[rrd-users] how to use a CDEF to turn anything close to 0 to NAN

[Hongyun Sun]

Hello,

I'm very new to rrdtool, and I have a similar problem to ticket #31 
(http://oss.oetiker.ch/rrdtool-trac/ticket/31), the answer to the 
problem is "use a CDEF to turn anything close to 0 to NAN ... then you 
should be all set ... the problem is that it is not sufficient to turn 0 
into NAN you have to define a sensible cut-off point ...", but how and 
where to define CDEF?

I have a plot description like the following:

$PLOT_DESCRIPTION="\
--vertical-label 'jobs' \
--width $width \
--height $height \
--alt-autoscale-max \
--lower-limit 0 \
--logarithmic \
--units=si \
--lazy \
DEF:LABEL0=/var/lib/ganglia/rrds/Admin/gridweb.triumf.ca/{$SITE}_activated.rrd:sum:AVERAGE 
\
LINE2.0:LABEL0#000000:activated \
";

Thanks for help!
Hongyun