Database Systems Practice Test

Which concept best describes the cost associated with a query’s execution, used by the optimizer to compare plans?

recovery log query optimization query cost operational information

Correct Answer:

query cost

Explanation:

In query optimization, the optimizer assigns a numeric estimate of the work required to run a plan, called the query cost. This cost reflects expected resource use—primarily I/O and CPU, and sometimes memory—based on statistics and a cost model. Plans with lower estimated costs are preferred because they are expected to execute more efficiently, so the optimizer can compare options and pick the cheapest one. The recovery log is about durability and crash recovery, not about planning or comparing query plans. The broader process is query optimization itself, not the single metric used to evaluate plans. Operational information isn’t the standard term for the plan-cost measure either.

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