[rabbitmq-discuss] ShutdownSignalException second 'channel.open'

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Hi Steve,

Couple of things

1. Purpose of _Return queues
   Say App1 Queues has 10 messages and first one is processed by
calling an external system. This system
   operates in asynchronous manner and just returns task-id. I put it
on App1_Return queue and keep on
   polling this queue, get task-id and query external system for
status. If task is still going on, I
   re-queue the message to App1_Return queue.
   To process any message on App1 queue, I check if there is any
message on App1_Return queue. If there
   is none, only then can I process message from App1 queue as
otherwise, it indicates that previous
   operation is on App1 is still not complete.
   App1_Return queue at any point of time will only have at most one
message.
   This probably can be done using an external db, but why introduce
another system.

2.
> Just because you have thousands of queues doesn't mean you need to have
> thousands of Consumer instances -- it is quite ok to use the same Consumer on
> several basicConsume calls. The consumerTag is passed to every Consumer callback
> so the Consumer code can distinguish for which basicConsume it is called.
Can you give me an elegant pattern for
- Process message from Main Queue
- Declare/Redeclare appropriate Queue
- Attach a consume on this queue doing ch.basicConsume(...) only
  if there are no consumers already on this queue
- When cleaning method kicks in
  - do ch.basicCancel on all queues, wait till you get
    handleCancelOk on all consumers
  - check message count of all queues
  - delete all queues which are empty and have 0 consumers
    btw, I use http://localhost:55672/api/queues/%2f?columns=name,messages,consumers
    to get queues, consumers and messages and then fire
    foreach(queue)
    if(messages == 0 && consumers == 0)
        ch.queueDelete(queue, true, true)
    Is this call http://localhost:55672/api/queues/%2f?columns=name,messages,consumers
    reliable?

