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What is VSAM reorganisation ?

 
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mijanurit
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PostPosted: Tue Sep 02, 2008 8:09 pm    Post subject: What is VSAM reorganisation ?
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What is VSAM reorganisation and how frequently we need to do it?

Rahman
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Robert Sample

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PostPosted: Tue Sep 02, 2008 8:29 pm    Post subject:
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You reorganize a VSAM file by unloading the data from it, deleting, defining, and reloading the data into it. This is done to remove CI/CA splits, which slow down data access. As to how frequently you need to do it, that depends entirely upon the circumstances. A file that has no CI/CA splits isn't going to benefit from a reorganization. A file that splits hundreds or thousands of times a day probably needs a reorganization every night. You have to balance the resources required to reorganize the file versus the additional access required by a file with splits.
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Garry Carroll

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PostPosted: Wed Sep 03, 2008 1:46 am    Post subject:
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Where a file is getting a high level of CI/CA splits, consideration should be given to adjusting the FREESPACE values. Be aware that the CA freespace should likely be a lower percentage than CI freespace. This is because the freespace is cumulative - i.e. given 100 cyls, CA FSPC of 20 leave 80% available for CIs (80Cyl). If CI FSPC is also 20, then only 80% of that remaining space is available (64Cyl) for initial load of data. Overall, that means 36% of the data area is unused after re-organisation.

CA split only occurs where a CI split requires use of another CA, so these are less frequent than CI splits.

Garry.
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