RE: Physics of the FILTER operation within SQL_PLANE.
- From: J.Velikanovs@xxxxxxxx
- To: oracle-l@xxxxxxxxxxxxx
- Date: Wed, 30 Jun 2004 12:32:32 +0300
Lex,
Thank for comment,
I use RBO just for proof of concept.
I am sure that the same situation can be emulated with CBO, but in this
case it was easy for me to use RBO.
>> about the optimizer not being able to calculate differences
Even if would use CBO it will not be able to calculate difference in case
of FILTER operation, was my point.
Jurijs
"Lex de Haan" <lex.de.haan@xxxxxxxxxxxxxx>
Sent by: oracle-l-bounce@xxxxxxxxxxxxx
30.06.2004 12:30
Please respond to oracle-l
To: <oracle-l@xxxxxxxxxxxxx>
cc:
Subject: RE: Physics of the FILTER operation within
SQL_PLANE.
Hi Jurijs,
allow me one comment about your statement below,
about the optimizer not being able to calculate differences:
you are forcing RBO behavior, a technology now obsolete in 10g
and untouched by Oracle development for many, many years...
(interesting email thread, by the way)
Kind regards,
Lex.
---------------------------------------------
visit my website at http://www.naturaljoin.nl
---------------------------------------------
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx]On Behalf Of J.Velikanovs@xxxxxxxx
Sent: Wednesday, June 30, 2004 10:02
To: oracle-l@xxxxxxxxxxxxx
Subject: Re: Physics of the FILTER operation within SQL_PLANE.
If your hypnotize is true (regerding remembering last value), then I have
one more interesting conclusion:
The cost of the same SQL with the same execution plans can differ
depending on rows ordering in the driving rowset.
Like with index range scan and clustering factor, but with one little
difference - Oracle optimizer in case of FILTER operation can't evaluate
this cost (in case of range scan - clustering factor statistics
available).
Even more, if your hypnotize is true, then cost difference can appears not
from bigger LIO count, but also because in one case Oracle need to manage
hash table in other doesn't (just use last remembered value).
For my point demonstrating purpose, I have a little bit modified my
initial testcase (1,2).
Take a look: the same SQL, the same ExplPlan, time differs by 18% and
Oracle optimizer can't caltulate this difference.
Jurijs
TESTCACE 1
===================================================
SELECT /*+ RULE */ count(m.v) from main_tab m
where
exists
(select v from
filter_tab f where f.n=m.n and f.v like 'a%')
TESTCACE 2
===================================================
SELECT /*+ RULE */ count(m.v) from main_tab m
where
exists
(select v from
filter_tab f where f.n=m.n and f.v like 'a%')
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