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.
For this procedure we recommend using the tool SQLYog which allows easy execution of commands and allows easy copying between two databases without having to export the database.
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
You can refer to this article for help on performing the backup. Once you have the backup files - copy them to the backup server and then restore the backup there.
Running A Backup Before Updating Your Flow Data Server
You can also do this easily using a took called SQLYog
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.
This method requires having pre-setup the connection on the primary master server to both itself and the backup server you wish to copy to.
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.
