Re: Auto stats gathering is not sufficient - what now?
- From: Kellyn Pedersen <kjped1313@xxxxxxxxx>
- To: greg@xxxxxxxxxxxxxxxxxx, david@xxxxxxxxxxxxxxxxxx
- Date: Thu, 10 Feb 2011 10:15:45 -0800 (PST)
I was thrilled when Greg sent this link to me after I had complained about this
for the umpteenth time, (sill girl just argued the point on her research
instead
of looking for data from Oracle that would validate it... :)) I agree and do
tire of seeing dynamic sampling as the top elapsed time in a database that has
sorely neglected statistics and erratic execution plans. Dynamic sampling
should only *enhance* the statistics in a database environment for the CBO, not
replace it....
OK, off my soapbox and I promise to go take a deep breath... :)
Kellyn Pedersen
Multi-Platform Database Administrator
www.pythian.com
http://www.linkedin.com/in/kellynpedersen
http://dbakevlar.com
________________________________
From: Greg Rahn <greg@xxxxxxxxxxxxxxxxxx>
To: david@xxxxxxxxxxxxxxxxxx
Cc: tkiernan@xxxxxxxxxxx; oracle-l@xxxxxxxxxxxxx
Sent: Thu, February 10, 2011 10:31:48 AM
Subject: Re: Auto stats gathering is not sufficient - what now?
I would advise against that. Dynamic Sampling (DS) does not have the
same information that you get from dbms_stats.
"The most common misconception is that DS can be used as a substitute
for optimizer statistics." 2nd sentence from
http://blogs.oracle.com/optimizer/2010/08/dynamic_sampling_and_its_impact_on_the_optimizer.html
On Thu, Feb 10, 2011 at 12:16 AM, David Aldridge
<david@xxxxxxxxxxxxxxxxxx> wrote:
> You could consider not gathering statistics at all -- delete current
> statistics and lock the table statistics -- and rely on dynamic sampling.
> The usual duration of reporting queries against large tables, particularly
> the consequences for the duration if the execution plan is incorrect,
> generally make the dynamic sampling overhead acceptable.
--
Regards,
Greg Rahn
http://structureddata.org
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