Idempotency Replay

Overview

Meaning and scope

Idempotency replay is the resubmission of a request with the same idempotency identity so that the service can reproduce the original result without repeating the side effect. Idempotency replay is a reliability technique, not an unrestricted replay mechanism. It should repeat the observation of one operation, not create another financial action.

Mechanism and operation

A client may replay after a timeout, dropped connection, or uncertain response. The server looks up the key, verifies that the request matches, and returns the stored status or response; if processing is still underway, it may return an in-progress or conflict response. A replay after key expiration can execute as a new operation. Replaying a mutated payload creates a conflict, while returning a stale response without current access checks may expose data or mislead the caller. Important failure modes include duplicate or out-of-order delivery, incompatible schemas, lost acknowledgements, unbounded retries, stale consumers, forged messages, and replay that creates a second financial action.

Practical payment example

An API repeats a response for an already processed operation without causing another merchant settlement instruction.

Operational checks

Safe replay requires durable key storage, request fingerprinting, concurrency control, consistent response retention, and clear handling of server errors. Authentication and authorization must be reevaluated as appropriate rather than assuming the key itself grants permission. The contract should define identifiers, schema and version, authentication, ordering, idempotency, retry behavior, error handling, and the service responsible for authoritative state.

Distinctions and limits

These records support Duplicate API Request and let an operator reproduce the result from authoritative evidence rather than relying on a dashboard snapshot or a provider’s latest status alone.

Related reading

Related definitions: Duplicate API Request, Payment Retry.