Oracle 执行计划中一些参数的含义


card是指计划中这一步所处理的行数；cost指cbo中这一步所耗费的资源，这个值是相对值；bytes指cbo中这一步所处理所有记录的字节数，是估算出来的一组值。

·Cost：The cost assigned to each step of the query plan by the CBO. The CBO worksby generating many different execution paths/plans for the same query andassigns a cost to each and every one. The query plan with the lowest cost wins.

·Card：Card is short for Cardinality. It is the estimated number of rows that will flow outof a given query plan step.

·Bytes：The size in bytes of the data the CBO expects each step of the plan toreturn. This is dependent on the number of rows (Card) and the estimated widthof the rows.

相关内容