Using Unit-of-Order with OSB. Download the test project. Unit-of-Order (UOO) is an Oracle (BEA) extension to standard JMS. It enforces the order of messages with the same key so that the messages are consumed in the order they were added to the queue. This functionality works in a cluster, too, by assigning each UOO key to one and only one managed server. When Ordered Updates Are Needed Suppose I update my phone number on a site.