[jira] [Assigned] (KAFKA-19668) processValues() must be declared as value-changing operation

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

     [ https://issues.apache.org/jira/browse/KAFKA-19668?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Matthias J. Sax reassigned KAFKA-19668:
---------------------------------------

    Assignee: Matthias J. Sax

> processValues() must be declared as value-changing operation
> ------------------------------------------------------------
>
>                 Key: KAFKA-19668
>                 URL: https://issues.apache.org/jira/browse/KAFKA-19668
>             Project: Kafka
>          Issue Type: Bug
>          Components: streams
>    Affects Versions: 3.3.0
>            Reporter: Matthias J. Sax
>            Assignee: Matthias J. Sax
>            Priority: Blocker
>
> When adding `KStreams#processValues()` we missed to declare the operation as "value changing". This can lead to an "incorrectly" built topology.
> The main problem is, that `processValues()` is the replacement of `transformValues()` which we removed with AK 4.0.0 release. Thus, if users rewrite existing programs from `transformValues()` to the new `processValues()` (what will be required when upgrading to 4.x release), they might observe this change as a regression.
> The impact of the changed topology is, that local state is effectively lost, and must be restored from the changelog topic, resulting in downtime after an upgrade.
> Note: the bug does only surface, if topology optimization is used, in particular the "merge repartition topics" rewrite.



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