Release 10.1B: Progress Fathom Replication
User Guide


Overview of database failure recovery

When you enable Fathom Replication, you replicate a database on a primary machine to one or two (at most) secondary databases on a different machine or machines. In the event of a failure of either the primary database or the machine on which it runs, database activity can be failed over to one of the secondary databases. Activity continues on that second database and machine until the primary database or machine is again available.

Typically, a failure is indicated by a loss of communications between the replication server on the primary database and the replication agent on the secondary database. In this situation, the replication agent enters a state known as pretransition, in which the agent waits until either the replication server reconnects or you perform transition. Once you transition the secondary database to a source database, all database update activity is failed over to the secondary database. Once the primary machine is again available, all database update activity can be failed back to it.

In addition to providing the automated failover process, Fathom Replication now provides a process for moving the database activity from the secondary database back to the original primary database. This process is known as failback. Failback is essentially a failover from the secondary to the primary machine.

Once the failback process completes, all database update operations are again performed on the primary database, and the secondary database returns to read-only access.


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