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https://issues.apache.org/jira/browse/KAFKA-992?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13724789#comment-13724789
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Guozhang Wang commented on KAFKA-992:
-------------------------------------
We can differentiate this edge case from a temporal connection loss by adding a
timestamp into the broker ZK string so that the conflict will be reflected.
Then we can check if the host:port are the same. If this is the case, then we
can treat this ephemeral node as written by the broker itself but from a
previous session, hence backoff for it to be deleted on session timeout and
retry creating the ephemeral node. This will make the temporal connection loss
a false positive case, but it should be fine since this case happens rarely.
> Double Check on Broker Registration to Avoid False NodeExist Exception
> ----------------------------------------------------------------------
>
> Key: KAFKA-992
> URL: https://issues.apache.org/jira/browse/KAFKA-992
> Project: Kafka
> Issue Type: Bug
> Reporter: Guozhang Wang
> Assignee: Guozhang Wang
>
> There is a potential bug in Zookeeper that when the ZK leader processes a lot
> of session expiration events (this could be due to a long GC or a fsync
> operation, etc), it marks the session as expired but does not delete the
> corresponding ephemeral znode at the same time.
> Meanwhile, a new session event will be fired on the kafka server and the
> server will request the same ephemeral node to be created on handling the new
> session. When it enters the zookeeper processing queue, this operation
> receives a NodeExists error since zookeeper leader has not finished deleting
> that ephemeral znode and still thinks the previous session holds it. Kafka
> assumes that the NodeExists error on ephemeral node creation is ok since that
> is a legitimate condition that happens during session disconnects on
> zookeeper. However, a NodeExists error is only valid if the owner session id
> also matches Kafka server's current zookeeper session id. The bug is that
> before sending a NodeExists error, Zookeeper should check if the ephemeral
> node in question is held by a session that has marked as expired.
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