[jira] [Created] (KAFKA-6599) KTable KTable join semantics violated when caching enabled

["Jan Filipiak (JIRA)" <ji...@apache.org>]

Jan Filipiak created KAFKA-6599:
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             Summary: 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


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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