[rrd-users] Additional "Unknown"-Value

Tobias Oetiker tobi at oetiker.ch
Mon Jun 8 12:03:56 CEST 2009

Hi n1LL3,

Today n1LL3 wrote:

> Hello,
> I am working with a monitoring tool, which uses the rrdtools for creating
> graphs.
> When I am sending an update-command to the RRD with no data, for which I am
> using the "U", what is mentioned in the documentation (If there is no data
> for a certain data-source, the letter U (e.g., N:0.1:U:1) can be
> specified.), in the RRD is a "NaN". When the RRD gets the next
> update-command with data and the heartbeat-value has not reached, an average
> rate will be calculated and added to this and to the previous data-source.
> But for monitoring tools it would be nicer: If there is no data, the graph
> should break.
> This could be realised by adding a new value, for e.g. "unknown-status",
> which I can edit with the update-command too. When this option is set, the
> heartbeat will be ignored and the graph will break.
> With this option, I can see the real breakdown of my monitoring.
> Otherwise the RRD creates data, which does not really exist.
> What would you say about this?

My sugestion would be that you set your mrhb to only a bit more
than your sampleing interval ... (as it should be) now, when you
miss samples, or you log 'U' rrdtool will turn the stored data into
NaN aka Unknown which will cause the graph to 'disapear' ...

My phanstasy is that you want to see the graph break for intervals
shorter than your step size ?

> Thanks!

Tobi Oetiker, OETIKER+PARTNER AG, Aarweg 15 CH-4600 Olten, Switzerland
http://it.oetiker.ch tobi at oetiker.ch ++41 62 775 9902 / sb: -9900

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