I never said CBO came up with smarter plans...what I
said was that you get a optimizer decision that is
very similar to rule-based (which is where the
original posted is migrating from) and as a bonus,
rather than just choosing "any old index" as the rule
based optimizer does, the cbo will hopefully make a
smarted choice about which index to use (whilst still
leaning toward the NL plans).
I never claimed this was optimal - but what it *does*
do is result in a fairly easy way to slowly move from
rule-based to cost-based.
hth
connor
- Binley Lim <Binley.Lim_at_ird.govt.nz> wrote: >
> That parameter does not make CBO comes up with any
> smarter plans - just more likely to choose NLJ
> whether its better or not. HJ can outperform all
> other joins in a lot of cases if you maintain
> statistics judiciously, including the appropriate
> use of histograms.
>
> >>> hamcdc_at_yahoo.co.uk 11/21/02 12:24a.m. >>>
> One quick hack is to set the "optimizer_..." params
> to
> make indexes look super-wonderful, which then gives
> you a rule-based "look and feel" with hopefully a
> little smarter selection of indexes as a bonus
>
> hth
> connor
>
> --- VIVEK_SHARMA <VIVEK_SHARMA_at_infosys.com> wrote:
> >
> > Consider using OUTLINES for Fixed Execution plans
> > especially for Batch Queries
> >
> > This will prevent a Sudden Increment in Processing
> > Time due to Optimizer choosing NON-Optimal paths
> >
> >
> > -----Original Message-----
> > Sent: Wednesday, November 20, 2002 3:20 AM
> > To: Multiple recipients of list ORACLE-L
> >
> >
> > We will be in the same process soon.
> > We'll have to consolidate over 100 instances to
> > something between 40-60 instances and switch from
> > RBO
> > to CBO.
> >
> > Any tips are welcome.
> >
> >
> > --- Steve McClure <smcclure_at_usscript.com> a écrit
> :
> > >
> > I am just starting to look at converting to the
> cost
> > > based optimizer, and am
> > > hoping a few of you can share insights from
> having
> > > done so in the past. Our
> > > application is an oltp system developed on
> 7.3.4.
> >
> > > We made liberal use of
> > > +0 and other RBO "hints", and I am wondering if
> > > these are going to cause us
> > > troubles when switching to CBO.
> > >
> > > We have been on 8i since April of this year,
> and
> > I
> > > am just now starting to
> > > gather information on the inner workings of the
> > CBO.
> > > I know it is where I
> > > want to be, I am just looking to see how
> > > painful/painless the transition
> > > will be.
> > >
> > > Steve McClure
> > >
>
>
> --
> Please see the official ORACLE-L FAQ:
> http://www.orafaq.com
> --
> Author: Binley Lim
> INET: Binley.Lim_at_ird.govt.nz
>
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Received on Thu Nov 21 2002 - 02:48:25 CST
