Re: consistency in cost?

Actually, changing the number of CPU's in the box will affect when hash joins are used.

Jared

On Tuesday 08 May 2001 11:12, Nicoll, Iain (Calanais) wrote:
> 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

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-- 
Author: Jared Still
  INET: jkstill_at_cybcon.com

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