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In a distributed ObjectGrid environment, the client side has a near cache by default when using the optimistic locking strategy or when locking is disabled. This near cache has its own local cached data. If an ObjectGrid client commits an update, this update goes to its near cache and server. However, other ObjectGrid clients do not receive this update information and might have data that is out of date. Applications must be aware of this stale data issue in ObjectGrid client. You can use the built-in Java Message Service (JMS)-based ObjectGridEventListener class, com.ibm.websphere.objectgrid.plugins.builtins.JMSObjectGridEventListener, to enable the client invalidation mechanism within a distributed ObjectGrid environment that is known as an ObjectGrid cluster.
The client invalidation mechanism is the solution for the issue of stale data in client near cache in distributed ObjectGrid environment. This mechanism ensures that the client near cache is synchronized with servers or other clients. However, even with this JMS-based client invalidation mechanism, the client near cache does not immediately update. A delay occurs when the ObjectGrid runtime publishes updates.
Two models are available for client invalidation mechanism in a distributed ObjectGrid environment:
- Client-server model: In this model, all server processes are in a publisher role that publishes all the transaction changes to the designated JMS destination. All client processes are in receiver roles and receive all transactional changes from the designated JMS destination.
- Client as dual roles model: In this model, all server processes have nothing to do with the JMS destination. All client processes are both JMS publisher and receiver roles. Transactional changes that occur on the client are published to the JMS destination and all the clients receive these transactional changes.
For detailed information regarding enabling client invalidation mechanism, see Class JMSObjectGridEventListener in the ObjectGrid API documentation
Client-server model
In client-server model, the servers are in a JMS publilsher role and the client is in JMS receiver role.
<?xml version="1.0" encoding="UTF-8"?>
<?xml version="1.0" encoding="UTF-8"?>
<objectGridConfig xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://ibm.com/ws/objectgrid/config ../objectGrid.xsd"
xmlns="http://ibm.com/ws/objectgrid/config">
<objectGrids>
<objectGrid name="AgentObjectGrid">
<bean id="ObjectGridEventListener"
className="com.ibm.websphere.objectgrid.plugins.builtins.JMSObjectGridEventListener">
<property name="invalidationModel" type="java.lang.String" value="CLIENT_SERVER_MODEL" description="" />
<property name="invalidationStrategy" type="java.lang.String" value="PUSH" description="" />
<property name="mapsToPublish" type="java.lang.String" value="agent;profile;pessimisticMap" description="" />
<property name="jms_topicConnectionFactoryJndiName" type="java.lang.String" value="defaultTCF" description="" />
<property name="jms_topicJndiName" type="java.lang.String" value="defaultTopic" description="" />
<property name="jms_topicName" type="java.lang.String" value="defaultTopic" description="" />
<property name="jms_userid" type="java.lang.String" value="" description="" />
<property name="jms_password" type="java.lang.String" value="" description="" />
<property name="jndi_properties" type="java.lang.String"
value="java.naming.factory.initial=org.apache.activemq.jndi.ActiveMQInitialContextFactory;java.naming.provider.url=tcp://localhost:61616;connectionFactoryNames=defaultTCF;topic.defaultTopic=defaultTopic"
description="jndi properties" />
</bean>
<backingMap name="agent" readOnly="false" pluginCollectionRef="agent" preloadMode="false"
lockStrategy="OPTIMISTIC" copyMode="COPY_ON_READ_AND_COMMIT" ttlEvictorType="LAST_ACCESS_TIME"
timeToLive="28800" />
<backingMap name="profile" readOnly="false" pluginCollectionRef="profile" preloadMode="false"
lockStrategy="OPTIMISTIC" copyMode="COPY_ON_READ_AND_COMMIT" ttlEvictorType="LAST_ACCESS_TIME"
timeToLive="2700" />
<backingMap name="pessimisticMap" readOnly="false" pluginCollectionRef="pessimisticMap" preloadMode="false"
lockStrategy="PESSIMISTIC" copyMode="COPY_ON_READ_AND_COMMIT" ttlEvictorType="LAST_ACCESS_TIME"
timeToLive="2700" />
<backingMap name="excludedMap1" readOnly="false" pluginCollectionRef="excludedMap1" preloadMode="false"
lockStrategy="OPTIMISTIC" copyMode="COPY_ON_READ_AND_COMMIT" ttlEvictorType="LAST_ACCESS_TIME"
timeToLive="2700" />
<backingMap name="excludedMap2" readOnly="false" pluginCollectionRef="excludedMap2" preloadMode="false"
lockStrategy="OPTIMISTIC" copyMode="COPY_ON_READ_AND_COMMIT" ttlEvictorType="LAST_ACCESS_TIME"
timeToLive="2700" />
</objectGrid>
</objectGrids>
<backingMapPluginCollections>
<backingMapPluginCollection id="agent">
<bean id="ObjectTransformer" className="com.ibm.ws.objectgrid.test.scenario.AgentObjectTransformer" />
</backingMapPluginCollection>
<backingMapPluginCollection id="profile">
<bean id="ObjectTransformer" className="com.ibm.ws.objectgrid.test.scenario.ProfileObjectTransformer" />
<bean id="Evictor" className="com.ibm.websphere.objectgrid.plugins.builtins.LRUEvictor">
<property name="maxSize" type="int" value="2000" description="set max size for LRU evictor" />
<property name="sleepTime" type="int" value="15" description="evictor thread sleep time" />
<property name="numberOfLRUQueues" type="int" value="50" description="set number of LRU queues" />
</bean>
</backingMapPluginCollection>
<backingMapPluginCollection id="pessimisticMap" />
<backingMapPluginCollection id="excludedMap1" />
<backingMapPluginCollection id="excludedMap2" />
</backingMapPluginCollections>
</objectGridConfig>
Client as dual roles model
In client as dual roles model, each client has both JMS publisher and receiver roles. The client publishes every commited transactional change to designated JMS destination and receives all the committed transactional changes from other clients. The server has nothing to do with JMS in this model.
