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Home -> Community -> Mailing Lists -> Oracle-L -> Re: Cost vs Rule
Bill,
There are some good notes on Metalink about why CBO avoids using an index when one is available. I'll see if I can find a note number but you might try searching on index and optimizer.
Sometimes you need to modify the code in order to get better performance under CBO. Can you test modified code. Harrison has a good book Oracle SQL High-Performance Tuning which is very good. Burleson also has a book Oracle High-Performance SQL Tuning which is very good.
If you're not under tremendous schedule pressure, I'd recommend that you tune the poorly performing SQL to run better under CBO. RBO is not getting any new features and will eventually go away. CBO continues to evolve and get better so if this is a new project, it's best to start out with CBO, in my opinion.
If you have to, you can set the entire database to CBO and then add rule-based hints to the poorly-performing statements, if there aren't too many of them. That is, if you have the capability to add hints.
Cherie Machler
Oracle DBA
Gelco Information Network
"Magaliff, Bill"
<Bill.Magaliff_at_len To: Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
dware.com> cc:
Sent by: Subject: Cost vs Rule
root_at_fatcity.com
03/07/02 01:23 PM
Please respond to
ORACLE-L
I work in a dev shop - most of the sql is canned and pretty basic. We've
been running CBO in all of our dev environments, but we have a few long
txns
that just take forever. At the request of some savvy developers, I turned
on RBO, and it brought down execution times dramatically.
I've been analyzing affected tables often (we do a lot of bulk load/unload
for testing), and have played with partitioning and clustering,
particularly
on one table that's just a dog. CBO will always do a FTS where RBO uses
the
PK to retrieve data.
Where to go next? I've been unable to alter the costs dramatically enough to make any real difference in execution time.
thx
-- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: Magaliff, Bill INET: Bill.Magaliff_at_lendware.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-LReceived on Fri Mar 08 2002 - 07:28:18 CST
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also send the HELP command for other information (like subscribing). -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: INET: Cherie_Machler_at_gelco.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
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