VSAM Tuning Tips
- 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 is clearly explained in express edition.
- 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)