Some LDAP client applications perform subtree searches with search base set to the rootDSE (empty DN).
Oracle Unified Directory (OUD) nicely routes the search to every top level suffix automatically.
When the replication is enabled, OUD automatically publicizes all changes that have occurred in a
directory server database in the cn=changelog suffix. This is particularly useful for synchronizing the LDAP directory with
other subsystems. The cn=changelog suffix may contains millions of changes depending on the modification rate on the replication topology and the change retention policy (purge delay).
Subtree searches with search base set to the rootDSE are routed to the cn=changelog suffix as well as long as the replication is enabled. In general, this is not a problem in testing/stagging area, because the changelog is almost empty. However, in production, this may have big impact on performances as this suffix may contain many entries. Furthermore, custom indexes corresponding to client access pattern do not exist on that suffix, so they can't be used to speed up entry processing.
In order to address that problem, you can disable the so-called external changelog, without disabling the underlying replication changelog used by the replication. To do so, run the following command on the OUD servers for each user suffixes:
dsconfig -h <hostname> -p <admin port> -D "cn=directory manager" -w <admin password> -n \
--provider-name "Multimaster Synchronization" --domain-name <your suffix> \
Note: some provisoning apps may require the external changelog to synchronize with external systems. If so, keep the external changelog enabled on a couple of OUD servers and reserve them for these apps.