Re: How are SQL Profiles calculated?

From: Greg Rahn <>
Date: Thu, 8 Jan 2009 09:36:11 -0800
Message-ID: <>

On Thu, Jan 8, 2009 at 8:02 AM, Charles Schultz <> wrote:
> How does Oracle come up with those scale numbers?

Basically by using the estimated vs. actual cardinality numbers.

> How are those scale numbers more significant than gathering a complete statistical picture?

They are generally more accurate as they are a result of executing portions of the full plan to get the actual cardinality. The optimizer estimates (forecasts) the number of rows based on what data points it knows, but dbms_sqltune is using hindsight. SCALE_ROWS is basically the "fudge factor" to "reconcile" the optimizer's estimate to result in the actual row source cardinality.

Hope that helps.

Greg Rahn
Received on Thu Jan 08 2009 - 11:36:11 CST

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