[rrd-users] Graphing values based on CDEF

[W. James Showalter, Jr.]

Hello,

I am somewhat confused by the output of a graph I am working on.
Here are the RRA constructs:

DS:TXDPKTS:GAUGE:120:U:U \
DS:RXDPKTS:GAUGE:120:U:U \
RRA:AVERAGE:.5:1:288

Here are the pertinent graph parameters

DEF:tx=data.rrd:TXDPKTS:AVERAGE \
DEF:rx=data.rrd:RXDPKTS:AVERAGE \
CDEF:drops=tx,rx,-


The RRAs for tx are always 50.  I am sending out 50 ICMP echoes. The rx is
usually 50 with all others being 49.  I have verified this by inspection
using rrdfetch.

What is confusing to me is that no matter what I do, I always seem to plot
.5 instead of 1.  I assume that the CDEF above will either b 0 or 1 based
on stated values of rx and tx.  Yet when I plot the graph, it always plots
it at .5 no matter how I try and manipulate the y-axis (I tried -u with
different values, --unit-exponent 0, etc).  If I change CDEF to:

CDEF:drops=tx,rx,-,2,*

It works as required (although I am not certain why). Any explanation
would be appreciated.  And is there any way to print out a CDEF calculated
value to track what is going on?


Thanks,
Jim







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