@Raju Botu  please see the following post.

A description of the stored procedure DDL can be found in other forum questions. such as this,  this one. and this one.

Procedure sppr_sys_reservequeueitem_b is an internal Pega procedure. The procedure is a common driver for all standard mode agent processing.

Info about SLA processing can be found here.

SLA agent would run typically for every 30 sec and would search for queue entry. If there are queue entry corresponding to an assignment it would get processed.

Common cause of performance issues in queue table access are
- lack of timely database maintenance (table fragmentation, space reclamation, index statistics)
- Improper parameters passed to stored procedure.
- improper stored procedure version
- improper indexing on a standard or custom queue table

Review the state and content of agent queues to assess whether data access issues are impacting ability of agents to keep up with load and demand. For each queue table check the record count by status. For items that are scheduled, get count of how many records are set with  pyMinimumDateTime less than current time. If many items have state scheduled and pyMinimumDateTime for processing is less than current time, this means that the agent(s) have fallen behind and application owners must be engaged. 

 Please check the following Pega article regarding known performance issues with sppr_sys_reservequeueitem_b.