RE: CBO irregularity

From: Cary Millsap <cary.millsap_at_hotsos.com>
Date: Tue, 8 Jun 2004 01:04:18 -0500
Message-ID: <020501c44d1e$72fbaab0$6801a8c0@CVMLAP02>

True. The Oracle kernel also collects this information when you use dbms_stats.gather_database_stats.

Cary Millsap
Hotsos Enterprises, Ltd.
http://www.hotsos.com
Nullius in verba

Upcoming events:
- Performance <http://www.hotsos.com/courses/PD101.php> Diagnosis 101: 6/22
Pittsburgh, 7/20 Cleveland, 8/10 Boston
- SQL Optimization <http://www.hotsos.com/courses/OP101.php> 101: 5/24 San
Diego, 6/14 Chicago, 6/28 Denver
- Hotsos Symposium 2005: March 6-10 Dallas

Visit www.hotsos.com for schedule details...

-----Original Message-----
From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Satheesh.Babu_at_iflexsolutions.com Sent: Tuesday, June 08, 2004 12:47 AM
To: oracle-l_at_freelists.org
Subject: RE: CBO irregularity

P3 of "db file scattered read" waits will show the size of the multiblock read actually performed.

Thanks and Regards,

Satheesh Babu.S

Bangalore.

From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Naveen, Nahata (IE10)
Sent: Tuesday, June 08, 2004 10:49 AM
To: oracle-l_at_freelists.org
Subject: RE: CBO irregularity

Make sure that your system statistics reasonably represent the operational characteristics of your system. For example, if your system really averages 3.7 blocks per multi-block read, then CBO will make dumb decisions about whether to do full-table scans on systems were db_file_multiblock_read_count=128.

[Naveen Nahata] Can you please elaborate on how I can find, how many blocks my system reads on an average per oracle multi-block read request?

Regards
Naveen

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 Tue Jun 08 2004 - 01:02:22 CDT