RE: CBO - default no of rows

From: Christopher Spence <cspence_at_FuelSpot.com>
Date: Fri, 14 Sep 2001 05:36:54 -0700
Message-ID: <F001.0038E5B3.20010914054017@fatcity.com>

!! Please do not post Off Topic to this List !!

If you delete the stats it will use rule based, unless a table being join does have stats, then the other objects will be estimated (which I believe is simply based on the number of blocks).

"Do not criticize someone until you walked a mile in their shoes, that way when you criticize them, you are a mile a way and have their shoes."

Christopher R. Spence
Oracle DBA
Phone: (978) 322-5744
Fax: (707) 885-2275

Fuelspot
73 Princeton Street
North, Chelmsford 01863

-----Original Message-----
Sent: Friday, September 14, 2001 7:11 AM To: Multiple recipients of list ORACLE-L

!! Please do not post Off Topic to this List !!

Ooooh, correct me if I'm wrong on this one, but doesn't the CBO just use the stats that are on the table. Hence if you actually delete the stats for the tables that don't have upto date stat values, you can actually get a performance increase,

my tuppence worth.

K.
"hit any user to continue"

Kevin Thomas
Technical Analyst
Deregulation Services
Calanais Ltd.
(2nd Floor East - Weirs Building)
Tel: 0141 568 2377
Fax: 0141 568 2366
http://www.calanais.com <http://www.calanais.com/>

-----Original Message-----
Sent: 14 September 2001 11:25
To: Multiple recipients of list ORACLE-L

My question of the day is :-
What value does the CBO use as a default number of rows for a table.

Background: -

We all know that if any tables in a query have been analyzed then CBO is used for the query not RBO (couple of caveats I know but let's continue).

So if 3 tables are used in a query and table a has 500 rows (analyzed) table b has 50 rows (never analyzed) and table c has 3500000 rows (never analyzed) all things being equal then CBO is used but what values does the CBO use for tables b or c to decide which execution plan is best.

On a development system yesterday a query was running slow. I realised that we had put in a very large data load (3.5M rows). I analyzed the table and indexes and the query came back in sub second response time. I am trying to figure what value was being used for num_rows prior to the analyze. It cannot be based on blocks allocated/used as thet would have increased after the dataload

Thanks

John

Oracle DBA
BTcellnet

* john.hallas_at_btcellnet.net 
* 0113 388 6062    Desk 
* 07713 066194      BT Mobile 




**********************************************************************

This email and any attachments may be confidential and the subject of legal professional privilege. Any disclosure, use, storage or copying of this email without the consent of the sender is strictly prohibited. Please notify the sender immediately if you are not the intended recipient and then delete the email from your inbox and do not disclose the contents to another person, use, copy or store the information in any medium.

--

Please see the official ORACLE-L FAQ: http://www.orafaq.com
--

Author: Thomas, Kevin
INET: Kevin.Thomas_at_calanais.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).
--

Please see the official ORACLE-L FAQ: http://www.orafaq.com
--

Author: Christopher Spence
INET: cspence_at_FuelSpot.com

Fat City Network Services    -- (858) 538-5051  FAX: (858) 538-5051
San Diego, California        -- Public Internet access / Mailing Lists
--------------------------------------------------------------------