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regarding CA and CI in VSAM

 
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RM0C13920

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PostPosted: Thu Jun 10, 2010 9:08 pm    Post subject: regarding CA and CI in VSAM
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How the performance affected when we will have more number of CI and CA in VSAM file?
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dbzTHEdinosauer

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PostPosted: Thu Jun 10, 2010 9:20 pm    Post subject:
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IBM Redbook VSAM Demystified
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Bill O'Boyle

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PostPosted: Thu Jun 10, 2010 10:24 pm    Post subject: Reply to: regarding CA and CI in VSAM
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After reviewing VSAM Demystified, you should understand how an optimized CISZ (which blossoms into a CA) and its relationship with the RECSZ and FSPC, is something that must be taken into serious consideration. Bad VSAM components/definitions can have adverse effects for both CICS and Batch.

Many times, I'll find programmers who just copy an existing VSAM DELETE/DEFINE and then modify the RECSZ, CISZ, FSPC, etc.

This is all well and good, providing that a review of these components will fit well with this new (or existing) DEFINE.

But, if it's just a COPY and little review is done, you could be perpetuating bad DEFINE's and cause an uninvited (and perhaps, continued) ripple effect across the system.

Bill
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Robert Sample

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PostPosted: Thu Jun 10, 2010 11:32 pm    Post subject:
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To add to dick and bill's comment, it is not at all clear what you mean. Are you referring to an increase in the CI size? an increase in the number of CI's allocated? an increase in the number of CI's used? something else -- if so, what?

What do you mean by "performance" -- CPU time used, I/O counts, CI splits, CA splits, elapsed time of the job, or something else entirely? Performance impacts can be very different for batch and online applications using VSAM files so that would also be a factor in any answer we could give you. Not to mention whether or not the file is LSR or NSR, the access pattern (sequential, skip sequential, or random), buffer allocation, and so forth. There are many factors that can affect 'performance" so the first step is usually to determine what performance means in a given context.
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