[jira] [Created] (KAFKA-12317) Relax non-null key requirement for left KStream-KTable join

["Matthias J. Sax (Jira)" <ji...@apache.org>]

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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