What is an optimizer ?

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What is an optimizer ?

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An optimizer is an Oracle process that determines the best plan for executing a statement. The optimizer uses built-in rules and cost methods for determining the best plan. The Oracle server uses two optimization methods:

  • Cost-based optimization
  • Rule-based optimization
In the cost-based optimization method, the Oracle server chooses the plan that has the lowest cost out of the plans that are available for the statement issued. The cost factors that are considered are I/Os, CPU cycles consumed, and the number of sortings performed.

In the rule-based optimization method, the Oracle server uses some predefined rules for selecting the execution plan. The optimizer uses the rule-based approach if there are no statistics present in the data dictionary for any of the accessed objects.


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