Re: Dynamic Sampling: some questions about the guts
- From: "Rajeev Prabhakar" <rprabha01@xxxxxxxxx>
- To: sacrophyte@xxxxxxxxx
- Date: Sat, 1 Dec 2007 19:48:10 -0500
One more thing, can you try deleting histograms and give it a try.
On Dec 1, 2007 7:29 PM, Rajeev Prabhakar <rprabha01@xxxxxxxxx> wrote:
> Charles
>
> Unless you have already tried it, could you try the following
> and let us know the results :
>
> a) gathering stats with compute OR high sample (not AUTO).
> b) use dbms_stats.set_column_stats for the relevant column.
>
> -Rajeev
>
> On Dec 1, 2007 5:34 PM, Charles Schultz <sacrophyte@xxxxxxxxx> wrote:
>
> >
> >
> > The interesting part is that if I calc stats (estimate_percent => null),
> > the CBO chooses an index for C3. We do not have an index for all 4 columns,
> > but under certain circumstances, the CBO will choose that other index for
> > C2, using three of the four columns in an access path, and CURR_REC_IND as a
> > filter. Those of you with astute eyes will notice the VPD column and
> > correctly assume we are using FGAC as well. That ends up being the most
> > optimal path, and I trying to understand why. Obviously, there is a whole
> > lot more information I could share, but first I wanted to understand how
> > dynamic sampling was playing a part in this.
> >
> >
> > Rajeev, to answer your questions:
> > 1) Have tried with bucket 1, default and 254.
> > 2) exact
> > 3) Yes, all the time, every day. =) The parameters depend on what I am
> > trying to do. I like to calc stats in these cases to give the CBO as much
> > info as possible.
> >
> > Not sure how those questions/answers help, but there you go.
> >
> >
> > Thanks all,
> >
> >
> > --
> > Charles Schultz
>
>
>
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