Re: consistency in cost?

Interesting...CHOOSE means Oracle will decide whether to use RULE or COST. But a CHOOSE hint will force use of COST. Kind of diminishes the meaning of CHOOSE, doesn't it? Seems like a pointless hint...

>>> rabbit_at_emirates.net.ae 05/08/01 11:45PM >>>
If the system is Rule based and you code Hints, the CBO will be automatically invoked
Sam

• Original Message ----- To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com> Sent: Tuesday, May 08, 2001 10:12 PM

> Forgive my ignorance but I thought hints were only for cost based
optimizer.
>
>
> Have you checked in case anybody has changed any parameters while the
system
> is running as I know that changing the hash_area_size can change the
> execution plan?. Are you using parallelism as if a table had to be
> recreated for any reason and its degree changed it might do a FTS?
>
> Cheers
>
> Iain Nicoll
>
>
> -----Original Message-----
> Sent: 08 May 2001 17:31
> To: Multiple recipients of list ORACLE-L
>
>
> Jared,
> The only difference is about a weeks worth of extra data. Well, the
hardware
> is also different (Ultra450 vs. Ultra 5000. Also 1 vs 4 CPU). But
> regardless, shouldn't init.ora optimizer_mode=choose be identical to
> optimizer_mode=rule with hint=choose? If I have the time, I'll try to set
up
> a couple of systems and examine by moving stats and taking some 10053
dumps.
> (one of the ones giving me a problem is in production so I have limited
play
> time there).
>
> Henry
>
> -----Original Message-----
> Sent: Tuesday, May 08, 2001 12:56 AM
> To: ORACLE-L_at_fatcity.com; Henry Poras
>
>
>
> Henry,
>
> You say 'nearly identical'.
>
> What are the differences?
>
> Are the 2 databases on the same platform?
>
> If not, what are the differences, hardware and OS?
>
> Jared
>
>
> On Monday 07 May 2001 21:55, Henry Poras wrote:
> > I am working with an 8.1.6 database on Solaris 2.6 and I am wondering if
> > there is any consistency in the optimizer. We have two nearly identical
> > databases (one a clone from two weeks ago). A five table join has nearly
> > the identical execution plan on the two databases. The difference is in
> the
> > access method of the fourth table in the join; in one case it is
accessed
> > by a FTS and in the other, by Index. This difference has a large effect
on
> > performance. Statistics are nearly identical for this table in both
> > databases (I looked at dba_tables, dba_indexes, dba_col_tables). Also,
the
> > init.ora is the same. When I changed the optimizer_mode to rule and
added
> a
> > 'choose' hint to the query, the execution plan was different again. I
will
> > look into this a bit further and post my results. Just wondering about
> > other's experiences. Thanks.
> >
> > Henry
> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.com
> --
> Author: Henry Poras
> INET: Henry.Poras_at_ctp.com
>
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-- 
Author: Sam Roberts
  INET: rabbit_at_emirates.net.ae 

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