[jira] [Updated] (KAFKA-12317) Relax non-null key requirement for left KStream joins

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

     [ https://issues.apache.org/jira/browse/KAFKA-12317?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Matthias J. Sax updated KAFKA-12317:
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    Summary: Relax non-null key requirement for left KStream joins  (was: Relax non-null key requirement for left KStream-KTable join)

> Relax non-null key requirement for left KStream joins
> -----------------------------------------------------
>
>                 Key: KAFKA-12317
>                 URL: https://issues.apache.org/jira/browse/KAFKA-12317
>             Project: Kafka
>          Issue Type: Improvement
>          Components: streams
>            Reporter: Matthias J. Sax
>            Priority: Major
>
> 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.
>  Note that this change also requires to change the behavior if we insert a repartition topic before the join: currently, we drop `null`-key record before writing into the repartition topic (as we know they would be dropped later anyway). We need to relax this behavior for a left/outer stream-table (and maybe left/outer 



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