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From David Sitsky <s...@nuix.com>
Subject Re: Contention in Queue.lock() via IndirectMessageReference.lock()
Date Fri, 08 Feb 2008 16:46:54 GMT
FWIW - since I don't use exclusive consumers in my application, I 
commented out the first three lines in IndirectMessageReference.lock() 
below, and that bottleneck has been removed.

if (!regionDestination.lock(this, subscription)) {
     return false;
}

Anyway - hopefully this is of interest to somebody.  Perhaps we can 
optimise this so that if we don't use exclusive consumers to make the 
above call a no-op?

Cheers,
David

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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