[smokeping-users] Re: RRDTool Filling In Unknown Values For Missing Pings

Chris Wilson chris at aidworld.org
Fri Jan 14 18:12:02 MET 2005

Hi all,
I think I have seen the same effect that Kennedy reported in
[http://www.ee.ethz.ch/~slist/smokeping-users/msg01301.html], i.e. "fake
smoke" (without fire) on my graphs.

I'm no expert at interpreting RRD data, but I have attached an example
in the hope that someone can help me to debug it.

The RRD database is defined for 20 samples every 60 seconds. The columns
are therefore: uptime, loss, median, ping1, ... ping20.

Here is a sample data value which has the "fake smoke" in the Smokeping

<!-- 2005-01-14 13:00:00 GMT / 1105707600 -->
	<v> NaN </v>			<!-- uptime -->
	<v> 6.0000000000e+00 </v>	<!-- loss   -->
	<v> 1.5517901667e+01 </v>	<!-- median -->
	<v> NaN </v>			<!-- ping1 -->
	<v> NaN </v>
	<v> NaN </v>
	<v> 1.4383288333e+01 </v>
	<v> 1.4629555000e+01 </v>
	<v> 1.4661940000e+01 </v>
	<v> 1.4898546667e+01 </v>
	<v> 1.5044710000e+01 </v>
	<v> 1.5159203333e+01 </v>
	<v> 1.5398535000e+01 </v>
	<v> 1.5517901667e+01 </v>
	<v> 1.5535275000e+01 </v>
	<v> 1.5542535000e+01 </v>
	<v> 1.5627283333e+01 </v>
	<v> 1.5643136667e+01 </v>
	<v> 1.5727450000e+01 </v>
	<v> 1.5794186667e+01 </v>
	<v> NaN </v>
	<v> NaN </v>
	<v> NaN </v>			<!-- ping20 -->

As you can see from the attached graph, the smoke at 13:00 goes all the
way down to zero, but there were no samples at zero, in fact all the
valid samples are in the range 14 to 16. Can anyone explain why this
happens for a poor confused Englishman?

By the way, this rather weird purple curve was caused by the ping times
to this site in Nigeria being longer than the default timeout of fping,
resulting in fping giving up when only half of the pings had returned.

I couldn't find a way to adjust fping's timeout in the Smokeping
options, so I had to hack FPing.pm to add the parameter '-t20000' to the
FPing command line. Please could we have an option for this in Smokeping
and/or a sensible (longer) default timeout?

Cheers, Chris.
(aidworld) chris wilson | chief engineer (chris at aidworld.org)

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