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Patterns

The building blocks combined under pressure: pushing live updates, handling contention, coordinating multi-step work, scaling reads and writes, moving large files, and running long jobs.

01Realtime updatesWhen the server has newsEvery lesson so far assumed the same shape the server has news, and it has to reach a client who isn't currently asking for anything.02ContentionWhen writes collideTwo people click "buy" on the last concert seat at the same instant. Both see "1 left," both pay, both get a confirmation — and the system just sold one seat twice. That's contention first inside one database, then across machines — where contention is joined by a second, easily-confused problem, and half the skill is keeping the two straight.