Jusang,
Thanks for that... But still ... Let us wait for more responses...
--
HTH
Regards,
Ganesh R
"Jusung Yang" <JusungYang_at_yahoo.com> wrote in message
news:130ba93a.0306091406.107a841b_at_posting.google.com...
> ganesh_at_gtfs-gulf.com (Ganesh Raja) wrote in message
news:<a8aed4.0306081930.45e2b27_at_posting.google.com>...
> > Hi,
> >
> > I am not sure If James Morle is part of this list but i know people
> > how are on par with him and who answer here .. so i Shoot ...
> >
> > In His Book in Scaling Oracle 8i in Page Number 278. [ He is tlaking
> > here about the Cursor Head and Cursor Body and how Bind Variables are
> > handled]
> > <Quote>
> > The Optimizer Plan can also change between executions, owing to the
> > existence of histograms for the value for a column. If a values is
> > supplied that can be approached in a more effeciaent way as a Reult of
> > cardinality, then a new plan is created and put into a new body ....
> > </Quote>
> >
> > All this while i was thinking that Bind variables dont use Histograms
> > and i here i find a diffrent stmt. Since if we use Hard Coded Values
> > then there will be two Cursor Heads since the Hash Value for them will
> > be diffrent and hence we will use Histograms since the Optimizer Knows
> > what value we have passed.
> >
> > Pls Enlighten.
> >
> > Thanks.
> >
> > Regards,
> > Ganesh R
>
>
> There are probably some misunderstandings somewhere...
>
> Histograms helps the optimizer determine or estimate the selectivity
> of the predicate in the queries. When bind variables are used in the
> predicates, histograms will not be used and selectivity are estimated
> as follows:
>
> 1. For equality predicates : 1/NDV (# of distinct values)
> 2. For range predicates : 5%
> 3. For predicates with like operator : 25%
>
>
> - Jusung Yang
Received on Mon Jun 09 2003 - 21:09:19 CDT
