Glossary term
What is At-most-once / At-least-once / Exactly-once? Meaning for developers
Delivery guarantees: may lose / may duplicate / effectively once. Example: Payments need at-least-once + dedup.
Learn it properly · System DesignLesson 37: At-Most-Once, At-Least-Once, Exactly-OnceAcknowledge too early and a crash loses the payment; acknowledge too late and it charges twice. At-most-once, at-least-once and why true exactly-once is impossible — plus idempotent consumers, Kafka's exactly-once and the transactional outbox.