I am working on a project to develop a Services Oriented Infrastructure with the  (Harry Pierson) and in just about every meeting lately, Harry mentions durable messaging at least once and why our project team needs to focus on getting others to understand this better so they can implement it in their solutions that require it.   According to  , web services without durability or reliability make no guarantee about preserving messages.

So why is durable messaging important in service oriented architecture or any architecture for that matter?  Because:

  1. It makes IT Operations life much easier.  Durable messaging allows IT Operations to track down messages much easier.  As an IT Ops person, I know when an application aborts, I know exactly where that message is and I can recover from a known state without losing messages.
  2. It makes Transactions more reliable.  When I have a transaction with multiple steps and one of the steps with in the transaction is to send an email, if the transaction aborts, the email will never get sent.  During the transaction, if the abort happens after the email submit but still within the scope of the transaction, the email is only tentatively sent and therefore, can be "rolled back" if the transaction aborts.   
  3. It adds durability to Reliable Messaging.  Durable messaging and reliable messaging are not the same, but they are somewhat related.  Reliable Messaging says if I send Message 1 and message 2 but the receivng system says I didn't get message 2, the sending system can then resend message 2...given that there was no system crash or reboot or other failure between the systems.  Reliable Messaging saves the state information in memory so if the systems fail or get rebooted, I have no way to recover from where I left off.   With Durable Messaging, the messages are written to the durable store so that if the systems do have some sort of failure, I can pick up where I left off in essence.
  4. Trying to make sure that a system completes in consisitent state.  This can be harder to do when transactions span organizational boundaries but can be done.