Windows Azure Service Bus Duplicate Detection

Windows Azure Service Bus Duplicate Detection

One great feature of Windows Azure Service Bus is the ability to identify duplicate messages. Using this feature we can automatically remove messages from the Service Bus Queue or Topic when we have more than one occurrence of the same message. This mechanism is deactivated by default, but we can activate it very easily.

Let’s see how this mechanism works. When we activate it, the Windows Azure Service Bus will start to store a history of our messages. This period of time can be configured to range from only a few minutes to days. If a duplicate message is sent to the Service Bus, the service will automatically ignore the message.

Because the content of each message needs to be serialised, the duplicate detection mechanism will look to the serialised items that were added to the message. If the content is the same than the message will be considered a duplicate. For example we have the following class that we add to each message:

[DataContract]
public Foo
{
[DataMember]
public string Id { get; set;}
[DataMember]
public string Name { get; set;}
}

If we will add two messages with objects Foo type objects with the same id and name, than the second message will be considered a duplicate. We will not receive any kind of notification when we will try to send the second message.

MessagingFactory factory = MessagingFactory.Create([uri], [tokenProvider]);
MessageSender sender = factory.CreateMessageSender("FooQueue")

Foo obj1 = new Foo() { Id = “1”, Name = “One” };
BrokeredMessage message1 = new BrokeredMessage(obj1);

Foo obj2 = new Foo() { Id = “1”, Name = “One” };
BrokeredMessage message2 = new BrokeredMessage(obj2);

sender.Send(message1);
sender.Send(message2);

It is very important to remember that the duplicate detection mechanism will use the space from our Service Bus for the old messages. That is why we need to be careful when we set the history time period.
This setting can be changed in two ways. You can change it from the portal, where you can activate this feature and set the history time period. This feature will only be available only if you select “Custom create”.

Windows Azure Configure queue

The second place where you can change the configuration is the code. In the moment when we create a new Service Bus Topic or Service Bus Queue we can specify our preferences in the create command. To be able to do this we will need to create a TopicDescription or a QueueDescription object. This object allows us to activate this functionality and set the history time period.

Topic:

TopicDescription fooTopicDescription = new TopicDescription("FooTopic")
{
RequiresDuplicateDetection = true,
DuplicateDetectionHistoryTimeWindow = new TimeSpan(10, 0, 0),
};
namespaceManager.CreateTopic(fooTopicDescription);

Queue:

QueueDescription fooQueueDescription = new QueueDescription("FooQueue")
{
RequiresDuplicateDetection = true,
DuplicateDetectionHistoryTimeWindow = new TimeSpan(10, 0, 0),
};

namespaceManager.CreateQueue(fooQueueDescription);

These policy settings for the Service Bus Queue or Service Bus Topic can be changed only at the time of creation. Afterwards, if we want to change the history time period or deactivate it, it will not be possible. To be able to do this, you will need to delete the resource and recreate it.

This is a great feature that can be used when we need to avoid duplicate messages in our Service Bus.

Tags: , ,

2 comments

[…] Windows Azure Service Bus Duplicate Detection […]

Hi,

What does it mean for message to be “duplicate”. Does it need to be all the same?
Say I have a message with a timestamp. Two servers sending the same message will have slightly different timestamp, but message is still a duplicate.
Is there any way to check duplicate messages by ID, or privide hash code?

Thanks

Leave a Reply

Your email address will not be published. Required fields are marked *