Four Systems in One Night (worked designs)

Four famous design questions worked in one sitting, with the same method each time, so that the one thing which actually changes between them becomes impossible to miss.

Before you start. You need the six steps every design question runs through: clarify what is being asked, estimate the scale, sketch the API, choose the data store, draw the design, then scale it. You also already own three of the parts this lesson assembles, which is enough to start: something that remembers answers so the slow thing gets asked less often, a book everyone reads at their own pace and nobody erases, and a store built to swallow writes faster than it hands them back.