【MySQL】innobackupex 长时间hang

mysql show processlist; +--------+-------------+--------------------+------+------------+---------+----------------------------------  | Id     | User        | Host               | db   | Command    | Time    |State                               +--------+-------------+--------------------+------+------------+---------+----------------------------------  |      1 | system user |                    | NULL | Connect    | 2684619 | Waiting for master to sendevent      |      2 | system user |                    | NULL | Connect    |      31 | Waiting for release of readlock                                ...... 4 rows in set (0.00 sec) system用户显示 Waiting for release of readlock 执行备份的用户为Xtraback 对应的time 列则每4s 循环一次。system user 的状态表示 xtraback 进程已经执行了flush tables with read only，并等待xtrabackup进程释放read lock。我们首先来了解一下xtrabackup 大致过程：  backup()并记录XTRABACKUP_BINARY信息  mysql_open()  启动管道链接的子进程连接mysql  mysql_check() 检查连接mysql的子进程是否OK，发送一个虚拟查询，等待mysql_response_timeout超时退出  mysql_close() 关闭连接mysql子进程  start_ibbackup() 创建子进程运行ibbackup来备份innodb数据和索引    如果不是远程备份，不是stream模式，进入wait_for_ibbackup_suspend() 检查ibbackup子进程是否还活着  mysql_open()  如果指定–safe-slave-backup 进入wait_for_safe_slave() ，通过每隔3s启停sql thread来不断检查实例上打开临时表数目是否为0  mysql_check()  如果没有指定–no-lock,进入 mysql_lockall()，执行FLUSH TABLES WITH READ LOCK;  backup_files() 拷贝除ibd外所有的文件  mysql_unlockall() 执行UNLOCK TABLES  如果指定–safe-slave-backup  START SLAVE SQL_THREAD  mysql_close() 问题出现在 发出flush tables with read lock 并获取了全局锁(systemuser 才在等待read lock) innodb 拷贝除ibd外所有的文件. xtrabackup源码  # flush tables with read lock         mysql_check(); --没有问题         mysql_lockall() if !$option_no_lock;  # timeout in seconds for a reply from mysql my $mysql_response_timeout = 900; sub mysql_send {     my $request = shift;     $current_mysql_request = $request;     print MYSQL_WRITER "$request\n";     mysql_check();     $current_mysql_request = ; sub mysql_lockall {     $now = current_time();     print STDERR "$now  $prefix Starting to lock all tables...\n";=     mysql_send "USE mysql;";     mysql_send "SET AUTOCOMMIT=0;";     if (compare_versions($mysql_server_version, 4.0.22) == 0         || compare_versions($mysql_server_version, 4.1.7) == 0) {         # MySQL server version is 4.0.22 or 4.1.7         mysql_send "COMMIT;";         mysql_send "FLUSH TABLES WITH READ LOCK;";     } else {         # MySQL server version is other than 4.0.22 or 4.1.7         mysql_send "FLUSH TABLES WITH READ LOCK;";         mysql_send "COMMIT;";     }     write_binlog_info;     write_slave_info if $option_slave_info;     $now = current_time();     print STDERR "$now  $prefix All tables locked and flushed to disk\n"; --在执行flush tables with read lock时，mysql_send函数执行超时900S，备份失败。我的实例的备份却一直表现为log scanned up to (3015320266621)。 记录一个疑问在这里。