Re: log file sync
- From: David Fitzjarrell <oratune@xxxxxxxxx>
- To: "Amir.Hameed@xxxxxxxxx" <Amir.Hameed@xxxxxxxxx>, "oracle-l@xxxxxxxxxxxxx" <oracle-l@xxxxxxxxxxxxx>
- Date: Mon, 6 Aug 2012 13:09:06 -0700 (PDT)
What is the I/O rate to the disk or disks where the redo logs reside? How
often does the application commt? Decreasing I/O time (increasing the I/O
rate/sec) can help with this, as can reducing commits (when possible). Are the
redo logs I/O bound? The array where the logs reside may be humming along
nicely while the 'pipe' to that storage may be the bottleneck.
I think there is more investigation to be done before a cause can be determined
and a course of action set.
David Fitzjarrell
________________________________
From: "Hameed, Amir" <Amir.Hameed@xxxxxxxxx>
To: oracle-l@xxxxxxxxxxxxx
Sent: Monday, August 6, 2012 1:55 PM
Subject: log file sync
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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