VSAM tuning: General objectives

Tuning consists of providing a satisfactory level of service from a system at an acceptable cost. A satisfactory service for VSAM is likely to be obtained by providing adequate buffers to minimize physical I/O, and allowing several operations concurrently on the data sets.

The costs of assigning additional buffers and providing for concurrent operations on data sets are the additional virtual and real storage that is required for the buffers and control blocks.

Several factors influence the performance of VSAM data sets, including whether to use local shared resources or nonshared resources. If you compress CICS® data sets to free storage and improve performance, you must do the compression while CICS is not running. To avoid shutting down CICS, use LIBRARY resources to easily take data sets offline for compression without affecting continuous availability. For details, see Using dynamic program LIBRARY resources.

Another factor in tuning is locking. Using entry-sequenced data sets (ESDS) can have a negative effect on the performance when you are adding records using multiple tasks. This is because adding a record requires an exclusive add-to-end lock to perform the write.