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From Christian Posta <>
Subject Re: Camel, concurrent consumers, message groups and prefetch size
Date Mon, 31 Mar 2014 21:09:44 GMT
On Fri, Mar 28, 2014 at 10:06 AM, Paul Gale <> wrote:
> Hi,
> I have an embedded Camel client that contains a single route. All messages
> the route consumes have their JMSXGroupID property set.
> What I need to know is how message grouping behaves in the context of
> concurrent consumers and how does the choice of the prefetch buffer size
> come into play (when not using the default)?

It's the same as if not using concurrent consumers, as described on
the ActiveMQ wiki... however,
each one of your consumers will compete for its own individual message group.

> Say I have route that looks like:
> from("activemq:some_queue?concurrentConsumers=5&maxConcurrentConsumers=5&destination.consumer.prefetchSize=5")
>   .bean(new SomeBean());
> - Is it guaranteed that a given message group will always be handled by the
> same consumer thread?
Same logical thread, yes. The same consumer will consume the messages
for which group it's assigned up until the group closes or the
consumer is closed.

> - Is the prefetch size applied at the consumer thread level or to the
> single underlying connection that they're all sharing?

It's applied at the individual consumer, not at the connection.

> - If the prefetch size is applied at the connection level, is it correct to
> assume that its value must be >= the number of concurrent consumers to
> avoid leaving threads idle when there are messages available to be
> processed, example: when consumer.prefetchSize=1?
> Yes, I have read this page:
> but it
> didn't answer my questions.
> Thanks,
> Paul

Christian Posta
twitter: @christianposta

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