问题
I would like to have Exactly-once semantics, but I don't want to read message with Consumer. I'd rather read messages with Kafka Streams AP. If I add processing.guarantee=exactly_once to Stream configuration, will exactly-once semantics be kept?
回答1:
Exactly-once processing is based on a read-process-write pattern. Kafka Streams uses this pattern and thus, if you write a regular Kafka Streams application that writes the result back to a Kafka topic, you will get exactly-once processing guarantees.
Note, that side-effects are not covered by this guarantee. Also note, that there might be retries internally in case of failure. Exactly-once implies, that the result you see in the output topic, is the same as if no error (and thus not retries) would have happened.
For more details, you might want to watch a talk recording about exactly-once guarantees in Kafka. There are multiple available at Confluent webpage (disclaimer: I am an employee at Confluent): https://www.confluent.io/resources/
来源：https://stackoverflow.com/questions/50698695/if-i-have-transactional-producer-in-kafka-can-i-read-exactly-once-messages-with