Directory Server Change Processing

When a modification occurs on a directory server, replication code on the directory server performs the following tasks:

• Assigns a change number

• Generates historical information

• Forwards the change to a replication server

• Updates the server state

Historical information is stored in the entry and must therefore be included in the operation before the server writes to the back end. The server uses the change number when generating historical information. The change number is therefore generated before the historical information. Both the change number and the historical information are performed as part of the pre-operation phase.

The operation is sent to the replication server before an acknowledgment for the update is sent to the client application that requested the operation. This ensures that a synchronous, assured replication mode can be implemented. For more information, see Assured Replication. The acknowledgment is therefore sent as part of the post-operation phase.

Changes are sent in the order defined by their change numbers. The correct order enables replication servers to make sure that all the changes are forwarded to other directory servers.

Because a directory server is multi-threaded, post-operation plug-ins can be called in a different order to pre-operation plug-ins, for the same operation. The replication code maintains a list of pending changes. This list includes changes that have started, and for which change numbers have already been generated, but that have not yet been sent to the replication server. Changes are added to the list of pending changes in the pre-operation phase. Changes are removed from the list when they are sent to the replication server. If a specific operation reaches the post-operation phase ahead of its change number-defined position, that operation waits until previous operations are sent before being sent to the replication server.

The server state is updated when the operation is sent to the replication server. For more information, see Replication Server State.