About Hub-And-Spoke Replication Environments

A hub-and-spoke replication environment is one in which a central database, or hub, communicates with secondary databases, or spokes. The spokes do not communicate directly with each other. In a hub-and-spoke replication environment, the spokes might or might not allow changes to the replicated database objects.

If the spokes do not allow changes, then they contain read-only replicas of the database objects at the hub. This type of hub-and-spoke replication environment typically has the following basic components:

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

• The hub has propagations that send the captured changes to each of the spokes.

• Each spoke has an apply process to apply changes from the hub.

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

Figure: Hub-and-Spoke Replication Environment with Read-Only Spokes shows a hub-and-spoke replication environment with read-only spokes.

If the spokes allow changes to the database objects, then typically the changes are captured and sent back to the hub, and the hub replicates the changes with the other spokes. This type of hub-and-spoke replication environment typically has the following basic components:

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

• The hub has propagations that send the captured changes to each of the spokes.

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

• Each spoke has a propagation that sends changes made at the spoke back to the hub.

• Each spoke has an apply process to apply changes from the hub and from the other spokes.

• The hub has a separate apply process to apply changes from each spoke. A different apply process must apply changes from each spoke.

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

Figure: Hub-and-Spoke Replication Environment with Read/Write Spokes shows a hub-and-spoke replication environment with read/write spokes.

Typically, in a hub-and-spoke replication environment that allows changes at spoke databases, you should configure conflict resolution to keep the replicated database objects synchronized. Some hub-and-spoke replication environments allow changes to the replicated database objects at some spokes but not at others.

You can configure a hub-and-spoke replication environment using the Setup Streams Replication Wizard in Oracle Enterprise Manager or the configuration procedures in the DBMS_STREAMS_ADM package.

See "When to Replicate Data with Oracle Streams" for information about when hub-and-spoke replication is useful.