RE: Optimizing File I-O in RPG IV/ I-Series

I'm sure the gurus can explain it better than I, but READE actually performs a 
bit counter-intuitively.

It actually resets the pointer every time it is invoked.  So you setLL the 
first time, then when you READE it looks at your key and reads through all the 
records again to get to the next one, and so on.  At least that's the way it's 
been explained to me.  We made it a standard in our shop to never use READE, 
and when we did, the performance of our programs improved dramatically.

Instead, we use:

Key SetLL File
DoW 1 = 1
Read File
If %Eof or Key <> Record
   Leave
EndIf
Process Record
EndDo


Greg

>-----Original Message-----
>From: rpg400-l-bounces@xxxxxxxxxxxx [mailto:rpg400-l-bounces@xxxxxxxxxxxx]
>On Behalf Of RPower@xxxxxxxxxx
>Sent: Wednesday, November 23, 2005 7:58 AM
>To: RPG programming on the AS400 / iSeries
>Subject: RE: Optimizing File I-O in RPG IV/ I-Series
>
>Huh?  I reade will progressively read thru record after record until it
>finds a non-matching record to the key.  Why would you want to skip the
>reade and then do an if comparision when reade does it all in one step?  A
>chain finds the very first record, a reade finds the next matching record.
> So they aren't the same.
>
>Ron Power
>Programmer
>Information Services
>City Of St. John's, NL
>P.O. Box 908
>St. John's, NL
>A1C 5M2
>709-576-8132
>rpower@xxxxxxxxxx
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>"Fleming, Greg \(ED\)" <GFLEMING@xxxxxxxxxxxxxxxxxxxx>
>Sent by: rpg400-l-bounces@xxxxxxxxxxxx
>2005/11/23 09:23 AM
>Please respond to
>RPG programming on the AS400 / iSeries <rpg400-l@xxxxxxxxxxxx>
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>To
>"RPG programming on the AS400 / iSeries" <rpg400-l@xxxxxxxxxxxx>
>cc
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>Subject
>RE: Optimizing File I-O in RPG IV/ I-Series
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>
>Don't do a READE.
>
>Do a READ and then leave when you get to a record you don't want.
>Doing a READE is like Chaining over and over again.
>
>Greg
>
>>-----Original Message-----
>>From: rpg400-l-bounces@xxxxxxxxxxxx
>[mailto:rpg400-l-bounces@xxxxxxxxxxxx]
>>On Behalf Of Weber, Richard
>>Sent: Wednesday, November 23, 2005 7:49 AM
>>To: 'RPG programming on the AS400 / iSeries'
>>Subject: RE: Optimizing File I-O in RPG IV/ I-Series
>>
>>Maybe you're already doing this: Skip the update statement for records
>>whose
>>data hasn't actually been changed.
>>
>>Rick Weber  |  TOYS 'Я' US International
>>
>>-----Original Message-----
>>From: Jim Wiant [mailto:Jim.Wiant@xxxxxxxxxxxxxxxx]
>>Sent: Tuesday, November 22, 2005 7:18 PM
>>To: rpg400-l@xxxxxxxxxxxx
>>Subject: Optimizing File I-O in RPG IV/ I-Series
>>
>>We have a series of programs that update files for assorted maintenance.
>>The time these programs are taking is becoming excessive.
>>
>>In most cases, the RPG code is very simple.
>>
>>Key             SETLL                                           file
>>Key             READE                                           file
>>                (Do until EOF)
>>                UPDATE                          record
>>Key             READE                                           file
>>                END DO
>>
>>I don't see how the code can get might tighter. Is there any reasonable
>>compiling options/ CL overrides, etc. that could improve such a routine
>>when it
>>needs to process a large number of records? We're not opposed to
>>changing code, but if just a few H spec changes and/or compiling options
>>could gain
>>us a bit of performance, it would help us out.
>>
>>I've tried a few of the basics (OPTIMIZE(*FULL), NoDEBUGIO, etc.) but
>>didn't see much of a change in my benchmarks.
>>
>>Thanks for any help
>>
>>Jim Wiant
>>
>>
>>Once a job is fouled up, anything done to improve it makes it worse.
>>Finagle
>>
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