Fixing "bdb_equality_candidates" errors on your OpenLDAP server

Repost from
http://muzso.hu/2010/04/26/fixing-bdb_equality_candidates-errors-on-your-openldap-server
OR
http://trac.zentyal.org/wiki/Documentation/Community/HowTo/LDAPoptimization

1. Stop the LDAP server:
   sudo stop slapd
2. Open the right OpenLDAP config file with an editor:
   sudo vi /etc/ldap/slapd.d/cn\=config/olcDatabase\=\{1\}hdb.ldif
3. Add new lines (after the one with olcDbIndex: objectClass eq in it) for the missing indexes.
   Eg.:
   olcDbIndex: cn eq
olcDbIndex: gidNumber eq
olcDbIndex: memberUid eq
olcDbIndex: uid eq
olcDbIndex: uidNumber eq
olcDbIndex: uniqueMember eq
4. Run the OpenLDAP indexer for your configuration:
   sudo -u openldap slapindex -F /etc/ldap/slapd.d/
5. Start the LDAP server:
   sudo start slapd

PS: don't forget to back up your OpenLDAP database (in /var/lib/ldap) before you touch it.