RE: OPTIMIZER_INDEX_COST_ADJ & OPTIMIZER_INDEX

From: Gogala, Mladen <MGogala_at_oxhp.com>
Date: Wed, 06 Jun 2001 10:54:29 -0700
Message-ID: <F001.0031EB7A.20010606105344@fatcity.com>

I was fiddling with those parameters but on an OLTP configuration. My goal was to strongly favor indexes and make CBO behave like RBO. I succeeded in doing so, mainly by setting OPTIMIZER_INDEX_COST_ADJ to 30 (making a cost of index read 30% of the ost of a table read).

-----Original Message-----

Sent: Wednesday, June 06, 2001 9:01 AM
To: Multiple recipients of list ORACLE-L

I was reading that paper yesterday as well. We have a 120 Gig data warehouse that uses partitions and a large fact table with many smaller dimension tables ( a modified star schema design). This database is currently on version 8.0.4 but will soon be 8.1.7 on Sun Solaris 2.6.

Can anyone tell me if they have a similar design that has benefitted from changing these two parameters?

Thanks in advance,

Cherie Machler
Oracle DBA
Gelco Information Network

                    John.Dailey_at_ing-

                    fsi-na.com              To:     Multiple recipients of
list ORACLE-L <ORACLE-L_at_fatcity.com>   
                    Sent by:                cc:

                    root_at_fatcity.com        Subject:
OPTIMIZER_INDEX_COST_ADJ & OPTIMIZER_INDEX_CACHING       
 

 

                    06/05/01 04:30

                    PM

                    Please respond

                    to ORACLE-L

Oracle 8.0.5.2.1 <-- yeah, I know I know... we are going to 8.1.7 eventually
AIX 4.3.3 Hey all.... Looking at our init parameters today after reading Tim Gorman's White Paper "The Search for Intelligent Life in the Cost Based Optimizer" and these 2 stood out like a sore thumb. Both are at the default values:

OPTIMIZER_INDEX_COST_ADJ = 100
OPTIMIZER_INDEX_CACHING = 0 We have an OLTP and a DSS database and I am looking at changing the OPTIMIZER_INDEX_CACHING = 90 for both and setting the OPTIMIZER_INDEX_COST_ADJ to a reasonable value based on db sequential reads vs. db scattered reads as a guideline.... any suggestions/recommendations/words of warning/flogging? There is some scattered info on this on Metalink but I'm looking for some real-world improvements or headaches.

Thanks to all in advance and hopefully I won't have to type HELP so someone can ask me if I'm an idiot....

:-)

John D.

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Author: Gogala, Mladen
INET: MGogala_at_oxhp.com

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RE: OPTIMIZER_INDEX_COST_ADJ & OPTIMIZER_INDEX_CACHING