Hi Jared,
My post was to meant to imply that (say) if (in a
single query - and thats the important bit I missed
out) there were two tables, one with stats, and one
without, then the one without will use defaults (as
quoted in chapter 8 of the same manual)
I was trying to imply that if you've only got half the
stats, then on a query-by-query basic, you're most
likely to toggle between
- 'good' CHOOSE (since all the stats are present for
the objects in this query)
- 'bad' CHOOSE (since some defaults are chosen for
object missing statistics)
- RULE (for queries where all objects have no stats)
Cheers
Connor
- Jared Still <jkstill_at_cybcon.com> wrote: > On
Tuesday 05 June 2001 01:20, Connor McDonald
> wrote:
> > Sounds like nonsense to me...If you have "half"
> > statistics, then the optimizer is going to use
> > defaults for the others,
>
> Conner,
>
> Are you sure about that?
>
> From the Optimizer chapter in the tuning manual:
>
> If the data dictionary contains statistics for at
> least one of the accessed
> tables, then the optimizer uses a cost-based
> approach and optimizes with a
> goal of best throughput. If the data dictionary
> contains no statistics for
> any of the accessed tables, then the optimizer uses
> a rule-based approach.
> This is the default value for the parameter.
>
> ...
>
> If the optimizer uses the cost-based approach for a
> SQL statement, and if
> some tables accessed by the statement have no
> statistics, then the optimizer
> uses internal information (such as the number of
> data blocks allocated to
> these tables) to estimate other statistics for these
> tables.
>
>
> That coupled with the fact that when viewing the
> plan table you can see
> the CBO's use of the statistic would make me think
> otherwise.
>
> Is there some documentation that I missed that
> supports the CBO using
> defaults for analyzed tables when some of them are
> _not_ analyzed?
>
> Or did I just misunderstand your post?
>
> Jared
> --
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> Author: Jared Still
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Received on Wed Jun 06 2001 - 04:32:03 CDT
