On 09/27/2010 03:46 AM, [email protected] wrote:
I set up a Listener on a queue and the callback method will take about 10 seconds. I the producer side, it sends 1000 messages to this queue. Then the Listener will take one from the queue and cause 10 seconds to do its job. Before the listener deal with the first message, will be the other 999 messages in the broker queue or they have been delivered to the Listener side?
That depends on the flow control options in use. With the c++ client API the default is for subscriptions to issue unlimited credit, in which case all messages will have been sent to the client queued up behind the Listener. You can alter that by changing the flow control in qpid::client::SubscriptionSettings.
In the new messaging API flow control is tied to the receivers capacity. By default this is 0, eliminating any prefetch. This means that a message will only be delivered in response to a fetch() call (which is the most intuitive in many cases, but does not perform as well). Setting the capacity to 10 will allow the client to 'prefetch' 10 messages to be held locally until obtained by the application through fetch() calls.
With the JMS client there is a value to control the maxprefetch (see http://qpid.apache.org/books/0.7/Programming-In-Apache-Qpid/html/ch03s02.html#id2589017). (I believe this can perhaps also be set as a system property? Can anyone more familiar with the JMS client confirm?)
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