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https://issues.apache.org/jira/browse/KAFKA-3543?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Greg Fodor updated KAFKA-3543:
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Summary: Allow a variant of transform() which can emit multiple values
(was: Allow a variant of transform() which allows emitting multiple values)
> Allow a variant of transform() which can emit multiple values
> -------------------------------------------------------------
>
> Key: KAFKA-3543
> URL: https://issues.apache.org/jira/browse/KAFKA-3543
> Project: Kafka
> Issue Type: Improvement
> Components: streams
> Affects Versions: 0.10.0.0
> Reporter: Greg Fodor
> Assignee: Guozhang Wang
>
> Right now it seems that if you want to apply an arbitrary transformation to a
> stream, you either have to use a TransformerSupplier or ProcessorSupplier
> sent to transform() or process(). The custom processor will allow you to emit
> multiple new values, but the process() method currently terminates that
> branch of the topology so you can't apply additional data flow. transform()
> lets you continue the data flow, but forces you to emit a single value for
> every input value.
> (It actually doesn't quite force you to do this, since you can hold onto the
> ProcessorContext and emit multiple, but that's probably not the ideal way to
> do it :))
> It seems desirable to somehow allow a transformation that emits multiple
> values per input value. I'm not sure of the best way to factor this inside of
> the current TransformerSupplier/Transformer architecture in a way that is
> clean and efficient -- currently I'm doing the workaround above of just
> calling forward() myself on the context and actually emitting dummy values
> which are filtered out downstream.
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