RE: Measuring the impact of Redo Log change
- From: "Roberts, David (GSD - UK)" <david.h.roberts@xxxxxxxxxx>
- To: <sharmakdeep_oracle@xxxxxxxxx>, <oracle-l@xxxxxxxxxxxxx>
- Date: Tue, 9 Sep 2008 09:47:03 +0100
While the following SQL isn't going to be able to tell you anything
about the performance of the application you are running, it may give an
indication of increased stability, and depending on the size of your
control file may give you data from both before and after the change for
you to compare.
One of the problems I have encountered is when redo logs are all on a
single disk device, there will be contention between the archive log
process and the log writer, which will be seen in an increasing amount
of time taken to archive logs (I'm assuming you're in archive log mode)
when the system is under duress.
SELECT recid,
To_Char( next_time, 'YYYY-MON-DD HH24:MI:SS' ),
(completion_time - next_time) * ( 24 * 60 * 60 ) "Seconds to
archive"
FROM v$archived_log
ORDER BY recid
If the peek or average time to archive logs has dropped, it would be
possible to argue that you have increased the theoretical throughput!
Obviously if you had the opportunity, placing redo log groups on
alternating physical devices would obviously be a better way to reduce
this form of contention!
Dave
David Roberts
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www.logica.com
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-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Deepak Sharma
Sent: 09 September 2008 05:33
To: oracle-l@xxxxxxxxxxxxx
Subject: Measuring the impact of Redo Log change
We recently (today) moved the redo logs from RAID5 to RAID1+0.
The obvious reason of doing this is to make things better in terms of
performance, as RAID1+0 is better suited for read/writes. Someone pls
correct me if that's not true.
What are different ways to measure the impact of this change?
The platform is AIX, DB is 10.2.0.3 and DB size is 55TB, and 2TB redo is
generated each day. There are plans underway to reduce the redo
generation using direct path etc. (so let's not get diverted by that).
We can try measuring the wait event stats using AWR, session stats etc.,
but what exactly to look for? 'log file switch completion', 'log file
sync', are some things that come to mind - what else?
Thanks,
Deepak
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