We are using cn=config and are modifying the index with ldapmodify, so over the LDAP protocoll. But - what can cause an index getting empty? Maybe a restart of the slapd? Or not optimal settings for the hdb database parameters?
Well, the indexing is a background operation, so yes, if you restarted slapd after adding the index, it could interrupt that task, and I don't believe it would resume. The point of cn=config is to not restart slapd. ;)
Also, you noted you are using RHEL6.4. I assume you are not running their broken packages but something current that is sanely built? ;)
--Quanah -- Quanah Gibson-Mount Lead Engineer Zimbra Software, LLC -------------------- Zimbra :: the leader in open source messaging and collaboration