RE: Chain doesn't set %EOF

[Paul Jackson <pjackson@xxxxxxxxxx>]

According to the ILE RPG Manual, even using the SETLL will cause blocking to
be disabled unless the BLOCK keyword is used on the "F" spec.

-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx
[mailto:rpg400-l-bounces@xxxxxxxxxxxx]On Behalf Of Barbara Morris
Sent: Tuesday, March 29, 2005 5:14 PM
To: rpg400-l@xxxxxxxxxxxx
Subject: Re: Chain doesn't set %EOF


Paul Morgan wrote:
> 
> Had a prior thread on DoW vs DoU read loops.
> 
> Who the heck was the IBMer who said never to use ReadE?  How long ago was
> the Common conference?  Possible old performance problems with ReadE?
> 
> I doubt Barbara would agree with this recommendation to never use ReadE.
> 

Right, I wouldn't, not that I'm an expert in database performance. 
While READE does prevent blocking, it does do the key comparison
correctly (*).  Using READ and checking the key yourself from the INFDS
can get you into a mess if you have any special key features like
ALTSEQ, ABSVAL, ALWNULL (see the READE documentation for the list of
things that can cause a problem if you do a character-by-character key
comparison).  You can get mysterious results if you use a SETLL (which
always sets %FOUND correctly) followed by a READ+compare (which might
cause even the first record not to match).

Even if you don't have special key features, and doing your own key
compare would always be valid, you have to weigh the blocking benefit
against the added complexity of your code getting the key value out of
the INFDS, plus the hidden requirement that your keys never have any
special features added.  And remember that your code might be used as a
pattern in some situation where the file does have special key features.

(*) Only the ILE RPG (RPG IV) compiler does the READE key comparison
(and SETLL EQ comparison) correctly.  The RPG/400 (RPG III) compiler
does a byte-wise comparison from the key in the feedback area, so using
a READE in RPG/400 wouldn't have any _correctness_ benefit over your own
READ + compare.

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