RE: Spool file journalling -- MIDRANGE-L



Actually these two statements are not the same.
First one will return all combinations: WRITE/SCREEN-REC, WRITE/SCREEN-FILE
, READ/SCREEN-REC, READ/SCREEN-FILE
Second one will only return:  WRITE/SCREEN-REC, READ/SCREEN-FILE


    Alexei Pytel
always speaking for myself




                      "Joe Pluta"
                      <joepluta@PlutaBro        To:       
<midrange-l@midrange.com>
                      thers.com>                cc:
                      Sent by:                  Subject:  RE: Spool file 
journalling
                      midrange-l-admin@m
                      idrange.com


                      10/29/2002 09:56
                      AM
                      Please respond to
                      midrange-l





Here's why I have problems with SQL.  Take a look at the following
statements:

select * from sccc1 a, sccc1 b
 where a.c1flag3 = 'V' and
 a.c1source in ('WRITE', 'READ')
 and a.c1kwid = b.c1prnt
 and b.c1source in ('SCREEN-REC', 'SCREEN-FILE')

select * from sccc1 a, sccc1 b
 where a.c1flag3 = 'V' and
 ((a.c1source = 'WRITE'
   and a.c1kwid = b.c1prnt
   and b.c1source = 'SCREEN-REC') or
 (a.c1source = 'READ'
   and a.c1kwid = b.c1prnt
   and b.c1source = 'SCREEN-FILE'))

Both are trying to do the same thing - use a COBOL cross-reference to
determine READs and WRITEs to a workstation.  READs use the file name,
WRITEs use the record name.  The references to "c1kwid/c1prnt", which are
the same in both queries, are used to make sure the cross-reference lines
are related.

The first one, which is a little more inclusive (it would include READs on
the record and WRITEs to the file) runs in milliseconds.  The second one I
fired off and it chewed up 73% of my machine for over 30 seconds before I
shut it down.  (Eventually CFINT kicks in and grinds the thing to a halt,
even though it's the only job on the machine.)

My observation has several parts:

1. Would any of the SQL gurus like to point out any serious problems in my
syntax?  Are there better ways to do this?

2. I looked at the joblog under debug to determine the access paths, and
while the optimizer recommends I create a logical over C1SOURCE, the two
statements use the exact same paths.

3. Why would what seems like a pretty simple syntax change cause such
drastic difference in response time?


=======UPDATE=========

By adding the logical over C1SOURCE as the optimizer suggested, the second
runtime dropped to milliseconds.  Evidently, the second syntax somehow
causes the index to be rebuilt over and over again.

Joe

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