Re: cost base optimization

From: Ronald <ronr_at_wxs.nl>
Date: Mon, 21 Dec 1998 20:10:14 +0100
Message-ID: <01HW.B2A45BA60005EA03127E4B70@news.wxs.nl>

On Fri, 18 Dec 1998 18:40:45 +0100, Andreas Doerler wrote (in message <914002785.561490_at_news.vbs.at>):
>
> hi!
>
> im running a 7.3.3 db with currently no analyzed tables. i recently tried to
> enable cost based optimization on certain schemas using the
> dbms_utility.analyze_schema procedure.
>
> some queries were really faster. some queries did take the worst-case path
> without using existing indexes and took up to 3000% more resources than
> running in rule-based mode (after deleting the analysations)
>
> whats wrong? why the optimizer ignores existing indexes when a schema is
> fully analyzed? is o733 not capable using the benefits of cbo?
>
> thanks in advance!
>
> <ad>

Check the index stats. You probably hve some indexes that have only a few distinct values. Without histograms the optimizer will NOT use them based on only those stats.

cheers,
--
Ronald.

http://home.wxs.nl/~ronr/RonR.html
The best way to accelerate your computer running windows is at 9.8 m/s^2 ! Received on Mon Dec 21 1998 - 13:10:14 CST