[collectd] Varnish plugin

[Florian Forster]

Hi Jérôme,

On Fri, Jun 11, 2010 at 07:29:23PM +0200, Jerome Renard wrote:
> I tested the "cache_result" type, and when the DERIVE type is used, I
> do not get the correct numbers.

> If I compare the output I get from varnishstat and the result I get
> from the rrd generated graphs the values are completely different.

as far as I see, varnishstat divides counter values with the uptime. The
result is therefore roughly the all-time average rate of that counter.

With collectd, you get the rate of the last $Interval seconds, for
example the last 10 seconds in the default configuration. This value may
of course be *much* smaller or larger, depending on how busy the system
was compared to the average usage.

> I guess this is due to de derive type.

"COUNTER" and "DERIVE" only differ in the overflow and counter-reset
cases. Since overflows are next to impossible with 64bit counters, and
because the counters are reset to zero when varnish is restarted, I
opted for optimizing for the latter case, i.e. used "DERIVE".

You can find a more in-depth explanation of the difference between
"COUNTER" and "DERIVE" in the collectd wiki at [0].

> But the problem is that I never get any value, it is always set to
> zero, here is what I get from the debug:

Is the counter value actually increasing? Otherwise a rate of (close to)
zero is expected and normal.

Regards,
-octo

[0] <http://collectd.org/wiki/index.php/Data_source>
-- 
Florian octo Forster
Hacker in training
GnuPG: 0x91523C3D
http://verplant.org/
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