Re: Optimizer

Hi.

 There is a new feature called QUERY OUTLINE from 8.1.5 and up.  I didn't try it yet, but it's supposed to solve the problem  of execution plan stability in CBO environment.

 Anyway RBO can not garantee you anything, because index selection  is dependant on index creation time ( drop indexes and re-create them  in different from original sequence and bingo - RBO may select another  index ). Anothe question is what happens when you add/drop indexes?

 HTH. Michael.

In article <8fpk5p$uh8$1_at_nnrp1.deja.com>,   Allan Plesniarski <aplesnia_at_my-deja.com> wrote:
> When you want to guarantee the same execution plan for a query in all
> cases, the rule hint is still required. If the cost based optimizer
 is
> not generating efficient plans for all volumes of data, the sql may be
> re-written to best use the rule based approach.
>
> In article <958415535.8780.0.pluto.d4ee154e_at_news.demon.nl>,
> "Sybrand Bakker" <postbus_at_sybrandb.demon.nl> wrote:
> > Rule based optimization is obsolete since 7.1. It is not enhanced
 anymore,
> > so no parallel query, no bitmap indexes, no hints, no nothing.
> > That alone is a reason to forget about it.
> > And yes you can run into wrong query plans because of 'aged'
 statistics.
> >
> > Hth,
> >
> > Sybrand Bakker, Oracle DBA
> >
> > Jeff Hunter <marist89_at_excite.com> schreef in berichtnieuws
> > 391f5eec_at_defiant.btitelecom.net...
> > > I thought I read somewhere that Rule-based optimization will be
 going away
> > > in future versions... When using cost based optimization, your
 objects
 need
> > > to be optimized on a regular basis.
> > >
> > > RL <mark_at_mark-it.demon.co.uk> wrote in message
> > > news:958301705.11737.0.nnrp-14.9e9864e7_at_news.demon.co.uk...
> > > > I appreciate this is probably a huge topic, but can anyone point
> > > > me in the direction of information about the Oracle optimizer.
> > > > In particular, what should the optimizer rule be
> > > > set to (CHOOSE, RULE etc). If the optimizer is using cost
> > > > based optimization, is it necessary to analyze tables regularly
 or
> > > > can it be run once. Does the cost based optimizer always give
 better
> > > > results that the rule based optimizer or are there too many
 variables
> > > > to decide this.
> > > >
> > > > Are there are good tools to help with optimization, (where to
 add
> > > > indexes etc), I found tkprof output very cryptic.
> > > >
> > > > Many thanks
> > > >
> > > >
> > > >
> > >
> > >
> >
> >
>
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> Before you buy.
>

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Before you buy. Received on Mon May 15 2000 - 00:00:00 CDT