Re:Multitasking - is it worth it?

Discussion created by ca.portal.admin on Oct 2, 2008
I have a system which is purely Batch and CICS. There is no IDMS DC or ADS.

Would multitasking bring me any advantage or would it just be an overhead?

R16 SP6 . Z/OS 1.9. 4 processor large IBM thing - I lose track of the model=

My system is well buffered and uses dataspaces extensively CPU availability=
is my issue. There is no paging and I/O is not a problem.

Thanks for any tips.


Chris Trayler, IXD
Bank Julius Baer & Co. Ltd.
P. O. Box, CH-8010 Z=FCrich, Switzerland
Telephone +41 (0)58 887 4332, Fax +41 (0)58 887 4969 <ht=

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Re: Multitasking - is it worth it?
"Yes multitasking in my environment and a former shop is well worth it. IDMS only has one TCB, so if a CPU burner is running, IDMS has other work it can do if we have multitasking turned on. True, we are not in this mode 95% of the time, but why stack work load if we have CPU cycles available. I was at a former shop (12.0) where we ran with multitasking and Tech Support wanted us to turn it off for we were maxed out on CPU and they were looking for relief. We turned it off for the next days cycle of the CV, by noon we were asked to restart the CV to place multitasking back on. For CICS and IDMS were running much worse, and response time was in the tank. Last time at that shop multitasking was ever questioned on its benefits to the system, and even without a lot of extra CPU IDMS and CICS ran better with multitasking. To me this make sense, for stacking long dispatch chains is ""threshing"" with ne real performance improvement. All tuning classed both in CICS and IDMS talk about a few bad task can impact the whole environment.

A few years ago, my current shop was having similar issues. I kept saying as you are, that I saw no real issues with IDMS, I saw active task bump up on occasions, but IDMS was handing the workload. For years, I wanted to implement Multitasking, during this performance stress, I was allowed to implement Multitasking on my Production CV's, and using CICSBATCH we set Stall time to 15 seconds also set ADS2 (does not apply to you, stall time to 25 seconds). Note: Stall or external wait defaults to 600 seconds, and for batch this is a good thing, tape mounts, etc, but for online it is a real issue).

Along with making the above changes, SYSDUMPS were sent to IBM and CA, (CA was on site and could not find any issues, as well as IBM). What was actually found by IBM looking at the dumps, they found that IDMS had the ECB posted but CICS was not picking them up. With workload manager more CPU was given to CICS. Our Tech in CICS apologized to me, for the years he was saying he was waiting for ECB's from IDMS and I had a problem (he was unaware they were actually posted and CICS itself was waiting for them). He said he was amazed how much IDMS could process.

With adjusting the STALL for online (not batch) and doing it in a gradual reduction, we found that we were having stalls on our system (600 seconds) that was impacting performance but we were not seeing the stalls as an abend for these tasks were completing before the old ""Stall 600 seconds"" interval was being triggered (this was not good, for the needs of the many must out-way the need of the few task causing issues, you can only imagine how long dispatching chains got during these period of times), some pains did occur to fix the bad programs, but it has been well worth it.

With these changes we have been running great. We just ran through our last Spring and Fall peak processing with no issues within IDMS, even though volume was higher (in past years with had many issues and problems).

Note: I still want to reduce the stall times, much lower for online, but management is saying if ""it's not broke"" don't fix it. I most likely would not have been give authority to do the above changes but we were having serious issues we were having, an management allowed these changes to be made. We as DBA's know that we want DEADLOCKS to be resolve quickly, but DBKEY waits that do not result in deadlocks, is a very big issue that impacts dispatching chains in CICS as well as IDMS.

Note the multitasking reduced IDMS task chains, and setting Stall times lower for online, allowed the ""Good"" task to run, and reduced bottlenecks and long dispatching chains in CICS and IDMS. So by abending ""STALLS waiting for DBKEYS really helped us, for we were not spinning though worthless work load.