computer science

Ping-pong scheme

Ping-pong scheme 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 Ping-pong scheme rather than just read about it. In short: Algorithms said to employ a ping-pong scheme exist in different fields of software engineering. They are characterized by an alternation between two entities.

Key takeaways

Ping-pong scheme 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 Ping-pong scheme to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Ping-pong scheme from memory before moving on to harder problems.

Reference excerpt

Algorithms said to employ a ping-pong scheme exist in different fields of software engineering. They are characterized by an alternation between two entities. In the examples described below, these entities are communication partners, network paths or file blocks.

Databases In most database management systems durable database transactions are supported through a log file. However, multiple writes to the same page of that file can produce a slim chance of data loss. Assuming for simplicity that the log file is organized in pages whose size matches the block size of its underlying medium, the following problem can occur: If the very last page of the log file is only partially filled with data and has to be written to permanent storage in this state, the very same page will have to be overwritten during the next write operation. If a crash happens during that later write operation, previously stored log data may be lost. The ping-pong scheme described in Transaction Processing eliminates this problem by alternately writing the contents of said (logical) last page to two different physical pages inside the log file (the actual last page i and its empty successor i+1). Once said logical log page is no longer the last page (i.e. it is completely filled with log data), it is written one last time to the regular physical position (i) inside the log file. This scheme requires the usage of time stamps for each page in order to distinguish the most recent version of the logical last page one from its predecessor.

Software In software, such as game development, a ping-pong function may refer to any functions that oscillates between a minimum value and a maximum value. Some game engines, such as Unity offer a dedicated function in the engine's math library for this purpose.

An example of this code in C++ would be as follows:

Networking

Internet A functionality which lets a computer A find out whether a computer B is reachable and responding is built into the Internet Control Message Protocol (ICMP). Through an "Echo Request" Computer A asks B to send back an "Echo Reply". These two messages are also sometimes called "ping" and "pong" for historical purposes.

Routing In routing, a Ping-Pong scheme is a simple algorithm for distributing data packets across two paths. If you had two paths A and B, then the algorithm would randomly start with one of the paths and then switch back and forth between the two. If you were to get the next path from a function call, it would look like this in Python:

References

Worked examples

Example 1 — a first encounter with Ping-pong scheme

Start with the simplest possible case. Write down what Ping-pong scheme 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 Ping-pong scheme 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 Ping-pong scheme 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 Ping-pong scheme

In research: Ping-pong scheme 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 Ping-pong scheme 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: Ping-pong scheme is common in secondary-school and first-year university syllabi. It links to neighbouring topics Algorithms, so understanding it makes those chapters shorter.
In everyday life: Look for Ping-pong scheme 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 Ping-pong scheme in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Ping-pong scheme 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 Ping-pong scheme out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Ping-pong scheme in simple terms?

Algorithms said to employ a ping-pong scheme exist in different fields of software engineering. They are characterized by an alternation between two entities.

Why does Ping-pong scheme 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 Ping-pong scheme?

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 Ping-pong scheme.