Re: Rule-based vs cost-based optimization

Keep in mind that any CBO query will never run any faster than a properly constructed RBO query. In other words, CBO will _at best_ only be as good as RBO (done properly). IMO, there is really no reason to go with CBO if you have a good handle on RBO. If you are not familiar with the ins and outs of RBO, then CBO is the way to go, at least according to Oracle. I happen to disagree, but that's just me...

"Ketan Shah" <shahkn_at_home.com> wrote in message news:Bd3J6.50345$B22.12644057_at_news1.rdc2.pa.home.com...
> There is no rule of thumb that will tell you that a query using RULE based
> optimizer will run faster than the CBO. Having said that, oracle has
> improved CBO so much that the tuning experts now agree that the CBO will
> make correct decisions most of the times. On top of that you can look into
> init.ora parameters that will change the weights given to each operations
 in
> CBO. Unfortunately, i dont have my documentation cd handy or else I would
> have given much more precise info. Please go to the following sites for
> further reference :
> technet.oracle.com
> www.hotsos.com
> www.ixora.com.au
> www.orapub.com
>
> These sites have some great documentation and/or white papers and scripts.
>
> Ketan
> "Chris" <me_at_nospam.com> wrote in message
> news:WbKF6.14214$q51.148808_at_news1.gvcl1.bc.home.com...
> > Hope everyone can stand one more question on rule-based vs. cost-based
> > optimization.
> >
> > I know that Oracle recommends that new applications be developed with
 CBO
> > and that Oracle has said that at some point RBO will no longer be
 supported.
> > I also know that some advanced features in 8i won't work with RBO. Can
> > anyone tell me if RBO is still supported in 9i?
> >
> > We have had CBO as a default for years but I am finding that developers
 have
> > been using the RULE hint here and there throughout various applications.
> > They tell me that they just couldn't get decent performance using CBO.
 Does
> > anyone know whether there are certain types of queries that give CBO
 trouble
> > and what (in general) the characteristics of those queries are?
> >
> > If anyone can help, TIA!!
> > --
> > Chris
> >
> >
> >
> >
>
>
Received on Wed May 09 2001 - 15:18:36 CEST