<?xml version="1.0" encoding="UTF-8"?>
<objectGridConfig xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://ibm.com/ws/objectgrid/config ../objectGrid.xsd"
xmlns="http://ibm.com/ws/objectgrid/config">
<objectGrids>
<objectGrid name="AgentObjectGrid">
<bean id="ObjectGridEventListener"
className="com.ibm.websphere.objectgrid.plugins.builtins.JMSObjectGridEventListener">
<property name="invalidationModel" type="java.lang.String" value="CLIENT_AS_DUAL_ROLES_MODEL" description="" />
<property name="invalidationStrategy" type="java.lang.String" value="PUSH" description="" />
<property name="mapsToPublish" type="java.lang.String" value="agent;profile;pessimisticMap" description="" />
<property name="jms_topicConnectionFactoryJndiName" type="java.lang.String" value="defaultTCF" description="" />
<property name="jms_topicJndiName" type="java.lang.String" value="defaultTopic" description="" />
<property name="jms_topicName" type="java.lang.String" value="defaultTopic" description="" />
<property name="jms_userid" type="java.lang.String" value="" description="" />
<property name="jms_password" type="java.lang.String" value="" description="" />
<property name="jndi_properties" type="java.lang.String"
value="java.naming.factory.initial=org.apache.activemq.jndi.ActiveMQInitialContextFactory;java.naming.provider.url=tcp://localhost:61616;connectionFactoryNames=defaultTCF;topic.defaultTopic=defaultTopic"
description="jndi properties" />
</bean>
<backingMap name="agent" readOnly="false" pluginCollectionRef="agent" preloadMode="false"
lockStrategy="OPTIMISTIC" copyMode="COPY_ON_READ_AND_COMMIT" ttlEvictorType="LAST_ACCESS_TIME"
timeToLive="28800" />
<backingMap name="profile" readOnly="false" pluginCollectionRef="profile" preloadMode="false"
lockStrategy="OPTIMISTIC" copyMode="COPY_ON_READ_AND_COMMIT" ttlEvictorType="LAST_ACCESS_TIME"
timeToLive="2700" />
<backingMap name="pessimisticMap" readOnly="false" pluginCollectionRef="pessimisticMap" preloadMode="false"
lockStrategy="PESSIMISTIC" copyMode="COPY_ON_READ_AND_COMMIT" ttlEvictorType="LAST_ACCESS_TIME"
timeToLive="2700" />
<backingMap name="excludedMap1" readOnly="false" pluginCollectionRef="excludedMap1" preloadMode="false"
lockStrategy="OPTIMISTIC" copyMode="COPY_ON_READ_AND_COMMIT" ttlEvictorType="LAST_ACCESS_TIME"
timeToLive="2700" />
<backingMap name="excludedMap2" readOnly="false" pluginCollectionRef="excludedMap2" preloadMode="false"
lockStrategy="OPTIMISTIC" copyMode="COPY_ON_READ_AND_COMMIT" ttlEvictorType="LAST_ACCESS_TIME"
timeToLive="2700" />
</objectGrid>
</objectGrids>
<backingMapPluginCollections>
<backingMapPluginCollection id="agent">
<bean id="ObjectTransformer" className="com.ibm.ws.objectgrid.test.scenario.AgentObjectTransformer" />
</backingMapPluginCollection>
<backingMapPluginCollection id="profile">
<bean id="ObjectTransformer" className="com.ibm.ws.objectgrid.test.scenario.ProfileObjectTransformer" />
<bean id="Evictor" className="com.ibm.websphere.objectgrid.plugins.builtins.LRUEvictor">
<property name="maxSize" type="int" value="2000" description="set max size for LRU evictor" />
<property name="sleepTime" type="int" value="15" description="evictor thread sleep time" />
<property name="numberOfLRUQueues" type="int" value="50" description="set number of LRU queues" />
</bean>
</backingMapPluginCollection>
<backingMapPluginCollection id="pessimisticMap" />
<backingMapPluginCollection id="excludedMap1" />
<backingMapPluginCollection id="excludedMap2" />
</backingMapPluginCollections>
</objectGridConfig>
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