Why Pressing the Button Twice Shouldn't Double Your Bill: Understanding Idempotency

Automated excerpt

If you get impatient and press that same button ten more times, the system does not dispatch ten separate elevators, nor does it charge the building's electrical system ten times over. The elevator button is an everyday example of an idempotent interface. Without idempotency, the payment gateway would treat each retry as a brand-new transaction, charging your credit card multiple times for a single order.

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