Latency, Throughput, and Walking on Escalators

A constrained space such as an escalator can comfortably hold more than twice the number of standing pedestrians as walking pedestrians. So stop walking up them. https://t.co/7Dey11CXvP

My first reaction was “that’s dumb - a highway can hold more cars at 20mph than 65mph; it’s throughput that matters.” Then I read the article and realized that the summary was what was dumb. The actual study was not, and illustrates computer systems concepts, as I’ll explain:

The important metrics for a lot of systems are latency and throughput. Throughput is how much work gets done per unit time (so in this case, people transported per minute), and latency is how long each individual piece of work takes (how long each person is on the escalator).

These two concepts are related, and Little’s Law gives the simplest relation. It says that the number of people on the escalator is equal to the rate of people getting on multiplied by the average time each person spends on the escalator.

(Note that the rate of getting on and the rate of getting off had better be the same, or there’s something very strange going on.)

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