Pretty interesting. Maybe it's possible, but a simpler explanation is that something about your workload either during or maybe immediately before your batch job was different.
The most common case in which I've seen 'free buffer waits' waits is when all the forces of nature combine to make DBWR's job really difficult for some critical period. There are several ways for that to happen. Most that I've seen involve either bad SQL that does a lot of reads that compete with DBWR's writes to the same devices. I'm not sure it's relevant in your case, but use of RAID level 5 disk arrays increase the odds of having symptoms like you've seen. RAID level 5 implementations convert each DBWR single-block write into four distinct I/O calls, which of course might be more I/O calls than your array was designed to handle. Also, in periods of partial outage (when the array is reconstructing itself to recover from a single disk outage), one would likely notice this same type of performance problem you've noticed. There are lots of ways it could have happened... Cary Millsap Hotsos Enterprises, Ltd. http://www.hotsos.com Upcoming events: 2003 Hotsos Symposium on Oracle® System Performance, February 9–12 Dallas Hotsos Clinic, July 9–11 New York City Hotsos Clinic, July 23–25 Chicago -----Original Message----- Zanen Sent: Friday, June 14, 2002 2:23 AM To: Multiple recipients of list ORACLE-L Hi All, As mysteriously as it took over 6 hours to run yesterday, it was back at 35 minutes today. Free buffer waits dropped out of the top 10 again as well. My question now is: If nothing changed to the database (we did not modify anything because we could not find the source of all evil) and there are no different processes running (it's the same batch job every day) and there are no users connected (listener.ora file), could it be that for some reason my DBWR processes weren't able to write to disk and Oracle did not report an error on it???? Jack "Cary Millsap" <cary.millsap@hot To: Multiple recipients of list ORACLE-L <[EMAIL PROTECTED]> sos.com> cc: (bcc: Jack van Zanen/nlzanen1/External/MEY/NL) Sent by: Subject: RE: Free Buffer Waits [EMAIL PROTECTED] 13-06-2002 19:08 Please respond to ORACLE-L "free buffer waits" waits indicate that your DBWR can't keep up with its workload. Often caused by inefficient SQL competing with DBWR for an I/O device. Cary Millsap Hotsos Enterprises, Ltd. [EMAIL PROTECTED] http://www.hotsos.com -----Original Message----- Zanen Sent: Thursday, June 13, 2002 4:04 AM To: Multiple recipients of list ORACLE-L Hi All, We have a production database that has a batch job running on it for months now. Last night one part of the batch job that normally takes between 20-30 minutes took well over 6 hours. The only difference I can see between today & other days is that the Free Buffer Wait event was the top wait event, which it not normally is (not even top 10) This database goes down every night for backup and this is the timings I got. Total waits:22055 Total timeouts:22052 Time waited: 2225285 (is this ms or cs?) Avg.wait:100.8971 This whole thing puzzles me a bit since nothing changed to the database and nothing was in the Alert log. Also system was virtually idle during the 6 hours (no activity according to UNIX boys) I was sound asleep when this happened so I don't have much more than this info. Can anybody explain why this could have happened or point me to some documents that can. Standard answer you'll find that your DBWR can't keep up, but I have 4 of them and the sytem was idle. THX =================================================================== De informatie verzonden in dit e-mailbericht is vertrouwelijk en is uitsluitend bestemd voor de geadresseerde. 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De algemene voorwaarden worden u op verzoek kosteloos toegezonden. ===================================================================== The information contained in this communication is confidential and is intended solely for the use of the individual or entity to whom it is addressed. You should not copy, disclose or distribute this communication without the authority of Ernst & Young. Ernst & Young is neither liable for the proper and complete transmission of the information contained in this communication nor for any delay in its receipt. Ernst & Young does not guarantee that the integrity of this communication has been maintained nor that the communication is free of viruses, interceptions or interference. If you are not the intended recipient of this communication please return the communication to the sender and delete and destroy all copies. In carrying out its engagements, Ernst & Young applies general terms and conditions, which contain a clause that limits its liability. A copy of these terms and conditions is available on request free of charge. =================================================================== -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: Jack van Zanen INET: [EMAIL PROTECTED] Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051 San Diego, California -- Public Internet access / Mailing Lists -------------------------------------------------------------------- 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 FAX: (858) 538-5051 San Diego, California -- Public Internet access / Mailing Lists -------------------------------------------------------------------- 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). ================================================================== De informatie verzonden in dit e-mailbericht is vertrouwelijk en is uitsluitend bestemd voor de geadresseerde. Openbaarmaking, vermenigvuldiging, verspreiding en/of verstrekking van deze informatie aan derden is, behoudens voorafgaande schriftelijke toestemming van Ernst & Young, niet toegestaan. Ernst & Young staat niet in voor de juiste en volledige overbrenging van de inhoud van een verzonden e-mailbericht, noch voor tijdige ontvangst daarvan. Ernst & Young kan niet garanderen dat een verzonden e-mailbericht vrij is van virussen, noch dat e-mailberichten worden overgebracht zonder inbreuk of tussenkomst van onbevoegde derden. Indien bovenstaand e-mailbericht niet aan u is gericht, verzoeken wij u vriendelijk doch dringend het e-mailbericht te retourneren aan de verzender en het origineel en eventuele kopieën te verwijderen en te vernietigen. Ernst & Young hanteert bij de uitoefening van haar werkzaamheden algemene voorwaarden, waarin een beperking van aansprakelijkheid is opgenomen. De algemene voorwaarden worden u op verzoek kosteloos toegezonden. ===================================================================== The information contained in this communication is confidential and is intended solely for the use of the individual or entity to whom it is addressed. You should not copy, disclose or distribute this communication without the authority of Ernst & Young. Ernst & Young is neither liable for the proper and complete transmission of the information contained in this communication nor for any delay in its receipt. Ernst & Young does not guarantee that the integrity of this communication has been maintained nor that the communication is free of viruses, interceptions or interference. If you are not the intended recipient of this communication please return the communication to the sender and delete and destroy all copies. In carrying out its engagements, Ernst & Young applies general terms and conditions, which contain a clause that limits its liability. A copy of these terms and conditions is available on request free of charge. =================================================================== -- Please see the official ORACLE-L FAQ: http://www.orafaq.com -- Author: Jack van Zanen INET: [EMAIL PROTECTED] Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051 San Diego, California -- Public Internet access / Mailing Lists -------------------------------------------------------------------- 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 FAX: (858) 538-5051 San Diego, California -- Public Internet access / Mailing Lists -------------------------------------------------------------------- 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).
