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From Rob Davies <rajdav...@gmail.com>
Subject Re: Contention in Queue.lock() via IndirectMessageReference.lock()
Date Fri, 08 Feb 2008 16:50:29 GMT
Its there for message exclusive consumers  - will look at changing ;)
On Feb 8, 2008, at 4:09 PM, David Sitsky wrote:

> In my application, I have a large number of threads in the broker,  
> which are calling dispatchPending() on their subscriptions, but are  
> unable to make fast progress, as can be seen in the following stack  
> trace:
>
> "ActiveMQ Transport: tcp:///192.168.222.75:56495" daemon prio=4  
> tid=0x4be82000 n
> id=0x1028 waiting for monitor entry [0x54fdf000..0x54fdfb00]
>   java.lang.Thread.State: BLOCKED (on object monitor)
>        at org.apache.activemq.broker.region.Queue.lock(Queue.java:166)
>        - locked <0x0a60bf58> (a java.lang.Object)
>        at  
> org 
> .apache 
> .activemq 
> .broker 
> .region.IndirectMessageReference.lock(IndirectMessageReference.java: 
> 143)
>        at  
> org 
> .apache 
> .activemq 
> .broker.region.QueueSubscription.canDispatch(QueueSubscription.java: 
> 119)
>        at  
> org 
> .apache 
> .activemq 
> .broker 
> .region 
> .PrefetchSubscription.dispatchPending(PrefetchSubscription.java:466)
>        - locked <0x0b55bd78> (a java.lang.Object)
>        at  
> org 
> .apache 
> .activemq 
> .broker 
> .region.PrefetchSubscription.acknowledge(PrefetchSubscription.java: 
> 347)
>        at  
> org 
> .apache 
> .activemq 
> .broker.region.AbstractRegion.acknowledge(AbstractRegion.java:342)
>        at  
> org 
> .apache 
> .activemq.broker.region.RegionBroker.acknowledge(RegionBroker.java: 
> 461)
>        at  
> org 
> .apache 
> .activemq 
> .broker.TransactionBroker.acknowledge(TransactionBroker.java:194)
>        at  
> org 
> .apache.activemq.broker.BrokerFilter.acknowledge(BrokerFilter.java:73)
>        at  
> org 
> .apache.activemq.broker.BrokerFilter.acknowledge(BrokerFilter.java:73)
>        at  
> org 
> .apache 
> .activemq 
> .broker.MutableBrokerFilter.acknowledge(MutableBrokerFilter.java:87)
>        at  
> org 
> .apache 
> .activemq 
> .broker 
> .TransportConnection.processMessageAck(TransportConnection.java:440)
>        at  
> org.apache.activemq.command.MessageAck.visit(MessageAck.java:196)
> ....
>
> I am trying to understand why IndirectMessageReference.lock() would  
> require synchronisation on the entire Queue object it is associated  
> with?
>
> This is why the performance in my application is grinding... each  
> time a prefetch/queue subscription is testing to see if they can  
> dispatch a message, we are effectively serialising on the Queue  
> object.
>
> Any ideas on how we can fix this?  I have some ideas, but thought  
> the experts are better qualified. :)
>
> This became evident when I had 20 consumers hammering away.  With 2,  
> you'd never see this.
>
> Cheers,
> David


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