Re: log file sync

From: Kevin Closson <ora_kclosson_at_yahoo.com>
Date: Wed, 22 Aug 2012 12:38:13 -0700 (PDT)
Message-ID: <1345664293.70926.YahooMailNeo_at_web161701.mail.bf1.yahoo.com>

how did this turn out?

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 From: "Hameed, Amir" <Amir.Hameed_at_xerox.com> To: Greg Rahn <greg_at_structureddata.org> Cc: oracle-l_at_freelists.org
Sent: Wednesday, August 8, 2012 6:53 AM
Subject: RE: log file sync  

I had an offline discussion with Kevin Closson. The issue seems to be with the scheduling latency of LGWR. Here is information on the LFPW histogram. I have added a column showing the LFS latency corresponding to each LFPR:

                                                            % of Waits

---

                                  Total

LFS(ms) Event                      Waits  <1ms  <2ms  <4ms  <8ms <16ms
<32ms  <=1s  >1s

• -------------------        ----- ----- ----- ----- ----- ----- ----- ----- -----

48(ms)  log file parallel write    4270  100.0

45(ms)  log file parallel write    4105  100.0

41(ms)  log file parallel write    6913  100.0

41(ms)  log file parallel write    3409  100.0

38(ms)  log file parallel write    7335  100.0

I am going to run LGWR in RT mode and then test again.

From: Greg Rahn [mailto:greg_at_structureddata.org] Sent: Tuesday, August 07, 2012 6:46 PM
To: Hameed, Amir
Cc: oracle-l_at_freelists.org
Subject: Re: log file sync

You may find the this of use when looking at log file sync and log file parallel write issues using the AWR report (there is usually more to the issue than the lines you provided):

http://structureddata.org/2011/12/20/visualizing-active-session-history- ash-data-with-r/

On Mon, Aug 6, 2012 at 12:55 PM, Hameed, Amir <Amir.Hameed_at_xerox.com> wrote:

Hi all,
My AWR report shows 'log file sync' among the top five events. When I look at the 'Foreground Wait Events', I see the following: ...
My question is that if the LGWR is not waiting for the 'log file parallel write' during synchronous writes (avg. wait time=0) then why is the average wait time of 'log file sync' event for the foreground and background processes (DBWR, LMS etc.) is high?

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Regards,

Greg Rahn  |  blog <http://bit.ly/u9N0i8>   |  twitter


<http://bit.ly/v733dJ>   |  linkedin <http://linkd.in/gregrahn> 



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Received on Wed Aug 22 2012 - 14:38:13 CDT