Does VSAM I/O impact Performance



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Does VSAM I/O impact Performance

Postby shivareddy_cet » Tue Apr 10, 2012 2:48 am

For our requirement - we want to use either ONE of the 2 different CICS modules that perform M/F Top level Security check. say CALL0001 and CALL0002 are the 2 modules called from Driver module(Say DRIV0000) that is designed to do Security Validation. CALL0002 has been developed to improve the performance upto 30 %.However, since all application use the driver module big time - with an avg. transactional count of 10,000,000 per week, replacing new module with the OLD one needs a control switch to have a better control. The switches are controlled thru CICS online screen that uses CICS VSAM file.

Question - Instead of simply replacing the new module CALL0002, having a switch with each transaction doing a VSAM look up ? Does VSAM file look up within driver program DRIV0000 to selectively call CALL0001 or CALL0002 severly impact performance ?
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Re: Does VSAM I/O impact Performance

 

Re: Does VSAM I/O impact Performance

Postby Robert Sample » Tue Apr 10, 2012 3:58 am

Does VSAM file look up within driver program DRIV0000 to selectively call CALL0001 or CALL0002 severly impact performance ?
This is not the kind of question that can be answered easily. There are many, many, many factors that impact VSAM performance and hence could impact the answer: things like how scattered are the records you're reading through the file? is the file in an LSR pool? does the LSR pool have adequate data and index buffers to support your reads? how many reads will you be doing for each of those 10 million transactions? are there other high-usage files in the same LSR pool? does the CICS region have adequate memory for buffers? are there enough threads assigned? etc etc etc
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Re: Does VSAM I/O impact Performance

Postby mongan » Tue Apr 10, 2012 12:15 pm

And how many records are you talking about, how big are the records? You might want to make it a resident table or consider other options - like read the records into storage.
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Re: Does VSAM I/O impact Performance

Postby shivareddy_cet » Tue Apr 10, 2012 6:47 pm

Thanks for your reply.
The VSAM file has all the necessary prerequisites like availability of adequate buffer pool, CICS region has adequate memory for buffers, Not sure about the threads assigned. The table(VSAM File) being read to use it as a switch has very few entries and it is keyed. So direct hit on the record intended.
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Re: Does VSAM I/O impact Performance

Postby Robert Sample » Tue Apr 10, 2012 7:03 pm

Have your CICS support group monitor the file for string (thread) waits -- which, hopefully, they are already doing. Basically, if the LSR pool supports 3 strings and you're getting waits, then 3 simultaneous access are not enough.
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Re: Does VSAM I/O impact Performance

Postby shivareddy_cet » Tue Apr 10, 2012 7:09 pm

Okay. That helps. Thank you very much for a quick response.
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