Re: Log File Syncs

I wonder if the load process is in fact comparable. It looks like you have the same number of log file write events, but 1000x the number of log file sync events on the fast system.

Is this a repeatable test? If so I'd definitely trace the sessions with waits recorded and run the tracefiles through a profiler (if you don't have one tkprof .... sort=prsela,exeela,fchela ) and review the profiles for where the time is being spent. your numbers for log file sync above appear to account for approx 1 minute of elapsed time difference (and that in favour of the slow system) so likely you are looking at the wrong thing.

On Thu, Mar 24, 2016 at 3:58 PM, Osborne, Chris <Chris.Osborne_at_sky.uk> wrote:

> Hi All,
>
>
>
> I was wondering if someone could maybe help me out with an unusual
> observation I have on a couple of test systems.
>
> I have a user reporting that they are seeing differences in performance
> between the database on a VM (which is running ‘fast’) and a database on a
> physical (which is running slow)
>
>
>
> They are performing a load from MongoDB via a PHP app into the oracle
> database. In both tests the same source database is being used.
>
>
>
> I’ve done a quick overview on each of the systems and the only thing that
> is jumping out at me is that on the faster DB the log file sync time is
> much lower on the faster one. (the output was gather using oratop) Both
> DB’s are 12.1.0.2. The faster one is on CentOS 6.6 and the Slower one on
> Redhat 5.11.
>
>
>
>
>
> Slow DB
>
> EVENT (Real-Time) AVG: TOT WAITS TIME(s) AVG_MS PCT WAIT_CLASS
>
> log file parallel write 20008284 23783 1.2 100 System I/O
>
> log file sync 1730 9 5.2 0 Commit
>
> DB CPU 0 0
>
>
>
>
>
> Fast DB
>
> EVENT (Real-Time) AVG: TOT WAITS TIME(s) AVG_MS PCT WAIT_CLASS
>
> log file parallel write 20389439 28216 1.4 100 System I/O
>
> log file sync 179674 74 0.4 0 Commit
>
> SQL*Net message to client 7 0 0.0 0 Network
>
> DB CPU 0 0
>
>
>
> I’m also a bit confused as to how the log file sync time can be shorter
> than the log file write time.
>
>
>
> Any assistance or advice would be appreciated.
>
>
>
> Regards,
>
>
>
>
>
>
>
> *Christopher Osborne*
>
>
>
>
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Niall Litchfield
Oracle DBA
http://www.orawin.info

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