regards, Yogesh

On Feb 1, 3:35 pm, Steve Powell <st... at rabbitmq.com> wrote:
> Yogesh,
>
> Thanks for your explanation of your application structure, and the version you
> are running.
>
> I do not know how the second channel.open AMQP command (for the same channel)
> was sent to the broker; can you send some more diagnostics of this failure (log,
> full stack trace) so I can raise a bug. If possible, a demonstrating small
> program. Thanks.
>
> I see your difficulty. I would hope that creating 20000 queues (which are empty
> almost all of the time) would not take up too much room, so I think you should
> consider not deleting them at all. This would solve most of your problem.
>
> The x-expires attribute for queues, really ought to have a 'only-if-empty'
> option. I'll raise a bug (24722) for this, and see how difficult it would be.
>
> I do not understand what the _Return queues are for. They look as though you are
> using them as a private persistent store for each App. It would be better if you
> put this information somewhere else, but heigh-ho -- you can safely delete these
> queues since this app is in complete control of them, and the events are
> processed serially.
>
> One of the reasons, I don't do basicConsume on queues is, I am going to have
> thousands of queues. I rather thought it would be easier to have a thread pool,
> each consuming just one message from a queue in round-robin fashion.
>
> Just because you have thousands of queues doesn't mean you need to have
> thousands of Consumer instances -- it is quite ok to use the same Consumer on
> several basicConsume calls. The consumerTag is passed to every Consumer callback
> so the Consumer code can distinguish for which basicConsume it is called.
>
> By default, the Java client will allocate a pool of 5 threads for each
> connection, and dispatch Consumer callbacks onto one of those threads for you.
> So your thread pool might be unnecessary if you used basicConsume(). I'd
> consider doing that since basicGet() can be slow, and you'd have to get from
> each potential queue just to tell if there is a message for it!
>
> Steve Powell  (a happy bunny)
> ----------some more definitions from the SPD----------
> vermin (v.) Treating the dachshund for roundworm.
> chinchilla (n.) Cooling device for the lower jaw.
> socialcast (n.) Someone to whom everyone is speaking but nobody likes.
>
> On 31 Jan 2012, at 13:56, Yogesh Ketkar wrote:
>
>
>
>
>
>
>
>
>
> > I am using RabbitMQ server version 2.7.1.
> > Java Client Jar used is
> > rabbitmq-java-client-bin-2.7.1/rabbitmq-client.jar
>
> >> The Shutdown seems to be being called because the channel is being opened twice.
> >> The broker complains about this and closes the connection. Are you creating
> >> channels on different threads simultaneously?
> > Yes indeed, I am creating channels on different threads.
>
> >> I don't think the basicPublish will fail if the queue doesn't exist. Why would
> >> you create a new channel in this case?
> > Yes, you are right. I will basically lose the message in this case.
>
> > Now about overall problem statement.
> > My application has a main queue which looks like
> > MainQueue
> >  - App1-Event1
> >  - App2-Event1
> >  - App1-Event2
> >  - App1-Event3
> >  - App3-Event1
> >  - App3-Event2
> >  - App2-Event2
>
> > Basically there are going to be events from different Apps (there can
> > be thousands of apps) and events belonging to an App must
> > be processed sequentially. Events across different apps can and should
> > be be processed in parallel.
> > So I have only one consumer on MainQueue (using basicConsume) which
> > reads events from MainQueue and just moves it to appropriate declared/
> > redeclared queue.
> > So this is how new queue structure would look like.
>
> > App1
> >  - App1-Event1
> >  - App1-Event2
> >  - App1-Event3
>
> > App2
> >  - App2-Event1
> >  - App2-Event2
>
> > App3
> >  - App3-Event1
> >  - App3-Event2
>
> > Now again when Event1 is processed from Queue App1, Event2 of App1
> > can't be processed unless processing of Event1 is complete.
> > Processing of event involves asynchronous communication with external
> > systems, so once Event1 is fetched (and acknowledged) from queue
> > App1,
> > I create another queue like
> > App1_Return
> >  - App1-Event1-TaskId
>
> > I need to query external system using TaskId after certain time
> > interval, to check status of event processing of Event1. Once I get
> > the status (either sucess or failure)
> > I discard App1-Event1-TaskId and ready to process App1-Event2. So all
> > _Return queues will only have one event at any point of time.
>
> > An event on an app might even occur once a day. So I don't want to
> > keep so many queues (potentially 20000 if there are 10000 apps)
> > hanging around.
> > Both auto_delete and x-expires are not very useful as in both the
> > schemes, queues get deleted even when they have messages.
> > Ideally whenever last message from any Queue (except MainQueue) is
> > consumed, I want to delete that queue. Of course, one has to make sure
