Exactly Once

Log-based brokers (Kafka), stateless topology primitives, partition assignment, windowing, late event strategies, watermarks vs stream time, reprocessing, state stores (internal/external, changelog, hot replicas), effectively once processing, heavyweight vs lightweight framework comparison, stream joins, exactly-once fault tolerance; Kafka production mechanics: producer batching (acks/idempotence), consumer commit semantics, semantic partitioning, consumer groups, ISR