Re: Which plan is better - what COST really means ?

From: Jonathan Lewis <jonathan_at_jlcomp.demon.co.uk>
Date: Fri, 14 Jan 2005 22:00:32 -0000
Message-ID: <00b101c4fa84$7bb9fcb0$6702a8c0@Primary>

Note in-line

Regards

Jonathan Lewis

http://www.jlcomp.demon.co.uk/faq/ind_faq.html The Co-operative Oracle Users' FAQ

http://www.jlcomp.demon.co.uk/seminar.html Public Appearances - schedule updated Dec 23rd 2004

Cary Millsap wrote:

>If I recall correctly, 10g has some operational memory built into the =
>CBO
>that allows the CBO to use operationally measured response times for a =
>given
>query as an input into computing the next plan.
>

I think you may be remembering the explanation I gave in one of my Oracle 11! demonstrations to explain how the HAL optimizer could change its mind in mid-stream.

When 9i came up with v$segstat and v$sql_plan_statistics, it became obvious that Oracle Corp. could start writing an extension to the optimizer that could use results from previous queries, and object-level cache hit rates as the basis for changing its estimated cost of a query.

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Received on Fri Jan 14 2005 - 15:55:47 CST