The BigMemory WAN Replication Service offers two replication modes: Unidirectional and Bidirectional. Unidirectional mode replicates data in one direction only, from Master to Replica, and is used for active-passive deployments such as disaster recovery. Bidirectional mode replicates data in two directions, from Master to Replica and from Replica to Master, and is used for active-active deployments where updates from more than one region should be incorporated into the Master cache's authoritative data set.

For comparison of unidirectional and bidirectional modes, see the section Replication Modes.

With Bidirectional mode, Replica caches notify their Master cache of any modification they receive, and the Master cache either applies or rejects the modification based upon its tracking of each cache element.

Although a conflict resolution algorithm is employed within the product, it is still highly likely that data inconsistency between regions can occur if the same cache entries are receiving rapid concurrent modifications. If data consistency is important to your use case, we strongly recommend against using this feature.

In the figure below, Master caches in Region 1 are distributed between the application servers and the Terracotta servers of the TSA. Cache modifications in either region are communicated through the Orchestrators, and the Master caches determine which modifications become part of the authoritative data set.