10
Using Message Unit-of-Order 10-1
10
Using Message Unit-of-Order
The following sections describe how to use Message Unit-of-Order to provide strict message ordering when using WebLogic JMS:
■
Section 10.1, What Is Message Unit-Of-Order?
■
Section 10.2, Understanding Message Processing with Unit-of-Order
■
Section 10.3, Message Unit-of-Order Case Study
■
Section 10.4, How to Create a Unit-of-Order
■
Section 10.5, Message Unit-of-Order Advanced Topics
■
Section 10.6, Limitations of Message Unit-of-Order
10.1 What Is Message Unit-Of-Order?
Message Unit-of-Order is a WebLogic Server value-added feature that enables a stand-alone message producer, or a group of producers acting as one, to group
messages into a single unit with respect to the processing order. This single unit is called a Unit-of-Order and requires that all messages from that unit be processed
sequentially in the order they were created.
10.2 Understanding Message Processing with Unit-of-Order
The following sections compare message processing as described by the JMS specification with message processing enhanced by using WebLogic Servers Message
Unit-of-Order feature.
■
Section 10.2.1, Message Processing According to the JMS Specification
■
Section 10.2.2, Message Processing with Unit-of-Order
■
Section 10.2.3, Message Delivery with Unit-of-Order
10.2.1 Message Processing According to the JMS Specification
While the Java Message Service Specification, at http:www.java.sun.comproductsjmsdocs.html
, provides an ordered message delivery, it does so in a very strict sense. It defines order between a single
instance of a producer and a single instance of a consumer, but does not take into account the following common situations:
■
Many consumers on one queue. See Chapter 9, Using Distributed Destinations.
10-2 Programming JMS for Oracle WebLogic Server
■
Multiple producers within a single application acting as a single producer. See Chapter 9, Using Distributed Destinations.
■
Message recoveries or transaction rollbacks where other messages from the same producer can be delivered to another consumer for processing. See
Section 10.5.1, What Happens When a Message Is Delayed During Processing?
.
■
Use of filters and destination sort keys. See Section 10.5, Message Unit-of-Order
Advanced Topics.
10.2.2 Message Processing with Unit-of-Order
The WebLogic Server Unit-of-Order feature enables a message producer or group of message producers acting as one, to group messages into a single unit that is
processed sequentially in the order the messages were created. The message processing of a single message is complete when a message is acknowledged,
committed, recovered, or rolled back. Until message processing for a message is complete, the remaining unprocessed messages for that Unit-of-Order are blocked.
This section provides information on rules for JMS acknowledgement modes, described at
http:www.java.sun.comproductsjmsdocs.html , when
using Message Unit-of-Order:
■
No messages from a Unit-of-Order are processed in parallel when the acknowledgement mode is CLIENT_ACKNOWLEDGE, AUTO_ACKNOWLEDGE, or
DUPS_OK_ACKNOWLEDGE.
■
When the consumer is closed, the current message processing is completed, regardless of the sessions acknowledge mode.
■
CLIENT_ACKNOWLEDGE – The application calling Message.acknowledge and Session.recover indicate which messages are completely processed in the
Unit-of-Order.
■
AUTO_ACKNOWLEDGE – The session automatically acknowledges a clients receipt of a message when it has either successfully returned from a call to receive or
when the MessageListener that was called returns successfully.
– Asynchronous mode: Successful completion or exception of
onMessagemsg indicates when a message is completely processed.
– Synchronous mode: For a given consumer, such as consumer A,
consumerA.receive is completed when one of the following occurs: consumerA.receive, consumerA.setMessageListener, or
consumerA.close.
■
DUPS_OK_ACKNOWLEDGE – The session automatically acknowledges a clients receipt of a message when it has either successfully returned from a call to
receive or when the MessageListener that was called returns successfully.
– Asynchronous mode: Successful completion or exception of
onMessagemsg indicates when a message is completely processed.
– Synchronous mode: For a given consumer, such as consumer A,
consumerA.receive is completed when one of the following occurs: consumerA.receive, consumerA.setMessageListener, or
consumerA.close.
■
NO_ACKNOWLEDGE – The session provides no order processing guarantees. Messages can be processed in parallel to different available consumers.
Using Message Unit-of-Order 10-3
10.2.3 Message Delivery with Unit-of-Order
