Re: log file sync vs log file parallel write probably not bug 2669566

From: joel garry <joel-garry_at_home.com>
Date: Thu, 6 Nov 2008 13:15:50 -0800 (PST)
Message-ID: <43e8a313-82e8-4ba5-9f7f-ccf26bb1550e@i20g2000prf.googlegroups.com>


On Nov 6, 2:24†am, "Vladimir M. Zakharychev" <vladimir.zakharyc..._at_gmail.com> wrote:
> On Nov 6, 10:51†am, HansP <hans-peter.sl..._at_atosorigin.com> wrote:
>
>
>
>
>
> > > This is a wild guess, based on the 10g docs, which may or may not
> > > apply or work the same:
>
> > > The log file parallel write includes the I/O time only. †The log file
> > > sync includes the time the log writer has to wait for the db writer
> > > to
> > > tell the log writer the redo is done (all those "private strand flush
> > > incomplete" notifications in the 10g alert log), as well as all the
> > > other
> > > overhead of the interprocess communication.
>
> > >http://download.oracle.com/docs/cd/B19306_01/server.102/b14237/waitev...
>
> > > jg
> > > --
> > > @home.com is bogus.
> > > Ya win some, ya lose some.
>
> > Yes the includes waiting for the log file parallel write by the log
> > writer and some overhead (signalling each other etc)
> > Therefore I would expect the for the log file sync be a little more
> > than the time for the log file parallel write but not 10 to 20 time
> > the
> > time for the log file parallel write.
>
> > regards Hans-Peter
>
> This includes the time spent by the process waiting for signal that
> log file sync is complete and then time spent in the OS run queue
> waiting for the CPU, plus the time occasionally spent by the LGWR in
> the run queue. Kevin Closson covered this issue in great detail in his
> blog here:http://kevinclosson.wordpress.com/2007/07/21/manly-men-only-use-solid....
> One of the suggestions in that post is to renice the LGWR to the
> highest priority possible so that it always gets CPU time when it
> needs before anything else does, and is not preempted by less
> important processes. Another post that might be helpful is here:http://www.pythian.com/blogs/1098/tuning-log-file-sync-event-waits.
>
> Hth,
> † †Vladimir M. Zakharychev
> † †N-Networks, makers of Dynamic PSP(tm)
> † †http://www.dynamicpsp.com

Thanks Vladimir, I even thanked Kevin on that thread, so it was kind of burbling around in the back of my head, I couldn't remember where from.

jg

--
@home.com is bogus.
"Donít do this if you like your database..." - Kevin Closson
Received on Thu Nov 06 2008 - 15:15:50 CST

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