Matthias J. Sax created KAFKA-12317:
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Summary: Relax non-null key requirement for left KStream-KTable
join
Key: KAFKA-12317
URL: https://issues.apache.org/jira/browse/KAFKA-12317
Project: Kafka
Issue Type: Improvement
Components: streams
Reporter: Matthias J. Sax
Currently, for a stream-table join KafkaStreams drops all stream records with a
null-key, because for a null-key the join is undefined: ie, we don't have an
attribute the do the table lookup (we consider the stream-record as malformed).
Note, that we define the semantics of _left_ join as: keep the stream record if
no KTable record was found.
We could relax the definition of _left_ join though, and not drop non-key
stream records, and call the ValueJoiner with a `null` table record instead: if
the stream record key is `null`, we could treat is as "failed table lookup"
instead of treating the stream record as corrupted.
If we make this change, users that want to keep the current behavior, can add a
`filter()` before the join to drop `null`-key records from the stream
explicitly.
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