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Maximum size VSAM file allocation in CICS

 
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Arun6578

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Joined: 23 Jul 2007
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Location: CBE

PostPosted: Mon Apr 27, 2009 9:56 pm    Post subject: Maximum size VSAM file allocation in CICS
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Hi,

I have a requirement where i need to allocate a VSAM file in the various CICS regions in share mode. Initially the file will have 46 Million records with lrecl as 150. The data in the file will be increasing daily or updated daily thru some batch process. I am really not sure if it is worth to use a VSAM file ? Will it impact any performance of the transactions?
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Robert Sample

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Joined: 06 Jun 2008
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PostPosted: Mon Apr 27, 2009 10:42 pm    Post subject:
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Transaction performance shouldn't be impacted -- unless you're planning on reading sequentially through the file. The VSAM file will need to be defined as extended format (which is a site-specific option you'll have to get from your site support storage group) since it'll be over 4 GB in size. However, we've got 15-20 GB VSAM files in our CICS regions and consistently get sub-second response times (except when someone tries to pull out several thousand records for an online report). The size of the VSAM file doesn't make a lot of difference in performance of CICS -- it's more the application and how it handles the files that affects performance.
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Arun6578

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PostPosted: Mon Apr 27, 2009 11:46 pm    Post subject: Reply to: Maximum size VSAM file allocation in CICS
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Thanks. Whether 4 GB size is any limitation?[/Search]
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Bill O'Boyle

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PostPosted: Tue Apr 28, 2009 12:07 am    Post subject: Reply to: Maximum size VSAM file allocation in CICS
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IMHO, a data-CISZ of 18432 and an index-CISZ of 2048 should do the trick. Have your CICS Sysprog add the file to a 20K LSR Data-Pool and a 2K Index-Pool. Also, ensure that the Sysprog has allocated enough buffers in the given pools.

If at all possible, place this file in a LSR Pool whose files are used less frequently than this new file. This is known as the "Reverse Robin Hood Theory" (steal from the poor and give to the rich).

Regards,
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Robert Sample

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PostPosted: Tue Apr 28, 2009 12:09 am    Post subject:
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VSAM Demystified Redbook wrote:
1.10 Extended addressability
With extended addressability the 4 GB VSAM architectural limit for data set size
imposed by using the 4-byte field for the relative byte address (RBA) was
eliminated.
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