[rrd-users] Re: rrdGraph help

Simon Hobson linux at thehobsons.co.uk
Thu Nov 30 11:49:03 MET 2006

Kant, D (Dave) wrote:

>Sometimes my sensor goes offline and the RRD archives contain 
>Unknown datapoints.
>I can set them to zero using CDEF statments. This results in large gaps in
>the graph. (See the first graph at http://tinyurl.com/ve6d8).
>Is there a way - similar to the second graph - to fill these gaps to 
>indicate that
>no data is present due to sensor failure. Can someone send me an example?

How about having another cdef which is set to unknown when the data 
is present, and to the upper Y axis limit (or at least some positive 
value) when the data is absent. Then plot this cdef as an area.

That way, when your data is unknown (leave it that way rather than 
set it to zero) it will not be plotted, but a rectangle of a 
different colour will get plotted in the gap. When data is known it 
will be plotted, and your extra cdef will not be plotted as it will 
be unknown.

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