Stateful Session Bean Failover

Stateful session beans (SFSBs) contain client-specific state. There is a one-to-one relationship between clients and the stateful session beans. At creation, the EJB container gives each SFSB a unique session ID that binds it to a client.

An SFSB’s state can be saved in a persistent store in case a server instance fails. The state of an SFSB is saved to the persistent store at predefined points in its life cycle. This is called

checkpointing. If enabled, checkpointing generally occurs after the bean completes any transaction, even if the transaction rolls back.

However, if an SFSB participates in a bean-managed transaction, the transaction might be committed in the middle of the execution of a bean method. Since the bean’s state might be undergoing transition as a result of the method invocation, this is not an appropriate time to checkpoint the bean’s state. In this case, the EJB container checkpoints the bean’s state at the end of the corresponding method, provided the bean is not in the scope of another transaction when that method ends. If a bean-managed transaction spans across multiple methods, checkpointing is delayed until there is no active transaction at the end of a subsequent method.

The state of an SFSB is not necessarily transactional and might be significantly modified as a result of non-transactional business methods. If this is the case for an SFSB, you can specify a list of checkpointed methods, as described in Specifying Methods to Be Checkpointed

If a distributable web application references an SFSB, and the web application’s session fails over, the EJB reference is also failed over.

If an SFSB that uses session persistence is undeployed while the GlassFish Server instance is stopped, the session data in the persistence store might not be cleared. To prevent this, undeploy the SFSB while the GlassFish Server instance is running.

Configuring Availability for the EJB Container

To enable availability for the EJB container use the asadmin set command to set the following three properties for the configuration:

• availability-service.ejb-container-availability.availability-enabled

• availability-service.ejb-container-availability.sfsb-persistence-type

• availability-service.ejb-container-availability.sfsb-ha-persistence-type

For example, if config1 is the configuration name, use the following commands:

asadmin> set --user admin --passwordfile password.txt
--host localhost
--port 4849
config1.availability-service.
ejb-container-availability.availability-enabled="true"

asadmin> set --user admin --passwordfile password.txt --host localhost --port
4849
config1.availability-service.
ejb-container-availability.sfsb-persistence-type="file"
asadmin> set --user admin --passwordfile password.txt
--host localhost
--port 4849
config1.availability-service.
ejb-container-availability.sfsb-ha-persistence-type="replicated"

Configuring the SFSB Session Store When Availability Is Disabled

If availability is disabled, the local file system is used for SFSB state passivation, but not persistence. To change where the SFSB state is stored, change the Session Store Location setting in the EJB container. For information about configuring store properties, see the Administration Console online help.

Configuring Availability for an Individual Application or EJB Module

You can enable SFSB availability for an individual application or EJB module during deployment:

• If you are deploying with the Administration Console, check the Availability Enabled checkbox.

• If you are deploying using use the asadmin deploy or asadmin deploydir commands, set the --availabilityenabled option to true. For more information, see deploy(1) and deploydir(1).

Configuring Availability for an Individual Bean

To enable availability and select methods to be checkpointed for an individual SFSB, use the glassfish-ejb-jar.xml deployment descriptor file.

To enable high availability session persistence, set availability-enabled="true" in the ejb element.

Example 10-1 Example of an EJB Deployment Descriptor With Availability Enabled

<glassfish-ejb-jar>
    ...
    <enterprise-beans>
        ...
        <ejb availability-enabled="true">
            <ejb-name>MySFSB</ejb-name>
        </ejb>
        ...
    </enterprise-beans>
</glassfish-ejb-jar>

Specifying Methods to Be Checkpointed

If enabled, checkpointing generally occurs after the bean completes any transaction, even if the transaction rolls back. To specify additional optional checkpointing of SFSBs at the end of non-transactional business methods that cause important modifications to the bean’s state, use the checkpoint-at-end-of-method element in the ejb element of the glassfish-ejb-jar.xml deployment descriptor file.

The non-transactional methods in the checkpoint-at-end-of-method element can be:

• create() methods defined in the home interface of the SFSB, if you want to checkpoint the initial state of the SFSB immediately after creation

• For SFSBs using container managed transactions only, methods in the remote interface of the bean marked with the transaction attribute TX_NOT_SUPPORTED or TX_NEVER

• For SFSBs using bean managed transactions only, methods in which a bean managed transaction is neither started nor committed

  Any other methods mentioned in this list are ignored. At the end of invocation of each of these methods, the EJB container saves the state of the SFSB to persistent store.

Example 10-2 Example of EJB Deployment Descriptor Specifying Methods Checkpointing

<glassfish-ejb-jar>
    ...
    <enterprise-beans>
        ...
        <ejb availability-enabled="true">
            <ejb-name>ShoppingCartEJB</ejb-name>
            <checkpoint-at-end-of-method>
                <method>
                    <method-name>addToCart</method-name>
                </method>
            </checkpoint-at-end-of-method>
        </ejb>
        ...
    </enterprise-beans>
</glassfish-ejb-jar>