[jira] [Commented] (CASSANDRA-13480) nodetool repair can hang forever if we lose the notification for the repair completing/failing

["Tania S Engel (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-13480?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16378919#comment-16378919 ] 

Tania S Engel commented on CASSANDRA-13480:
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[~mbyrd] : I have reason to believe I just hit this in 3.11.1, I at the very least ran into a repair which has never completed on an 11 node cluster. Is there a way to get this fix in 3.11?

> nodetool repair can hang forever if we lose the notification for the repair completing/failing
> ----------------------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-13480
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-13480
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Tools
>            Reporter: Matt Byrd
>            Assignee: Matt Byrd
>            Priority: Minor
>              Labels: repair
>             Fix For: 4.0
>
>
> When a Jmx lost notification occurs, sometimes the lost notification in question is the notification which let's RepairRunner know that the repair is finished (ProgressEventType.COMPLETE or even ERROR for that matter).
> This results in nodetool process running the repair hanging forever. 
> I have a test which reproduces the issue here:
> https://github.com/Jollyplum/cassandra-dtest/tree/repair_hang_test
> To fix this, If on receiving a notification that notifications have been lost (JMXConnectionNotification.NOTIFS_LOST), we instead query a new endpoint via Jmx to receive all the relevant notifications we're interested in, we can replay those we missed and avoid this scenario.
> It's possible also that the JMXConnectionNotification.NOTIFS_LOST itself might be lost and so for good measure I have made RepairRunner poll periodically to see if there were any notifications that had been sent but we didn't receive (scoped just to the particular tag for the given repair).
> Users who don't use nodetool but go via jmx directly, can still use this new endpoint and implement similar behaviour in their clients as desired.
> I'm also expiring the notifications which have been kept on the server side.
> Please let me know if you've any questions or can think of a different approach, I also tried setting:
>  JVM_OPTS="$JVM_OPTS -Djmx.remote.x.notification.buffer.size=5000"
> but this didn't fix the test. I suppose it might help under certain scenarios but in this test we don't even send that many notifications so I'm not surprised it doesn't fix it.
> It seems like getting lost notifications is always a potential problem with jmx as far as I can tell.



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