[jira] [Resolved] (KAFKA-13197) KStream-GlobalKTable join semantics don't match documentation

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

     [ https://issues.apache.org/jira/browse/KAFKA-13197?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Matthias J. Sax resolved KAFKA-13197.
-------------------------------------
    Fix Version/s: 3.6.0
                   3.5.2
       Resolution: Fixed

> KStream-GlobalKTable join semantics don't match documentation
> -------------------------------------------------------------
>
>                 Key: KAFKA-13197
>                 URL: https://issues.apache.org/jira/browse/KAFKA-13197
>             Project: Kafka
>          Issue Type: Bug
>          Components: documentation, streams
>    Affects Versions: 2.7.0
>            Reporter: Tommy Becker
>            Assignee: Florin Akermann
>            Priority: Major
>             Fix For: 3.6.0, 3.5.2
>
>
> As part of KAFKA-10277, the behavior of KStream-GlobalKTable joins was changed. It appears the change was intended to merely relax a requirement but it actually broke backwards compatibility. Although it does allow {{null}} keys and values in the KStream to be joined, it now excludes {{null}} results of the {{KeyValueMapper}}. We have an application which can return {{null}} from the {{KeyValueMapper}} for non-null keys in the KStream, and relies on these nulls being passed to the {{ValueJoiner}}. Indeed the javadoc still explicitly says this is done:
> {quote}If a KStream input record key or value is null the record will not be included in the join operation and thus no output record will be added to the resulting KStream.
>  If keyValueMapper returns null implying no match exists, a null value will be provided to ValueJoiner.
> {quote}
> Both these statements are incorrect.
> I think the new behavior is worse than the previous/documented behavior. It feels more reasonable to have a non-null stream record map to a null join key (our use-case is event-enhancement where the incoming record doesn't have the join field), than the reverse.



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