[rrd-developers] NAN Values

[Daniel.Pocock at barclayscapital.com]

> Hi friends,
>         Please tell how to deal with the NAN values due to 
> xff in RRD graphs. I saw the ADDNAN patch, it is very useful 
> to get most of the graphs but i dont know how to use it. Also 
> send any other choices left to deal with NAN values.


This is something that interests me too - if Ganglia (gmetad) isn't
running quickly enough, data isn't fed to rrdtool at a sufficient rate
to satisfy the xff setting.

It would be useful to have some way of putting a label on the graph to
say that, for example, 20% of the data is missing.   Looking at the RPN
functions for a VDEF, there doesn't appear to be a function that can
count the number of NaNs in a set.  The COUNT function described doesn't
work for VDEFs, and whether NaNs can be counted is not clear anyway,
because NaN != NaN.  Maybe we would need a function isnan() for
constructing a CDEF, and then count the number of true values in the new
CDEF.

In the worst case, some users see the gaps, and they think the value is
0 instead of NaN.  

Regards,

Daniel
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