问题描述
innobackupex备份过程需要保证备份数据一致性，通过刷新表缓存和加全局读锁(FLUSH TABLES WITH READ LOCK)获取备份位点，而为防止锁等待超时，会先设置：
SET SESSION lock_wait_timeout=31536000
在MySQL中，导致FLUSH TABLES WITH READ LOCK操作获取锁超时的场景有：
1、超长事务或超大DML操作 2、超大表DDL操作
如果要解决锁超时问题，可以从加锁和KILL超长查询两方面入手，innobackupex命令有如下参数：
--no-lock Use this option to disable table lock with "FLUSH TABLES WITH READ LOCK". Use it only if ALL your tables are InnoDB and you DO NOT CARE about the binary log position of the backup. This option shouldn't be used if there are any DDL statements being executed or if any updates are happening on non-InnoDB tables (this includes the system MyISAM tables in the mysql database), otherwise it could lead to an inconsistent backup. If you are considering to use --no-lock because your backups are failing to acquire the lock, this could be because of incoming replication events preventing the lock from succeeding. Please try using --safe-slave-backup to momentarily stop the replication slave thread, this may help the backup to succeed and you then don't need to resort to using this option. --no-backup-locks This option controls if backup locks should be used instead of FLUSH TABLES WITH READ LOCK on the backup stage. The option has no effect when backup locks are not supported by the server. This option is enabled by default, disable with --no-backup-locks. --kill-long-query-type=name This option specifies which types of queries should be killed to unblock the global lock. Default is "all". --kill-long-queries-timeout=# This option specifies the number of seconds innobackupex waits between starting FLUSH TABLES WITH READ LOCK and killing those queries that block it. Default is 0 seconds, which means innobackupex will not attempt to kill any queries.
如果在从库上执行备份，可以考虑暂停复制进程来防止阻塞：
--safe-slave-backup Stop slave SQL thread and wait to start backup until Slave_open_temp_tables in "SHOW STATUS" is zero. If there are no open temporary tables, the backup will take place, otherwise the SQL thread will be started and stopped until there are no open temporary tables. The backup will fail if Slave_open_temp_tables does not become zero after --safe-slave-backup-timeout seconds. The slave SQL thread will be restarted when the backup finishes. --safe-slave-backup-timeout=# How many seconds --safe-slave-backup should wait for Slave_open_temp_tables to become zero. (default 300)