Microsoft SQL Server 2008 R2 Unleashed- P199:SQL Server 2005 provided a number of significant new features and enhancements over what was available in SQL Server 2000. This is not too surprising considering there was a five-year gap between these major SQL Server 2008 is not as much of a quantum leap forward from SQL Server 2005 | 1974 CHAPTER 49 SQL Server Service Broker Planning Conversations Between Services A conversation is a dialog between two services. The purpose of this dialog is of course the sending and receiving of messages which ultimately leads to the completion of a task. A powerful feature of Service Broker messaging is that it guarantees exactly-once-in-order EOIO messaging. This means that messages are sent exactly once there s no chance that a message can be sent twice because of a system issue so the receiver doesn t have to check whether a message has already been processed. It also means that messages are always ordered in their queue in the same order in which they were sent. The queuing_order column of the queue indicates this order. Service Broker makes sure of this even in cases in which the send order somehow gets out of sync. Transactions are an integral part of Service Broker conversations. When a message is sent within the scope of a transaction it is not actually moved to the destination queue unless the transaction commits. This has to do with the fact that before being placed in a queue messages are stored in internal tables called transmission queues which are viewable via the catalog view . Similarly a message is not deleted from a queue after it is received unless the transaction commits except in cases in which the RETENTION flag for the queue is set to ON . This point is very important because it means that any database operations as well as any messaging operations belong to the same transaction and they are controlled by the same transactional system. This is a unique feature of messaging with Service Broker and is part of the rationale for having messaging built in to the database. The BEGIN CONVERSATION DIALOG statement is the cornerstone of the process of creating conversations. It specifies the services participating TO SERVICE and FROM SERVICE and the contract to which they will be adhering during the dialog ON CONTRACT . It
