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 Originally Posted by vnktummala
when I am generating explain plan for one of my queries, I have observed the note "rule based optimizer used (consider using cbo)".
optimizer_mode=choose
what made Oracle to user rule based optimizer? any clue will be much appreciated.
Database is 10.2.0.4
If i generate the plan for same query with some hint then it is using cbo which is expected.
Check if there are statistics on all referenced tables - Oracle will choose rule based optimizer if tables have no stats.
The reason why is that with no statistics Oracle can't figure out the cost so it makes no sense to use CBO.
Last edited by PAVB; 08-10-2010 at 08:32 AM.
Reason: Typo
Pablo (Paul) Berzukov
Author of Understanding Database Administration available at amazon and other bookstores.
Disclaimer: Advice is provided to the best of my knowledge but no implicit or explicit warranties are provided. Since the advisor explicitly encourages testing any and all suggestions on a test non-production environment advisor should not held liable or responsible for any actions taken based on the given advice.
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