Re: why rule based optimizer performs better than cost based?
- From: "Jonathan Lewis" <jonathan@xxxxxxxxxxxxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Sat, 26 Jun 2004 08:15:16 +0100
Regards
Jonathan Lewis
http://www.jlcomp.demon.co.uk
http://www.jlcomp.demon.co.uk/faq/ind_faq.html
The Co-operative Oracle Users' FAQ
http://www.jlcomp.demon.co.uk/seminar.html
Optimising Oracle Seminar - schedule updated May 1st
----- Original Message -----
> Take a serious look at two init parameters:
>
> Optimizer_index_caching
> Optimizer_index_cost_adj
>
> The default values are 0 and 100 respectively which inform the optimizer =
> that a) you will never find an index in the buffer cache and b) scanning =
> an index is just as expensive as a table. If any of you are familiar =
> with Dan Hotka, he recently presented his "Index Advance Tuning" seminar =
> at the NOUG DBA SIG here in Boston. His recommendation is to set these =
> to 90 and 30(OLTP) or 50(DSS) respectively. I've tried it, it helps and =
> does not appear to have any unpleasant side effects.
>
There is a side-effect to worry about with OICA, especially
at low values. see:
http://www.dbazine.com/jlewis18.shtml
> Dick Goulet
> Senior Oracle DBA
> Oracle Certified 8i DBA
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