> > while a queue is getting deleted, there might be an event destined for
> > that. So if one guy is doing
> > queueDelete('somequeue', true, true) and other guy is doing
> > queueDeclare, queueBind, basicPublish. If queueDelete gets executed
> > after
> > queueBind, message will be lost.
>
> > One of the reasons, I don't do basicConsume on queues is, I am going
> > to have thousands of queues. I rather thought it would be easier to
> > have a thread pool, each consuming just one message from a queue in
> > round-robin fashion.
>
> > As was mentioned in some other response, I will certainly not create a
> > new channel in every thread, but would rather try and reuse them.
>
> > Thanks for all the help.
> > Regards, Yogesh
>
> > On Jan 31, 5:19 pm, Steve Powell <st... at rabbitmq.com> wrote:
> >> Yogesh,
>
> >> Please can you provide some information about your environment? And your
> >> application? What version of RabbitMQ (and client) are you using?
>
> >> In your stack trace the ShutdownListener you registered is apparently being
> >> called, because the Connection is being shut down. It is not clear why this
> >> exception (and its associated stack trace) appears, it seems to come from your
> >> Listener code, but perhaps that does nothing.
>
> >> The Shutdown seems to be being called because the channel is being opened twice.
> >> The broker complains about this and closes the connection. Are you creating
> >> channels on different threads simultaneously? (Looking at your app 'design' you
> >> might be.) Depending upon the version of RabbitMQ this might cause a problem.
>
> >> I'm afraid your application design is unclear:
>
> >>> This is how I handle doing basicPublish and basicGet on potentially
> >>> non-existent queues
> >>> - publish involves 3 steps
> >>>  queueDeclare
> >>>  queueBind
> >>>  basicPublish
> >>>  If some other thread deletes the queue after either queueDeclare or
> >>> queueBind, basicPublish fails and I again create a new
> >>>  channel and do these operations
>
> >> I don't think the basicPublish will fail if the queue doesn't exist. Why would
> >> you create a new channel in this case?
>
> >> Please explain why you expect the queue might be deleted by some other thread.
>
> >>> - if basicGet fails, I simply ignore it
>
> >> What do you mean by ignoring it? Do you poll the queue periodically? Why aren't
> >> you using basicConsume and a Consumer to get messages (which will be notified if
> >> the queue is deleted)?
>
> >> Steve Powell  (a loopy bunny)
> >> ----------some more definitions from the SPD----------
> >> vermin (v.) Treating the dachshund for roundworm.
> >> chinchilla (n.) Cooling device for the lower jaw.
> >> socialcast (n.) Someone to whom everyone is speaking but nobody likes.
>
> >> On 30 Jan 2012, at 04:33, Yogesh Ketkar wrote:
>
> >>> Only operations I ever do with com.rabbitmq.client.Connection in the
> >>> code are
> >>>    c.addShutdownListener
> >>>    c.createChannel
>
> >>> What does this error signify?
>
> >>> 2012-01-30 09:44:45,158 ERROR  [ConnectionShutdownHandler]
> >>> ShutdownListener
> >>> com.rabbitmq.client.ShutdownSignalException: connection error; reason:
> >>> {#method<connection.close>(reply-code=503, reply-text=COMMAND_INVALID
> >>> - second 'channel.open' seen, class-id=20, method-id=10), null,
> >>> "[B at 105691e"}
> >>>    at com.rabbitmq.client.impl.AMQConnection.shutdown(AMQConnection.java:
> >>> 641)
> >>>    at
> >>> com.rabbitmq.client.impl.AMQConnection.handleConnectionClose(AMQConnection. java:
> >>> 599)
> >>>    at
> >>> com.rabbitmq.client.impl.AMQConnection.processControlCommand(AMQConnection. java:
> >>> 571)
> >>>    at com.rabbitmq.client.impl.AMQConnection
> >>> $1.processAsync(AMQConnection.java:88)
> >>>    at
> >>> com.rabbitmq.client.impl.AMQChannel.handleCompleteInboundCommand(AMQChannel .java:
> >>> 144)
> >>>    at com.rabbitmq.client.impl.AMQChannel.handleFrame(AMQChannel.java:
> >>> 91)
> >>>    at com.rabbitmq.client.impl.AMQConnection
> >>> $MainLoop.run(AMQConnection.java:500)
>
> >>> Some additional info.
> >>> I create and close thousands of channels in the code. But at any point
> >>> of time there are not more than 20/21 channels open.
> >>> This is how I handle doing basicPublish and basicGet on potentially
> >>> non-existent queues
> >>> - publish involves 3 steps
> >>>  queueDeclare
> >>>  queueBind
> >>>  basicPublish
> >>>  If some other thread deletes the queue after either queueDeclare or
> >>> queueBind, basicPublish fails and I again create a new
> >>>  channel and do these operations
> >>> - if basicGet fails, I simply ignore it
>
> >>> regards, Yogesh
> >>> _______________________________________________
> >>> rabbitmq-discuss mailing list
> >>> rabbitmq-disc... at lists.rabbitmq.com
> >>>https://lists.rabbitmq.com/cgi-bin/mailman/listinfo/rabbitmq-discuss
>
> >> _______________________________________________
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>
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