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How to reduce elapsed time?

 
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itjagadesh

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Joined: 05 Dec 2006
Posts: 89
Location: chennai

PostPosted: Wed Dec 03, 2008 6:15 pm    Post subject: How to reduce elapsed time?
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Hi Team,

One of my JOB taking so much Elapsed time compared to CPU time.
Example - CPU TIME = 10 MIN but ELAPSED TIME = 120 min in one of our JOB.
(Job contains COBOL,Eazytrive program. Database used - DB2,IMS and flat file are used in this JOB)
1)What could be the possible reason?

2)Is there any option availabe to reduce elapsed time?

3)What are all the loop holes for this reason(more elapse)?


Please help me on this

Regards
Jagadesh
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Robert Sample

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Joined: 06 Jun 2008
Posts: 8057
Location: East Dubuque, Illinois, USA

PostPosted: Wed Dec 03, 2008 6:32 pm    Post subject:
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For an active system, your ratio doesn't seem unusual -- I looked at one of our jobs that ran yesterday during month-end processing and it used 8.25 minutes of CPU time in 124 minutes of elapsed time, and our CPU runs 100% busy during month-end processing. Just in the last two weeks this job has run anywhere from 95 to 129 minutes doing the same basic work.

Elapsed time is a notoriously unstable measure of batch jobs since it depends on how busy the system is, the service class of the job, the WLM performance goal settings, I/O contention, etc, etc.

Options that may (and I emphasize, may or may not) improve elapsed time: moving datasets from tape to disk, recoding key parts of the algorithm, increasing buffers, changing service class, updating WLM. If you're serious about this, first you have to determine what's the bottleneck for your job -- is it CPU time, or is it I/O? If I/O, look at ways to improve the I/O performance and if CPU, look at ways to speed up processing within the program. And be aware that no matter what you do, if you're running during the peak processing time for your site then you almost certainly won't have much impact on elapsed time, no matter what you do.
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Terry Heinze

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Joined: 14 Jul 2008
Posts: 1249
Location: Richfield, MN, USA

PostPosted: Wed Dec 03, 2008 9:39 pm    Post subject:
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To add to Robert's reply, I would think the 1st thing you want to do is determine which step in your job is the biggest culprit. You indicated several steps.
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dick scherrer

Site Director


Joined: 23 Nov 2006
Posts: 19270
Location: Inside the Matrix

PostPosted: Wed Dec 03, 2008 10:14 pm    Post subject:
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Hello,

Quote:
One of my JOB taking so much Elapsed time compared to CPU time.
Example - CPU TIME = 10 MIN but ELAPSED TIME = 120 min in one of our JOB.
It is almost never a good idea to make this comparison in an effort to reduce elapsed time.

Most elapsed time is related to i/o - regardless of where the i/o is done (database(s), vsam, or other file). If you can reduce the i/o, you will reduce the elapsed time.

As was suggested, you may want to start by identifying which step(s) consistently take the most time.
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