Retro Change Log and Multi-Master Replication

When a retro change log is enabled with replication, the retro change log receives updates from all master replicas in the topology. The updates from each master replica are combined in the retro change log. The following figure illustrates the retro change log on two servers in a multi-master topology.

Figure 4–7 Retro Change Log and Multi-Master Replication

The retro change log uses the following attributes during replication:

changeNumber (cN)

Identifies the order in which an update is logged to the retro change log

replicationCSN (CSN)

Identifies the time when an update is made to a given replica

replicaIdentifier (RI)

Identifies the replica that is updating the retro change log

The diagram shows that the retro change logs, RCL1 and RCL2, contain the same list of updates, but that the updates do not have the same order. However, for a given replicaIdentifier, updates are logged in the same order on each retro change log. The order in which updates are logged to the retro change log is given by the changeNumber attribute.