Rrdtool

RRDtool

Original author(s)	Tobi Oetiker
Stable release	1.6.0 / May 9, 2016
Written in	C
License	GNU General Public License
Website	oss.oetiker.ch/rrdtool/

RRDtool (round-robin database tool) aims to handle time series data such as network bandwidth, temperatures or CPU load. The data is stored in a circular buffer based database, thus the system storage footprint remains constant over time. This is distinct from the computer science concept of round-robin scheduling.

It also includes tools to extract round-robin data in a graphical format, for which it was originally intended. Bindings exist for programming languages Perl, Python, Ruby, Tcl, PHP and Lua. There is an independent full Java implementation called rrd4j.

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.

After the data has been consolidated, the resulting CDP is stored in a round-robin archive (RRA). A round-robin archive stores a fixed number of CDPs and specifies how many PDPs should be consolidated into one CDP and which CF to use. The total time covered by an RRA can be calculated as follows:

After this time the archive will "wrap around": the next insertion will overwrite the oldest entry. This behavior in this context is referred to as "round-robin" and is the reason for the program's name. However this is different from the common computer science definition, which is a method of distributing resources among multiple consumers or processes.