Hi Stefan,
I didn`t notice that in the webpage.. Thanks a lot for your help!
That makes me understand the delivery guarantees more clearly.
Best
Henry
> 在 2018年9月20日，下午5:02，Stefan Richter <[email protected]
> <mailto:[email protected]>> 写道：
>
> Hi,
>
> I think this part of the documentation is talking about KafkaProducer, and
> you are reading in the source code of KafkaConsumer.
>
> Best,
> Stefan
>
>> Am 20.09.2018 um 10:48 schrieb 徐涛 <[email protected]
>> <mailto:[email protected]>>:
>>
>> Hi All,
>> In document of Flink 1.6, it says that "Before 0.9 Kafka did not
>> provide any mechanisms to guarantee at-least-once or exactly-once semantics”
>> I read the source code of FlinkKafkaConsumer08, and the comment says:
>> “Please note that Flink snapshots the offsets internally as part of its
>> distributed checkpoints. The offsets
>> * committed to Kafka / ZooKeeper are only to bring the outside view of
>> progress in sync with Flink's view
>> * of the progress. That way, monitoring and other jobs can get a view of
>> how far the Flink Kafka consumer
>> * has consumed a topic"
>> Obviously, the kafka partition offsets are checkpointed periodically.
>> And when some error happens, the data are read from kafka, continued from
>> the checkpointed offset. Then source and other operator states restart from
>> the same checkpoint. Then why does the document say “Before 0.9 Kafka did
>> not provide any mechanisms to guarantee at-least-once or exactly-once
>> semantics” ?
>>
>> Thanks a lot.
>>
>>
>> Best
>> Henry
>
