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https://issues.apache.org/jira/browse/KAFKA-3561?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15315545#comment-15315545
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ASF GitHub Bot commented on KAFKA-3561:
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Github user dguy closed the pull request at:
https://github.com/apache/kafka/pull/1453
> Auto create through topic for KStream aggregation and join
> ----------------------------------------------------------
>
> Key: KAFKA-3561
> URL: https://issues.apache.org/jira/browse/KAFKA-3561
> Project: Kafka
> Issue Type: Bug
> Components: streams
> Reporter: Guozhang Wang
> Assignee: Damian Guy
> Labels: api
> Fix For: 0.10.1.0
>
>
> For KStream.join / aggregateByKey operations that requires the streams to be
> partitioned on the record key, today users should repartition themselves
> through the "through" call:
> {code}
> stream1 = builder.stream("topic1");
> stream2 = builder.stream("topic2");
> stream3 = stream1.map(/* set the right key for join*/).through("topic3");
> stream4 = stream2.map(/* set the right key for join*/).through("topic4");
> stream3.join(stream4, ..)
> {code}
> This pattern can actually be done by the Streams DSL itself instead of
> requiring users to specify themselves, i.e. users can just set the right key
> like (see KAFKA-3430) and then call join, which will be translated by adding
> the "internal topic for repartition".
> Another thing is that today if user do not call "through" after setting a new
> key, the aggregation result would not be correct as the aggregation is based
> on key B while the source partitions is partitioned by key A and hence each
> task will only get a partial aggregation for all keys. But this is not
> validated in the DSL today. We should do both the auto-translation and
> validation.
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