From: "J. Bruce Fields" <bfields@fieldses.org>
Subject: Re: [PATCH] NFS: Zeroing NFS and kNFSD stats
Date: Tue, 13 Jul 2004 14:01:08 -0400
Sender: nfs-admin@lists.sourceforge.net
Message-ID: <20040713180108.GF3023@fieldses.org>
References: <40F3D483.8020507@RedHat.com> <20040713143044.GA3023@fieldses.org> <40F3FAD8.7090707@RedHat.com> <20040713151759.GC3023@fieldses.org>
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Cc: Linux NFS Mailing List <nfs@lists.sourceforge.net>
To: Steve Dickson <SteveD@redhat.com>
In-Reply-To: <20040713151759.GC3023@fieldses.org>
Errors-To: nfs-admin@lists.sourceforge.net

On Tue, Jul 13, 2004 at 11:17:59AM -0400, J. Bruce Fields wrote:
> On Tue, Jul 13, 2004 at 11:08:08AM -0400, Steve Dickson wrote:
> > Starting up a test run, zeroing out the stats give you a very clear
> > picture of what exactly is going on...
> 
> But you could exactly the same thing by recording the values at the
> beginning of the test run and then subtracting.  In practice this is
> likely to be annoying, so you'd want to write utilities that did this
> for you, like say
> 
> checkpoint_stats stats.txt
> display_stats --since stats.txt
> 
> That'd do what you want, right?

The problem I have, by the way, is that zeroing is going to cause
confusing problems whenever there are two simultaneous attempts to
collect statistics.

For example, imagine that your NFS server has a persistent
performance-monitoring daemon that checks the statistics every now and
then and emails the adminstrator a summary once a week.

Then imagine that one day you have a problem with the server, so you log
in and do a quick check of some statistics, zeroing them in the process.
Now the daemon has no more hope of getting its numbers right.  Murphy's
law being what it is, you and the adminstrator that gets the summary
email are probably different people, and by the time he/she gets the
very odd-looking end-of-week report you've forgotten that you zeroed the
statistics once.  Head-scratching ensues.

Writing a script to do the subtraction is just as simple and avoids any
such problems.

--b.


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