Matthias J. Sax created KAFKA-19668:
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Summary: 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
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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