About Two-Database Replication Environments

A two-database replication environment is one in which only two databases share the replicated database objects. The changes made to replicated database objects at one database are captured and sent directly to the other database, where they are applied. In a two-database replication environment, only one database might allow changes to the database objects, or both databases might allow changes to them.

If only one database allows changes to the replicated database objects, then the other database contains read-only replicas of these database objects. This is a one-way replication environment and typically has the following basic components:

• The first database has a capture process or synchronous capture to capture changes to the replicated database objects.

• The first database has a propagation that sends the captured changes to the other database.

• The second database has an apply process to apply changes from the first database.

• For the best performance, each capture process and apply process has its own queue.

Figure: One-Way Replication in a Two-Database Replication Environment shows a two-database replication environment configured for one-way replication.

In a two-database replication environment, both databases can allow changes to the replicated database objects. In this case, both databases capture changes to these database objects and send the changes to the other database, where they are applied. This is a bi-directional replication environment and typically has the following basic components:

• Each database has a capture process or synchronous capture to capture changes to the replicated database objects.

• Each database has a propagation that sends the captured changes to the other database.

• Each database has an apply process to apply changes from the other database.

• For the best performance, each capture process and apply process has its own queue.

Figure: Bi-Directional Replication in a Two-Database Replication Environment show a two-database replication environment configured for bi-directional replication.

Typically, in a bi-directional replication environment, you should configure conflict resolution to keep the replicated database objects synchronized. You can configure a two-database replication environment using Setup Streams Replication Wizard in Oracle Enterprise Manager or the configuration procedures in the DBMS_STREAMS_ADM package.