众所周知MySQL5.1的Replication是比较烂的。MySQL的每一个版本更新关于同步方面每次都是可以看到一大堆。但MySQL 5.1性能是比较突出的。所以经不住诱惑使用MySQL 5.1。所以也要经常遇到一些Bug。如：
mysql> show slave status\G
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 192.168.10.118
Master_User: repl_wu
Master_Port: 3306
Connect_Retry: 30
Master_Log_File: mysql-bin.005121
Read_Master_Log_Pos: 64337286
Relay_Log_File: relay-bin.003995
Relay_Log_Pos: 18446697137031827760
Relay_Master_Log_File: mysql-bin.005121
Slave_IO_Running: Yes
Slave_SQL_Running: No
Replicate_Do_DB:
Replicate_Ignore_DB:
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: 4
Relay_Log_Space: 64337901
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.
1 row in set (0.00 sec)
从上面可以看到是中继日值或是Master上的日值出问题了。
首先如果是中继日值坏掉，那只需要找到同步的时间点，然后重新同步，这样就可以有新的中继日值了。如果Master上的日值坏了就麻烦了。
从经验来看，这是中继日值出问题了。处理方法：
需要找到同步的点。
日值为：Master_Log_File: mysql-bin.005121，Relay_Master_Log_File: mysql-bin.005121以Relay_Master_Log_File为准，Master_Log_File为参考。
日值执行时间点：
Exec_Master_Log_Pos: 4
那么现在就可以：
mysql>stop slave;
mysql>change master to Master_Log_File='mysql-bin.005121', Master_Log_Pos=4;
mysql>start slave;
mysql>show slave status\G;
进行确认。
建议：
在使用MySQL-5.1.36以下的版本的同学，请尽快升级到MySQL-5.1.40 & MySQL-5.1.37sp1