Re: CBO irregularity

From: Jonathan Lewis <jonathan_at_jlcomp.demon.co.uk>
Date: Mon, 7 Jun 2004 22:13:51 +0100
Message-ID: <01b001c44cd4$5853a130$7102a8c0@Primary>

Note in-line

Regards

Jonathan Lewis

http://www.jlcomp.demon.co.uk

http://www.jlcomp.demon.co.uk/faq/ind_faq.html The Co-operative Oracle Users' FAQ

http://www.jlcomp.demon.co.uk/seminar.html Optimising Oracle Seminar - schedule updated May 1st

:----- Original Message -----
:From: "Cary Millsap" <cary.millsap_at_hotsos.com>
:To: <oracle-l_at_freelists.org>
:Sent: Monday, June 07, 2004 9:08 PM
:Subject: RE: CBO irregularity
:

:It's what CBO is built to do: take into account a tremendous number of
:variables, each of which has a right to influence the optimizer's choice
for
:best plan. CBO tends to work pretty well when (a) you give it the
:information it needs, and (b) you let it do its job (okay, and maybe also
:"(c) you wait 'til 9.2 to use it").

I think

    (a)     you give it the information it needs
    (b)    you don't lie to it
    (c)    you don't try to mislead it
    (d)    you don't try to cheat it
    (e)    you don't try to decieve it
    (f)    you don't mess with hints you don't understand
    (g)    you don't just fiddle until something works
    (h)
            .....

(z) you give it a little help to work around a few teensy, weensy buggettes

But the optimizer in 10g is so much better than the ones that went before - it's going create havoc when people upgrade because so
many bugs have been fixed. The optimizer keeps working out the right answers - which means any work arounds you have in place now may cause problems on your 10g upgrade.

Please see the official ORACLE-L FAQ: http://www.orafaq.com

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Received on Mon Jun 07 2004 - 16:10:45 CDT