当slave意外宕机时，有可能会损坏中继日志relay-log，再次开启同步复制时，会出现报错。
解决方法：找到同步的binlog日志和POS点，然后重新进行同步，这样就可以有新的中继日志了。
下边看个案例，模拟了中继日志损坏的情况，查看到的信息如下：

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mysql> show slave status \G
ERROR 2006 (HY000): MySQL server has gone away
No connection. Trying to reconnect...
Connection id:4
Current database: test

*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 10.10.10.200
Master_User: repl
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: mysql-bin.000005
Read_Master_Log_Pos: 220
Relay_Log_File: mysql-relay-bin.000010
Relay_Log_Pos: 283
Relay_Master_Log_File: mysql-bin.000004
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: 1032
Last_Error: Could not execute Update_rows event on table test.test01; Can't find record in 'test01', Error_code: 1032; handler error HA_ERR_END_OF_FILE; the event's master log mysql-bin.000004, end_log_pos 310
Skip_Counter: 0
Exec_Master_Log_Pos: 120
Relay_Log_Space: 2251
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: 1032
Last_SQL_Error: Could not execute Update_rows event on table test.test01; Can't find record in 'test01', Error_code: 1032; handler error HA_ERR_END_OF_FILE; the event's master log mysql-bin.000004, end_log_pos 310
Replicate_Ignore_Server_Ids:
Master_Server_Id: 1
Master_UUID: 4adfcd1d-4059-11e7-9532-080027d597f9
Master_Info_File: mysql.slave_master_info
SQL_Delay: 0
SQL_Remaining_Delay: NULL
Slave_SQL_Running_State:
Master_Retry_Count: 86400
Master_Bind:
Last_IO_Error_Timestamp:
Last_SQL_Error_Timestamp: 170808 11:45:26
Master_SSL_Crl:
Master_SSL_Crlpath:
Retrieved_Gtid_Set:
Executed_Gtid_Set:
Auto_Position: 0

其中，涉及几个重要的参数：
slave_IO_Running:接受master的binlog的信息
master_Log_file:正在读取master上binlog日志名
Read_master_Log_Pos:正在读取master上当前binlog日志POS点。
slave_SQL_Running:执行写操作
Relay_master_Log_File:正在同步master上的binlog日志名。
Exec_master_Log_Pos:正在同步当前binlog日志的POS点。
以Relay_master_Log_File参数值和Exec_master_Log_Pos参数值为基准。
Relay_Log_File: mysql-relay-bin.000010
Relay_Log_Pos: 283
接下来开始重置主从复制：

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mysql> stop slave;
Query OK, 0 rows affected (0.04 sec)

mysql> change master to master_log_file='mysql-relay-bin.000010',master_log_pos=283;
Query OK, 0 rows affected (0.06 sec)

mysql> start slave;
Query OK, 0 rows affected (0.12 sec)

通过这种方法可以修复中继日志，但是在MySQL5.5版本之后，在slave的my.cnf配置文件中加入relay_log_recovery=1就可以了。