Monitors the number of items in the AD Replication queue. If this number becomes too large, there may be a delay in AD replication.
Possible causes include the following:
The domain controller is undergoing initial replication post promotion.
The domain itself has undergone a lot of changes and created a large number of objects to be replicated.
The replication topology is not optimal and needs to be reconfigured.
An application is placing a heavy load on the domain controller. This is usually caused by inefficient, CPU-intensive operations such as non-indexed queries.
The domain controller is critically low on memory.
The domain controller is under a denial-of-service attack.
View the overall system performance of the machine to determine if it needs additional resources.
Add additional domain controllers to help load-balance the load.
Ensure that there are a sufficient number of DCs in the active AD sites.
Run 'repadmin /showrepl' and 'repadmin /replsum' to ensure there are no replication failures with other domain controllers.
Troubleshooting Active Directory Replication Problems
How Active Directory Replication Topology Works