Re: [Fwd: Re: System Statistics and the CBO]
- From: Mladen Gogala <mgogala@xxxxxxxxxxxxxxxxxxxx>
- To: Wolfgang Breitling <breitliw@xxxxxxxxxxxxx>
- Date: Fri, 17 Jun 2005 15:22:16 -0400
Wolfgang Breitling wrote:
For the "benefit" of those following this thread.
Patty had sent me 10053 traces privately and the attached is my
response after looking at them.
Since I'm not 100% satisfied with my analysis, I am not sure how much
benefit there is.
Wolfgang, this might be a problem with cost_adjust parameter or it might
be a consequence of a bug in the optimizer.
I believe that the search for intelligent life in CBO is still in vain
and that it will not be capable of making 100%
of correct decisions. There will be some queries that will have to
influenced by hints. This is one such case. Jonathan's
example, same as Patty's problem, tricks the optimizer into choosing
wrong index by funny rounding errors. The
optimizer_index parameters will resolve 96.85%... problems. The
remaining 3.14...% of the problems will have to be
solved manually. The number 3.14.... is the ratio between the area of
the circle with radius R and area of the square with
side equal to R.
--
Mladen Gogala
Oracle DBA
Ext. 121
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