title: Azure Service Bus - Express queues and topics explanations
body: <p>I've just read this article:</p>
  
  <ul>
  <li><a href="https://azure.microsoft.com/en-us/documentation/articles/service-bus-performance-improvements/#express-queues-and-topics" rel="nofollow">Best Practices for performance improvements using Service Bus brokered messaging</a></li>
  </ul>
  
  <p>And found an interesting point about <code>Express queues and topics</code> :</p>
  
  <blockquote>
    <p><strong>Express entities</strong> enable high throughput and reduced latency scenarios. With express entities, if a <strong>message</strong> is <strong>sent</strong> to a queue or topic is, it is <strong>not immediately stored in the messaging store</strong>. Instead, the <strong>message is cached in memory</strong>. If a message remains in the queue for more than a few seconds, it is automatically written to stable storage, thus protecting it against loss due to an outage. Writing the message into a memory cache increases throughput and reduces latency because there is no access to stable storage at the time the message is sent. Messages that are consumed within a few seconds are not written to the messaging store. The following example creates an express topic.</p>
  </blockquote>
  
  <pre><code>TopicDescription td = new TopicDescription(TopicName);
  td.EnableExpress = true;
  namespaceManager.CreateTopic(td);
  </code></pre>
  
  <blockquote>
    <p>If a message containing critical information that must not be lost is sent to an express entity, the sender can force Service Bus to immediately persist the message to stable storage by setting the <strong>ForcePersistence</strong> property to true.</p>
  </blockquote>
  
  <p>If I create an express queue that has only one sender and the sender send <code>BrokeredMessage</code> with the property <code>ForcePersistence = true</code>, is there any interest to create an Express queue ?</p>
  
  <p>I guess this is useless but don't really understand how is it working ...</p>
  
  <p>Any clarification appreciated ^^</p>