[rrd-users] wrong values when graphing with RRD

Fernando Nieto fnieto at satec.es
Tue Apr 20 17:24:38 MEST 2004

Hi everybody!, 
  I'm having problems when graphing with RRD. The problem is that I'm
getting different outputs when I create the *same* graph with different
sizes. At first I thought it was a resolution problem but then I noticed
that legend values were also different!!.

  You can see this in the attached graphs. Both shows the last 2 days data,
I have only changed its width and height when I have created them.  Both
graphs should show a peak of 5% near midnight, but in the "small" one is
showed a 2.5% value and that's what the legend also says!! why??. If
resolution was the problem, at least, the legend should show the correct
value, don't you think so?
  I'm giving you some further information about how i'm doing. The RRD data
is the following (the only the non-zero value):

                      numRTT        packetLossSD     packetLossSD
     1082410500: 1.9000000000e+01 0.0000000000e+00 1.0000000000e+00

     rrdtool graph file.png \
         -a PNG --lazy --step=300 -e now -s e-2d \
         -w 460 -h 120 \
         -t "Loss percentage" -v % --units-exponent=1 \
         DEF:loss1=900002220.rrd:packetLossSD:AVERAGE \
         DEF:loss2=900002220.rrd:packetLossDS:AVERAGE \
         DEF:numrtt=900002220.rrd:numRTT:AVERAGE \
         CDEF:numerador=loss1,loss2,+ \  
         CDEF:denominador=numerador,numrtt,+ \
         CDEF:perdidas=100,numerador,denominador,/,* \
         LINE1:perdidas#0050FF:"MAD-LON-0 (max, avg, cur)\:" \
         GPRINT:perdidas:MAX:"%5.2lf %%" \
         GPRINT:perdidas:AVERAGE:"%5.2lf %%" \
         GPRINT:perdidas:LAST:"%5.2lf %%\c" \
         HRULE:0.5#FF0000:"Threshold 0.5 %\c"

  The graph shows the CDEF:
100*(packetLossSD+packetLossDS)/(numRTT+packetLossSD+packetLossDS), that is:
100*(1/20) = 5 %. The RRD file keeps 300 seconds samples during 8 days, i'm
graphing 2 days, that is 288*2 samples in the x-axis.   

  This problem it's getting me crazy, I hope someone could help me, maybe
it's something petty but I'm not able to see it.

Thank you very much in advance.

Best regards,


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