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From Gordon Sim <g...@redhat.com>
Subject Re: A few clustering/failover questions
Date Thu, 05 Mar 2009 09:53:44 GMT
Sandy Pratt wrote:
> I've been experimented with failover on a cluster of two brokers, and
> I often see this log item when a broker fails:
> 
> 2009-mar-04 17:11:19 debug Exception constructed: Attempted size
> underflow on dequeue(21): size: max=104857600, current=0; count: unli
>  mited; type=flow_to_disk (qpid/broker/QueuePolicy.cpp:54)
> 
> What does underflow mean here?

The policy maintains a running count of enqueued messages and the 
aggregate size. Underflow here means that more data was dequeued than 
was enqueued which indicates some logical error.

What version of the code are you using? M4 or latest from trunk?

> The broker seems to have died:
> 
> [prattrs@hsvrhm5 qpidd]$ sudo /sbin/service qpidd status qpidd dead
> but pid file exists
> 
> The test I was running failed over to the other broker and completed
> after a timeout expired.
> 
> A subsequent test immediately failed over to the other broker and
> completed (which makes sense because qpid on the first broker was
> probably dead before it started).
> 
> In a general sense, what are the steps required to recover from a
> broker failure?  What I am looking for is step #3 below:
> 
> Assume a cluster of two brokers, A and B 1) A dies 2) clients fail
> over to B 3) do something to recover A without interrupting clients
> of B 4) A and B are again interchangeable
> 
> I've looked through the docs and haven't seen anything about this.
> Apologies if I missed it.  I also tried simply restarting A, which
> doesn't seem to work.

What errors/symptoms do you see when simply restarting A? (As Carl says, 
this _should_ be all that is required).



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