[rrd-users] merging 2 or more DEF data sources into one CDEF?

[Simon Hobson]

Ryan Kubica wrote:
>What I am trying to do is take two or more datasources with 
>different time ranges and merge them into one CDEF for display 
>(graph and legend.)
>
>Example:
>
>    ds foo1 - start 7 days ago, end 6 days ago
>    ds foo2 - start 6 days ago, end 5 days ago
>    ds foo3 - start 5 days ago, end now
>
>    cdef is foo1 or foo2 or foo3
>
>I have the correct time alignments for the adjacent time intervals, 
>ie: foo1 ends 60 seconds before foo2 starts on a 60 second interval 
>step.

OK, for two data sources I have this in a graph definition :

         DEF:data1=${RRDPath1}/${RRDName1}:${Selection}:AVERAGE
         DEF:data2=${RRDPath2}/${RRDName2}:${Selection}:AVERAGE

         CDEF:data=TIME,${ChangeDate},LT,data1,data2,IF

It's part of a shell script, so using normal Bash variable sustitutions.

For three sources just expand as required, I think this would do it 
(with the proviso that changedate2>changedate1) :

 
CDEF:data=TIME,${ChangeDate1},LT,data1,TIME,${ChangeDate2},LT,data2,data3,IF,IF