Re: Different execution plans for same query with same cost
- From: Wolfgang Breitling <breitliw@xxxxxxxxxxxxx>
- To: jo_holvoet@xxxxxxxx
- Date: Thu, 03 Mar 2005 10:39:18 -0700
The optimizer IS deterministic. If it generates a different plan - even
with the same cost - then something that affects its decision path was
different - even if you think everything is the same.
How about posting some details.
jo_holvoet@xxxxxxxx wrote:
> Hi all,
>
> Oracle 8.1.7.4 on 64-bit Solaris 8.
> I've run into a situation where the same query run on the same instance
> from the same session gets a different execution plan from one run to the
> next (confirmed this with the STAT-lines in a 10046 trace). Both execution
> plans apparently get the same cost from CBO. Am I right in thinking that
> in such a case the CBO is not "deterministic" (i.e. it will not arrive at
> the same plan every time) but randomly arrive at one of the plans with the
> same lowest cost ?
>
"Both execution plans apparently get the same cost from CBO"
How do you know?
--
Regards
Wolfgang Breitling
Centrex Consulting Corporation
www.centrexcc.com
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