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https://issues.apache.org/jira/browse/KAFKA-6905?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16476522#comment-16476522
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David Glasser commented on KAFKA-6905:
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Thanks Matthias. I'm a little confused about what file is the source for truth
for the Streams developer guide.
Is it
[https://github.com/apache/kafka/blob/trunk/docs/streams/developer-guide/processor-api.html]
or
[https://github.com/apache/kafka-site/blob/asf-site/11/streams/developer-guide/processor-api.html]
or something else entirely (as that HTML really doesn't strike me as
hand-crafted)?
> Document that Processor objects can be reused
> ---------------------------------------------
>
> Key: KAFKA-6905
> URL: https://issues.apache.org/jira/browse/KAFKA-6905
> Project: Kafka
> Issue Type: Improvement
> Components: documentation, streams
> Reporter: David Glasser
> Priority: Major
>
> We learned the hard way that Kafka Streams will reuse Processor objects by
> calling init() on them after they've been close()d. This caused a bug in our
> application as we assumed we didn't have to reset all of our Processor's
> state to a proper starting state on init().
> As far as I can tell, this is completely undocumented. The fact that we
> provide Processors to Kafka Streams via a ProcessorSupplier factory rather
> than just by passing in a Processor object made it seem likely that in fact
> Streams was creating Processors from scratch each time it needed a new one.
> The developer guide
> ([https://docs.confluent.io/current/streams/developer-guide/processor-api.html)]
> doesn't even allude to the existence of the close() method, let alone the
> idea that init() may be called after close().
> The Javadocs for Processor.init says: "The framework ensures this is called
> once per processor when the topology that contains it is initialized." I
> personally interpreted that as meaning that it only is ever called once! I
> can see that you could interpret it otherwise, but it's definitely unclear.
> I can send a PR but first want to confirm that this is a doc problem and not
> a bug!
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