[rrd-users] RRDs Coding Question - Dynamic Multiple RRD Data Sources

Simon Hobson linux at thehobsons.co.uk
Wed Sep 26 16:03:29 CEST 2012

Wesley Wyche wrote:
>So, since you say an Unknown (NaN) plus some value equals Unknown again


>then I can't use this in this way.  These values in the various 
>node's rrds must be merged together to represent a single snapshot 
>of what is happening.

See my earlier post - you can handle this with a bit of RPN

>Makes absolutely no sense (to me anyway).

Makes complete sense - add <something unknown> to a number and the 
result cannot be anything other than unknown. Different users will 
want different things - you may want to just ignore the unknown data 
(see the RPN I posted earlier), others may wish for the whole lot to 
be unknown because that's what *their* data means.

Also, note that the same applies when stacking data - if something is 
unknown, then anything stacked on top of it in a graph will also not 
be drawn.

Simon Hobson

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