Basic UOW Terminology Rules For Processing UOW Messages

11-2 Programming JMS for Oracle WebLogic Server

11.2.1 Basic UOW Terminology

Table 11–1 defines the terms used to define UOW.

11.2.2 Rules For Processing UOW Messages

The following rules apply to UOW messages. ■ Rule One: All Messages Required For Processing No message within the UOW will be available until all of them are available on the terminal destination. ■ Rule Two: Message Reordering No matter what order the messages arrive to the terminal destination, they will be put into the order specified by the UOW producer. ■ Rule Three: Gap Freedom Table 11–1 Unit-of-Work Terminology Term Definition Unit-of-Work UOW A set of JMS messages that need to be processed as a single unit. UOW Component Message A message that is part of a UOW. In order for WebLogic JMS to identify a message as part of a UOW, the message must have the JMS properties described in Section 11.3.1, How To Write a Producer to Set UOW Message Properties. UOW Producer A producer that needs to split its work into multiple parts i.e., a creator of a UOW. Multiple producers can concurrently contribute component messages to a UOW message, as illustrated in Section 11.2.3, Message Unit-of-Work Case Study. If fact, a UOW producer can close midway through a UOW and a new producer can complete the UOW message, while maintaining the same strict component message integrity e.g., detect duplicates, etc.. Intermediate Destination A destination whose consumers have the job of processing component messages separately rather than as a unit. No special UOW configuration is required for intermediate destinations. When a component message arrives on an intermediate destination it will be made available without waiting for other component messages to arrive. Further, if the intermediate destination is a distributed destination, no special routing need occur. See Section 11.3.2, How to Write a UOW ConsumerProducer For an Intermediate Destination. Terminal Destination A destination whose consumers have the job of processing a full UOW. A destination is identified as a terminal destination by the Unit-of-Work Message Handling Policy parameter on standalone destinations, distributed destinations, or JMS templates. See Section 11.3.3, Configuring Terminal Destinations. AvailableVisible Messages Equivalent JMS terms that refer to a message becoming ready for consumption, pending the reception of any messages that precede it. For example, a JMS message is not available until its birth time has been reached or a JMS message that is sent as part of a transaction is not visible until that transaction is committed. Using Unit-of-Work Message Groups 11-3 The group of messages will be delivered to the user without gaps. That is, all messages in the group will be delivered to the user before messages from any other group or part of no group at all. ■ Rule Four: Single Consumer Consumption The group of messages will be delivered to the same consumer.

11.2.3 Message Unit-of-Work Case Study