Rich, I think the answer to your question #1 is, "Because a lot of people aren't careful." They repeat something because they heard or read it, or because they tried it once and it worked. Trying something once and seeing it work is not sufficient to prove a cause-effect relationship. The index thing is a great example of people completely missing the relevant parameter for two whole decades.
In response to #2, there's a standard format for bad advice. Any time you see a statement of fact that contains no where-clause, then it's probably not true. If the statement doesn't contain the word "if" or "when" or "depend," then it's probably a good idea to construct a test (or find someone who is willing to produce the details of one, which is what guys like Tom Kyte, Steve Adams, and Jonathan Lewis are so excellent at doing). On the other hand, the TUSC/Oracle Press tuning tips & techniques book expresses ideas almost exclusively in this where-clause-free format. Actually, though, the extraordinarily high ratio of this book's false ideas to total ideas, combined with the book's prodigious size, make it quite an inspirational source for someone who wants to create interesting performance tests. Cary Millsap Hotsos Enterprises, Ltd. http://www.hotsos.com Upcoming events: - Hotsos Clinic, Dec 9-11 Honolulu - 2003 Hotsos Symposium on OracleR System Performance, Feb 9-12 Dallas - Jonathan Lewis' Optimising Oracle, Nov 19-21 Dallas -----Original Message----- Rich 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. 1) Why is this? 2) What other pearls of performance wisdom from Oracle Corp should I completely disregard as false? 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 [EMAIL PROTECTED] 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: [EMAIL PROTECTED] 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: [EMAIL PROTECTED] (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). -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: Cary Millsap INET: [EMAIL PROTECTED] 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: [EMAIL PROTECTED] (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).
