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From "Simon (JIRA)" <j...@apache.org>
Subject [jira] Created: (AMQ-2571) Sender sometimes, involuntary, autocreates new, consumerless, TempQueue when trying to send to removed TempQueue.
Date Fri, 15 Jan 2010 21:46:43 GMT
Sender sometimes, involuntary, autocreates new, consumerless, TempQueue when trying to send
to removed TempQueue.
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                 Key: AMQ-2571
                 URL: https://issues.apache.org/activemq/browse/AMQ-2571
             Project: ActiveMQ
          Issue Type: Bug
          Components: Broker
    Affects Versions: 4.1.1
         Environment: Ubuntu 9.10, P4 2.6 GHz HT, 3 GB RAM. 
            Reporter: Simon


Please see this post for discussion:
http://old.nabble.com/Problems-with-prefetch-and-TemporaryQueues-td27130529.html

I've tested this on 4.1.1, and briefly on 5.3.0 with the same result.

Scenario:
We have a server and a client. The client posts a message on the servers queue in order to
subscribe to updates.
The server takes the reply address from the client and starts sending messages to a TempQueue
created by the client.

When the client disconnects without notifying the server the following might happen:
1. The temporary queue is removed correctly when the client exists and closes its connection.

>From here we have three scenarios:
2.a The server gets an exception the next time it tries to send a message to the TempQueue.
This is wanted behaviour. It can then simply drop the "subscription".

2.b The server isn't notified in time and sends some messages before it gets the exception.
Due to AutoCreateDestination being enabled one of these messages creates a new TempQueue with
the same name as the one removed. It is of course missing a consumer.
But since the server gets the exception it will stop posting to the TempQueue. However, when
the server closes its connection the TempQueue is not removed and is left lying around with
no consumer.

2.c The server recreates the TempQueue in the same way as in 2.b, but here it never gets the
exception for some reason. The server then has no idea that the client left and keeps pilling
up messages on the TempQueue until the broker object hits its memory limit and everything
connected to the broker halts.


I think there are three problems here:
1. The exception is not thrown every time.
2. When the TempQueue is recreated it is not removed when the server closes its connection.
3. Due to AutoCreateDestination being enabled by default for TempQueues, every post to a TempQueue
could result in unknowingly creating a new TempQueue.


Suggestions
Settings AutoCreateDestination to false for TempQueues solves all three problems.
So exposing that option in an easily accessible way is important.

But even then, 1 and 2 should perhaps be examined separately.

I'll attach a JUnit test case for this. Unfortunately it is not 100% reliable in detecting
the problem. One has to run it multiple times.
On my test setup it failed correctly 8 times out of 10 runs. You might be able to improve
it.

Best Regards
Nimos

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