Re: Chain vs SetLL/ReadE

Totally agreed with Vern.

I've seem coding like below:
Setll (myKey) myFile;
If %equal();
reade (myKey) myFile;
if not %eof();
do stuff...
endif;
Endif;


As compare to a more straight forward approach of
Chain (myKey) myFille;
If %found();
do stuff....
Endif;



RPG io is so efficient that I just don't think one can gain much
performance between these two approaches.



<vhamberg@xxxxxxxxxxx> wrote in message
news:<mailman.7860.1220371652.2545.rpg400-l@xxxxxxxxxxxx>...

Jeff

In theory that is better - but not enough to make it my choice - the

only gain in the loop is one READE - how many jobs running this same
code would have to be running for this to matter? The simplicity of
leaving out the IF %equal() improves readability and makes maintenance
easier IMO. Hence the recommendation on optimization - Don't - applies
primarily to "cute" techniques that don't offer much gain but are arcane
and mysterious. Not that this one is, but a simpler form is nearly as
good vis-a-vis performance.

I think!
Vern

-------------- Original message --------------
From: Jeff Pusateri <JPusateri@xxxxxxxxxxxxxxx>

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
--
This is the RPG programming on the AS400 / iSeries (RPG400-L)

mailing list

To post a message email: RPG400-L@xxxxxxxxxxxx
To subscribe, unsubscribe, or change list options,
visit: http://lists.midrange.com/mailman/listinfo/rpg400-l
or email: RPG400-L-request@xxxxxxxxxxxx
Before posting, please take a moment to review the archives
at http://archive.midrange.com/rpg400-l.