The most notable new feature is Exactly Once Semantics (EOS). Kafka’s EOS capabilities provide more stringent idempotent producer semantics with exactly once, in-order delivery per partition, and stronger transactional guarantees with atomic writes across multiple partitions. Together, these strong semantics make writing applications easier and expand Kafka’s addressable use cases. You can learn more about EOS in the online talk on June 29, 2017.
“Exactly once,” if done right, would be crazy—there’s a reason most brokers are either “at least once” or “best effort.”