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https://issues.apache.org/jira/browse/KAFKA-6599?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17600611#comment-17600611
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Jan Filipiak commented on KAFKA-6599:
-------------------------------------
Just jumping in here as I'm prepping with this included now.
Anyone looked at the fix i suggested of just letting streams use the underlying
store? That should fix it instantly?
Maybe someone can explain the whole
{quote}I think a more general issue here is that the joined table is not
materialized
{quote}
? [~guozhang] maybe? If he joined table is not materialized we don't have
correct KTable-KTable join semantics anyways. So i don't know how one ends in
this position but i would think its not to relevant to fixing it?
{quote}the old joined value == new joined value,
{quote}
I made a point 5 years back. that filtering these should actually be a user
operation. It is not possible from streams to know at wich point this makes
sense todo. After the join there could be an immediate mapper only preserving a
few fields and the comparison would run much more efficient there.
> 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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