Method R Discussion GroupMethod R helps developers, DBAs, and decision-makers optimize Oracle-based software in every phase of the software life cycle. |
||
Discuss Method R products, techniques, and events. Ask new questions or post your own responses. |
What is the difference between EXPLAIN PLAN and EXECUTION PLAN?
EXPLAIN PLAN is an Oracle command that allows you to ask the Oracle kernel what sequence of steps it "believes" it would use to execute a given SQL statement. EXPLAIN PLAN produces a *predicted execution plan*.
An execution plan is the actual sequence of steps that the Oracle kernel has used (past tense) to execute a given SQL statement. EXPLAIN PLAN is a pretty good predictor of execution plans, but it's not perfect. Sometimes it tells you one plan, but when you actually run a query, Oracle uses a different plan. The cases in which this occurs are well documented in our SQL Optimization courses. |
Powered by FogBugz