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How to change an existing database from rule based optimizer to cost based optimizer

Posted on 2010-11-23
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Last Modified: 2012-10-06
Hi can anyone tell me how we can change existing Database which is running on Rule based optimizer converting it to cost based optimizer.
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Question by:iabhinay_dba
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by:slightwv (䄆 Netminder)
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The optimizer_mode init parameter.  On mobile so I can't provide an exact link but it's in the online docs.
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sdstuber earned 168 total points
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http://download.oracle.com/docs/cd/E11882_01/server.112/e17110/initparams167.htm#i1131532

It's not documented after 9i but you can also set the value to "CHOOSE"
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by:anand_20703
anand_20703 earned 166 total points
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Above answer is right and CHOOSE parameter is recommended because optimizer will select between RULE and COST , accordingly generates the explain plans. RULE based optimizer is old and was recommended only in Oracle ERP applications older than 11i.
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To reap the benefits(performance) of  COST/CHOOSE optimizer enabled Databases, gathering statistics periodically is very important.
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