Yong, The point I want to make is that "the" buffer cache hit ratio actually *is* useful, in the following way. If its value is greater than about 99%, then I can practically guarantee that there is some high-LIO SQL inside the application whose repair will greatly improve system performance.
Connor's script is a neat means of jarring someone out of the belief that a "good hit ratio necessarily indicates good performance." Cary Millsap Hotsos Enterprises, Ltd. http://www.hotsos.com Upcoming events: - Performance Diagnosis 101: 1/27 Atlanta - SQL Optimization 101: 2/16 Dallas - Hotsos Symposium 2004: March 7-10 Dallas - Visit www.hotsos.com for schedule details... -----Original Message----- Yong Huang Sent: Wednesday, December 24, 2003 11:09 AM To: Multiple recipients of list ORACLE-L [This message is not technical, but educational. Readers interested in technical info only may want to skip] Hi, Cary and Gopal, My last message is misunderstood. Nowadays most DBAs that still use buffer cache hit ratio as a primary performance tuning method are those that rarely browse public forums. When we convince them that's a wrong method, we should not say "Look. I can bump up BCHR to an arbitrary value". If he doesn't think, he'll say "Indeed. If I can get any value, it must be rubbish". But if he's a logical person and thinks for a few minutes, he'll say "It's unfair to run that choose_a_hit_ratio program to get an arbitrary hit ratio and say the method is wrong, because you can use the same logic to write a program to get an arbitrary library cache hit ratio, OS in-core inode cache hit ratio or directory name cache hit..." My last message is not meant to revive the outdated and probably never correct tuning method. Instead it's meant to let oracle-l members know that when you need to convince those DBAs that still use that method, you need to accuse the BCHR method for correct reason, namely, BCHR does not contain sufficient information for tuning, not because you can raise its value by constantly scanning a table in Oracle; you won't be able to convince some stubbon DBAs who enjoy thinking in a quiet place. I agree that "It's not the ratio that needs condemning, it's the advice about..." What I disagree is the wrong educational tool people on public forums have recently used again and again to show the inadequacy of the BCHR tuning method. Yong Huang __________________________________ Do you Yahoo!? New Yahoo! Photos - easier uploading and sharing. http://photos.yahoo.com/ -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Yong Huang 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.net -- 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).
