Matthias J. Sax created KAFKA-14747:
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Summary: 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
FK-join 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 hash matches, because a different hash implies that the
left hand side row 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.
A similar thing can happen on a right hand side update that triggers a
response, that might be dropped if the left hand side row 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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