5. After receiving a confirmation receipt, the local queue removes the original information
from the queue. It will only remove it from the local queue if it??™s sure the
remote queue has received it; otherwise, it will continue to retry the original send.
Message queuing is only concerned with guaranteeing queue-to-queue communication.
What happens outside of the queues (in Figure 8-9, DB1 and DB2) is irrelevant.
Queuing is effective when working with data connections that may disconnect periodically,
or when asynchronous communication is desired. Establishing some sort of direct
CHAPTER 8 n DATABASE MIRRORING 203
connection from one database to another tends to result in trouble and frustration once
a network issue occurs (I??™ll discuss hardware implications in greater detail in Chapter 10).
Queuing is implemented in many different ways. The idea and technology has been
around for quite some time. We have Microsoft Message Queuing (MSMQ) and IBM Web-
Sphere MQ, not to mention a plethora of handwritten queuing techniques. Database
mirroring uses a new queuing technology native to SQL Server 2005 only: Service Broker.
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