• Always use efficient Data and Index CI sizes.
  • Assuming your record size permits, 4K or 8K works best for the Data CI size of
  • CICS online files. The Index CI should be large enough to hold all of the index entries for a DATA

    VSAM Tuning Tips
  • For large keys that do not compress well, this could be 8K or 16K. Too small an Index CI may result in unnecessary CA splits.
  • The Index CI should be also large enough so that Index Levels is no more than 2 if possible. You can make it too big but 2K is often too small.
  • Always define your VSAM clusters with the SPEED parameter.
  • CI and CA Splits can greatly reduce CICS response time.
  • Code CI and CA Freespace very carefully and monitor regularly.
  • REORG of files does NOT fix splitting problems. It just covers the problem up for a short period of time.
  • Allocate better FREESPACE.
  • Never use SHROPT 4 if at all possible.
  • Do not use ERASE ever.
  • Do not use WRITECHECK ever.
  • Do not use IMBED or REPLICATE, they are no longer supported and they waste DASD space.
  • Optimize VSAM performance for both random and sequential processing by always specifying the appropriate number of NSR or LSR buffers.
  • Remove Catalog Orphans from the Catalog.
  • Make all ESDS files use the SPANNED parameter. (ref: IBM)