| Oracle FAQ | Your Portal to the Oracle Knowledge Grid | |
 |
 | |||
| Oracle FAQ | Your Portal to the Oracle Knowledge Grid | |
|
| |||
Home -> Community -> Mailing Lists -> Oracle-L -> RE: optimizer_features_enabled
Some of our teams have found that your SQL statements could get consistent
execution plans between the versions of Oracle..
In some cases, we had the execution plans/explain plans take a nose dive for
performance in 9.2 CBO. So without re-writing the SQL; the
"optimizer_features_enabled" feature "assisted" some to obtain similar
performance as the 817 CBO provided. In a couple of cases; we used it rather
successfully. And the latest effort it was not an option after performing
testing. The dev team identified some undocumented parameters that assisted
in providing better results.
But the end game was to weed out the SQL in testing; and change it so the 92
optimizer "liked" it better..
greg
-----Original Message-----
From: Wolfgang Breitling [mailto:breitliw_at_centrexcc.com]
Sent: Friday, August 20, 2004 12:00 AM
To: oracle-l_at_freelists.org
Subject: Re: optimizer_features_enabled
I have not done exhaustive tests with that parameter, but based on my
experience and from what I read from other people on newsgroups I have the
impression that it is only certain features which get disabled when
backdating optimizer_features enabled (just as the name suggests). You
don't get total 8.1.7 behaviour by setting optimizer_features_enabled =
8.1.7. New algorithms and heuristics appear to be unaffected. But I could
be wrong.
There is a metalink note that explains which features are enabled based on
which setting.
At 07:23 PM 8/19/2004, you wrote:
>Hi,
>
>I have a question around the
>optimizer_features_enabled parameter. If we set this
>parameter to 8.1.7 in a 9.2 database does the RDBMS
>kernel use 8.1.7 optimization algorithms only or does
>it use the 9.2 optimization algorithms but limit the
>CBO to only using 8.1.7 CBO features?
>
>Any clarification on this would be much appreciated.
>
>Regards,
>
>Mark
Regards
Wolfgang Breitling
Centrex Consulting Corporation
http://www.centrexcc.com
-- Archives are at http://www.freelists.org/archives/oracle-l/ FAQ is at http://www.freelists.org/help/fom-serve/cache/1.html ----------------------------------------------------------------- ---------------------------------------------------------------- Please see the official ORACLE-L FAQ: http://www.orafaq.com ---------------------------------------------------------------- To unsubscribe send email to: oracle-l-request_at_freelists.org put 'unsubscribe' in the subject line. -- Archives are at http://www.freelists.org/archives/oracle-l/ FAQ is at http://www.freelists.org/help/fom-serve/cache/1.html -----------------------------------------------------------------Received on Fri Aug 20 2004 - 06:50:58 CDT
 |
 |