最近发现MySQL备份服务器竟然出现数据不同步的问题。
报错信息：
mysql> show slave status \G
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 192.168.11.202
Master_User: 223backup
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: binlog.000021
Read_Master_Log_Pos: 705618329
Relay_Log_File: localhost-relay-bin.002879
Relay_Log_Pos: 515550
Relay_Master_Log_File: binlog.000021
Slave_IO_Running: Yes
Slave_SQL_Running: No
Replicate_Do_DB:
Replicate_Ignore_DB: mysql,test
Replicate_Do_Table:
Replicate_Ignore_Table:
Replicate_Wild_Do_Table:
Replicate_Wild_Ignore_Table:
Last_Errno: 1594
Last_Error: Relay log read failure: Could not parse relay log event entry. The possible reasons are: the master's binary log is corrupted (you can check this by running 'mysqlbinlog' on the binary log), the slave's relay log is corrupted (you can check this by running 'mysqlbinlog' on the relay log), a network problem, or a bug in the master's or slave's MySQL code. If you want to check the master's binary log or slave's relay log, you will be able to know their names by issuing 'SHOW SLAVE STATUS' on this slave.
Skip_Counter: 0
Exec_Master_Log_Pos: 676992028
Relay_Log_Space: 29206302
Until_Condition: None
Until_Log_File:
Until_Log_Pos: 0
Master_SSL_Allowed: No
Master_SSL_CA_File:
Master_SSL_CA_Path:
Master_SSL_Cert:
Master_SSL_Cipher:
Master_SSL_Key:
Seconds_Behind_Master: NULL
Master_SSL_Verify_Server_Cert: No
Last_IO_Errno: 0
Last_IO_Error:
Last_SQL_Errno: 1594
Last_SQL_Error: Relay log read failure: Could not parse relay log event entry. The possible reasons are: the master's binary log is corrupted (you can check this by running 'mysqlbinlog' on the binary log), the slave's relay log is corrupted (you can check this by running 'mysqlbinlog' on the relay log), a network problem, or a bug in the master's or slave's MySQL code. If you want to check the master's binary log or slave's relay log, you will be able to know their names by issuing 'SHOW SLAVE STATUS' on this slave.
Replicate_Ignore_Server_Ids:
Master_Server_Id: 2
1 row in set (0.00 sec)
报错信息： Relay log read failure: Could not parse relay log event entry. The possible reasons are: the master's binary log is corrupted (you can check this by running 'mysqlbinlog' on the binary log), the slave's relay log is corrupted (you can check this by running 'mysqlbinlog' on the relay log), a network problem, or a bug in the master's or slave's MySQL code. If you want to check the master's binary log or slave's relay log, you will be able to know their names by issuing 'SHOW SLAVE STATUS' on this slave.
二、原因分析
报错信息为从库“无法读取relay log 里的条目”，可能原因为master库的binglog错误，或slave库的中继日志错误。或者为网络问题及bug原因。
一般是由于网络故障或slave库压力过大，导致relay-log格式错误造成的。找到当前已经同步的时间点，重新设置主从同步，就会产生新的中继日志，恢复正常
三、问题处理
从"show slave status\G"的输出中，找到如下信息：
Relay_Master_Log_File: binlog.000021 //slave库已读取的master的binlog
Exec_Master_Log_Pos: 676992028 //在slave上已经执行的position位置点
四.问题解决：
停掉slave，以slave已经读取的binlog文件，和已经执行的position为起点，重新设置同步。会产生新的中继日志，问题解决
mysql>stop slave;
mysql>change master to master_log_file='binlog.000021' , master_log_pos=676992028
//在slave上已经执行的position位置点;
mysql>start slave;
四、验证结果
再次查看，错误已经解决，slave 开始追 master 的日志
mysql>show slave status\G
Exec_Master_Log_Pos: 702086896 //slave上已经执行的position已经变化
Seconds_Behind_Master: 79006 //slave 落后主库的时间，单位秒
过几秒钟，再次查看。离与master同步更近了
mysql>show slave status\G
Exec_Master_Log_Pos: 703743817
Seconds_Behind_Master: 60672