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In Oracle Enterprise Manager, in "Performance > Top Activity", you can click a SQL that is being executed and then go to the Plan tab to see SQL execution plan.

For the execution plan, the Enterprise Manager shows a table with the execution plan steps. That table has the following columns:

Operation   Object	Object Type	Order	Rows	Size (KB)	Cost	Time (sec)	CPU Cost	I/O Cost

I'd like to understand the meaning of each one of these columns, but I did not find any documentation on this.

Can you recommend me any document or explain the meaning of the columns?

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up vote 2 down vote accepted

These columns are all coming from the V$SQL_PLAN table, so you can use the documentation for that view. The documentation is somewhat limited, however, because exactly how the optimizer makes some of these estimates is very complicated, depending on the specific operation, system statistics, object statistics, and optimizer parameters among other things. And every version of Oracle will likely calculate things a bit differently because the optimizer group is constantly tweaking their formulas. Jonathan Lewis's Cost-Based Oracle Fundamentals is the most comprehensive source for learning exactly how the optimizer costs different operations.

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Thanks for the suggestions Justin! – b.roth Nov 15 '09 at 21:33

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