Re: Dynamic Sampling: some questions about the guts

Charles

Unless you have already tried it, could you try the following and let us know the results :

1. gathering stats with compute OR high sample (not AUTO).
2. use dbms_stats.set_column_stats for the relevant column.

-Rajeev

On Dec 1, 2007 5:34 PM, Charles Schultz <sacrophyte_at_gmail.com> 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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