Under heavy load, accessing the replication queue can become a bottleneck, thus impacting the general performance.
This issue is fixed by CQ5.3 hotfix package #31039. Please raise a DayCare ticket to obtain this package.
Note : When you install this hotfix, make sure that all replication queues are empty and no users are starting new replications. If any old replication jobs exist from prior to installing this hotfix then they would be made invalid by applying this patch. This is due to the object serialization used by sling eventing jobs.