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Method R Discussion Group

Laredo uses the explain plan for impact analysis. The execution plan, in most cases, is different from the explain plan. If you use the explain plan, you may expose yourself to errors in the execution plan. How does Hotsos deal with this?

First of all, your assumption is incorrect.

The output of EXPLAIN PLAN, a predicted execution plan, is almost always the actual execution plan given a large (e.g., 10,000+) population of plannable SQL statements.

But even if your assumption were correct, it would be irrelevant because when EXPLAIN PLAN gives the wrong answer it always gives the same wrong answer given a fixed set of inputs. In other words, the EXPLAIN PLAN command's behavior is predictable. If you change the inputs you get a different plan.

The primary purpose of Laredo is identify the minimal number of statements whose execution plans have changed. Even if Laredo doesn't assess the efficiency of a predicted execution plan, at least it narrows the number of statements whose execution plans you have to assess. That, by itself, is an amazing time saver.