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Home -> Community -> Mailing Lists -> Oracle-L -> RE: Is nothing sacred? (Oracle vs The Experts)
Rich - Actually, if you took an Oracle Performance Tuning class from Oracle
Education right now, you would find the BHR mentioned little and Oracle
waits emphasized a great deal. I took that class about a month ago and the
instructor described how Cary had prevailed in convincing the people at
Oracle that counted and the class materials were being rewritten for the
next class after mine.
Well, being a computer professional is a hard burden, what with the
underlying assumption ever changing. Actually, given the extensive
discussions we've had on this forum about BHR vs. waits, I'm surprised it
caught you unawares. This was where I'd first heard about the new emphasis
on waits. Of course, with waits becoming the conventional wisdom, Cary and
others will have to find another windmill to tilt at. Cary - anything lined
up?
Dennis Williams
DBA, 40%OCP
Lifetouch, Inc.
dwilliams_at_lifetouch.com
-----Original Message-----
Sent: Monday, November 11, 2002 10:58 AM
To: Multiple recipients of list ORACLE-L
So, there I am, on 8.1.7.2 (and .4) on HP/UX 11.0, with a process that runs 20 minutes out of every hour of the day (despite my protests to it's design). After it starts having problems (go figure), it becomes a priority to speed it up.
Thanks to a 10046 trace, we see that the query taking the most elapsed time does FTSs on each of two very small tables (1 block and 4 blocks -- 8K blocksize). These tables are not indexed, as per the official Oracle recommendation. After reading the excellent Hotsos paper "When to index a table" (THANKS, CARY!), I added an index to reduce elapsed time on this query by 50% (150 to 75 seconds in test), proving to me that the paper is valid. And I've only read to page four!
OK, first I'm taught by Oracle to look at Buffer Cache Hit Ratios as a measure of performance, then told (and thoroughly convinced) by experts that this is bunk. Now, I found out that the 15% (or 10% or whatever, depending on version) ratio of rows returned to total rows in determining when to use an index in a query is garbage.
I know there's an Oracle Fallacy website somewhere...
It just looks bad on me, our department, and Oracle when, once again, something I've been preaching to our developers as gospel turns out to be completely false.
Maybe I'm grumpy because it's snowing on my leaves right now... <sigh>
Rich
Rich Jesse System/Database Administrator Rich.Jesse_at_qtiworld.com Quad/Tech International, Sussex, WI USA
Disclaimer: I only said the Packers would be 12-4 this year -- I never said
that they couldn't do better! WOO-HOO! :)
--
Please see the official ORACLE-L FAQ: http://www.orafaq.com
--
Author: Jesse, Rich
INET: Rich.Jesse_at_qtiworld.com
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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: ListGuru_at_fatcity.com (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). Received on Mon Nov 11 2002 - 14:03:54 CST
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