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Service Bus Queues from Windows Azure - How to retry to consume messages and death letter

In the last blog post when I talked about poison messages that can exist in Service Bus Queues I told you how simple is to detect if a message was not processes with success for three times and throw him to the death letter sub-queue from Service Bus Queues. If you want to find more information about death letter please follow this link.
As a recap, each queue has a sub-queue where we can throw messages that were not processes – death letter. Service Bus automatically throw messages in this queue when the TTL expired, we reach the maxim limit of messages in a queue or when we don’t have enough space in the queue. The Service Bus is not the only one that can mark messages as death letter. We can do this also from the code and there are situations where is very useful.
Remarks: A messages that was marked as death letter cannot be added to the queue. We need to recreate it.
This is very useful when we try to process messages from a queue but because of an unknown cause we cannot process the messages with success. In this case if we use the Peer-Look Receive Mode and a message is not removed from the queue until we call the complete action, these messages will hang in the queue until TTL expired. In the same time, the consumers will try to process these messages over and over again. This is a waste of resources and there are some cases when a message cannot be processes first time but if after 3 attempts we could not process the messages than we should mark him as poison messages.
In the following example I defined a consumer that tries to consume messages from Service Bus Queues. For the messages that are the 3th time when the system try to process them without success they are marked as death letters. Another system will process them letter on and can do more actions with them or only log it.
 QueueClient qc =
    QueueClient.CreateFromConnectionString(
    myFooConnectionString, "FooQueue");
while(true)
{
    BrokeredMessage message = qc.Receive();
    if(message == null)
    {
        Thread.Sleep(1000);
        continue;
    }
   
    try
    {
        // process our message.
        message.Complete()
    }
    catch(Exception ex)
    {   
            if( message.DeliveryCount > 3 )
            {
                message.DeadLetter();
            }
            message.Abandon();
    }
}
In this code sample the key is DeliveryCount. This is a property of a BrokeredMessage that is automatically incremented when someone retrieves the message from Service Bus Queue. When this value reach 3 then we mark the message as dead letter and we will not be able to access it from the queue.
In the following code sample I will retrieve all the messages that were marked as death letter.
QueueClient qcdl =
    QueueClient.CreateFromConnectionString(
    myFooConnectionString, QueueClient.FormatDeadLetterPath("FooQueue"));
while(true)
{
    BrokeredMessage message = qcdl.Receive();
    if(message == null)
    {
        Thread.Sleep(1000);
        continue;
    }

    // Process message.
}
Notified how I get the name of the queue where I stored the deferral messages? QueueClient.FormatDeadLetterPath("FooQueue") – don’t forget about this helper functions that framework offer to us.
In this post we saw how we can mark messages as deferral when we try for 3 types to process them without success.

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