Re: cost based optimization

From: <michael_bialik_at_my-deja.com>
Date: Sat, 28 Aug 1999 18:46:51 GMT
Message-ID: <7q9aqq$ko8$1@nnrp1.deja.com>

In article <37C7854E.BCD1E518_at_synergy-infotech.com>, Anurag Minocha <anurag_at_synergy-infotech.com> wrote:
> Hi,
> I am a little confused about Cost Based Optimization.Please help me
out.
>
> 1.Does the cost based optimization work on those sql queries which
dont
> have hints specified in them.?
>
> 2. How frequently should the tables be analysed.
>
> Any help will be greatly appreciated.
>
> Thanks
> anurag
>
> also reply to
> anurag_at_synergy-infotech.com
>
>

Hi.

Yes. CBO works for queries accessing any of the analyzed tables. If you are making a join of n tables and only one of them is analyzed - CBO assumes that all other tables have 0 rows and usually uses FULL access for them.
Analyze your table after EXP/IMP, initial load and any data load that may affect data distribution. Consider using "ESTIMATE STATISTICS" instead of "COMPUTE" for large tables.

Good luck. Michael.

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Share what you know. Learn what you don't. Received on Sat Aug 28 1999 - 13:46:51 CDT