The retro changelog receives updates from all master replicas in the topology. The updates from each master replica are combined in the retro changelog. The retro changelog provides a way for applications to track changes so that they can be synchronized. Directory Server enables you to access a coherent version of the retro changelog on any master in a multimaster topology. You can also update your application to manage its state according to change numbers. This makes it possible to fail over between retro changelogs on different servers.
The global retro changelog contains all of the changes. If two changes occur on the same entry in two different locations, the retro changelog provides an ordered change description. If you query the retro changelog from any server, it will contain similar information.
See Replication and the Retro Change Log Plug-In in Sun Java System Directory Server Enterprise Edition 6.1 Reference for background information about the retro changelog.