Hi,
I'm trying to virtually "concatenate" two RRDs together at graphing time. Let's
say there are 3 points in time a, b, and c where a < b < c. I want to use the
data in a.rrd between a and b, and the data in b.rrd between b and c.
"rrd graph" is called with the --start option set to a, and the --end option
set to c. The defs are as follows:
DEF:data_a=a.rrd:data:AVERAGE:start=$a:end=$b
DEF:data_b=b.rrd:data:AVERAGE:start=$b:end=$c
This works, I can graph data_a and data_b separately.
Now, to combine them into one value:
CDEF:data=data_a,data_b,ADDNAN
Unfortunately, this does not work except when time = b (the only point where
there is both data_a and data_b).
What works is:
DEF:data_a=a.rrd:data:AVERAGE:start=$a:end=$c
DEF:data_b=b.rrd:data:AVERAGE:start=$a:end=$c
CDEF:data=TIME,$b,LT,data_a,data_b,IF
What I want to know is, why can't the first CDEF (the one with ADDNAN) work?
The solution with the IF would be longer if there are 3 or 4 RRDs to use.
-- william
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