Comments on: Faulty Quotes 1 – OPTIMIZER_INDEX_COST_ADJ http://hoopercharles.wordpress.com/2009/12/06/faulty-quotes-1-optimizer_index_cost_adj/ Miscellaneous Random Oracle Topics: Stop, Think, ... Understand Mon, 13 May 2013 14:10:06 +0000 hourly 1 http://wordpress.com/ By: Charles Hooper http://hoopercharles.wordpress.com/2009/12/06/faulty-quotes-1-optimizer_index_cost_adj/#comment-406 Sat, 20 Feb 2010 15:26:37 +0000 http://hoopercharles.wordpress.com/?p=185#comment-406 Girish,

Thank you for the compliment.

I think that you will find that the majority of people who have performed testing regarding what happens to access path cost calculations (and the resulting execution plans) will recommend using the system (CPU) statistics to increase the calculated cost of various access paths, rather then using the OPTIMIZER_INDEX_COST_ADJ parameter to decrease (or increase if set to a value greater than 100) the calculated cost of index type accesses.

It is important to collect the system statistics when the server is under a moderate to heavy load in order to improve the accuracy of the statistics. After collecting the system statistics, verify that odd statistic values were not collected, such as MREADTIM set to a value that is lower than SREADTIM, or MBRC set to too high of a value.

See the following for an example of what might happen if MBRC is set to too high of a value:
High Value for MBRC Causes High BCHR, High CPU Usage, and Slow Performance

Jonathan Lewis has a couple of very good articles on his blog regarding system statistics:
System Statistics
System Stats Strategy
Upgrades

]]> By: panu78 http://hoopercharles.wordpress.com/2009/12/06/faulty-quotes-1-optimizer_index_cost_adj/#comment-405 Sat, 20 Feb 2010 14:45:37 +0000 http://hoopercharles.wordpress.com/?p=185#comment-405 Hi Charles,

Excellent explanation.

One question on this – So as per this article its better to gather system statistics rather than setting the individual parameters for improving the database performance ?

Thanks
Girish

]]> By: Charles Hooper http://hoopercharles.wordpress.com/2009/12/06/faulty-quotes-1-optimizer_index_cost_adj/#comment-19 Thu, 17 Dec 2009 17:54:45 +0000 http://hoopercharles.wordpress.com/?p=185#comment-19 Joze,
Thanks for the compliment. There are a number faulty Oracle-related expert quotes floating around the Internet that undoubtedly cause a great deal of confusion. Please feel free to borrow the “Faulty Quotes” idea for your own blog posts.

]]> By: Joze Senegacnik http://hoopercharles.wordpress.com/2009/12/06/faulty-quotes-1-optimizer_index_cost_adj/#comment-18 Thu, 17 Dec 2009 16:57:00 +0000 http://hoopercharles.wordpress.com/?p=185#comment-18 Charles,
Excellent idea to gather this kind of faulty “expert” advices in one place. I expect that I’ll frequently use a link to this post in my writings.

Have a nice time, Joze

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