Rahul Agarwal explains what “exactly-once” means in terms of message-passing systems:
Until recently most organizations have been struggling to achieve the holy grail of message delivery, the exactly-once delivery semantic. Although this has been an out-of-the-box feature since Apache Kafkas 0.11, people are still slow in picking up this feature. Let’s take a moment in understanding exactly-once semantics. What is the big deal about it and how does Kafka solve the problem?
Apache Kafka offers following delivery guarantees. Let’s understand what this really means:
In a distributed system, having true exactly-once processing is extremely difficult to achieve.