Before building OpenLDAP with debugging symbols and no optimization, we noticed some possible locks (with db_stat) on the bdb (4.8.30) back-ends, that we can reproduce with the main Java application that interacts with OpenLDAP. It uses to occur when we create a few users. So, it could possibly be a problem with the way our Java application works with OpenLDAP, even if once OpenLDAP is frozen, other usual LDAP clients such a ApacheDirectoryStudio or ldapsearch can't connect (bind request sent but no response) to OpenLDAP. Also, the same main Java application didn't use to freeze our previous (Sun DS 6) directory.
So, we now first intend to replace bdb and test with hdb or possibly some other database back-end, before testing with debugging symbols and no optimization. I'll let you know the results of of our tests ..