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https://issues.apache.org/jira/browse/KAFKA-6599?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17298306#comment-17298306
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Matthias J. Sax commented on KAFKA-6599:
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Thanks for the detailed report! This is super helpful. – I guess the current
workaround it to disable caching. We have some discussion about caching in
general and might rework some parts of the code base, so it's unclear to me
right now, if it's worth to fix this right away or wait until we rework those
part of the code and let it (hopefully) resolve naturally. \cc [~guozhang] for
visibility.
> KTable KTable join semantics violated when caching enabled
> ----------------------------------------------------------
>
> Key: KAFKA-6599
> URL: https://issues.apache.org/jira/browse/KAFKA-6599
> Project: Kafka
> Issue Type: Bug
> Components: streams
> Reporter: Jan Filipiak
> Priority: Critical
> Labels: bug
>
> Say a tuple A,B got emmited after joining and the delete for A goes into the
> cache. After that the B record would be deleted aswell. B's join processor
> would look up A and see `null` while computing for old and new value (at this
> point we can execute joiner with A beeing null and still emit something, but
> its not gonna represent the actual oldValue) Then As cache flushes it doesn't
> see B so its also not gonna put a proper oldValue. The output can then not be
> used for say any aggregate as a delete would not reliably find its old
> aggregate where it needs to be removed from filter will also break as it
> stopps null,null changes from propagating. So for me it looks pretty clearly
> that Caching with Join breaks KTable semantics. be it my new join or the
> currently existing once.
>
> this if branch here
> [https://github.com/apache/kafka/blob/1.0/streams/src/main/java/org/apache/kafka/streams/state/internals/CachingKeyValueStore.java#L155]
> is not usefull. I think its there because when one would delegate the true
> case to the underlying. One would get proper semantics for streams, but the
> weiredest cache I've seen.
>
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