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Home -> Community -> Mailing Lists -> Oracle-L -> RE: Stored Outlines and Optimizer Mode
Paula,
Please let me know if this works out and what you did. As far as I know, stored outlines do not work under RULE as they are a CBO feature. However, it will still work without database statistics, if you are telling the query what to do (as we would in RULE). For example, we have OPTIMIZER_MODE=CHOOSE at our site and we use a mixture of RULE and COST optimized queries. We do not use any database statistics - instead we use HINTS (in some of the queries, which make them use CBO), but since the query is already optimally written (using RULEs), we are able to make the best use of a RULE-COST combination.
Watch out for when you upgrade to 9i - since the CBO is still undergoing enhancements and the RBO is sitting still, you may hit unanticipated problems with queries mis-behaving.
Cheers,
Vasan (x5707)
Mailpoint 28
Vasan Srinivasan * 020 8313 5707 Infrastructure Service Manager * 020 8313 5646Oracle Technologies
of my Employer
============================================
-----Original Message-----
From: Paula Winkler [mailto:pw41972_at_yahoo.com]
Sent: 19 March 2004 04:07
To: oracle-l_at_freelists.org
Subject: RE: Stored Outlines and Optimizer Mode
Thank you Dennis, John, and Jared -
Our database configuration setting is OPTIMIZER_MODE=RULE in Oracle 8.1.7.4 with no database statistics. We came up with the optimal plans for the exceptional SQLs by running the 3rd-party application under CBO in one of our test environment which mirror Production. We can't use hints as we have no control over the generated SQLs. We can't move the application completely to CBO therefore thought using stored outlines in a Oracle8i RULE-based optimizer environment may be a solution. Our intention is stay with the OPTIMIZER_MODE=RULE without any database statistics and with the addition of the handful of stored outlines. It seems stored outlines under Oracle8i+ doesn't require 1) OPTIMIZER_MODE to be CHOOSE or COST and 2) the collection of database statistics.
Just wanted to get some insights from gurus on this great list before we conduct additional validation testing.
Jared.Still_at_radisys.com wrote:
Oh, but you *will* get CBO if you use hints.
I mention this because it was referred to earlier in this thread.
Oracle uses default values when statistics are lacking.
This is 9.2.0.4 on RH 7.1
Jared
16:32:44 SQL>
16:32:44 SQL>alter session set optimizer_mode = rule;
Session altered.
16:32:44 SQL>
16:32:44 SQL>drop table cbo;
Table dropped.
1 6:32:44 SQL>
16:32:44 SQL>create table cbo 16:32:44 2 as 16:32:44 3 select owner, object_name, object_type 16:32:44 4 from dba_objects 16:32:44 5 /
Table created.
16:32:45 SQL> 16:32:45 SQL> 16:32:45 SQL>create index cboidx on cbo(owner, object_name) 16:32:45 2 /
Index created.
16:32:46 SQL> 16:32:46 SQL> 16:32:46 SQL>delete from plan_table;
6 rows deleted.
16:32:46 SQL>
16:32:46 SQL>commit;
Commit complete.
16:32:46 SQL> 16:32:46 SQL>explain plan 16:32:46 2 set statement_id 'Q1' 16:32:46 3 for 16:32:46 4 select count(*) 16:32:46 5 from cbo 16:32:46 6 /
Explained.
16:32:46 SQL> 16:32:46 SQL> 16:32:46 SQL>explain plan 16:32:46 2 set statement_id 'Q2' 16:32:46 3 for 16:32:46 4 select /*+ index(cbo cboidx) */ count(*) 16:32:46 5 from cbo 16:32:46 6 /
Explained.
16:32:46 SQL> 16:32:46 SQL> 16:32:46 SQL>@showplan9i Q1 16:32:46 SQL> 16:32:46 SQL>-- showplan9i.sql 16:32:46 SQL> 16:32:46 SQL>SET PAUSE OFF 16:32:46 SQL>SET VERIFY OFF 16:32:46 SQL>set trimspool on 16:32:46 SQL>set line 200 arraysize 1 16:32:46 SQL>clear break 16:32:46 SQL>clear compute 16:32:46 SQL> 16:32:46 SQL> 16:32:46 SQL>select * 16:32:46 2 from table(dbms_xplan.display( 'PLAN_TABLE', '&&1')) 16:32:46 3 /
PLAN_TABLE_OUTPUT
| 0 | SELECT STATEMENT | | | | | | 1 | SORT AGGREGATE | &nb sp; | | | | | 2 | TABLE ACCESS FULL | CBO | | | | --------------------------------------------------------------------
Note: rule based optimization
10 rows selected.
16:32:46 SQL> 16:32:46 SQL> 16:32:46 SQL> 16:32:46 SQL>@showplan9i Q2 16:32:46 SQL> 16:32:46 SQL>-- showplan9i.sql 16:32:46 SQL> 16:32:46 SQL>SET PAUSE OFF 16:32:46 SQL>SET VERIFY OFF 16:32:46 SQL>set trimspool on 16:32:46 SQL>set line 200 arraysize 1 16:32:46 SQL>clear break 16:32:46 SQL>clear compute 16:32:46 SQL> 16:32:46 SQL> 16:32:46 SQL>select * 16:32:46 2 from table(dbms_xplan.display( 'PLAN_TABLE', '&&1')) 16:32:46 3 /
PLAN_TABLE_OUTPUT
| 0 | SELECT STATEMENT | | 1 | | 19 | | 1 | SORT AGGREGATE | | 1 | | | | 2 | TABLE ACCESS FULL | CBO | 2000 | | 19 | --------------------------------------------------------------------
Note: cpu costing is off
10 rows selected.
16:32:46 SQL>
16:32:46 SQL>
DENNIS WILLIAMS <DWILLIAMS_at_LIFETOUCH.COM>
Sent by: oracle-l-bounce_at_freelists.org
03/18/2004 02:10 PM
Please respond to oracle-l
To: "'oracle-l_at_freelists.org'" <oracle-l_at_freelists.org>
cc:
Subject: RE: Stored Outlines and Optimizer Mode
Paula
How are you ensuring RULE is used today? Not analyzing tables? That is an issue because CBO needs you to analyze, which will cause everything to be CBO. If the SQL has a hint, then analyze won't be a problem, but you won't get CBO anyway.
Dennis Williams
DBA
Lifetouch, Inc.
dwilliams_at_lifetouch.com
-----Original Message-----
From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org]On
Behalf Of Paula Winkler
Sent: Thursday, March 18, 2004 3:35 PM
To: oracle-l_at_freelists.org
Subject: RE: Stored Outlines and Optimizer Mode
Thank you Niall and Lex for your responses.
We have a 3rd-party Oracle8i system running under the RULE-based optimizer. We have identified a handful of poor performing SQLs. We can't change the generated SQLs therefore we are looking into using stored outlines to store the access plans for those exceptional SQLs. Our thought is CBO would kick in for the SQLs with the stored outlines and RBO would kick in for the other acceptable SQLs. Does this sound like it will work?
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