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cbo optimer

In a simple way what is the meaning of cost base optimizer..
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slightwv (䄆 Netminder) Commented:
It is code that uses statistics to choose the best execution plan for whatever the task is.

The old way was rule based.  It had strict rules to follow.  For example, if an index exists, use it no matter what.

The problem here is at times using an index will actually slow down the execution.

See if this helps fill in the gaps:
DavidSenior Oracle Database AdministratorCommented:
Hi walker, for every statement, the Oracle system will attempt to optimize the execution cost.  As slight mentioned, statistics provide the metadata used to evaluate the size and distribution of data.

Is that simple enough? <grins>
Geert GOracle dbaCommented:
it's all in the words
optimize the work based on the cost
the work is the exection of a query following a certain plan
every step in the plan has a certain cost
the best plan usually has the lowest cost

your next question could be what is a hard parse ...
hard parse is working out that execution plan
Chakravarthi AyyalaDatabase AdministratorCommented:
Let me see if i can provide any inputs here.

In a simple way what is the meaning of cost base optimizer..
  => when we go to a market to buy something, we choose a product of low cost(ofcourse, not compromising on the quality).
  => Similarly, Oracle calculates the cost(for each unit of operation viz. performing a full table scan/index unique scan/range scan etc., )and gives us each step in the execution plan and the the cost associated with it.

Just my 2 cents.
walkerdbaAuthor Commented:
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