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VSAM I/O time

 
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Amit Manas Dubey
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Joined: 15 Dec 2006
Posts: 22
Location: Mumbai

PostPosted: Mon Feb 18, 2008 11:38 pm    Post subject: VSAM I/O time
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Hi All,

I have a VSAM file LRECL = 6500, Key length = 22, No of records in the file = 1064949.

I need to know what impact would it have on I/O (Random read) for 1 single record, if we increase the Record length by 600 bytes ?

Will it have any difference at all, and if yes, approx how much ?

Best regards,
Amit.
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stodolas

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Posts: 632
Location: Wisconsin

PostPosted: Mon Feb 18, 2008 11:57 pm    Post subject:
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Of course there is some impact. However, it is probably somewhere between unmeasurable and minimal.
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dick scherrer

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Joined: 23 Nov 2006
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PostPosted: Tue Feb 19, 2008 12:51 am    Post subject:
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Hello,

Quote:
it is probably somewhere between unmeasurable and minimal
Yup, i'd go with this. . . icon_wink.gif

Given that the index structure has not changed and that the number of index entries has not changed, the time to locate the specific index entry should stay the same as it is now. Reading one 6.5k record versus one 7k record should be "between unmeasurable and minimal".
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Bill O'Boyle

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Joined: 14 Jan 2008
Posts: 2502
Location: Atlanta, Georgia, USA

PostPosted: Tue Feb 19, 2008 1:57 am    Post subject: VSAM I/O time
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An optimal CISIZE, for both Data and Index will also have a significant affect on performance as well as the AMORG parameters utilized and BLSR.

If you're truly issuing RANDOM Reads, then ensure that your program specifies ACCESS IS RANDOM as opposed to ACCESS IS DYNAMIC.

HTH....

Regards,

Bill
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