Re: What are the gory details behind DBMS_STATS.AUTO_SAMPLE_SIZE?

Hi

It isn't documented and is subject to change from version to version and patchset to patchset. That all said sql_trace can be enlightening here. You even get some curious hints to play with in your sandbox.

cheers
Niall

On 6/2/06, Schultz, Charles <sac_at_uillinois.edu> wrote:
>
> I am curious how the algorithms behind DBMS_STATS.AUTO_SAMPLE_SIZE actually
> pick a sample size (10.2.0.1). We have witnessed a case where the sample
> size for a particular column was reduced 91.6%, causing the number of
> distinct values to be inaccurate, further causing a query to choose an FTS
> rather than an index. As far as I can tell, the skew has not changed that
> much, if at all, and the overall volume has increased by ~1%.
>
> I am aware of workarounds (compute stats, lock stats, use an outline,
> etc), but like I said, I am really curious why the algorithm made such a
> drastic jump in the first place. I could not easily locate an appropriate
> white paper on metalinks, and I get too many hits on Google. Can anyone help
> satiate my burning desire to know? =)
>
> *charles schultz*
> *oracle dba*
> *aits - adsd*
> *university of illinois*
>
>

-- 
Niall Litchfield
Oracle DBA
http://www.orawin.info

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