TWS for z/OS - CURRENT PLAN VSAM LSR BUFFERING PERFORMANCE OPTIMIZATION
KatB 0600023DBB Visits (3083)
this entry describes a performance enhancement involving the current plan VSAM dataset LSR buffering to be used in case of big workloads. Apar PM12394 that implements the enhancement, is available all TWS for z/OS releases (8.3.0 and later).
The use of parameters CPBPLIM and CPDTLIM in controller OPCOPTS can cause performance issues when storage fragmentation occurs due to big plans execution.
CPBPLIM allows to choose which percentage of the available storage can be used to allocate the buffers, CPDTLIM allows to choose the percentage of the current plan to be used for buffers. The result is that the buffer pool, allocated by means of this options, is strictly linked and dependent on the current plan size. Any time the current plan is closed (i.e. at any backup and at each new current plan generation) the buffer pool is deallocated and then allocated again according to these parameters. The allocation is performed by means of a conditional GETMAIN that in case of big amounts of processed data, when storage fragmentation occurs, it results in allocating a smaller and smaller storage amount. The consequence is that LSR buffering gets less effetive causing performance issues in current plan handling.
Apar PM12394 implemented a performance enhancement, allowing the specification of CPBPLIM as "Permanent Storage" by simply adding the keyword PS to the parameter value. Here is an example of the Permanent Storage spec
For an effective use of Permanent Storage specification in parameter CPBPLIM, a tuning activity is suggested to decide the most suitable percentage of the available storage can be reserved for the CP buffering. Messages in the controller EQQMLOG explaining buffer pool creation and connection give any detail about the buffers (number and size) allocated and used, to facilitate the tuning and help TWS for z/OS administrator choose the best value to be set in CPBPLIM specification.