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From "Matthias J. Sax (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (KAFKA-6599) KTable KTable join semantics violated when caching enabled
Date Tue, 27 Feb 2018 19:08:00 GMT

     [ https://issues.apache.org/jira/browse/KAFKA-6599?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Matthias J. Sax updated KAFKA-6599:
-----------------------------------
    Priority: Critical  (was: Major)

> 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
>
> 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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