Re: db file scattered read

From: Wolfgang Breitling <breitliw_at_centrexcc.com>
Date: Sun, 15 Aug 2004 11:11:21 -0600
Message-Id: <6.1.0.6.2.20040815111031.02f964d0@pop.centrexcc.com>

Mladen,

Read my original statement. Nowhere did I say that dynamic sampling does not work. I only stated that only non-analyzed tables are guaranteed to be sampled - and if none of the tables are analyzed you have to first force the use of the CBO - and that in the case of dynamic sampling of analyzed tables, the CBO may discard the sampling results and stay with the dictionary statistics.

At 10:58 AM 8/15/2004, you wrote:

>Wolfgang, my impression was that your original statement was that dynamic
>sampling
>doesn't work. I just wanted to show that it does work, provided the use of
>CBO is
>forced. Unless the CBO is conscienceously forced, the database will use
>RBO if none
>of the tables have statistics. I'm experimenting with ALL_ROWS and and
>OPTIMIZER_INDEX
>parameters to get the desired database behavior. My ultimate goal is to
>convert an 8i
>database using RBO (forced directly by parameter and a periodic job that
>deletes
>statistics from any new table) into a 10g database using CBO, without much
>degradation
>in query performance.
>
>--
>Mladen Gogala
>Oracle DBA

Regards

Wolfgang Breitling
Centrex Consulting Corporation
www.centrexcc.com

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Received on Sun Aug 15 2004 - 12:07:12 CDT