Re: Better cardinality estimate when dialing optimizer_features_enable back

  • From: Neil Kodner <nkodner@xxxxxxxxx>
  • To: Randolf Geist <info@xxxxxxxxxxxxxxxxxxxxx>
  • Date: Tue, 24 Nov 2009 17:52:29 -0500

Would it help that I have optimizer_dynamic_setting at 2 at the database
level?  I tried using a dynamic_sampling hint with a value of 4; that didn't
make a difference on the cardinality estimate.

On Tue, Nov 24, 2009 at 5:47 PM, Randolf Geist
<info@xxxxxxxxxxxxxxxxxxxxx>wrote:

> > So.... looking through this thread.... any way that dynamic sampling
> > could be a bad boy here?
> >
> > Just a wild, off the cuff thought....
> >
> > RF
> >
> > Robert G. Freeman
> > Oracle ACE
>
> That is actually very good idea  (all the time I had the impression I
> missed something obvious) - in principle dynamic sampling should be able to
> get the selectivity right.
>
> In this particular case the question would be if the overhead induced by
> dynamic sampling would outweigh the benefit of it. It depends largely on the
> sample level required to get helpful estimates - it might be worth a try to
> add a "DYNAMIC_SAMPLING(LETTER_BIN 2)" hint - starting with a low sample
> level (may be even 1). Higher sampling levels will get the selectivity right
> but the overhead might be significant then.
>
> Regards,
> Randolf
>
> Oracle related stuff blog:
> http://oracle-randolf.blogspot.com/
>
> Co-author of the forthcoming "OakTable Expert Oracle Practices" book:
> http://www.apress.com/book/view/1430226684
>
> http://www.amazon.com/Expert-Oracle-Practices-Database-Administration/dp/1430226684
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