computer science

RRDtool

RRDtool is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand RRDtool rather than just read about it. In short: RRDtool (round-robin database tool) is a data logging and graphing system for time series data such as network bandwidth, temperatures, and CPU load. The data is stored in a circular buffer-based database, thus the system storage footprint remains constant over time.

Key takeaways

RRDtool belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect RRDtool to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of RRDtool from memory before moving on to harder problems.

Reference excerpt

RRDtool (round-robin database tool) is a data logging and graphing system for time series data such as network bandwidth, temperatures, and CPU load. The data is stored in a circular buffer-based database, thus the system storage footprint remains constant over time. It also includes tools to extract round-robin data in a graphical format, for which it was originally intended. Bindings exist for several programming languages, including Perl, Python, Ruby, Tcl, PHP and Lua. There is an independent full Java implementation called rrd4j.

General data storage RRDtool assumes time-variable data in intervals of a certain length. This interval, usually named the 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, after interpolation, 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, and 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:

time covered = (#CDPs stored) × (#PDPs per CDP) × (step time length) After this time the archive will "wrap around": the next insertion will overwrite the oldest entry. This behavior is referred to as "round-robin" and is the reason for the program's name. To cover several timespans and/or use several consolidation functions, an RRD file may contain multiple RRAs. The data retrieval function of RRDtool automatically selects the archive with the highest resolution that still covers the requested timespan. This mechanism is also used by RRDtool's graphing subsystem.

Release history

The following table contains the release history of RRDtool, showing its major releases.

Other tools that use RRDtool

Illustrations

Worked examples

Example 1 — a first encounter with RRDtool

Start with the simplest possible case. Write down what RRDtool claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to RRDtool before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about RRDtool ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of RRDtool

In research: RRDtool appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses RRDtool in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: RRDtool is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1999 software, Free database management systems, Free network management software, so understanding it makes those chapters shorter.
In everyday life: Look for RRDtool outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study RRDtool in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what RRDtool means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain RRDtool out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is RRDtool in simple terms?

Why does RRDtool matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study RRDtool?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on RRDtool.