Hello,
I migrated my OpenLDAP data from bdb to mdb in a Multi-Master Replication architecture that is working for years now.
Unfortunately using only 2.4.31-2+deb7u2 from Debian 7.

In the 2nd server (yyyyyy in the configuration below), I noticed new log lines for each LDAP entry.
nonpresent_callback: rid=002 present UUID 345d766c-b2d5-1030-9b6b-85786c41386a, dn uid=tve0320,ou=people,dc=univ-tlse2,dc=fr
It occurs if the server yyyyyy is down, a modification is done on the server xxxxx and yyyy is started.
I saw it's related to the "PRESENT" step on replication.
I haven't the sync logs for long so I cannot say if it happened with the previous backend.

So, is this a warning about a data problem or does it only mean "I'm looking for the existence on rid=002 and that's fine, here are the UUID and dn" ?

Here is part of my conf, also replicated :
/etc/ldap/slapd.d/cn=config.ldif:olcServerID: 1 ldap://xxxxxxx/
/etc/ldap/slapd.d/cn=config.ldif:olcServerID: 2 ldap://yyyyyyy/

olcSyncrepl: {0}rid=002 provider=ldap://xxxxxxx/ binddn="--------" bindmethod=simple credentials=----
 searchbase="dc=univ-tlse2,dc=fr" type=refreshAndPersist retry="5 5 300 +" attrs="*,+" tls_reqcert=never
olcSyncrepl: {1}rid=003 provider=ldap://yyyyyyy/ binddn="--------" bindmethod=simple credentials=----
 searchbase="dc=univ-tlse2,dc=fr" type=refreshAndPersist retry="5 5 300 +" attrs="*,+" tls_reqcert=never

olcMirrorMode: TRUE

olcDbCacheSize: 10000
olcDbCheckpoint: 512 5
olcDbNoSync: TRUE
olcDbMaxSize: 3221225472

olcIndex: entryUUID,entryCSN,contextCSN eq

Thanks for your advices,
Florent Lartet
University of Toulouse Jean Jaurès