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VSAM performance tuning...help required.

 
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anoopn1985

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Joined: 23 Apr 2007
Posts: 16
Location: tvm

PostPosted: Wed May 13, 2009 3:00 pm    Post subject: VSAM performance tuning...help required.
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Hi,

I have one program A which read a flat file and copy some data to a VSAM file. In FILE-CONTROL, VSAM file is declared as

ACCESS IS RANDOM
ORGANIZATION IS INDEXED

I have one other program B, which reads the above VSAM file and performing REWRITE operation to the same VSAM file. The number of records getting processed is very high (arounf 1.5lakh records in VSAM file). In program B, I declare the VSAM file as below.

ACCESS IS DYNAMIC
ORGANIZATION IS INDEXED

The same job executes program A and B. The job takes around 8 hours to completion. When I gave AMP=('BUFND=50,BUFNI=50') parameter while accessing VSAM, the job took only 4hours. I'm looking for more performance improvement. I defined VSAM file with below properties.

CYL(400 100)
RECORDSIZE(80 80)
INDEXED KEYS(18 0)
SPEED
REUSE
SHR(1,3)
VOL(PRODDA,PRODDA)
FREESPACE(25 20))
INDEX (NAME(XXXX.YYY.I)
CISZ(2048))
DATA (NAME(XXXX.YYY.D)
CISZ(4096))


Can anyone help me? If I increase CISIZ, will it make any sense?
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dbzTHEdinosauer

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Joined: 20 Oct 2006
Posts: 6968
Location: porcelain throne

PostPosted: Wed May 13, 2009 3:40 pm    Post subject:
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you would be better off learning about VSAM,
the Redbook VSAM Demystifed
which will provide you with information about tuning VSAM.
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expat

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Joined: 14 Mar 2007
Posts: 8593
Location: Back in jolly old England

PostPosted: Wed May 13, 2009 3:48 pm    Post subject:
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It is a while since I have been heavily involved in VSAM tuning.

What is the difference between acces RANDOM and DYNAMIC. Is DYNAMIC used for skip sequential ?

For RANDOM I have always used higher values for the BUFNI and either low or default for BUFND. This allows more index buffers to be loaded.

If possible, it is better to have the reference dataset sorted in VSAM key sequence to avoid backward and forward movement through the VSAM file and causing buffer reloads. That way the VSAM index will only need to be read once for the whole job.

Excessive use of buffers can be detrimental as it may cause more frequent paging and delay the job.

Changes to the CISIZE may well further reduce elapsed times, but a larger CISIZE may be detrimental to online applications. No point in speeding up batch if you then clobber the online.

Have a read of the IBM redbook "VSAM demystified" for a good overview of VSAM and tuning.
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Bill O'Boyle

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Joined: 14 Jan 2008
Posts: 2504
Location: Atlanta, Georgia, USA

PostPosted: Wed May 13, 2009 3:54 pm    Post subject: Reply to: VSAM performance tuning...help required.
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Go to ===> http://www.ctrekcorp.com and review the Technical Papers, which can be downloaded for free.

Regards,
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Robert Sample

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Joined: 06 Jun 2008
Posts: 8166
Location: East Dubuque, Illinois, USA

PostPosted: Wed May 13, 2009 4:52 pm    Post subject:
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expat, DYNAMIC allows for skip sequential processing -- COBOL can read the file sequentially (once a current record pointer is established) or randomly.

BLSR, if enabled at your site, may make a difference -- although you've probably gotten most of the benefits of BLSR by adding buffers. If your site has an execution analysis tool like STROBE, you can find out if the program is CPU-bound or I/O-bound; that would help you determine how to proceed. Otherwise, increasing the CI may not help if the records are being read randomly and rewritten since that would mean more data coming in and going out of the buffer. And I reiterate the suggestions to read the Redbook.
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iamthecreaturefromuranus

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Joined: 20 Jun 2006
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PostPosted: Sat May 23, 2009 2:31 pm    Post subject: Re: VSAM performance tuning...help required.
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anoopn1985 wrote:
Hi,



Can anyone help me? If I increase CISIZ, will it make any sense?


Speak to your Storage Administration team about using System Managed Buffers(SMB). Your VSAM datasets will need to be in extended format before SMB will work. bufnd=50 and bufni=50 shows that you are just guessing at the correct amounts of buffers required.. guesswork is usually not the best way to do things.
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