MDSAL Notification pool threads not getting spawned besides the core threads

MDSAL Default Notification pool is currently configured as follows:
Core threads: 4
Max threads : 32
Queue: Unbounded Linkedblockingqueue

During cbench tests, its observed the # of threads working on the queue, dont ever go beyond 4.
It should ideally hit 32, as the notification Q is not getting drained at a faster rate.