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https://issues.apache.org/jira/browse/QPID-4394?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13483568#comment-13483568
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Alan Conway commented on QPID-4394:
-----------------------------------
We don't have a stand-alone reproducer of this, but by inspection it's clear
that QMF events can be send in the wrong order.
This is not just a HA problem: any qmf client can receive mis-ordered events.
> HA replication hangs when QMF events arrive out of order
> --------------------------------------------------------
>
> Key: QPID-4394
> URL: https://issues.apache.org/jira/browse/QPID-4394
> Project: Qpid
> Issue Type: Bug
> Components: C++ Clustering
> Affects Versions: 0.19
> Reporter: Alan Conway
> Assignee: Alan Conway
>
> With the new replication-based clustering in 0.18 MRG-M, it is possible for
> the replication to hang if the QMF events arrive in the wrong order. I am
> running the following test that generates the hanging:
> - Start a client with 2 threads
> - Each thread creates its own Connection, Session, and a Receiver using the
> address "someQueue; {create:always, node: {x-declare: {auto-delete:True}}}"
> - Run a loop like this (pseudocode):
> while(receiver.get(message)) {
> // do stuff
> if at least 5 seconds have passed {
> connection.close();
> reconnectAndRecreateReceiver();
> receiver.setCapacity(1000);
> }
> }
> During this loop, the 2 threads will disconnect and reconnect every 5
> seconds. When connecting, 1 of them will create a queue. When
> disconnecting, the queue will be deleted. At some point, the queue creation
> event will possibly arrive at the backup broker before the queue deletion
> event (i.e. in the wrong order) because there is no lock that governs when
> queue creation/deletion events are emitted. When this happens, the backup
> broker doesn't subscribe to the primary to replicate the queue in question,
> and things hang.
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