates the number of digits by which to increase the scale of the result of division operations performed with the / operator. The default value is 4. The minimum and maximum values are 0 and 30, respectively. The following example illustrates the effect of increasing the default value.

mysql> SELECT 1/7;
+--------+
| 1/7    |
+--------+
| 0.1429 |
+--------+
mysql> SET div_precision_increment = 12;
mysql> SELECT 1/7;
+----------------+
| 1/7            |
+----------------+
| 0.142857142857 |
+----------------+

dragnet.log_error_filter_rules

控制 log_filter_dragnet 错误日志过滤组件操作的过滤规则。如果未安装 log_filter_dragnet，则 dragnet.log_error_filter_rules 无法使用。如果安装了 log_filter_dragnet 但未启用，对 dragnet.log_error_filter_rules 的更改将不会生效。The filter rules that control operation of the log_filter_dragnet error log filter component. If log_filter_dragnet is not installed, dragnet.log_error_filter_rules is unavailable. If log_filter_dragnet is installed but not enabled, changes to dragnet.log_error_filter_rules have no effect.

默认值的效果类似于使用设置为 log_error_verbosity=2 的 log_sink_internal 过滤器执行的过滤操作。The effect of the default value is similar to the filtering performed by the log_sink_internal filter with a setting of log_error_verbosity=2.

可以查询 dragnet.Status 状态变量，以确定最近一次对 dragnet.log_error_filter_rules 的赋值结果。dragnet.Status status variable can be consulted to determine the result of the most recent assignment to dragnet.log_error_filter_rules.

enterprise_encryption.maximum_rsa_key_size

此变量限制 MySQL 企业加密生成的 RSA 密钥的最大大小。仅当安装了 MySQL 企业加密组件 component_enterprise_encryption 时，该变量才可用。This variable limits the maximum size of RSA keys generated by MySQL Enterprise Encryption. The variable is available only if the MySQL Enterprise Encryption component component_enterprise_encryption is installed.

最低设置为 2048 位，这是当前最佳实践可接受的最小 RSA 密钥长度。默认设置为 4096 位。最高设置为 16384 位。生成更长的密钥可能会消耗大量 CPU 资源，因此您可以使用此设置将密钥限制为在满足安全需求的同时平衡资源使用的长度。有关更多信息，请参见第 8.6.2 节，“配置 MySQL 企业加密”。The lowest setting is 2048 bits, which is the minimum RSA key length that is acceptable by current best practice. The default setting is 4096 bits. The highest setting is 16384 bits. Generating longer keys can consume significant CPU resources, so you can use this setting to limit keys to a length that provides adequate security for your requirements while balancing this with resource usage. See Section 8.6.2, “Configuring MySQL Enterprise Encryption” for more information.

enterprise_encryption.rsa_support_legacy_padding

此变量控制 MySQL 企业加密生成的使用旧 openssl_udf 共享库函数的加密数据和签名是否可以被 MySQL 企业加密组件 (component_enterprise_encryption) 解密或验证。此变量仅在安装了 MySQL 企业加密组件时可用。This variable controls whether encrypted data and signatures that MySQL Enterprise Encryption produced using the old openssl_udf shared library functions can be decrypted or verified by the MySQL Enterprise Encryption component (component_enterprise_encryption). The variable is available only if the MySQL Enterprise Encryption component is installed.

为了使组件函数支持对旧的 openssl_udf 共享库函数生成的内容进行解密和验证，您必须将系统变量 padding 设置为 ON。当设置为 ON 时，如果组件函数在假设内容使用 RSAES-OAEP 或 RSASSA-PSS 方案（由组件使用）时无法解密或验证，它们会再次尝试假设内容使用 RSAES-PKCS1-v1_5 或 RSASSA-PKCS1-v1_5 方案（由 openssl_udf 共享库函数使用）。当设置为 OFF 时，如果组件函数无法使用其正常方案解密或验证内容，它们会返回空输出。有关更多信息，请参见 第 8.6.2 节，“配置 MySQL 企业加密”。For the component functions to support decryption and verification for content produced by the old openssl_udf shared library functions, you must set the system variable padding to ON. When ON is set, if the component functions cannot decrypt or verify content when assuming it has the RSAES-OAEP or RSASSA-PSS scheme (as used by the component), they make another attempt assuming it has the RSAES-PKCS1-v1_5 or RSASSA-PKCS1-v1_5 scheme (as used by the openssl_udf shared library functions). When OFF is set, if the component functions cannot decrypt or verify content using their normal schemes, they return null output. See Section 8.6.2, “Configuring MySQL Enterprise Encryption” for more information.

end_markers_in_json

优化器 JSON 输出是否应添加结束标记。请参阅第 10.15.9 节，“end_markers_in_json 系统变量”。Whether optimizer JSON output should add end markers. See Section 10.15.9, “The end_markers_in_json System Variable”.

eq_range_index_dive_limit

该变量指示在优化器估算符合条件的行数时，对于相等比较条件中的相等范围数量，优化器应从使用索引深入查找改为使用索引统计信息。它适用于评估具有以下等效形式的表达式，其中优化器使用非唯一索引查找col_name值：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

在这两种情况下，表达式都包含N个等值范围。优化器可以使用索引深入或索引统计来进行行估计。如果eq_range_index_dive_limit大于 0，当存在eq_range_index_dive_limit个或更多等值范围时，优化器会使用现有索引统计而不是索引深入。因此，要允许最多N个等值范围使用索引深入，请将eq_range_index_dive_limit设置为N + 1。若要禁用索引统计并始终使用索引深入，而不管N的值是多少，将eq_range_index_dive_limit设置为 0。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.

欲了解更多信息，请参见 多值比较的相等范围优化。For more information, see Equality Range Optimization of Many-Valued Comparisons.

要更新表索引统计以获得最佳估计，请使用 ANALYZE TABLE。To update table index statistics for best estimates, use ANALYZE TABLE.

error_count error_count