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Compare VSAM files using DFSORT

 
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pshongal

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Joined: 14 Jun 2012
Posts: 96
Location: India

PostPosted: Thu Nov 23, 2017 10:24 am    Post subject: Compare VSAM files using DFSORT
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Hi,
I have 2 files to be compared each having around 50MM records.

When I do this comparison on flat files, DFSORT takes less time, but when I do this using VSAM files, it takes more time.

I tested in test region with some 400K records (max record length=1450).

Both are variable length files.

Flat file comparison took 0.9 seconds
VSAM file comparison took 9.4 second.

Is there a way I can optimize this?
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Nic Clouston

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Joined: 10 May 2007
Posts: 2247
Location: Hampshire, UK

PostPosted: Thu Nov 23, 2017 4:09 pm    Post subject:
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Try using data sets rather than files. And why not try unloading the data sets and comparing the unloads? And those times - are they CPU or wall?
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enrico-sorichetti

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Joined: 14 Mar 2007
Posts: 10631
Location: italy

PostPosted: Thu Nov 23, 2017 4:19 pm    Post subject:
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it is common knowlege that VSAM processing is heavier than PS processing

Quote:
... why not try unloading the data sets and comparing the unloads?
And those times - are they CPU or wall?


why read twice the input data ( repro + compare )
apart the extra disk space
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pshongal

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Joined: 14 Jun 2012
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PostPosted: Thu Nov 23, 2017 6:44 pm    Post subject:
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As Nic mentioned, I have already tried by unloading VSAM and then compare. It works little better but not a huge impact because its double operation as Enrico mentioned
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steve-myers

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Joined: 30 Nov 2013
Posts: 758
Location: The Universe

PostPosted: Thu Nov 23, 2017 6:53 pm    Post subject:
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In my opinion, Mr. Sorichetti's first sentence should read, "It is common knowledge that sequential VSAM processing requires more CPU time than an equivalent non-VSAM sequential data set."

In addition, you have to unload each data set (s-l-o-w) before the compare (much quicker). You really haven't gained anything!
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enrico-sorichetti

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Location: italy

PostPosted: Thu Nov 23, 2017 7:06 pm    Post subject: Reply to: Compare VSAM files using DFSORT
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I stand corrected...
if it is the same for You I would prefer to sit corrected, it is more comfortable icon_wink.gif
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