LOCK INSTANCE FOR BACKUP

UNLOCK INSTANCE

LOCK INSTANCE FOR BACKUP 获得实例级 backup lock，允许在线备份时使用 DML，同时防止可能导致快照不一致的操作。LOCK INSTANCE FOR BACKUP acquires an instance-level backup lock that permits DML during an online backup while preventing operations that could result in an inconsistent snapshot.

执行 LOCK INSTANCE FOR BACKUP句需要 BACKUP_ADMIN权限。BACKUP_ADMIN权限会自动授予拥有 RELOAD 权限的用户，适用于从早期版本升级到 MySQL 8.4。Executing the LOCK INSTANCE FOR BACKUP statement requires the BACKUP_ADMIN privilege. The BACKUP_ADMIN privilege is automatically granted to users with the RELOAD privilege when performing an in-place upgrade to MySQL 8.4 from an earlier version.

多个会话可以同时持有备份锁。Multiple sessions can hold a backup lock simultaneously.

UNLOCK INSTANCE 释放当前会话持有的备份锁。会话被终止时，会话持有的备份锁也会被释放。UNLOCK INSTANCE releases a backup lock held by the current session. A backup lock held by a session is also released if the session is terminated.

LOCK INSTANCE FOR BACKUP 防止文件被创建、重命名或移除。REPAIR TABLE TRUNCATE TABLE， OPTIMIZE TABLE，账户管理语句被阻挡。参见 第 15.7.1 节，“账户管理语句”。修改 InnoDB 文件且未记录在 InnoDB 重录日志中的操作也被阻止。LOCK INSTANCE FOR BACKUP prevents files from being created, renamed, or removed. REPAIR TABLE TRUNCATE TABLE, OPTIMIZE TABLE, and account management statements are blocked. See Section 15.7.1, “Account Management Statements”. Operations that modify InnoDB files that are not recorded in the InnoDB redo log are also blocked.

LOCK INSTANCE FOR BACKUP 允许仅影响用户创建的临时表的 DDL 操作。实际上，属于用户创建的临时表中的文件可以在备份锁保持期间被创建、重命名或删除。也允许创建二进制日志文件。LOCK INSTANCE FOR BACKUP permits DDL operations that only affect user-created temporary tables. In effect, files that belong to user-created temporary tables can be created, renamed, or removed while a backup lock is held. Creation of binary log files is also permitted.

PURGE BINARY LOGS时，无法发布 LOCK INSTANCE FOR BACKUP句，因为该命令通过移除服务器文件违反了备份锁的规则。PURGE BINARY LOGS cannot be issued while a LOCK INSTANCE FOR BACKUP statement is in effect for the instance, because it contravenes the rules of the backup lock by removing files from the server.

通过 LOCK INSTANCE FOR BACKUP 获取的备份锁独立于事务锁和通过 FLUSH TABLES tbl_name [, tbl_name] ... WITH READ LOCK 获取的锁，并且允许以下语句序列：A backup lock acquired by LOCK INSTANCE FOR BACKUP is independent of transactional locks and locks taken by FLUSH TABLES tbl_name [, tbl_name] ... WITH READ LOCK, and the following sequences of statements are permitted:

LOCK INSTANCE FOR BACKUP;
FLUSH TABLES tbl_name [, tbl_name] ... WITH READ LOCK;
UNLOCK TABLES;
UNLOCK INSTANCE;

FLUSH TABLES tbl_name [, tbl_name] ... WITH READ LOCK;
LOCK INSTANCE FOR BACKUP;
UNLOCK INSTANCE;
UNLOCK TABLES;

lock_wait_timeout 设置定义了 LOCK INSTANCE FOR BACKUP 语句在放弃之前等待获取锁的时间。The lock_wait_timeout setting defines the amount of time that a LOCK INSTANCE FOR BACKUP statement waits to acquire a lock before giving up.