What To Do When DMan Replication Status is Red

The master server writes each incoming command to a binlog file. The slave server processes each line of the file in queue. DMan monitors this process for several factors that would indicate that replication is not working or falling behind.

Slave is behind master N seconds

When the slave server starts to fall behind, the DMan status will report the difference in time. This could be due to network latency or I/O problems on the slave or master. Monitor the delta time between the slave and master and ensure it is getting smaller and not larger. If the time that the slave is behind continues to grow you will need to evaluate the I/O problem.

Error - Unable to process N

Sometimes the slave comes across a command in the master binlog file that it cannot process. When this happens the slave stops processing the queue and if left for a while the slave can get very behind in the queue. Evaluate the line that was unable to process on the slave, take corrective steps, and run the Resynchronize Your Replication Servers procedure below.

Resynchronize Your Replication Servers

If your replication has been blocked by a command line that cannot process on the slave server, it may have gotten out of synch to an extent that the easiest way is to resynch with a data duplication.

Start by opening SQLYog and connecting to both the master and backup server. Be sure to use an account when connecting to the slave server that has the create privilege as later in the process you will be copying the data over through this connection.

STEP 1 - stop the slave process. On the slave server command window execute:

STOP SLAVE;
RESET SLAVE;

STEP 2 - copy the database from the master to the slave

In SQLYog on the master server tab, right click the BL database and select COPY DATABASE TO DIFFERENT HOST. Choose the slave version of the database as the target.

STEP 3 - reset the master binlog and output pointer. On the master server execute the following command in the command window:

RESET MASTER;

STEP 4 - restart the slave replication process. On the slave server execute the following command in the command window:

START SLAVE;

Replication will now be back in synch. Check DMan status periodically over the next 24 hours to verify smooth synchronization.