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grajeevg
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Joined: 11 Jun 2004
Posts: 5
Topics: 2
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 Posted: Mon Jan 03, 2005 12:39 pm Post subject: Question about CA/CI splits |
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Can anybody clarify my following doubts about VSAM..
1. How do we know that control split is happened in control area?
2. How do we map a particular record in particular control interval?
Rajeev |
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kolusu
Site Admin
Joined: 26 Nov 2002
Posts: 12372
Topics: 75
Location: San Jose
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| Posted: Mon Jan 03, 2005 12:55 pm Post subject: |
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Rajeev,
Please follow the forum rules.
Use meaningful topics (don't use the Forum name for the topic). The title "vsam" does not convey the actual requirement. A better title would be " Question about CA/CI splits" will be more approriate. I am changing the title to reflect the requirement.
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1. How do we know that control split is happened in control area?
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Answer : CI and CA splits occur as a result of data record insertions. If a record is to be inserted and there is not enough free space in the CI, the CI will be split.
Approximately half of the records in the CI are transferred to a free CI and the record to be inserted is placed in the original CI.
If there are no free CIs and a record is to be inserted, a CA split occurs.
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How do we map a particular record in particular control interval?
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Answer : NO. you really cannot the map the record to Control Interval. The relative byte address (RBA) is used to determine the position of a record in a VSAM data set. It is the physical location of a logical record contained in a data set. The RBA is the offset of a logical record from the beginning of the data set.
The first record in the VSAM data set has an RBA of zero; the second record has an RBA equal to the length of the first record, and so on. The RBA of a logical record depends only on the record's position in the sequence of records. The RBA is always expressed as a full word binary integer.
The RBA of a record includes the free space and control information in the CI. RBAs might change when a control interval split occurs or when records are added, deleted, or changed in size. With compressed data sets, the RBAs for compressed records are not predictable. Therefore, access by address is not suggested for normal use.
I suggest that you read this excellent Redbook on VSAM
http://publib-b.boulder.ibm.com/abstracts/sg246105.html?Open
Hope this helps...
Cheers
Kolusu
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Kolusu
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Bill Dennis
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Joined: 03 Dec 2002
Posts: 579
Topics: 1
Location: Iowa, USA
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| Posted: Mon Jan 03, 2005 5:04 pm Post subject: |
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Q. How do you know a split happened?
A. Check the output of LISTCAT or IDCAMS batch to see the number of CI/CA splits that have occurred. |
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grajeevg
Beginner
Joined: 11 Jun 2004
Posts: 5
Topics: 2
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| Posted: Tue Jan 11, 2005 3:39 am Post subject: |
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Thanks Kolusu,
the URL was very much helpful |
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