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Home -> Community -> Mailing Lists -> Oracle-L -> Re: Why CBO choose wrong way?
Hi Lex,
Interesting.
I am dealing with a new version of a COTS package that does that in a login trigger. (sets FIRST_ROWS that is)
This had me rather confused for a few minutes when I would get a good plan for some problem queries when logged in as myself, and a very poor plan for the same query when logged in as the application account.
At that point I started looking for a trigger.
I am now working on convincing them to drop the trigger and stick with the default 'CHOOSE', or at least change to FIRST_ROWS_n.
Jared
On 5/28/05, Lex de Haan <lex.de.haan_at_naturaljoin.nl> wrote:
>
> From: info [mailto:info_at_naturaljoin.nl]
> Sent: Saturday, May 28, 2005 10:18
> To: 'zhai_jingmin_at_yahoo.com'; 'oracle-l_at_freelists.org'
> Subject: RE: Why CBO choose wrong way?
> the CBO thinks it saves an expensive(?) sort this way, to satisfy the
> order by
> clause.
> why do you have optimizer_mode set to FIRST_ROWS? and even if you need it,
> then
> you should at least use the flavors with a trailing number. FIRST_ROWS is
> only
> maintained for backward compatibility, and is based on heuristics rather
> than
> statistics. and why do you have optimizer_index_cost_adj set to 30?
>
>
-- Jared Still Certifiable Oracle DBA and Part Time Perl Evangelist -- http://www.freelists.org/webpage/oracle-lReceived on Mon May 30 2005 - 18:24:20 CDT
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