1、报错原因：

今日收到zabbix磁盘报警，通过du命令查找到mysql目录过大，发现relay日志没有设置过期时间，所以手动删除从库中继日志，之后重启mysql后主从复制状态异常：

 du  -h --max-depth=1 / |sort   #查看根目录下各目录大小，并进行排序

2、报错信息：

    [ERROR] Slave SQL: Slave failed to initialize relay log info structure from the repository, Error_code: 1872

3、查看mstaer log日志记录点

mysql> show master status \G
*************************** 1. row ***************************
             File: mysql-bin.000033
         Position: 199787569
     Binlog_Do_DB: 
 Binlog_Ignore_DB: 
Executed_Gtid_Set: 950c9b3d-737f-11e7-8956-000c29fb7e00:1-38188942
1 row in set (0.00 sec)

mysql> show master status;
+------------------+-----------+--------------+------------------+-------------------------------------------------+
| File             | Position  | Binlog_Do_DB | Binlog_Ignore_DB | Executed_Gtid_Set                               |
+------------------+-----------+--------------+------------------+-------------------------------------------------+
| mysql-bin.000033 | 199787569 |              |                  | 950c9b3d-737f-11e7-8956-000c29fb7e00:1-38188942 |
+------------------+-----------+--------------+------------------+-------------------------------------------------+
1 row in set (0.00 sec)

4、由于是rm删除中继日志，导致mysql无法进一步处理相关日志，此时需要停掉slave stop 然后 reset初始化

通过上面的报错以及relay log介绍，很容易知道由于mysql.slave_relay_log_info表中保留了以前的复制信息，导致新从库启动时无法找到对应文件，那么我们清理掉该表中的记录不就可以了。再次提醒，不要手动删该表数据，MySQL已经提供工具给我们了：reset slave：

mysql>reset slave   

mysql>change master to master_log_file='mysql-bin.000033',master_log_pos=199787569 ;   #与masterbinlog点进行关联
mysql>start slave;

4.1 reset slave功能介绍：

1、删除slave_master_info ，slave_relay_log_info两个表中数据；
2、删除所有relay log文件，并重新创建新的relay log文件；
3、不会改变gtid_executed 或者 gtid_purged的值

5、 验证主从状态

mysql> show slave status\G
*************************** 1. row ***************************
               Slave_IO_State: Waiting for master to send event
                  Master_Host: 192.168.0.37  #master主库
                  Master_User: rep
                  Master_Port: 3306
                Connect_Retry: 60
              Master_Log_File: mysql-bin.000033
          Read_Master_Log_Pos: 199850445
               Relay_Log_File: DB03-relay-bin.000003
                Relay_Log_Pos: 25581
        Relay_Master_Log_File: mysql-bin.000033
             Slave_IO_Running: Yes  #主要看这里
            Slave_SQL_Running: Yes  #主要这里
              Replicate_Do_DB: 
          Replicate_Ignore_DB: 
           Replicate_Do_Table: 
       Replicate_Ignore_Table: 
      Replicate_Wild_Do_Table: 
  Replicate_Wild_Ignore_Table: 
                   Last_Errno: 0
                   Last_Error: 
                 Skip_Counter: 0
          Exec_Master_Log_Pos: 199850445
              Relay_Log_Space: 25958
              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: 0
Master_SSL_Verify_Server_Cert: No
                Last_IO_Errno: 0
                Last_IO_Error: 
               Last_SQL_Errno: 0
               Last_SQL_Error: 
  Replicate_Ignore_Server_Ids: 
             Master_Server_Id: 1
                  Master_UUID: 950c9b3d-737f-11e7-8956-000c29fb7e00
             Master_Info_File: /application/mysql-5.6.35/data/master.info
                    SQL_Delay: 0
          SQL_Remaining_Delay: NULL
      Slave_SQL_Running_State: Slave has read all relay log; waiting for the slave I/O thread to update it
           Master_Retry_Count: 86400
                  Master_Bind: 
      Last_IO_Error_Timestamp: 
     Last_SQL_Error_Timestamp: 
               Master_SSL_Crl: 
           Master_SSL_Crlpath: 
           Retrieved_Gtid_Set: 950c9b3d-737f-11e7-8956-000c29fb7e00:38188963-38188981
            Executed_Gtid_Set: 291d8a91-75f5-11e7-995f-000c29ea7194:1-8,
950c9b3d-737f-11e7-8956-000c29fb7e00:1-38188981
                Auto_Position: 1
1 row in set (0.00 sec)