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From "Alan Conway (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (QPID-4349) HA duplicates messages with alternate exchangee.
Date Wed, 03 Oct 2012 18:30:14 GMT

    [ https://issues.apache.org/jira/browse/QPID-4349?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13468725#comment-13468725
] 

Alan Conway commented on QPID-4349:
-----------------------------------

This is a race condition and hard to reproduce.

When a queue is deleted, observeDequeue is called for each message in turn, which updates
ReplicatingSubscription's dequeued set. That set is sent to the backup it it's connection
thread.

Once all messages are dequeued, raiseEvent is called to send a QMF QueueDelete message. This
is also sent to the backup in it's conection thread.

The problem is there's no guarantee of ordering between the two events. If the dequeus are
processed before the delete event then there's no duplicationl If after then there is duplication.
                
> HA duplicates messages with alternate exchangee.
> ------------------------------------------------
>
>                 Key: QPID-4349
>                 URL: https://issues.apache.org/jira/browse/QPID-4349
>             Project: Qpid
>          Issue Type: Improvement
>          Components: C++ Clustering
>    Affects Versions: 0.18
>            Reporter: Alan Conway
>            Assignee: Alan Conway
>
> If a queue has an alternate-exchange then deleting the queue will route messages to it.
The problem is that this will route the messages twice: once on the primary and once on the
backup.
> Reproduce:
> - Declare a queue q1 with alternate exchange amq.fanout
> - Bind a queue q2 to amq.fanout
> - Send messages to q1
> - Delete q1
> - Verify that messages appear twice on q2.

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