RE: Log File Syncs

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_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Mladen Gogala Sent: 26 March 2016 04:11
To: oracle-l_at_freelists.org
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

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Mladen Gogala

Oracle DBA

Tel: (347) 321-1217

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http://www.freelists.org/webpage/oracle-l Received on Tue Mar 29 2016 - 14:56:51 CEST