Service Bus - Optimize consumers using prefetch and maximum concurent calls features

From same version ago, Windows Azure Service Bus supports 'event notification'. This means that we can register to an event that will be triggered each time when a new message is available for us.

QueueClient client = QueueClient.Create("queue1");
client.OnMessage(
    OnMsgReceived, 
    new OnMessageOptions());
...
void OnMsgReceived(BrokeredMessage message)
{
    ...
}

This is a great feature, that usually make our life easier. By default, when we are consuming messages in this way, we will make a roundtrip to the Service Bus for each message. When we have applications that handle hundreds of messages, the roundtrip to the server for each message can cost us time and resources.
Windows Azure Service Bus offer us the possibility to specify the number of messages that we want to prefetch. This means that we will be able to fetch 5, 10, 100, .. messages from the server using a single request. We could say that is similar to the batch mechanism, but can be used with the event notification feature.

QueueClient client = factory.CreateQueueClient("queue1");
client.PrefetchCount = 200;

We should be aware that the maximum numbers of messages that can be prefetch by one request is 200. I think that this an acceptable value, if we take into the consideration that this will trigger 200 notification events.
This value need to be set when we create and setup the subscription client. Theoretically you can set this value before receiving the first message from the server, but I recommend to make all this configuration at the setup and initialization phase.
When we are using this mechanism of prefetching, we need to know exactly how many concurrent calls  we can have. Because of this, the Service Bus client give us the possibility to specify how many concurrent calls we can have in the same time.

client.OnMessage(CalculateEligibility,new OnMessageOptions()
            {
                MaxConcurrentCalls = 100
            });

For example if we would have the prefetch count set to 200, and the maxim concurrent calls sett to 100, we will have the following behavior:
Make a roundtrip to the server
Receive 200 messages (we suppose that there are 200 messages available)
Consume first 100 messages
Consume the other 100 messages
Messages are consumed in a async way. This means that from the first 100 messages, when 1 will be processed on the client, another message receive event will be triggered.
We saw in this post how we can consume the messages in parallel when using Windows Azure Service Bus and event notification. Using this features we can increase our application performance.
Good luck with Windows Azure Service Bus.

PS: Bonus picture - This is a picture from Seattle airport, where I am now, waiting the flight back home.