RE: Chain vs SetLL/ReadE

To keep us in this misery. If a CHAIN doesn't get a hit... no data is
being moved around correct? So there shouldn't be an I/O impact. Fields
are not even cleared when no hit is found. And with the speed of today's
technology, is it really a concern on which method to use.

I have used SETLL to test for existence but that was because I'm trying to
decide which file I need to read from. If I'm going back to a "master"
file then it's always a chain.


Michael Schutte
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rpg400-l-bounces@xxxxxxxxxxxx wrote on 09/02/2008 10:41:37 AM:

Here is what I have been told, I believe from an IBM contactor ( its
been a while)...

The primary reason for using Setll/Reade instead of a Chain is
merely from an IO standpoint.

If you know that the record you are searching for definitely exists
a Chain is fine.

If however, you are not definitely sure the record exists, the
following is what is recommend:

SetLL (KeyFields) FIleName;
If %EQUAL(FIleName);
ReadE (KeyFields FIleName;
DoW Not %EOF(FIleName);
do my stuff
ReadE (KeyFields) FileName;
EndDo;
EndIf;
The true IO impact happens on the ReadE and Chain. The above example
will make your process more efficient.






From: Chandra Krieg
Sent: Tue 9/2/2008 8:34 AM
To: 'rpg400-l@xxxxxxxxxxxx'
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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