[jira] [Commented] (KAFKA-9500) Foreign-Key Join creates an invalid topology

["Adam Bellemare (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/KAFKA-9500?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17061804#comment-17061804 ] 

Adam Bellemare commented on KAFKA-9500:
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[~vvcephei]

Hey John - I ran across this while trying to port my Scala joiners to 2.4. I don't know enough about expectations of what serdes should be present in a KTable created via stream+groupByKey+reduce, but it doesn't seem to be what I expect. If it's normal for a table created that way to be missing the valueSerde, can you advise me and I can keep looking into it?

> Foreign-Key Join creates an invalid topology
> --------------------------------------------
>
>                 Key: KAFKA-9500
>                 URL: https://issues.apache.org/jira/browse/KAFKA-9500
>             Project: Kafka
>          Issue Type: Bug
>          Components: streams
>    Affects Versions: 2.4.0
>            Reporter: John Roesler
>            Assignee: John Roesler
>            Priority: Blocker
>             Fix For: 2.5.0, 2.4.1
>
>
> Foreign-Key Join results are not required to be materialized by default, but they might be needed if downstream operators need to perform lookups on the result (such as when the join result participates in an equi-join).
> Currently, if the result is explicitly materialized (via Materialized), this works correctly, but if the result is _not_ materialized explicitly, but _is_ needed, the topology builder throws an exception that the result store isn't added to the topology. This was an oversight in testing and review and needs to be fixed ASAP.



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