BCHR Tuning

From: Fink, Dan <Dan.Fink_at_mdx.com>
Date: Fri, 10 Jan 2003 07:19:42 -0800
Message-ID: <F001.0052C4F5.20030110071942@fatcity.com>

Here's an excellent real life example of why BCHR is not a good tuning metric and you should focus on reducing I/Os. A simple fix for a query and here is the resulting email to the client, who understands that BCHR is not good. A little techie humor...  

I have good news and I have bad news.

The good news is that the elapsed query time and total I/Os for the latest iteration dropped significantly.

Old --> 1:42 min 2,715,659 i/os (15,925 physical)

New --> 22 seconds 3318 i/os (2861)

However, the bad news is that the Buffer Cache Hit Ratio dropped dramatically!

Old --> 99.36%

New --> 13.77%

So, I have undone all the changes I made and will begin looking at other methods to improve performance!

--

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

Author: Fink, Dan
  INET: Dan.Fink_at_mdx.com

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