Exactly-Once

Diagram of Flink checkpoint barriers flowing through a streaming pipeline with aligned state snapshots.

Inside Apache Flink's Checkpointing Algorithm: How Exactly-Once State Guarantees Survive Pipeline Failures

How Apache Flink’s distributed snapshot algorithm coordinates barriers across operators, persists state to durable storage, and recovers jobs after failure without losing or duplicating records.

Diagram of a message pipeline with a duplicate filter.

Why Exactly-Once Delivery Requires Idempotence to Work

A deep dive into why exactly‑once delivery semantics depend on idempotent operations, with practical patterns, code samples, and testing strategies.

Illustration of a message broker with duplicate messages being filtered by an idempotent consumer.

Why Exactly-Once Delivery Requires Consumer Idempotency

Exactly-once delivery cannot be guaranteed without making consumers idempotent; this article breaks down the technical reasoning and shows how to implement idempotency in real systems.