Demystifying Kafka's Exactly-Once Semantics: Idempotence, Transactions, and Fencing

This blog post explains Kafka's exactly-once semantics, detailing how it ensures messages are delivered and persisted without duplication despite retries and failures. It covers three key components: producer idempotence for single-producer scenarios, the use of transactional IDs and epochs to manage problematic producers, and a two-phase commit protocol for atomic writes across partitions, emphasizing that these guarantees focus on delivery rather than message processing.