OpenEdge Replication typically occurs with activity between the Replication server on the source database on the primary machine and the Replication agent on the target database on the secondary machine. If the Replication agent loses communication contact with the Replication server (for example, if the primary machine were to shut down unexpectedly), you can move all database update activity from the source database to the target database through the transition process.
Once the primary machine becomes available again, you see another target available, and can fail over the database update activity to the primary database or machine. To minimize downtime to your application, you can schedule the failback process to run when you want.
The overall steps in the OpenEdge Replication process are as follows:
1. During primary (normal) replication, the primary database has the role of source database and the secondary database has the role of target database. The Replication server exists on the source database and the Replication agent exists on the target database.
2. If there is a failure on the machine hosting the primary database, the Replication agent on the target database loses communication contact with the source database's Replication server.
3. The Replication agent on the target database enters pretransition.
4. Transition then occurs (automatically or manually, depending on how you set the transition properties), making the secondary database (formerly a target) a source database.
5. All database activity is moved to the secondary database, which is now functioning as a source database. The secondary database now becomes the production database.
6. Once the machine hosting the primary database is fixed, the replication process continues as follows:
a. The primary database must be restored from a backup of the secondary database and then enabled as a target database before secondary replication can begin.
b. The new target can receive replicated data from the current source.
c. At a convenient time, you can perform the failback process to return the databases to the roles originally established, with the primary database as the source and the secondary database as the target. You can do this by transitioning the secondary database using the failover command.
