Definition
Each message takes effect once and only once — no loss, no duplicates — despite retries and crashes.
How it works
True exactly-once delivery over a network is impossible, so systems fake it: at-least-once delivery (retry until acked) plus idempotent consumers (dedupe by key) gives exactly-once effects. Kafka's "exactly-once" is this — transactional writes + offsets committed atomically. Aim for idempotency, not magic.
Common questions
What is Exactly-Once Delivery?
Each message takes effect once and only once — no loss, no duplicates — despite retries and crashes.
How does Exactly-Once Delivery work?
True exactly-once delivery over a network is impossible, so systems fake it: at-least-once delivery (retry until acked) plus idempotent consumers (dedupe by key) gives exactly-once effects. Kafka's "exactly-once" is this — transactional writes + offsets committed atomically.…
What is Exactly-Once Delivery used for in system design?
True exactly-once delivery over a network is impossible, so systems fake it: at-least-once delivery (retry until acked) plus idempotent consumers (dedupe by key) gives exactly-once effects. Kafka's "exactly-once" is this — transactional writes + offsets committed atomically.…