But that doesn't really explain why the optimizer chooses an FTS with a predicate that presumable is more selective (name like 'ABC%') and an index scan with a predicate that presumable is less selective (name like 'AB%'). I could understand it if it were the other way around.
Is there a histogram on the name column?


At 11:34 AM 11/5/2003, you wrote:
Sami,

Your problem is not with the index, but rather the cost based optimizer. Most of us have been beat severely over the head and shoulders through the years that full table scans are a BAD thing, me included BTW. Well, it's time for the old dog to learn new tricks. So that I'm not a long winded person, take a look in Select magazine, 3rd qtr 2003, for the article "In Defense of Full Table Scans" by Jeff Maresh. For a long time the CBO was a mystery to me as well especially when it did unexpected things like this. I've applied Jeff's ideas on computing an index's efficiency to see if it explained what the CBO did. Amazingly in 95% of the cases I've analyzed it made absolute sense.

I'm including Jeff with a courtesy copy of this message so that 1) I can pat him for making the waters clear and 2) so he can add anything he desires.

Dick Goulet
Senior Oracle DBA
Oracle Certified 8i DBA

Wolfgang Breitling
Oracle7, 8, 8i, 9i OCP DBA
Centrex Consulting Corporation
http://www.centrexcc.com



-- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Wolfgang Breitling INET: [EMAIL PROTECTED]

Fat City Network Services    -- 858-538-5051 http://www.fatcity.com
San Diego, California        -- Mailing list and web hosting services
---------------------------------------------------------------------
To REMOVE yourself from this mailing list, send an E-Mail message
to: [EMAIL PROTECTED] (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).

Reply via email to