> To ensure [[Idempotence|idempotency]] (i.e., guarantee that the processing of retried messages is harmless), the recipient entity is typically designed to remember that the message has been processed. Once it has been successfully processed, repeated messages will typically generate another response matching the behavior of the first message. ## Sources [Life Beyond Distributed Transactions](https://queue.acm.org/detail.cfm?id=3025012) by Pat Helland