Replication notes

[Howard Chu <hyc@symas.com>]

Slurpd and syncrepl really took opposite approaches to replication. While 
syncrepl allows consumers to be configured without any special configuration 
of the provider, slurpd allowed slaves to be configured without any special 
knowledge. This feature allowed slurpd to be used to replicate to pretty much 
anything that understood some flavor of LDAP.

With syncrepl, the consumer must minimally understand entryCSNs, entryUUIDs, 
and a contextCSN. This requirement would appear to limit our reach. But with 
delta-syncrepl, we actually need nothing more than a contextCSN to keep track 
of where we are in the changelog. And when using delta-syncrepl thru an LDAP 
proxy, there's actually no requirement that we store the contextCSN on the 
remote server.

We could simply store the contextCSN as a DB-specific attribute of the proxy 
DB's entry under cn=config. Whether we do this by explicitly modifying the 
syncrepl code, or by using an overlay to accomplish the sleight-of-hand 
doesn't seem to matter much. (Though there may be more uses for a 
customizing/mapping overlay here; e.g. translating LDAPv3 schema to MS AD.)

Just wanted to mention this here before I forgot it again.
--
  -- Howard Chu
  CTO, Symas Corp.           http://www.symas.com
  Director, Highland Sun     http://highlandsun.com/hyc/
  Chief Architect, OpenLDAP  http://www.openldap.org/project/