Re: CBO irregularity
- From: "Jonathan Lewis" <jonathan@xxxxxxxxxxxxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Mon, 7 Jun 2004 22:13:51 +0100
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@xxxxxxxxxx>
:To: <oracle-l@xxxxxxxxxxxxx>
: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.
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