Delivery

Getting a message — or its effect — to happen exactly once over a network that loses, duplicates, and reorders: delivery semantics, idempotency, and the exactly-once illusion.

Explainers

• Idempotency & the Exactly-Once Illusion — Over a lossy wire, “did it happen?” is unanswerable — so retries are the default reality. Exactly-once delivery is impossible; exactly-once effects are not. The property that buys them back is idempotency, drawn and computed.