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Home -> Community -> Mailing Lists -> Oracle-L -> RE: Free Buffer Waits/CNTD......
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_at_hot To: Multiple
recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>
sos.com> cc: (bcc: Jack van
Zanen/nlzanen1/External/MEY/NL)
Sent by: Subject: RE: Free Buffer
Waits
root_at_fatcity.com
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.
cary.millsap_at_hotsos.com
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
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INET: nlzanen1_at_EY.NL
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INET: cary.millsap_at_hotsos.com
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vriendelijk doch dringend het e-mailbericht te retourneren aan de
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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.
If you are not the intended recipient of this communication please
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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.
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Author: Jack van Zanen
INET: nlzanen1_at_EY.NL
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Author: Cary Millsap
INET: cary.millsap_at_hotsos.com
Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051 San Diego, California -- Public Internet access / Mailing Liststo: 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 Fri Jun 14 2002 - 17:38:22 CDT
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