java - Combine separate RRD files to a single graph -

using rrd4j, how can combine several .rrd files either single .rrd or (ideally) single graph?

more details:

i have several copies of same .rrd. each file records several sensor data readings, name sensor-1, sensor-2 across files. data1.rrd, data2.rrd contain data sources of sensor-1 etc.

the ds definition follows.

ds:sensor-1:gauge:35:u:u ds:sensor-2:gauge:35:u:u ds:sensor-3:gauge:35:u:u 

i can generate graph each individually adding data source graph this;

val graph = new rrdgraphdef() graph.datasource("sensor-1", data1.rrd", "sensor-1", average) graph.datasource("sensor-2", data1.rrd", "sensor-1", average) graph.line("sensor-1", green) graph.line("sensor-2", red) 

but if same data2.rrd (adding datasource same graph instance), seems loose preceding data , graphs 1 of file's data.

i suspect each ds having same name across files may problem.

suggestions on how achieve same regular rrd tool might helpful might able translate rrd4j

this statement: graph.datasource("varname", "filename.rrd", "dsname", average) defines new variable use called varname, corresponds ds dsname in file filename.rrd, consolodated using average consolodation function.

clearly, cannot have 2 variables in same graph same name; however, there nothing prevent pulling data multiple different rrd files, , nothing prevent using different varname ds name.

however, should use alphanumerics in variable name -- in particular, avoid '-', though supposed work. underscores ok.

so, valid: graph.datasource("sensora", "sitea.rrd", "sensor", average) graph.datasource("sensorb", "siteb.rrd", "sensor", average) , define 2 variables, sensora , sensorb corresponding same named ds in 2 different rrd files.

do not use sensor-1 varname, contains '-' symbol.

not having seen rrd4j code failing can't certain, suspect either because not renaming varname, making both variables share same name , overwrite 1 another, or because of '-' in varname.