MySQL主从报错1594

一、主从报错 Relay log read failure

问题原因，MySQL主从使用的是kvm虚拟机，物理机超分严重，在负载高的情况下会kill掉占用资源最多的虚拟机，再启动后导致主从失败

mysql> show slave status\G
*************************** 1. row ***************************
               Slave_IO_State: Waiting for master to send event
                  Master_Host: 10.0.0.230
                  Master_User: repl
                  Master_Port: 3306
                Connect_Retry: 60
              Master_Log_File: master-bin.002783
          Read_Master_Log_Pos: 812026
               Relay_Log_File: 10-0-0-236-relay-bin.000002
                Relay_Log_Pos: 83853
        Relay_Master_Log_File: master-bin.002781
             Slave_IO_Running: Yes
            Slave_SQL_Running: Yes
              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: 973991562
              Relay_Log_Space: 9657278
              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: 1128
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: f7c24af7-a54a-11e6-88b4-525400169c04
             Master_Info_File: /Data/work/local/mysql/master.info
                    SQL_Delay: 0
          SQL_Remaining_Delay: NULL
      Slave_SQL_Running_State: update
           Master_Retry_Count: 86400
                  Master_Bind: 
      Last_IO_Error_Timestamp: 
     Last_SQL_Error_Timestamp: 
               Master_SSL_Crl: 
           Master_SSL_Crlpath: 
           Retrieved_Gtid_Set: 
            Executed_Gtid_Set: 
                Auto_Position: 0
1 row in set (0.00 sec)

二、问题分析

 从上面的报错信息中我们可以看到应该是主库的binlog日志或者从库的relay日志损坏，导致从库读取日志的时候时候，从而导致从库复制线程报错。

主要原因是服务器断电导致从库的relay log损坏，从而导致从库复制线程报错。

三、解决方案

在show slave status\G中找到如下信息：
Relay_Master_Log_File: master-bin.002781    # slave库已读取的master的binlog
Exec_Master_Log_Pos: 968089314           # 在slave上已经执行的position位置点

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。
mysql> stop slave;
Query OK, 0 rows affected (0.08 sec)

mysql> change master to master_log_file='master-bin.002781', master_log_pos=968089314;
Query OK, 0 rows affected (1.03 sec)

mysql> start slave;
Query OK, 0 rows affected (0.41 sec)