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DFSVSAMP

Every IMS job should have a //DFSVSAMP card. Usually this will point at a member of a PDS that stores IMS buffer pool definitions. IMS first looks at the IMS buffer pools before it does I/O. If you provide enough buffer pools, IMS should do less I/O.

Hints

If a job does a great amount of updating, the buffers should be increased and page fixed. OSAM buffers are page-fixed by subpool as follows:

IOBF=(4K,40,Y,Y)

The two Ys on the IOBF command tell IMS to page fix these buffers, a good choice in a non-storage constrained environment for a batch updater.

For VSAM, buffer pools are not page fixed by subpools. Instead, page fixing is done in the OPTIONS control card in the following way:

4096,40 OPTIONS VSAMFIX=(BR.IOB)

Reference Sources

Gandolfo, P. "IMS Debugging, Performance, and Tuning." DATABASE PROGRAMMING & DESIGN, July 1989.