Because synchronization is implemented by using synchronization messages, you can monitor the status of the synchronization process by checking the status of the currently existing messages.
When a message is active, it is always persistent in some state in the system. The message is deleted from the databases only after it has been successfully processed. A message that is still in either the master database or a replica database is not completely processed. In most cases, an idle, persistent message means that a synchronization error has occurred.
This diagram illustrates store and forward messaging and shows the points in the process where messaging errors can occur.
There are three error prone areas:
▪ Message sent from the replica database to the master database
▪ Message executed in the master database
▪ Reply message sent from the master database to the replica database.
In all the previously mentioned cases, a failure stops the synchronization. A query of the following message information system tables provides the reason for the failure:
