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https://issues.apache.org/jira/browse/KAFKA-19668?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18018898#comment-18018898
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ASF GitHub Bot commented on KAFKA-19668:
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mjsax merged PR #721:
URL: https://github.com/apache/kafka-site/pull/721
> 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
> Fix For: 4.0.1, 4.2.0, 4.1.1
>
>
> 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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