Re: System Statistics and the CBO
- From: Wolfgang Breitling <breitliw@xxxxxxxxxxxxx>
- To: Mladen Gogala <mgogala@xxxxxxxxxxxxxxxxxxxx>
- Date: Fri, 17 Jun 2005 09:09:29 -0600
Mladen,
That's something I was wondering myself. My statement below may very
well be a bit too broad. I should rephrase it to
"From all I know, the CBO reverts back to the prior IO costing model if
mreadtim < sreadtim".
The cpu costing part of the new CBO cost algorithm may still be used.
On the other hand I am not sure how much trust to put into what
DBMS_XPLAN.DISPLAY is telling me. I have had cases where suddenly it
reported CPU cost percentages without system stats being present.
Finally, my experiences are mostly with 9iR2 and things like that could
work slightly, or not so slightly, differently in 10g.
Mladen Gogala wrote:
Wolfgang Breitling wrote:
Wolfgang, when I do SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY) it tells me
that "CPU costing is ON, despite
the fact that I fiddled with sys.aux_stats$ and changed sreadtime to be
mreadtime+1. Is DBMS_XPLAN lying to me? The
version is 10.1.0.4 on Linux.
--
Regards
Wolfgang Breitling
Centrex Consulting Corporation
www.centrexcc.com
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