How to calculate the actual Usage of CI

THINKSRINIII · New User Joined: 09 Jan 2009 Posts: 88 Location: India

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..

www.ibmmainframes.com/about9281.html

Cheers

expat · Posted: Thu Mar 19, 2009 6:01 pm

Are the records fixed or variable in length ?

THINKSRINIII · New User Joined: 09 Jan 2009 Posts: 88 Location: India

Apologies.. Missed that.. Its of Fixed length.. It would be Great to know what will happen when its of Variable length too..

expat · Posted: Thu Mar 19, 2009 6:31 pm

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.

THINKSRINIII · New User Joined: 09 Jan 2009 Posts: 88 Location: India

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.

Robert Sample · Posted: Thu Mar 19, 2009 7:22 pm

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.

THINKSRINIII · New User Joined: 09 Jan 2009 Posts: 88 Location: India

Thanks a lot Expat and Rob...

Cheers..

CICS Guy · Posted: Thu Mar 19, 2009 7:29 pm

And, after the first insert, now two CIs with almost 50% free (wasted) space.....