Re: Chain vs SetLL/ReadE

There is a lot of talk about disk access, blocking, and all, in that thread. I'm going to suggest, based on having worked with expert cache, that one can probably worry less about this issue. Use shared pools, set the paging option to *CALC, and let the system take care of you. Expert cache looks at a window of physical IO and determines the page size to use, depending on the degree of locality of reads - if lots of reads in the pool are close together on disk, larger pages are used, in order to minimize physical IOs. This would be blocking at the physical level. As I recall, the blocking referred to is at the logical level, a layer above the physical.

I'm sure there are chances to improve things but I think one can spend time better writing more code, rather than taking time to tweak the slightest benefit out of things. One writer says, 3 rules of optimization--

Don't
Don't
Don't

Vern

-------------- Original message --------------
From: Tommy.Holden@xxxxxxxxxxxxxxxxxxxxx

what timing! there's been an ongoing discussion about this on
systeminetwork forums
http://forums.systeminetwork.com/isnetforums/showthread.php?t=52004
Barbara Morris gave some good insight on this thread.

Thanks,
Tommy Holden



From:
Chandra Krieg
To:
"'rpg400-l@xxxxxxxxxxxx'"
Date:
09/02/2008 08:37 AM
Subject:
Chain vs SetLL/ReadE



Hello all,

I have been told that the preferred method of random record retrieval is
to use the SetLL, then do a ReadE and check for the %EOF indicator.

Why is this preferred over using a Chain with %found or even checking for
%Equal on the SetLL before reading the file? I have been told that the
Chain doesn't do what I'm expecting it to but I've never had issues in the
past.

I have read the archive posts and found opinions on the subject but no
concrete explenation as to why. As with some of the posts I don't
understand why you would want to readE the file if the SetLL didn't find
an %equal match or why if you plan to read the file a chain isn't
appropriate.

I'm being told to use the following code instead of a Chain.

SetLL (KeyFields) FIleName;
ReadE (KeyFields FIleName;
DoW Not %EOF(FIleName);
do my stuff
ReadE (KeyFields) FileName;
EndDo;

Any explanations would be helpful!

TIA!

Chandra Krieg
i5 Programmer/Analyst
RateWatch
(P) 1.800.348.1831 ext 311
(F) 1.920.568.1403
www.rate-watch.com
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