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VSAM file rebuilding methods

 
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kranti

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Joined: 10 Oct 2005
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PostPosted: Thu Sep 03, 2009 1:01 pm    Post subject: VSAM file rebuilding methods
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Hi,

we are dealing with one of the biggest VSAM file in our application which occupies 10,000 cylinders, which is due to the reason that the file is being undergone for thousands of writes/rewrites and deletes in a singles day.
which might be the reason for the spaces consumption.

As it has large amount of data, we tried rebuilding the file and the size drastically came down to 2,500 cylinders. But next day after the EOD it came up to 7,500 cylinders.

we thought that the best way to reduce the file is to rebuild every day but it leades to stop our application for so much time which might ending up some financial loss to us.

Could you please help us to suggest any way to release such uneeded space caused by IO operations, with out actually rebulding the file?
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enrico-sorichetti

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PostPosted: Thu Sep 03, 2009 1:07 pm    Post subject: Reply to: VSAM file rebuilding methods
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the growth of the used space depends from the CI and CA splits
which in turn depend on the pattern of insertions
for a poorly chosen key pattern ( a sequential number for example )
You might find that in many cases of CI /CA splits the first CI/CA of the split is never reused
that's what is called crawling splits
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expat

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PostPosted: Thu Sep 03, 2009 1:29 pm    Post subject:
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What is the FREESPACE definition for the file
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kranti

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PostPosted: Thu Sep 03, 2009 1:52 pm    Post subject: Reply to: VSAM file rebuilding methods
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Below are the details of the cluster definition,

ATTRIBUTES
KEYLEN----------------27 AVGLRECL-------------100
RKP--------------------0 MAXLRECL-------------100
STRIPE-COUNT-----------1

BUFSPACE-----------13312 CISIZE--------------5632
EXCPEXIT----------(NULL) CI/CA----------------135

SHROPTNS(2,3) SPEED UNIQUE NOERASE
UNORDERED REUSE NONSPANNED EXTENDED

INDEXED NOWRITECHK NOIMBED NOREPLICAT
EXT-ADDR

STATISTICS (* - VALUE MAY BE INCORRECT)
REC-TOTAL-------19901374* SPLITS-CI---------442566*
REC-DELETED-----65738312* SPLITS-CA-----------6036*
REC-INSERTED----66360884* FREESPACE-%CI---------10
REC-UPDATED------------0* FREESPACE-%CA----------5
REC-RETRIEVED-2147483597* FREESPC-------4050585088*


EXCPS-----------18381515*
EXTENTS---------------55
SYSTEM-TIMESTAMP:
X'C4BB54C5495F4144'

ALLOCATION
SPACE-TYPE------CYLINDER HI-A-RBA------6918912000
SPACE-PRI------------100 HI-U-RBA------6861888000
SPACE-SEC------------100
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Robert Sample

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PostPosted: Thu Sep 03, 2009 4:40 pm    Post subject:
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Quote:
Could you please help us to suggest any way to release such uneeded space caused by IO operations, with out actually rebulding the file?
Why not ask for a perpetual motion machine at the same time? You cannot release the space without rebuilding the file.

You're showing 19,901,374 records in the file yet there's been 66,360,884 inserts and 65,738,312 deletes. With that much volatility, there's not much you are going to be able to do except take the time hit to rebuild the file frequently. You could try raising the free space percentages but that's probably just going to delay the rebuild, not eliminate the need for it.
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kranti

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PostPosted: Thu Sep 03, 2009 5:16 pm    Post subject: Reply to: VSAM file rebuilding methods
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Thanks alot for the reply.

We had tried rebuliding the file using IDCAMS-REPRO earlier by copying the original file into new one.

Aaprt from IDCAMS, there are other tools SORT, INSYNCH, SELCOPY are available to us.

Do you think that which would be fastest and efficient way to rebuild the file ?
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expat

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PostPosted: Thu Sep 03, 2009 5:19 pm    Post subject:
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IDCAMS EXPORT / IMPORT is also an option.
You will need to perform parallel runs to see which the best product is.
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dick scherrer

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Joined: 23 Nov 2006
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PostPosted: Thu Sep 03, 2009 8:42 pm    Post subject:
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Hello,

Quote:
yet there's been 66,360,884 inserts and 65,738,312 deletes
Why so many inserts/deletes for a file with 19mill records?

Might most of these be serviced with an update rather than a delete/add?
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