RRDtool

RRDtool (acronym for round-robin database tool) aims to handle time-series data like network bandwidth, temperatures, CPU load, etc. The data are stored in a circular buffer based database, thus the system storage footprint remains constant over time. Note that this is distinct from the computer science concept of round-robin scheduling.

It also includes tools to extract RRD data in a graphical format, for which it was originally intended.

Bindings exist for Perl, Python, Ruby, Tcl, PHP and Lua. And there is an independent full Java implementation, rrd4j.

General data storage

RRDtool assumes time-variable data in intervals of a certain length. This interval, usually named step, is specified upon creation of an RRD file and cannot be changed afterwards. Because data may not always be available at just the right time, RRDtool will automatically interpolate any submitted data to fit its internal time-steps.

The value for a specific step, that has been interpolated, is named a primary data point (PDP). Multiple PDPs may be consolidated according to a consolidation function (CF) to form a consolidated data point (CDP). Typical consolidation functions are average, minimum, maximum.