Store total online users in RRDtool given login/logout, checkin/checkout logs

Question

Given a log file with clear check-in and check-out messages per user, how can I feed this data into RRDtool to track the total users logged in to the site? (At this time, I do not care about unique users, but that would be nice too of course!)

I read about the DERIVE data source type. How do I get a hypothetical INTEGRAL type instead? Can this be done straightforwardly?

Of course, I could process the file myself, updating GAUGE into the RRD and saving state somehow.; however, I am hoping to avoid that if I can get away with it.

Answer 1

since rrdtool deals in 'rates' it can not really count as you would like it to. The best you could get would be to use an ABSOLUTE type data-source, but this would only work for creating something like a login/logout rate statistic ... you could answer how many logins and how many logouts per-hour you had ...

You would then do an rrdtool update login.rrd N:1 whenever you have a login.