WebSphere eXtreme Scale Best Practices for Operation and Management

Chapter 5. Grid configuration 91

</backingMapPluginCollections>

</objectGridConfig>

5.3.2 The ObjectGridEventListener plug-in

An ObjectGridEventListener plug-in provides WebSphere eXtreme Scale ObjectGrid shard

and transaction life-cycle events. These events include ObjectGrid shard initialization,

destroying, activation and deactivation, and transaction beginning and ending. WebSphere

eXtreme Scale provides two built-in implementations of the ObjectGridEventListener plug-in:

򐂰 JMSObjectGridListener

򐂰 TranPropListener

It is also possible to implement a custom version of this plug-in.

The JMSObjectGridEventListener plug-in

The JMSObjectGridEventListener is a Java Message Service (JMS) implementation of the

ObjectGridEventListener interface. You can use it for two purposes:

򐂰 Near cache invalidation

򐂰 Peer-to-peer replication

Near cache invalidation enables WebSphere eXtreme Scale client applications to keep their

near cache content synchronized with each other or with the content of the WebSphere

eXtreme Scale server cache when another client is updating the server cache. You can use

peer-to-peer replication to maintain the same data between two separate distributed or local

WebSphere eXtreme Scale servers.

Using the built-in JMSObjectGridEventListener plug-in is the preferred method when a client

application needs to be notified of updates that occur in the server grid. Notifications are

processed in the onMessage() method implementation. This method gives the client the

opportunity to update its near cache. It also requires you to configure JMS and Java Naming

and Directory Interface (JNDI) information. If you are running WebSphere Application Server,

you can use its default messaging provider. Otherwise, you need a JMS provider, such as

WebSphere MQ. Because of the asynchronous nature of JMS, notifications of updates in the

near cache occur after a certain delay.

To use near cache invalidation, you need to complete the following tasks:

1. Write a JMSObjectGridEventListener extension that implements the onMessage()

method. You can find an example of such an implementation in the WebSphere eXtreme

Scale Information Center:

http://publib.boulder.ibm.com/infocenter/wxsinfo/v7r1/topic/com.ibm.websphere.e

xtremescale.admin.doc/cxsjmsevntls.html

Peer-to-peer replication warning: Using the JMSObjectGridEventListener plug-in for

peer-to-peer replication is no longer recognized as a preferred practice. The plug-in can be

difficult to set up and does not scale well. The preferred practice for peer-to-peer

replication is to use the WebSphere eXtreme Scale multi-master replication feature.

Important: The built-in JMSObjectGridEventListener does nothing. It is designed to be

extended, and the user is in charge of writing an invalidation mechanism in the

onMessage() method.

92 WebSphere eXtreme Scale Best Practices for Operation and Management

2. Configure the JMS topic and the related JNDI names. We do not explain this task here,

but, remember, when designing the JMS topic connection factory, that each container

server in a publisher role creates one connection for each partition during the

JMSObjectGridEventListener initialization. You must size the connection pool size

according to your topology.

In addition to these tasks, you need to configure the JMSObjectGridEventListener plug-in by

adding the following elements in the ObjectGrid descriptor XML file:

򐂰 In the objectGrid element, add a bean element with the following settings:

–The ID attribute is set to JMSObjectGridEventlistener.

–The className attribute is set with the class name of your

JMSObjectGridEventListener extensions.

򐂰 In the JMSObjectGridEventListener bean element, add the following required property

elements: