Concepts of Multi-Master Replication

In a multi-master configuration, data is updated on multiple masters. Each master maintains a change log, and the changes made on each master are replicated to the other servers. Each master plays the role of supplier and consumer.

Multi-master replication can cause synchronization conflicts. Conflicts are usually resolved automatically by using the timestamp associated with each change, where the most recent change takes precedence. Some rare conflicts must be resolved manually. For more information, see Solving Common Replication Conflicts in Sun Java System Directory Server Enterprise Edition 6.3 Administration Guide.

Each supplier in a multi-master environment must have a replication agreement. The following figure shows two master servers and their replication agreements.

Figure 4–1 Multi-Master Replication Configuration (Two Masters)

In the preceding figure, Master A and Master B have a master replica of the same data. Each master has a replication agreement that specifies the replication flow. Master A acts as a master in the scope of Replication Agreement 1, and as a consumer in the scope of Replication Agreement 2.

Multi-master replication can be used for the following tasks:

• To replicate updates by using the replica ID.

  Updates by using the replica ID make it possible for a consumer to be updated by multiple suppliers at the same time, provided that the updates originate from different replica IDs.

• To enable or disable a replication agreement.

  Replication agreements can be configured but left disabled, then enabled rapidly when required. This feature provides flexibility in replication configuration. This can be done whether you use multiple masters or not.