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https://issues.apache.org/jira/browse/KAFKA-14747?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Matthias J. Sax resolved KAFKA-14747.
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Fix Version/s: 3.8.0
Resolution: Fixed
> FK join should record discarded subscription responses
> ------------------------------------------------------
>
> Key: KAFKA-14747
> URL: https://issues.apache.org/jira/browse/KAFKA-14747
> Project: Kafka
> Issue Type: Improvement
> Components: streams
> Reporter: Matthias J. Sax
> Assignee: Ayoub Omari
> Priority: Minor
> Labels: beginner, newbie
> Fix For: 3.8.0
>
>
> FK-joins are subject to a race condition: If the left-hand side record is
> updated, a subscription is sent to the right-hand side (including a hash
> value of the left-hand side record), and the right-hand side might send back
> join responses (also including the original hash). The left-hand side only
> processed the responses if the returned hash matches to current hash of the
> left-hand side record, because a different hash implies that the lef- hand
> side record was updated in the mean time (including sending a new
> subscription to the right hand side), and thus the data is stale and the
> response should not be processed (joining the response to the new record
> could lead to incorrect results).
> A similar thing can happen on a right-hand side update that triggers a
> response, that might be dropped if the left-hand side record was updated in
> parallel.
> While the behavior is correct, we don't record if this happens. We should
> consider to record this using the existing "dropped record" sensor or maybe
> add a new sensor.
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