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Home -> Community -> Mailing Lists -> Oracle-L -> RE: Correct way to accuse BCHR tuning method (Was: Hit ratio)
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
-----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My last message is not meant to revive the outdated and probably never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
-- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Yong Huang INET: yong321_at_yahoo.com 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). -- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Cary Millsap INET: cary.millsap_at_hotsos.com 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 Wed Dec 24 2003 - 12:19:25 CST
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