[collectd] Varnish plugin

[Jerome Renard]

Florian,

On Sat, Jun 12, 2010 at 9:57 AM, Florian Forster <octo at verplant.org> wrote:
> 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".

Yeah, I figured that out a bit earlier today. Actually we were serving
a different purpose, I wanted to fetch the exact numbers returned
by varnishstat and get them displaied by RRDTool and I completely
overlook the time interval part (like monitoring every 10 seconds) :/
So know everything is crystal clear and we are on the same page :)

>
> 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.

Yes, that is what I found by looking in uc_update() I'll fix my stuff :)

Thanks for your feedback.

Best Regards

--
Jérôme :)