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I am going to COMMON. My main mission this time is database performance.
Which, if any, of the sessions would best have helped me with this email I
just received from a coworker?
<snip>
There have been some UPDATE SQL statements taking a long time in the GDI
database, probably because its so large. Particularly, against files like
ECL. The WHERE ... IN appears to be the culprit. A "WHERE ... IN" type
statement doesn't seem to take advantage of reusable data very well, even
if the table being compared is fairly small. I suspect its like the
difference between scanning all data in a table vs. using a CHAIN. See
below for a similar but much more efficient statement.
Took 2 hours on HQ:
update gdidivf/ecl set
lnet=(select pfct1 from darren/hmi264254 where
ecl.lord=hmi264254.ord and ecl.lline=hmi264254.line)
where (lord,lline) in
(select lord,lline from darren/hmi264254)
Took 20 seconds:
update gdidivf/ecl set
lnet=(select pfct1 from darren/hmi264254 where
ecl.lord=hmi264254.ord and ecl.lline=hmi264254.line)
where exists
(select pfct1 from darren/hmi264254 where
ecl.lord=hmi264254.ord and ecl.lline=hmi264254.line)
P.S.
Please note that the selection criteria following the 'where exists' is
identical to the value being set in the actual update statement. What you
are selecting, pfct1 in this example, is not important, but it is easier
just to copy paste this way.
</snip>
By the way "HQ" is short for GDIHQ, which is an lpar with ninety 70GB disk
drives running at 60% full
% CPU used . . . . . . . : 34.9 Auxiliary storage:
% DB capability . . . . : 20.2 System ASP . . . . . . : 5433 G
Elapsed time . . . . . . : 00:00:14 % system ASP used . . :
60.0069
Jobs in system . . . . . : 31474 Total . . . . . . . . : 5433 G
% perm addresses . . . . : .347 Current unprotect used : 96810
M
% temp addresses . . . . : 7.740 Maximum unprotect . . : 501608
M
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