What is an idempotency key and why does it prevent double-charging or duplicate inserts?
An idempotency key is a unique identifier (usually a client-generated UUID plus timestamp) attached to every mutation. If the network fails after a successful server write but before the client receives the ACK, retrying with the same key tells the server 'I've already done this' and it returns the cached result instead of repeating the action.
Answered in
Optimistic UI: The Illusion of InstantApply mutations locally and reconcile in the background, collapsing perceived latency from 150 ms to instant. Rollback, idempotency keys, offline queues.
Read the full analysisOther questions this article answers
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- How does rollback work when the server rejects an optimistic mutation?
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