Re: CBO question ?
- From: "Radoulov, Dimitre" <cichomitiko@xxxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Thu, 2 Mar 2006 16:40:17 +0100
CHOOSE 'IS' CBO
pls read at <http://tahiti.oracle.com/> http://tahiti.oracle.com, perf
tuning guide.
?
Oracle 9i, Database Reference
Release 2 (9.2)
<quote>
choose
The optimizer chooses between a cost-based approach and a rule-based
approach based on whether statistics are available.
If the data dictionary contains statistics for at least one of the accessed
tables,
then the optimizer uses a cost-based approach and optimizes with a goal of
best
throughput. If the data dictionary contains only some statistics, then the
cost-based approach is used, and the optimizer must guess the statistics for
the
subjects without any statistics. This can result in sub-optimal execution
plans. If
the data dictionary contains no statistics for any of the accessed tables,
then the
optimizer uses a rule-based approach.
</quote>
Regards,
Dimitre
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