Control interval size for VSAM.

Virtual Storage Access method - ESDS, KSDS, RRDS & LDS. Basic direct access method, Basic sequential -, Queued sequential -, Basic partitioned -, Indexed sequential -, Object - access method.
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Tarun Bhardwaj
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Control interval size for VSAM.

Post by Tarun Bhardwaj »

Hi,

What is the best way to choose the control interval size for the data and index in VSAM? And should we even bother about it while defining a VSAM?

As of now I look at the existing VSAM, used for similar work and define the new VSAM file.
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Robert Sample
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Re: Control interval size for VSAM.

Post by Robert Sample »

The access pattern should help determine CI sizes. For a KSDS being read completely randomly, use a shorter data CI size; for a completely sequential access, use a longer data CI size. How long or how short? That depends on a lot of factors -- average record length, free space needed, etc. For the index CI size, the one thing you want to make sure of is that the CI size is big enough to allow access to all the data CI -- if not, you're wasting space.
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