are there really that many people who use hit ratio? > > From: "Cary Millsap" <[EMAIL PROTECTED]> > Date: 2003/12/23 Tue AM 11:49:33 EST > To: Multiple recipients of list ORACLE-L <[EMAIL PROTECTED]> > Subject: RE: Hit Ratio > > Yong, > > Connor's script is not a joke, it's a proof by counterexample that the > advice "You SQL is tuned if and only if it has a high hit ratio" is > rubbish. > > The buffer cache hit ratio is a tool. Used properly, nobody's objecting. > It's proper use? To answer the question, "What percentage of LIO calls > can be satisfied without an OS read call?" The correct point that many > on this list make over and over again, is that this is often the wrong > question to be asking. (And actually, the conventional "BCHR=(L-P)/L" > formula doesn't answer that question very well anyway; see Steve Adams's > site for more detail.) > > It's not the ratio that needs condemning, it's the advice about how to > use the ratio. The ratio just happens to be the emblem on the flag. > > > 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: Tuesday, December 23, 2003 9:29 AM > To: Multiple recipients of list ORACLE-L > > Hi, Carel-Jan and Rich, > > Connor's script to bump up buffer cache hit ratios is meant to be a > humor. Only > if you carefully comtemplate it will you see that there's no relevance > of the > fact that you can get any hit ratio to the fact that hit ratios are > insufficient in performance tuning. > > It would be equally easy to write scripts to bump up some wait event > times. If > you need very long db file reads, create a big table and keep scanning > it. If > you need long enqueue waits, create a table and insert a row. Create 10 > or 100 > sessions (depending on your patience) and delete from that table and > wait. The > fact that you can get arbitary wait times does not reduce the efficacy > of wait > event interface as a performance tuning tool. > > Buffer cache or library cache hit ratios are not sufficient, very > insufficient > used alone, to tune the database. The reason is that they don't contain > enough > information to tune the system with. This is the only reason we should > not > solely rely on them; in fact, not using them at all doesn't hurt much. > The > reason is not that we can get any value we want by playing pranks. > > Hit ratios are still used in other performance tuning and not condemned. > Although in UNIX performance tuning one looks at absolute numbers such > as scan > rate, CPU usage and netstat output more often, hit ratios in some sar > output > are still occasionally used. Most ratios could still be distored by a > rogue > user repeatedly doing, say, "find /" for inodes or "find / -exec grep > SomeThing > {} \;" for page cache. > > In any tuning practice, Oracle or OS, artificially distorting usage > patterns > invalidates your numbers even if you're using a well respected tuning > method. > So only play pranks on a play box, not production. > > Yong Huang > > At 11:14 22-12-03 -0800, you wrote: > >My BCHR is currently 96.62%. In the past, it was normally over 99%. > What > >should I do? > > > >I'll be waiting for Mladen's reply... :) > > > > > >Rich > > > >Rich Jesse System/Database Administrator > >[EMAIL PROTECTED] Quad/Tech Inc, Sussex, WI USA > > Go to www.oracledba.co.uk (Connor) or go to O'Reilly (download page of > Cary's book), and download one of the fabulous BCHR enhancement scripts. > > Especially when your bonus depends on it, this is a good time to perform > > some BCHR tuning. > > Regards, Carel-Jan > > __________________________________ > 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). >
-- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: <[EMAIL PROTECTED] 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).
