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https://issues.apache.org/jira/browse/KAFKA-7577?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16672341#comment-16672341
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Matthias J. Sax commented on KAFKA-7577:
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Thanks for clarification. Still try to understand the scenario. For regular
left join, we have test and those pass and thus leftjoin itself seems to be
correct
([https://github.com/apache/kafka/blob/trunk/streams/src/test/java/org/apache/kafka/streams/kstream/internals/KTableKTableLeftJoinTest.java).]
Just trying to figure out what the issue could be. There are two other bug
reports about KTable joins, but they seem to be different
(https://issues.apache.org/jira/browse/KAFKA-4609 and
https://issues.apache.org/jira/browse/KAFKA-6599).
What I am wondering: if you do Y.leftJoin(Z), it is only guaranteed that the Y
input will be in the output, while your example shows the B comes from input Z.
Can you verify that Y.leftJoin(Z) produces an output record that contains B ?
Can you reproduce the issue using `TopologyTestDriver`? This would be most
helpful to track down the root cause. Thanks a lot for your help!
> Semantics of Table-Table Join with Null Message Are Incorrect
> -------------------------------------------------------------
>
> Key: KAFKA-7577
> URL: https://issues.apache.org/jira/browse/KAFKA-7577
> Project: Kafka
> Issue Type: Bug
> Components: streams
> Affects Versions: 1.1.0
> Reporter: Daren Thomas
> Priority: Major
>
> Observed behavior of Table-Table join with a Null Message does not match the
> semantics described in the documentation
> ([https://docs.confluent.io/current/streams/developer-guide/dsl-api.html#ktable-ktable-join).]
> The expectation is:
> * Message A results in [A, null] from the Left Join
> * Message null (tombstone) results in null (tombstone) from the Left Join
> The observed behavior was that the null (tombstone) message did not pass
> through the Left Join to the output topic like expected. This behavior was
> observed with and without caching enabled, against a test harness, and
> against a local Confluent 5.0.0 platform. It was also observed that the
> KTableKTableLeftJoinProcessor.process() function was not called for the null
> (tombstone) message.
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