Hi, yes, all examples have at-least-once semantics because this is the only "mode" Kafka Streams supports -- you cannot "disable" it. (btw: we are currently working on exactly-once for Streams that you will be able to turn off/on).
There is not much documentation about how it work internally, because it uses the same mechanism Kafka consumer user to provide at-least-once semantics and there is good documentation for this: http://docs.confluent.io/current/clients/consumer.html The basic idea is, that input topic offsets get only committed after the processing is completely finished and all intermediate state/data is flushed to reliable storage -- to ensure nothing can get lost. If a failure happens, just retry from last committed offset (and because some output date might already be written which cannot be undone you might get duplicates). -Matthias On 1/29/17 8:13 PM, Mahendra Kariya wrote: > Hey All, > > I am new to Kafka streams. From the documentation > <http://docs.confluent.io/3.1.0/streams/architecture.html#processing-guarantees>, > it is pretty much clear that streams support at least once semantics. But I > couldn't find details about how this is supported. I am interested in > knowing the finer details / design of this. > > Is there some documentation around this? > Is there some documentation around what semantics are followed by the > various Kafka streams examples > <https://github.com/confluentinc/examples/tree/3.1.x/kafka-streams> > available on Github? Do all of them follow at least once? > > > Thanks, > Mahendra >
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