log file sync

From: Hameed, Amir <Amir.Hameed_at_xerox.com>
Date: Mon, 6 Aug 2012 15:55:46 -0400
Message-ID: <304F58144267C5439E733532ABC9A3A115A42B6F_at_USA0300MS02.na.xerox.net>

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:  

                                                             Avg

                                        %Time Total Wait    wait

Waits % DB

Event                             Waits -outs   Time (s)    (ms)

/txn time

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

log file sync                   166,765     0      3,575      21

1.1 3.3    

The 'Background Wait Events' section shows the following for 'log file sync' and 'log file parallel write':

                                                             Avg

                                        %Time Total Wait    wait

Waits % DB

Event                             Waits -outs   Time (s)    (ms)

/txn time

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

log file sync                        56     0          1      11
0.0     .0

log file parallel write         221,159     0          1       0
1.4     .0

 

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?  

Thanks

Amir  

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Received on Mon Aug 06 2012 - 14:55:46 CDT