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cost base optimization

From: Dave Marshall <dmarsh_at_istar.ca>
Date: Fri, 18 Dec 1998 12:15:00 -0800
Message-ID: <8Jye2.602$n4.5487803@WReNphoon2>


Hi,

If a table is relatively small and/or the index is not very selective, a full table scan can actually be faster than using an index lookup. The cost based optimizer therefore may choose a FTS over an index in some situations. The rule based optimizer always tries to use indexes if possible - a FTS is considered the least efficient way to retrieve records.

Of course, if you find that CBO isn't choosing the optimal execution plan, you can always overrule individual statements by using hints.

Good luck,

Dave Marshall

Received on Fri Dec 18 1998 - 14:15:00 CST

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