System Design AI

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Exactly onceClear filters

33. Idempotency Keys
Any request can time out after the server has already acted. The client cannot tell that from a request that never arrived, and the only safe response to uncertainty is to retry — which, without help, charges the card twice.
Product & backendMedium
Exactly once Idempotency Payments
+2
Reliability Retries
Worked design
Practice

Each design brings together the brief, practice, examples and discussion.