With this code I would think it would only be more efficient if most of the second file records did not exist. If CHAIN does actually do the same as a SETLL/READE then the different is the execution of the extra IF on every record read. If you're talking about a few thousand records being processed you would not see any difference. If you talking about a few million and most of those get a hit in the second file this code would be less efficient. If most of the records do not get a hit it would be more efficient with the two OP codes.
-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx [mailto:rpg400-l-bounces@xxxxxxxxxxxx] On Behalf Of Jeff Pusateri
Sent: Tuesday, September 02, 2008 10:42 AM
To: RPG programming on the AS400 / iSeries
Subject: RE: Chain vs SetLL/ReadE
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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