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Home -> Community -> Mailing Lists -> Oracle-L -> RE: cost
Yes, the CBO will ALWAYS choose the plan with the lowest cost. If you
have SQLs where higher cost plans are actually more efficient than lower
cost plans, then you ought to ask yourself why. One solution is always
to simply add hints and convince the optimizer to do what you want, but,
a better long-term approach is probably to try to understand WHY the CBO
thinks a particular plan is lower cost than another and then give the
CBO better information so that it can more accurately estimate plan
costs.
Ways to do this may include:
Mark J. Bobak
Oracle DBA
ProQuest Company
Ann Arbor, MI
"Post Hoc Ergo Propter Hoc"
-----Original Message-----
From: thump604_at_comcast.net [mailto:thump604_at_comcast.net]=20
Sent: Monday, April 05, 2004 10:32 AM
To: oracle-l_at_freelists.org
Subject: cost
DB - 8174
Does the CBO choose always the path based solely on lowest cost of all
plans?
We have noticed that best plan is not always of lowest cost, which is
why I ask.
If that is the case, is that where hints, outlines, etc come in?
-- - David=20 ---------------------------------------------------------------- Please see the official ORACLE-L FAQ: http://www.orafaq.com ---------------------------------------------------------------- To unsubscribe send email to: oracle-l-request_at_freelists.org put 'unsubscribe' in the subject line. -- Archives are at http://www.freelists.org/archives/oracle-l/ FAQ is at http://www.freelists.org/help/fom-serve/cache/1.html ----------------------------------------------------------------- ---------------------------------------------------------------- Please see the official ORACLE-L FAQ: http://www.orafaq.com ---------------------------------------------------------------- To unsubscribe send email to: oracle-l-request_at_freelists.org put 'unsubscribe' in the subject line. -- Archives are at http://www.freelists.org/archives/oracle-l/ FAQ is at http://www.freelists.org/help/fom-serve/cache/1.html -----------------------------------------------------------------Received on Mon Apr 05 2004 - 09:42:57 CDT
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