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ravikumar_sri2001 · Posted: Mon Apr 03, 2006 12:51 am Post subject: Optimize IO

Hi Gurus,

One of our production program runs for 5 hours (elapsed time). The program has two input file. One file is in tape (virtual tape) and it has 348,302,208 records. Another input file has 5,512 records and this file is in DASD. Both the input files are based on a common key. The program matches the input files based on key and writes the matching records in the single output file (virtual tape). Currently program takes 1:38.12 of CPU time and around 5 hours of elapsed time. I wanted to reduce the elapsed time. I heard that coding BUFNO in the DCB parameter will optimize the I/O. So i coded BUFNO=20 in the DD statement of input file which resides in VTS. After coding BUFNo parameter, the job took 1:39.93 of CPU time and around 1 hours 30 minutes of elapsed time. I expected CPU time will come down after coding BUFNO but contrary to this CPU time went up due to BUFNO. Any suggestions on how to optimize the I/O will be highly appreciated.

Thanks,
Ravikumar.

Mervyn · Posted: Mon Apr 03, 2006 3:31 am Post subject: Re: Optimize IO

ravikumar_sri2001 · Posted: Tue Apr 04, 2006 12:41 am Post subject:

Is there any way still reduce the elapsed time.

Thanks,
Ravikumar.

Mervyn · Posted: Tue Apr 04, 2006 3:25 am Post subject:

It's worth experimenting with BUFNO. Sometimes a larger figure will yield more benefit.

How complex is the program? Could you replace it with SORT?

Cheers,
Merv
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Bill Dennis · Posted: Tue Apr 04, 2006 11:21 am Post subject:

Are you having to wait for virtual tape mounts? Using UNIT=(TAPE,2) on input may help pre-stage the next volume(s).
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Regards,
Bill Dennis

Disclaimer: My comments on this foorum are my own and do not represent the opinions or suggestions of any other person or business entity.

ravikumar_sri2001 · Posted: Wed Apr 05, 2006 5:57 am Post subject:

No, i cannot replace the program with SORT.
The input tape file resides in one tape volume.

I will experient with BUFNO.

Thank you all for your valuable replies.

Thanks,
Ravikumar.