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https://issues.apache.org/jira/browse/KAFKA-6905?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16478128#comment-16478128
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ASF GitHub Bot commented on KAFKA-6905:
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glasser opened a new pull request #5026: KAFKA-6905: Document that Transformers
may be re-used by Streams
URL: https://github.com/apache/kafka/pull/5026
This is a follow-up to #5022 which added documentation to the Processor
interface. This commit adds similar documentation to Transformer and
ValueTransformer.
Also, s/processor/transformer/ in the close() docs.
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> 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
> Assignee: David Glasser
> Priority: Major
> Fix For: 2.0.0
>
>
> 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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