RE: log file sync

From: Hameed, Amir <>
Date: Wed, 8 Aug 2012 09:53:14 -0400
Message-ID: <>

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



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 [] Sent: Tuesday, August 07, 2012 6:46 PM
To: Hameed, Amir
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): ash-data-with-r/

On Mon, Aug 6, 2012 at 12:55 PM, Hameed, Amir <> 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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Received on Wed Aug 08 2012 - 08:53:14 CDT

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