I've just committed a patch for the session history support
which has been sitting in my commit queue for some time.
The session history patch is to support finite amount of session
history store for a set of replicas of a single sync content,
in order to reduce sync traffic among them.
If a sync request belongs to an existing session and
its cookie represents that the replica content can be synced
by using the history store, then [add+delete] mode of the
LDAP Content Sync protocol is used. Otherwise, [add+present]
is used unless there is no change in the context CSN value.
Currently the session history is memory based, hence non-persistent.
Todo items are the support of the persistent history and the
access control to the session history.