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How to calculate the actual Usage of CI

 
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THINKSRINIII
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PostPosted: Thu Mar 19, 2009 5:53 pm    Post subject: How to calculate the actual Usage of CI
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Hi Guys,

Could some one help me in calculating the actual usage of Control intervals. We are in process of Tuning some jobs.

Let us say for instance..

A KSDS has fixed length 250 Byte records. Initial load of 100,000 Records.
Each day an estimated insertion of 15%' The file is used online .. and so the Largest CI size is 4096 Bytes..
From this how to get the Number of bytes that will be lost per CI?

Had a look at the post below..

http://www.ibmmainframes.com/about9281.html

Cheers
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expat

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PostPosted: Thu Mar 19, 2009 6:01 pm    Post subject:
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Are the records fixed or variable in length ?
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THINKSRINIII
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PostPosted: Thu Mar 19, 2009 6:16 pm    Post subject:
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Apologies.. Missed that.. Its of Fixed length.. It would be Great to know what will happen when its of Variable length too.. icon_biggrin.gif
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expat

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PostPosted: Thu Mar 19, 2009 6:31 pm    Post subject:
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For each CI, there will be one CIDF of four bytes, and as the records are fixed, only two RDF's each of three bytes. So your CI is 4096 in length, then removing the space taken by the VSAM internals, will leave you 4086 bytes per CI to store your data in.

For example with a 250 Fixed byte record, 4086 / 250 = 16.344 = 16
16 * 250 = 4000
4086 - 4000 = 86 wasted bytes per CI

For variable length records there is no precise method as the number of RDF's will vary, and each RDF is 3 bytes. Also the record lengths will vary and without knowing the length of each individual record in that CI it will be impossible to make an accurate calculation.
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THINKSRINIII
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PostPosted: Thu Mar 19, 2009 6:48 pm    Post subject: Reply to: How to calculate the actual Usage of CI
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Thanks a lot Expat.. Your reply was Crisp..

One more question.. So, if I have to prevent the CI space from going waste..What would be the Best option..

1. Increase the CI size(up to 32K)
2. Any other Way??

Cheers.
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Robert Sample

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PostPosted: Thu Mar 19, 2009 7:22 pm    Post subject:
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86 bytes / 4096 bytes is about 2.1% wasted space. This is not something to waste a lot of time on.

And Expat's calculations are based on a freespace of (0 ?); if you have a freespace value, the calculations are slightly different.
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THINKSRINIII
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PostPosted: Thu Mar 19, 2009 7:24 pm    Post subject:
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Thanks a lot Expat and Rob... icon_biggrin.gif

Cheers..
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CICS Guy

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PostPosted: Thu Mar 19, 2009 7:29 pm    Post subject:
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And, after the first insert, now two CIs with almost 50% free (wasted) space..... icon_wink.gif
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