>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.
I might add that this 'on-the-fly' estimated statistics is not saved for
future use.
- Kirti
> -----Original Message-----
> From: Jared Still [SMTP:[EMAIL PROTECTED]]
> Sent: Tuesday, June 05, 2001 8:40 PM
> To: Multiple recipients of list ORACLE-L
> Subject: Re: Compute statisics
>
> 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
> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.com
> --
> Author: Jared Still
> INET: [EMAIL PROTECTED]
>
--
Please see the official ORACLE-L FAQ: http://www.orafaq.com
--
Author: Deshpande, Kirti
INET: [EMAIL PROTECTED]
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