web server - Borland Technical Publications

Transaction manager services
EJBs and 2PC transactions
With the introduction of messaging in the J2EE platform, a number of common
scenarios now exist involving access to multiple resources from EJBs in a single
transaction. As we know, when more than one resource is involved in a transaction, the
OTS engine is needed to reliably complete the transaction using the two-phase commit
protocol. Sample scenarios include:
■
■
A session bean accesses two types of entity beans in a transaction where each are
persisted in a different database.
A session bean accesses an entity bean and in the same transaction does some
messaging work, such as sending a message to a JMS queue.
■
In the onMessage method of a message-driven bean, access entity beans on
message delivery.
In each of the above examples, two heterogeneous resources need to be accessed
from within a session bean or a message-driven bean as part of a single transaction.
These EJBs have the REQUIRED transaction attribute defined and need access to the
OTS engine. However, if the OTS engine is running, then all modules deployed to that
Partition are able to discover it and can attempt to use it. The OTS engine will perform
a one-phase commit when only one resource is registered in a transaction, but suffers
the extra RMI overhead since it is an external process. Ideally, the in-process
Transaction Manager should be used for EJBs not involved in a two-phase commit
transaction. To better utilize the transaction services available in BES, a bean-level
property, ejb.transactionManagerInstanceName may be specified for EJBs that require
2PC transaction completion. This property provides the name of the OTS engine to be
used by the EJB container doing transaction demarcation on any of the methods for the
relevant bean. Both the Transaction Manager and the OTS engine may be available for
all EJBs but only those that do not have ejb.transactionManagerInstanceName specified
will discover the Transaction Manager.
This property can be commonly used for session or message-driven beans since
transactions are usually demarcated in a session bean facade or the onMessage method
of a message-driven bean.
To set the ejb.transactionManagerInstanceName property use the Management Console.
Navigate to your deployed EJB module, right-click on it and select “DDEditor”. In the
DDEditor select the required bean from the Navigation Pane. Select the “Properties”
tab and add the ejb.transactionManagerInstanceName property. Define the property as a
String and specify a unique name value such as “MyTwoPhaseEngine”.
Next, you must modify the OTS engine factory name with the
ejb.transactionManagerInstanceName value. In the Management Console, select the
OTS engine from the “corbaSample” configuration, identified as the “OTS engine”
managed object type. Right-click and select “Properties” from the drop-down menu. In
the Properties dialog choose the Settings tab and modify the value for “Factory Name”.
Click OK, and restart the service. The OTS engine may also be started from the
command line, independent of a BES server. The factory name can be provided using
property vbroker.ots.name as follows:
prompt> ots -Dvbroker.ots.name=
The EJB will now use the OTS engine named “MyTwoPhaseEngine”. As mentioned,
the Partition may be hosting several J2EE modules, but only those beans that have
ejb.transactionManagerInstanceName set go to the (non-default) OTS engine. Other
beans in the Partition that require method invocation in a transaction, but do not require
2PC, always find the Transaction Manager due to local service affinity.
Chapter 19: Transaction management 171