A messaging semantics: three, at least once, at most once, exactly once
1, at lest once: the message is not lost, but may be repeated
2, at most once: the message will be lost, but will not be repeated
3, Exactly Once: the message is not lost, nor repeated.
Second, to ensure data consistency: guaranteed message is not lost, the message will not be repeated
The message is not lost: a copy mechanism + ack, you can ensure that messages are not lost.
Data repeat: brocker saved messages after, before sending the ack is down, producer believes the message is not sent successfully retried, resulting in duplication of data.
Scrambled data: before sending a message fails, the message is sent successfully, and before a retry is successful, resulting in scrambled data.
Third, to ensure the consistency of the message: The main is to ensure Exactly Once, namely: data is not lost, the data is not repeated
1,0.11 kafka previous version:
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Reference blog: http://bigdata-star.com/archives/1507