AFAIK the HDB backend that was once the default for OpenLDAP has been replaced with the plain vanilla BerkeleyDB... so it seems that the replication scheme of the latter can be used. Is that right / does anyone see problems with that / ...?
BerkeleyDB6 and later does not have a license that is compatible with OpenLDAP. All support for it as a backend will be removed in the future. I wouldn't base anything on BDB's replication methods.
For multimaster, I'd advise using delta-syncrepl replication. I've had numerous clients with multimillion entry DBs where MMR works just fine. For there to really be an issue would require simultaneous updates to the same attribute on the same entry, which could happen theoretically but in practice is not something I've seen occur. And if you're particularly concerned about such things, then the correct route to go would be to set up a load balancer in front of the masters so only one specific master gets write traffic during a given interval, which is referred to as mirror mode in the admin guide.
Hope that helps. --Quanah -- Quanah Gibson-Mount Product Architect Symas Corporation Packaged, certified, and supported LDAP solutions powered by OpenLDAP: <http://www.symas.com>