CBO & RBO

What is CBO and RBO? What is diff between these two?

Questions by jagadeesh9   answers by jagadeesh9

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krishnaindia2007

  • Jun 20th, 2008
 

The job of optimizer is to decide the most efficient method to execute a
query.
There are two types of optimizers in oracle


RBO or Rule Based Optimizer since v6
CBO or Cost Based Optimizer since v7


Rule based optimizer uses set of rules to decide how to execute a given
statement whether to index or not etc. The RBO did not take into account data
distribution or the size of the table


The Cost Based Optimizer (CBO) is a SQL Query optimizer that uses data
statistics to identify the query plan with lowest cost before execution. The
cost is based on the number of rows in a table, index efficiency, etc
Rule based optimizer is not supported from oracle 10g onwards.

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