[hobbit] weird rrd output (using the NCV module)

[Henrik Stoerner]

On Thu, Sep 13, 2007 at 11:20:03AM -0400, Gary Baluha wrote:
> I'm seeing a weird output for one of my custom RRD graphs, using the NCV
> module.  The collector script on the client
> is creating an ncv-style output based on the bind 9 "rndc stats" command.
> These numbers are counter-style numbers,
> always increasing (until named is restarted).  As such, the default DERIVE
> format of the NCV module is correct.
> 
> The problem I'm seeing is that the numbers showing up in the RRD graph--as
> far as I can tell--have nothing at all to do
> with the actual "rndc stats" values.  For instance, the "last" and "current"
> values of the data was:
> 
> success : 283  ->  294  (11)
> referral : 0  ->  0  (0)
> nxrrset : 149  ->  156  (7)
> 
> The number in () above is the actual difference between the numbers, and the
> values I'm expecting to show up in the RRD graph.
> But the actual values that are showing up for the above example (for the
> "(cur)" value) are, respectively:
> 34.0m
> 0.0
> 20.8m


Everything is behaving the way it should, but it doesn't match your
expectation.

The problem is that rrdtool treats counters (and derive's) as RATES,
i.e. "this many X per second". So when you have 11 requests over a 5
minute period, rrdtool records (11 / 300) = 0,037 requests/second.
That's why you have that "34.0m" recorded - apparently there was
slightly more than 300 seconds between the two readings.

If you want the graph to show how many requests occurred over the 5
minute period, then the simplest way is to define the graph to use
a value which is 300 times the actual value recorded by rrdtool :-)


Regards,
Henrik