Re: Rule Based Optimization

"Terry Coccoli" <request_at_ifneeded.com> wrote in message news:nugbc.12259289$Of.2046158_at_news.easynews.com...
> Jim Kennedy wrote:
> > "Terry Coccoli" <request_at_ifneeded.com> wrote in message
> > news:Gi_ac.12190390$Of.2034190_at_news.easynews.com...
> >
> >>We have a Siebel implementation and for one query that was taking a long
> >>time to run I asked a DBA to evaluate the explain plan. I noticed that
> >>he chose to evaluate the Rule based optimization. I asked him why and
> >>he said that the Siebel application defaults to Rule based optimization.
> >>
> >>Not that I don't trust him, but I had the impression that Cost based was
> >>the way to go.
> >>
> >>Is it possible to set up a database schema so that it the optimizer
> >>always uses Rule based rather than Cost ? And if anyone knows Siebel,
> >>is this the actual default ?
> >>
> >>
> >>Thanks.
> >>
> >
> >
> > Siebel is rule based.
> > They are about 5 years behind in taking advantage of the database
 technology
> > that the system runs on. Yes, cost is the way to go but not with
 Siebel.
> > They won't support you if you use rule based. (which means you can't do
 a
> > whole bunch of things) One thing that you can do to get around this is
 that
> > if you have a specific query that is better under cost based you can use
 a
> > stored outline. (get Thomas Kyte's book)
> > Jim
> >
> >
>
>
> What happens if you throw in a hint like FIRST_ROWS? Would the
> optimizer accept the hint ?
>
No, because it is rule based. Also you don't have access to edit the SQL Siebel generates for the system. You can however use a logon trigger and set up stored outlines. See Tom Kyte's book for excellent examples of how to do this. (Expert 1 on 1 Oracle)

Jim Received on Sat Apr 03 2004 - 15:26:13 CEST