Re: FIRST_ROWS and the data dictionary

Have you recently generated stats from RAU?

Jared

                                                                                       
                                
                    "Boivin, Patrice                                                   
                                
                    J"                      To:     Multiple recipients of list 
ORACLE-L <ORACLE-L_at_fatcity.com>        
                    <BoivinP_at_mar.dfo-       cc:                                        
                                
                    mpo.gc.ca>              Subject:     FIRST_ROWS and the data 
dictionary                            
                    Sent by:                                                           
                                
                    root_at_fatcity.com                                                   
                                
                                                                                       
                                
                                                                                       
                                
                    12/14/01 11:00 AM                                                  
                                
                    Please respond to                                                  
                                
                    ORACLE-L                                                           
                                
                                                                                       
                                
                                                                                       
                                

FYI, I just logged a call with Oracle re. Designer 6.0 vs. all_cons_columns.

A developer noticed that whenever he queries that data dictionary table as part of generating database from server models, the process slows down to a crawl.

If the target doesn't have any constraints, no problem.

I am starting to wonder if it isn't because FIRST_ROWS was specified on this
database, most of the developers are developing forms (6i) so I set the init.ora parameter accordingly.

The Oracle documentation however implies that the CBO only switches to rule when there are no stats if optimizer_mode had been set to CHOOSE, if it's either ALL_ROWS or FIRST_ROWS it tries to use the CBO against the data dictionary anyway. How the CBO can run when there are no stats probably means it defaults to full table scans (?).

OPTIMIZER_MODE = { all_rows | first_rows | rule | choose }

The OPTIMIZER_MODE parameter specifies the approach and mode of the optimizer for your session.

See Also: Oracle8i Concepts <../../server.817/a76965/toc.htm> and Oracle8i Performance Guide and Reference <../../server.817/a76992/toc.htm> for information on how to choose a goal for the cost-based approach based on the
characteristics of your application

• all_rows specifies the cost-based approach and optimizes for best throughput.
• first_rows specifies the cost-based approach and optimizes for best response time.
• rule specifies the rule-based approach. (The rule-based optimizer does not use function-based indexes.)
• choose causes the optimizer to choose an optimization approach based on the presence of statistics in the data dictionary.

Is this correct? If so, then I suppose I should set the init.ora parameter back to optimizer_mode=choose, and tell each developer to put an alter session statement on their clients to alter their sessions automatically to first_rows. The developer using designer will then be able to run it in a timely manner.

Please tell me if my suspicion is correct.

If correct, it begs the question: why are first_rows and all_rows available
for the init.ora file???

Regards,
Patrice Boivin
Systems Analyst (Oracle Certified DBA)

--
Please see the official ORACLE-L FAQ: http://www.orafaq.com
--
Author: Boivin, Patrice J
  INET: BoivinP_at_mar.dfo-mpo.gc.ca

Fat City Network Services    -- (858) 538-5051  FAX: (858) 538-5051
San Diego, California        -- Public Internet access / Mailing Lists
--------------------------------------------------------------------
To REMOVE yourself from this mailing list, send an E-Mail message
to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in
the message BODY, include a line containing: UNSUB ORACLE-L
(or the name of mailing list you want to be removed from).  You may
also send the HELP command for other information (like subscribing).




-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.com
-- 
Author: 
  INET: Jared.Still_at_radisys.com

Fat City Network Services    -- (858) 538-5051  FAX: (858) 538-5051
San Diego, California        -- Public Internet access / Mailing Lists
--------------------------------------------------------------------
To REMOVE yourself from this mailing list, send an E-Mail message
to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in
the message BODY, include a line containing: UNSUB ORACLE-L
(or the name of mailing list you want to be removed from).  You may
also send the HELP command for other information (like subscribing).