Hello list,
While searching the web on how to calculate the 95th percentile from an
RRD, most results return something like:
rrdtool graph graph.png \
DEF:in=foo.rrd:in:AVERAGE \
DEF:out=foo.rrd:out:AVERAGE \
CDEF:inb=in,8,* \
CDEF:outb=out,8,* \
CDEF:allbits=inb,outb,MAX \
VDEF:pct=allbits,95,PERCENT \
However I find that the result produced this way is highly incorrect.
Not only that, but the result is greatly influenced by the width (-w)
option for generating the graph. On my test dataset changing -w from 400
to 1000 pixels (while keeping all other things the same) the 95Th
percentile swings back and forth between 17 and 38 Mbit. Am I doing
something wrong, or is this behaviour to be expected?
My create command, the measurements I'm inserting are 'bytes transferred
since last measurement'
# rrdtool create foo.rrd --start $start --step 300
DS:in:ABSOLUTE:600:0:U DS:out:ABSOLUTE:600:0:U RRA:AVERAGE:0.5:1:100000
Regards,
Marius
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