[rrd-users] RPN Question

Simon Hobson linux at thehobsons.co.uk
Wed Apr 18 09:05:17 CEST 2007

Wesley PA4WDH wrote:

>  > DEF:ds_one=rrdfile.rrd:foo:AVERAGE
>>  DEF:ds_two=rrdfile.rrd:bar:AVERAGE
>>  DEF:ds_three=other_rrdfile.rrd:baz:AVERAGE
>>  CDEF:total=\
>>  ds_one,UN,0,ds_one,IF,\
>>  ds_two,UN,0,ds_two,IF,+,\
>>  ds_three,UN,0,ds_three,IF,+
>>  Something like that would do the trick.
>This uses a different approach as i use now, so it's
>worth a try. But i have to say: I have about 200 DS's
>now. Is there any limit in the number of elements in
>an RPN expression ?

Don't know about that, but I have one graph with 510 elements on it - 
in and out traffic for 254 addresses. Each one has a DEF to get the 
data from a DS, and half of them (the out traffic) have an additional 
one to 'invert' the data (ie make it negative to plot below the x 
axis). The whole lot is then plotted as two big stacks.
So rrdgraph CAN handle some large graphs (it takes up to 1.5G of VM 
to draw the above graph depending on the timescale involved) !

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