Cheers Mark. I’ll have a look.
CPU differences were playing on mind a bit as a potential cause.
We’ve got 2 vCPU’s on the fast VM and 8 Cores/16 threads on the other.
I’ll double check the article.
Chris
Christopher Osborne
Lead Technical Specialist, Performance Engineering, OE Infrastructure Ops
Scotland
Sky UK
Email:chris.osborne@xxxxxx
Desk: +44 1506 325069 | Mobile: +44 7720 308941
[cid:image003.png@01D18364.A55BF350]
From: Mark W. Farnham [mailto:mwf@xxxxxxxx]
Sent: 29 March 2016 15:10
To: Osborne, Chris <Chris.Osborne@xxxxxx>; gogala.mladen@xxxxxxxxx;
oracle-l@xxxxxxxxxxxxx
Subject: RE: Log File Syncs
check whether the issues on CPU raised and described in Kevin’s “Real men…SSD”
blog are relevant to your specific case.
From: oracle-l-bounce@xxxxxxxxxxxxx<mailto:oracle-l-bounce@xxxxxxxxxxxxx>
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Osborne, Chris
Sent: Tuesday, March 29, 2016 8:57 AM
To: gogala.mladen@xxxxxxxxx<mailto:gogala.mladen@xxxxxxxxx>;
oracle-l@xxxxxxxxxxxxx<mailto:oracle-l@xxxxxxxxxxxxx>
Subject: RE: Log File Syncs
Hi Mladen,
In the end the develop changed the frequency of commits which made the issue
disappear as both ‘machine’ had comparible performance.
I’m not convinced that IO was anything to do with it as the IO wait event ‘log
file parallel write’ were very close in performance, and in fact the slower db
had *better* response times for log file writes.
The only other significant wait event was ‘log file sync’ which the slower DB
showed a longer wait.
The really weird thing is that the log file sync times average was less than
the Log file write time….I’m not sure how that can be possible given that a
part of the time spent in log file sync is spent waiting on LGWR doing it’s
writes
Chris
Christopher Osborne
From: oracle-l-bounce@xxxxxxxxxxxxx<mailto:oracle-l-bounce@xxxxxxxxxxxxx>
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Mladen Gogala
Sent: 26 March 2016 04:11
To: oracle-l@xxxxxxxxxxxxx<mailto:oracle-l@xxxxxxxxxxxxx>
Subject: Re: Log File Syncs
On 03/24/2016 12:53 PM, Osborne, Chris wrote:
The log file write time is also slightly faster on the ‘slow’ DB leading me to
believe that IO is not an issue.
Chris, the obvious answer is in the different versions of Linux. RH 5.x is
running an ancient kernel 2.6.18 while CentOS 6.6 is running much newer kernel
3.10. I don't know the underlying file systems, but I know that Red Hat 5.x did
not support Ext4, while CentOS 6.x does support it, it's a default FS in that
version.
There is a huge difference between those two file systems, one is block based,
another one is extent based. Block based file systems turn the vast majority of
IO into random access IO, while extent based file systems can write
sequentially, as is the nature of log file writes.
So, my two obvious candidates for the differences are much newer kernel and
different file system.
Regards
--
Mladen Gogala
Oracle DBA
Tel: (347) 321-1217
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