Re: The CBO Lie Detector
- From: Tanel Põder <tanel.poder.003@xxxxxxx>
- To: <rshamsud@xxxxxxxxxxxx>, <ric.van.dyke@xxxxxxxxxx>
- Date: Fri, 19 May 2006 22:08:11 +0800
The CBO Lie DetectorAFAIK, dynamic sampling can account for column data
correlations from starting level 4.
DBMS_SQLTUNE does quite exhaustive diagnostics & analysis statement execution,
not just deriving from CBO statistics, but it can actually run (parts of) the
statement.
Tanel.
----- Original Message -----
From: Riyaj Shamsudeen
To: ric.van.dyke@xxxxxxxxxx
Cc: sac@xxxxxxxxxxxxx ; oracle-l@xxxxxxxxxxxxx
Sent: Friday, May 19, 2006 9:50 PM
Subject: Re: The CBO Lie Detector
I don't think it is a good idea to detect the false information, without
correcting some of the fundamental CBO discrepancies. In few cases, We have
deliberately fed false information to get acceptable access plan and so, at
least, there should be a way to override the lie detector.
One nagging gripe I have is that there is no way to tell CBO that there is a
strong correlation exists between two different column predicates, at least
that I know of. [J.Lewis has excellent presentation exploring this issue in
detail ]. We have few such queries and we tried to use sql profiles in
conjunction with cursor_sharing. Every time we hit one or other issue that we
can not deal with it and finally resorted to feed "lies" to CBO.
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