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MERGECAT WHILE-OPEN Enhanced in IBM Tivoli Advanced Catalog Management for z/OS

By John Crossno posted Wed September 28, 2022 09:59 AM

  
MERGECAT Background Information
Normal MERGECAT WHILE-OPEN performs a lot of high overhead processing, resulting in much longer run times than standard MERGECAT. WHILE-OPEN is required when there are open VSAM datasets on the level. If there are allocated datasets but no open VSAM datasets, then WHILE-OPEN(OPTIMIZE) (OPTIMIZE is now the default for WHILE-OPEN) can be used to do only the basic WHILE-OPEN alias-level activity blocking, but bypass the high-overhead full WHILE-OPEN processing.  One operational difficulty with this is that MERGECAT WHILE-OPEN(OPTIMIZE) SIMULATE might run fast if there are no open VSAM data sets, but by the time the EXECUTE job is run, some VSAM data sets got open and the job will run for a lot longer because it now has to do the full WHILE-OPEN processing.
 
How to implement
MERGECAT WHILE-OPEN(OPTIMIZE-ONLY) can be specified. If it finds open VSAM data sets on the level, instead of continuing on using full WHILE-OPEN processing, it will wait a short time (user specifiable) and try again, for up to 5 minutes (user specifiable.) If it doesn't find a time with no open VSAM before the time limit expires, it will terminate with an appropriate message rather than falling back to doing full WHILE-OPEN processing and perhaps causing operational difficulties due to the unanticipated long run time.
 
For example, someone wanted to move the level containing their ZFSs.  The problem is that they're always open.  If they unmount them, they're closed for an instant but will probably get re-opened right away.  So WHILE-OPEN(OPTIMIZE-ONLY) gives them a chance of getting it to run without the long run-time of WHILE-OPEN.
 
Use Cases
In general, this will benefit any situation where you can only tolerate the level block for as long as normal MERGECAT takes to run, but not for the extended run-time of full WHILE-OPEN, and it's difficult or risky to submit a WHILE-OPEN(OPTIMIZE) EXECUTE based on the run time of a SIMULATE because a VSAM data set could get opened unexpectedly in the interim.
 
Value
This enhancement will benefit any situation where the Users of MERGECAT can only tolerate the level block for as long as normal MERGECAT takes to run, but not for the extended run-time of full WHILE-OPEN, and it's difficult or risky to submit a WHILE-OPEN(OPTIMIZE) EXECUTE based on the run time of a SIMULATE because a VSAM data set could get opened unexpectedly in the interim.

#OMEGAMON
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