Master-Slave replication is broken because of corrupted slave relay log on Slave server

It does not apply to Master-Master replication. We are not taking responsibility for data lost, caused by actions described in this manual.

Error shown in Slave server should look like:

mysql> show slave status\G;
*************************** 1. row ***************************
              Slave_IO_State: Waiting for master to send event
                 Master_Host: 111.111.111.111
                 Master_User: slave
                 Master_Port: 3306
               Connect_Retry: 60
             Master_Log_File: mysql-bin.000474
         Read_Master_Log_Pos: 228856355
              Relay_Log_File: slave-relay.001158
               Relay_Log_Pos: 949325382
       Relay_Master_Log_File: mysql-bin.000472
            Slave_IO_Running: Yes
           Slave_SQL_Running: No
             Replicate_Do_DB: mor
         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: 949325236
             Relay_Log_Space: 2376273076
             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: 20
1 row in set (0.00 sec)

Make sure that failure caused not by corruption of master binlog in Master server. On Main server use :

mysqlbinlog /var/lib/mysql/mysql-bin.000472 >/tmp/mysqlbinlog.txt

Open /tmp/mysqlbinlog.txt and search for certain position (949325236 in example above). Check text on lines above and below that position. If you can see distorted text or cannot find that position at all, problem is caused by master log problem and replication needs to be completely rebuilt.

Use same method to check Slave relay log on Slave server:

mysqlbinlog /var/lib/mysql/slave-relay.001158 >/tmp/mysqlbinlog.txt

You should find distorted text or get error that binlog is corrupted while running the command.

If it happens follow this manual.

On slave server where you see error:

Copy the output "show slave status\G".

Also check content of /var/lib/mysql/master.info . It will show what mysql user and password is used for connection to Master server.

Then:

mysql

stop slave;

reset slave all;

CHANGE MASTER TO MASTER_HOST='111.111.111.111', MASTER_USER='mor', MASTER_PASSWORD='yourpassword', MASTER_LOG_FILE='mysql-bin.000472', 
MASTER_LOG_POS=949325236;

start slave;

IP should be changed to Master server IP, MASTER_USER and MASTER_PASSWORD suppose to be same as it was on master.info.

MASTER_LOG_FILE should be taken from "show slave status\G" output "Relay_Master_Log_File" line.

MASTER_LOG_POS should be taken from "show slave status\G" output "Exec_Master_Log_Pos" line.

If all when fine, "show slave status\G" should show no errors and "Seconds_Behind_Master" line should indicate that data is flowing from Main server.