I read your answer about CICS overhead. I have received the same question in regard to combining regions. So, the...
file opens etc. will still be going on, just in another region. How can I tell how many MIPS and how much memory is consumed by just being a region? Ah! The first rejoinder - I hope it's the 1st of many.
This all comes down to how accurate you want the 'overhead' figure to be, and what is classed as 'overhead' in the first place.
The most commonly used definition is 'CPU consumed by CICS that is not associated with an user Transaction'. Under CICS TS 2.2, things run on other TCBs than the QR, so it is not sufficient just to work at the TCB level if you want an accurate figure.
In order to do a decent job, and get a suitably well-intentioned figure - you will need to turn on CICS' Monitoring Facility. This produces CMF records which are then analysed offline. How long during a region and for how many days you use CMF depends upon how valid you want the results to be. However, it costs around 10% extra CPU to collect the data, and each transaction-entry takes about 2k of disk space (so ensure that the stats files are big enough!)
Then, a crude idea of the CPU Overhead is to look at the Dispatcher CPU and subtract all the CPU associated with user transactions....and that is your CPU overhead (divide by the dispatch figure to get a percentage). The Ops & Utilities Guide shows how to process the CMF records
In reality, you will probably need some sort of tool to assist with the anaylsis. There are loads of vendor-supplied utilities around.
Hursley ships the 'CICS Performance Analyser' tool (documentation on the CICS Web Site under 'CICS Tools') which does this sort of analysis, includes info on DB2 activity initiated by CICS and can track things across various regions. Have a look at the doc and see what sort of things can be done with the tool to see if the type of info generated suits: It probably will!
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