Rule Based Optimization Going Away?

From: Norman Dunbar <Norman.Dunbar_at_lfs.co.uk>
Date: Fri, 4 Oct 2002 09:25:08 +0100
Message-ID: <E2F6A70FE45242488C865C3BC1245DA702BE73BA@lnewton.leeds.lfs.co.uk>

Morning Jonathan,

>> On top of this, Oracle 9.2 allows for dynamic
>> (query run time) sampling of statistics - and
>> this may turn out to be a good solution to
>> some problems of skewed data.

I had heard that this was the way of things before 9.2 in that any query using CHOOSE as the optimiser mode and where stats existed on at least one table,, then the stats would be dynamically gathered, used and discarded hence adding a performance overhead. If the same query was run again later, the stats would be gathered dynamically again and so on.

On the other hand, I've been told that in the event of a CHOOSE and some tables with no stats, Oracle would assume stats of something like 100 rows per block etc.

Have you any idea which is correct ?

Regards,
Norman.

PS. Did you reveive a couple of FAQ answers recently from me ?

Norman Dunbar
Database/Unix administrator
Lynx Financial Systems Ltd.
mailto:Norman.Dunbar_at_LFS.co.uk

Tel: 0113 289 6265
Fax: 0113 289 3146
URL: http://www.Lynx-FS.com
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Received on Fri Oct 04 2002 - 03:25:08 CDT