Re: Rule-based vs cost-based optimization

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 Sun May 06 2001 - 05:07:13 CEST