I have a data source which returns the number of messages sent since startup. I want to be able to graph this, but I'm unsure of the best way.
What I'm thinking is graphing the increase in messages since the last interval (the data source doesn't provide this method, so I'd need cacti to do it).
Any ideas?
Best Answer
This is exactly how interface counters are handled: They specify the number of bytes or packets received or sent over an interface. Cacti (resp. rrdtool) then calculates the difference between the current and the last reading and stores and graphs that value.
I guess it would be the best to check out the "Interface - Traffic" data template. The "Data Source Type" setting defines how cacti/rrdtool should handle the values. "COUNTER" or "DERIVE" is what you need. For an explanation of all the different data source types, check out the rrdtool docs.