Re:Limits and Statistics

Discussion created by ca.portal.admin on Jun 19, 2008
Hello Listers, At our site we are looking at ways to reduce the CPU usage of the IDMS CV's. I remember seeing some statistics stating that having statistics collection on added approximately 8 - 10% CPU overhead. Also, turning on LIMITS increased the CPU usage roughly 7%. I have found some internal documentation that states this, but I cannot find any 'official' CA documentation that does. Does anyone else on the list remember seeing similar statements about the CPU overhead of LIMITS & STATS? The reason for the question is that I ran some tests on one of our CV's. Using a testing tool we ran almost 70,000 tasks thru the CV with LIMITS enabled and STATISTICS collection on. We then shutdown the CV and recorded the # of tasks, CPU used, etc. Next we changed the SYSGEN to set LIMITS disabled and STATISTICS off. We also changed the #PMOPT macro to stop writing SMF data. We reran the exact same set of scripts. The results showed only a 2% reduction in CPU usage. Does this figure surprise anyone else? Any ideas what I could be missing to only see this small reduction? Thanks for any help you can give. Dan Hall GE Capital Solutions Database Administrator T 513.217.5060 E Middletown, OH 45042 General Electric Capital Corporation
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Re: Limits and Statistics
"A few random thoughts and/or recollections.

The killer in stats is asking it to differentiate between SYSTEM and USER
CPU, or at least it used to be. It required a operating system call every
time the system/user boundary was crossed, and then the info gathered had
little practical value.

If someone out there has STROBE (or similar product), and are willing to run
a series of staged tests, they may be able to actually see where in CV the
extra cycles come from.

I can't imagine limits adding all that much, a few hundred instructions in
the middle of each CV call of tens of thousands of instructions (maybe a
percent or fraction thereof). That said, if you have an external monitor
such as PreAlert, it can do something similar and only has to look at CV
every so often, rather than every call. Note: in order to play the game
this way, IDMS has to be collecting stats.

Note: I have no monetary interest in either product or vendor, but have used

Don Casey
Run Right, LLC