Re: How are SQL Profiles calculated?

From: Charles Schultz <sacrophyte_at_gmail.com>
Date: Thu, 8 Jan 2009 11:38:44 -0600
Message-ID: <7b8774110901080938w53ddc830t608c79178a604756_at_mail.gmail.com>

Yes, that explains a lot, thank you very much! It is exciting how 11g takes this concept ("cardinality feedback", thanks Wolfgang!) even further.

On Thu, Jan 8, 2009 at 11:36 AM, Greg Rahn <greg_at_structureddata.org> wrote:

> On Thu, Jan 8, 2009 at 8:02 AM, Charles Schultz <sacrophyte_at_gmail.com>
> 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.
>
> --
> Regards,
> Greg Rahn
> http://structureddata.org
>

-- 
Charles Schultz

--
http://www.freelists.org/webpage/oracle-l

Received on Thu Jan 08 2009 - 11:38:44 CST