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https://issues.apache.org/jira/browse/KAFKA-12815?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17348068#comment-17348068
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Guozhang Wang commented on KAFKA-12815:
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Yup, we are definitely fixing forward rather than regressing here as previously
people would just get the incorrect result silently. As for the longer term, I
kinda also agree that we can wait and see how large of an impact it would be to
not have topic/offsets be available; but what I'm pointing out is that this is
not an impossible task to do, we just need to be careful about our trade-offs
here. For some advanced users that may be using `transformValues` heavily but
do not leverage on topic/offsets, at least we should allow them to choose based
on their own knowledge.
> KTable.transformValue might have incorrect record metadata
> ----------------------------------------------------------
>
> Key: KAFKA-12815
> URL: https://issues.apache.org/jira/browse/KAFKA-12815
> Project: Kafka
> Issue Type: Bug
> Components: streams
> Reporter: Matthias J. Sax
> Assignee: Matthias J. Sax
> Priority: Major
> Fix For: 3.0.0
>
>
> In the DSL, Kafka Streams applies an optimization for non-materialized
> tables: when these are queried an upstream state store is accessed. To ensure
> that the correct value is returned from the lookup, all intermediate
> processors after the materialized store, and before the processor that
> triggers the lookup are re-applied (cf `KTableValueGetter`).
> For re-applying DSL operators like filter/mapValues that works fine. However,
> for transformValue(), the method is executed with the incorrect
> `RecordContext` (note that DSL operators like filter don't have access to the
> `RecordContext` and thus, are not subject to this bug). Instead of using the
> record context from the value that was received from the upstream state store
> (and that is re-processed), the transformer would see the context from the
> record that triggered the lookup.
> Thus, the information about timestamp, offset, partition, topic name, and
> headers is incorrect.
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