The CBO Lie Detector
- From: "Schultz, Charles" <sac@xxxxxxxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Fri, 19 May 2006 08:15:28 -0500
After reading Jonathan Lewis's books, Tom Kyte's posts and Joze
Senegacnik's presentations (and so many others out there who have
contributed), one message (among others) has been beaten into my head;
give the CBO all the facts, and the CBO will make the best choice. The
corollary is that if you lie to the CBO, it may (or may not) come up
with a sub-optimal plan.
So with all the automated features and collections in 10g, could not the
engine determine if it was being lied to by comparing the estimated
costs & cardinality to the actual end values? With all this talk about
"self-tuning", I would almost expect the database to come back and say
"Hey, you fed me false information!". At the very least. The next step
would be for the engine to go back and correct that false information.
Maybe the database already does this and I am missing it somehow. If so,
please correct me.
charles schultz
oracle dba
aits - adsd
university of illinois
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