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

Note that while the use of READE does prevent blocking and as I understand it 
generally performs worse that READ + your own test.

The benefit to READE is that does key comparisons correctly when using special 
key features such as ALTSEQ, ABSVAL, ALWNULL.

See this message from Barbara Morris:
http://archive.midrange.com/rpg400-l/200503/msg00899.html


HTH,

Charles Wilt
--
iSeries Systems Administrator / Developer
Mitsubishi Electric Automotive America
ph: 513-573-4343
fax: 513-398-1121
  

> -----Original Message-----
> From: rpg400-l-bounces@xxxxxxxxxxxx 
> [mailto:rpg400-l-bounces@xxxxxxxxxxxx] On Behalf Of Fleming, Greg (ED)
> Sent: Wednesday, November 23, 2005 8:05 AM
> To: RPG programming on the AS400 / iSeries
> Subject: 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
> >http://www.stjohns.ca/
> >_____________________________________________________________
> ______________
> >Success is going from failure to failure without a loss of 
> enthusiasm. -
> >Sir Winston Churchill
> >
> >
> >
> >
> >"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>
> >
> >
> >To
> >"RPG programming on the AS400 / iSeries" <rpg400-l@xxxxxxxxxxxx>
> >cc
> >
> >Subject
> >RE: Optimizing File I-O in RPG IV/ I-Series
> >
> >
> >
> >
> >
> >
> >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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