Designing a Messaging Bridge

Use the following information to help you design and configure a WebLogic Messaging Bridge:

When to use a Messaging Bridge

Store and Forward Messaging

A messaging bridge provides high availability for remote destinations. Store and forward messaging enables a local client to produce to a local destination and have those messages automatically forwarded to the remote destination when it is available. This allows a local client to continue to produce messages when a remote destination is not available. See Messaging Persistence.

Use the WebLogic Messaging Bridge to provide an administrative solution to store and forward messages between:

Replicating a Topic

A messaging bridge can be used to replicate a topic, similar to using the distributed topics feature available in WebLogic Server releases 7.0 and higher, consequently improving scalability and high availability in some scenarios. Topic replication is accomplished by configuring the bridge to subscribe to one topic and forward the topic's messages to another topic, in essence creating two topics with the same message stream. See Create messaging bridge instances in Administration Console Online Help.

When to Avoid using a Messaging Bridge

The following sections provide information on when to avoid using messaging bridge:

Receiving messages from a remote destination—Use a message driven EJB or implement a client consumer directly.
Sending messages to a local destination—Send directly to the local destination.
Environment with low tolerance for message latency. Messaging Bridges increase latency and may lower throughput. Messaging bridges increase latency for messages as they introduce an extra destination in the message path and may lower throughput because they forward messages using a single thread.
Forward messages between WebLogic 9.0 domains—Use WebLogic Store-and-Forward.

The following table summarizes information on when to use WebLogic Messaging Bridge or other forwarding technologies:

Table 3-1 Comparing Message Forwarding Technologies
Feature	Messaging Bridge	Message Driven Beans	WebLogic Store-and-Forward
Implementation mechanism	Administrative	Programmatic	Administrative
Support for foreign and legacy providers	Yes	No	No, use to forward messages between WebLogic 9.X domains.

Selecting a Quality-of-Service (QOS) Level

Exactly-once—The highest QOS guarantees that a message is sent to the remote endpoint once and only once. With Exactly-once, messages survive server crashes and network down time, while guaranteeing one occurrence of each message at the endpoint.
At-least-once—Guarantees that a message is sent to the remote endpoint, but with the possibility of duplicates. With At-least-once, multiple copies of a message might show up on the remote endpoint because of network failures or server crashes that occur when the message is in transit.
At-most-once—The lowest QOS guarantees that each message is sent to the remote endpoint only once, if at all. It does not guarantee that a message is sent to the endpoint. With At-most-once, messages may get lost because of network failures or server crashes. No duplicate messages will reach the endpoint.

In some instances, the target destination may not be able to provide the quality of service configured for the bridge. In these cases, configure the bridge instance to allow the quality of service to be degraded by setting the QOSDegradationAllowed flag. See Create messaging bridge instances in Administration Console Online Help.

Messaging Persistence

Store-and-forward messaging enables a local JMS client to produce messages to a local destination and have those messages automatically forwarded to a remote destination when it is available. The bridge will forward these messages to the target destination when it is restarted. A messaging bridge will store-and-forward messages to a target destination under the following conditions:

Message Ordering

If an application message is in a transaction, saving the message in the persistent store must be part of the user transaction to preserve exactly-once semantics. In particular, the message is removed from the persistent store as part of the transaction rollback if the application decides to rollback the transaction. However, forwarding is not part of the application transaction. The sending agent does not forward a transactional message until the transaction commits. Within a transaction, message ordering is preserved based on when the messages are sent.

To ensure message ordering, configure a message unit-of-order. See Using Message Unit-of-Order in Programming WebLogic JMS.

Setting the Number of Connection Factories

You may need to modify the capacity of the connection factory associated with each resource adaptor by adjusting the initial-capacity and max-capacity attributes the weblogic-ra.xml descriptor file. In general, the value of the max-capacity attribute should be at least two times the number of bridge instances. For example:

The default configuration sets the value of the max-capacity attribute to 20. This setting is adequate for environments that have up to ten message bridge instances targeted. If you increase the number of bridge instances to 15, increase the max-capacity attribute to 30.

Using the editor of your choice, update the attribute with the desired value. See Listing 3-1.
Deploy the updated adapter.
Stop and restart any bridge instance that requires the new values.

Listing 3-1 Example weblogic-ra.xml Descriptor File

<weblogic-connection-factory-dd>

     <connection-factory-name>WLSJMSConnectionFactoryLocal</connection-factory-name>

     <jndi-name>eis/jms/WLSConnectionFactoryJNDILocal</jndi-name>

          <pool-params>

               <initial-capacity>0</initial-capacity>

               <max-capacity>20</max-capacity>

          </pool-params>

</weblogic-connection-factory-dd>

Preserving Message Properties

Set PreserveMsgProperty to preserve message properties in a message header when a message is forwarded by a bridge instance. In previous releases, message properties are inherited from the Default Delivery Mode attribute on the connection factory used when a message is forwarded to its target destination. If the Default Delivery Mode is persistent, a non-persistent message is forwarded as a persistent message resulting in a significant performance loss.

When PreserveMsgProperty is enabled, an incoming non-persistent message is forwarded by the bridge to the target destination as a non-persistent message and an incoming persistent message is forwarded to the target destination as a persistent message. See Configure messaging bridge instances in Administration Console Online Help.

The behavior of a messaging bridge instance is determined according to the following guidelines:

The PreserveMsgProperty is not enabled. This setting provides the same forwarding behavior as previous releases.
The default value of PreserveMsgProperty when configuring a messaging bridge instance is not enabled.

The PreserveMsgProperty is enabled. Message properties are preserved as described the following table:

Table 3-2 Message Properties Preserved at Target Destination by WebLogic Server Release
Property	WebLogic Server 9.0 and Higher	WebLogic Server 8.1, 7.0, and 6.x	Foreign JMS Servers
Message ID	Yes	No	No
Timestamp	Yes	No	No
User ID	Yes	No	No
Delivery Mode	Yes	Yes	Yes
Priority	Yes	Yes	Yes
Expiration Time	Yes	Yes	Yes
Redelivery Limit	Yes	No	No
Unit-of-Order name	Yes	No	No

Using the JMSXUserID Property with a Messaging Bridge

The messaging bridge does not disclose a message's JMSXUserID across messaging bridge boundaries. A JMSXUserID is a system generated property that identifies the user sending the message, see the JMS Specification.

Using Distributed Destinations as Source and Target Destinations

A messaging bridge can send to and receive from distributed destinations. BEA Systems recommends the following configurations:

If the source is a distributed destination, the bridge is pinned to one of the members when it connects to the destination. It stays connected to that member until an event occurs that breaks the connection. On reconnection, the bridge uses the next available member. Once a bridge is connected, it does not receive messages from other members of the distributed destination. It is a best practice to configure one bridge for each member of a distributed destination using the member's JNDI Name.
If the target is a distributed destination, the best practice is to send to the distributed destination using the distributed destination's JNDI Name and disable server affinity. This allows the distributed destination to load balance incoming messages. See Load Balancing for JMS in Using WebLogic Server Clusters.

Tuning a WebLogic Messaging Bridge

The main objective when tuning a messaging bridge is to improve overall messaging performance. Raw speed, though important, is only one of several performance-related factors. Other performance factors include reliability, scalability, manageability, monitoring, user transactions, message-driven bean support, and integration with an application server. See " Tuning WebLogic Message Bridge" in WebLogic Server Performance and Tuning:

Configuring and Managing the WebLogic Messaging Bridge