Re: Expensive op codes

[Dave Murvin <davem@xxxxxxxx>]

Vanja Jovic wrote:

>         I wouldn't speculate on cost in terms of processor time, as I think
> that is irrelevant in today's real world. However, READ then IF (or DO
> WHILE key = constant) can be way faster than READE, again not because of
> the processor, but because of blocking. In this case, it's an I/O issue,
> and with today's state of hardware it can not be neglected.

I have been doing some testing on record blocking and reading of large files.
Some of these tests may have been unscientific, but I think they point the way 
to
go.

All tests were run in batch on a dedicated S10.  Test jobs were the only
application running.
File being read is a keyed logical with the physical file in the same sequence 
as
the key.
Number of records in file is 1,027,600 with record length of  191

Both test runs used OVRDBF FILE(ECLL02) SEQONLY(*YES 341)
Both test runs read the entire file by key.  Program 1 used READE, program 2 
used
READ and compare.

Program 1 elapsed time was 33 minutes 38 seconds.
Program 2 elapsed time was 12 minutes 38 seconds.

I think I will be using the READ/Compare model versus the READE model whenever
possible when I need to read by key.

By the way, reading the non keyed physical file with the same OVRDBF only took 1
minute 22 seconds.

Program 1:

 FECLL02  IF  E           K        DISK
  *
 C                     READ ECLL02                   90
 C                     MOVE LORD      ECLKEY  60
 C           TOP       TAG
 C           *IN90     DOWEQ*OFF
 C           ECLKEY    READEECLL02                   90
 C                     ENDDO
  *
 C           LORD      SETGTECLL02               LR
 C           *INLR     IFNE *ON
 C                     READ ECLL02                   90
 C                     MOVE LORD      ECLKEY
 C                     MOVE *OFF      *IN90
 C                     GOTO TOP
 C                     ENDIF

Program 2:
FECLL02  IF  E           K        DISK
 *
C                     READ ECLL02                   90
C                     MOVE LORD      ECLKEY  60
C           TOP       TAG
C           ECLKEY    DOWEQLORD
C           *IN90     ANDEQ*OFF
C                     READ ECLL02                   90
C                     ENDDO
 *
C           LORD      SETGTECLL02               LR
C           *INLR     IFNE *ON
C                     READ ECLL02                   90
C                     MOVE LORD      ECLKEY
C                     MOVE *OFF      *IN90
C                     GOTO TOP
C                     ENDIF

PS.  I don't normally use GOTOs and I try to use ILE/RPG whenever I can.
--
Dave Murvin
DRM Enterprises, Inc.
davem@drme.com


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