Oracle SQL Resource Usage, Some Concerns

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In this article I will discuss some important concerns related to database resource usage associated with Oracle SQL operations.

New execution plan columns:

Oracle9i and above provide several new execution plan columns. One can run specialized queries to see estimates of resource usage associated with specific steps of Oracle SQL execution:

CPU Cost of the operation:

• The CPU cost of the operation is estimated by the optimizer's cost-based approach.
• CPU_COST column is null for the statements that use the rule-based approach.
• The value of the CPU_COST column is proportional to the number of machine cycles required for the operation.

I/O cost of the operation: 

• The I/O cost of the operation is estimated by the optimizer's cost-based approach.
• IO_COST column is null for the statements that use the rule-based approach.
• The value of the IO_COST column is proportional to the number of data blocks read by the operation

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