Transaction support in WebSphere Application Server

This topic provides conceptual information about the support for transactions provided by the Transaction Service of WebSphere Application Server.

A transaction is unit of activity within which multiple updates to resources can be made atomic (as an indivisible unit of work) such that all or none of the updates are made permanent. For example, multiple SQL statements to a relational database are committed atomically by the database during the processing of an SQL COMMIT statement. In this case, the transaction is contained entirely within the database manager and can be thought of as a resource manager local transaction (RMLT) . In some contexts, a transaction is referred to as a logical unit of work (LUW). If a transaction involves multiple resource managers, for example multiple database managers, then an external transaction manager is required to coordinate the individual resource managers. A transaction that spans multiple resource managers are referred to as a global transaction . WebSphere Application Server is a transaction manager that can coordinate global transactions, be a participant in a received global transaction and also provides an environment in which resource manager local transactions can run. The way that applications use transactions depends on the type of application component, as follows:

• A session bean can either use container-managed transactions (where the bean delegates management of transactions to the container) or bean-managed transactions (component-managed transactions where the bean manages transactions itself).

• Entity beans use container-managed transactions.

• Web components (servlets) and application client components use component-managed transactions.

WebSphere Application Server is a transaction manager that supports the coordination of resource managers through their XAResource interface and participates in distributed global transactions with transaction managers that support the CORBA Object Transaction Service (OTS) protocol (for example, application servers) or Web Service Atomic Transaction (WS-AtomicTransaction) protocol. WebSphere Application Server also participates in transactions imported through J2EE Connector 1.5 resource adapters. WebSphere applications can also be configured to interact with (or to direct the WebSphere transaction service to interact with) databases, JMS queues, and JCA connectors through their local transaction support when distributed transaction coordination is not required.

Resource managers that offer transaction support can be categorized into those that support two-phase coordination (by offering an XAResource interface) and those that support only one-phase coordination (for example through a LocalTransaction interface). The WebSphere Application Server transaction support provides coordination, within a transaction, for any number of two-phase capable resource managers. It also enables a single one-phase capable resource manager to be used within a transaction in the absence of any other resource managers, although a WebSphere transaction is not necessary in this case. Under normal circumstances you cannot mix one-phase commit capable resources and two-phase commit capable resources in the same global transaction, because one-phase commit resources cannot support the prepare phase of two-phase commit. There are some special circumstances where it is possible to include mixed-capability resources in the same global transaction:

• In scenarios where there is only a single one-phase commit resource provider that participates in the transaction and where all the two-phase commit resource-providers that participate in the transaction are used in a read-only fashion. In this case, the two-phase commit resources all vote read-only during the prepare phase of two-phase commit. Because the one-phase commit resource provider is the only provider to actually perform any updates, the one-phase commit resource does not need to be prepared.

• In scenarios where there is only a single one-phase commit resource provider that participates in the transaction with one of more two-phase commit resource providers and where last participant support is enabled. Last participant support enables the use of a single one-phase commit capable resource with any number of two-phase commit capable resources in the same global transaction. For more information about last participant support, see Using one-phase and two-phase commit resources in the same transaction.

The ActivitySession service provides an alternative unit-of-work (UOW) scope to that provided by global transaction contexts. It is a distributed context that can be used to coordinate multiple one-phase resource managers. The WebSphere EJB container and deployment tooling support ActivitySessions as an extension to the J2EE programming model. EJBs can be deployed with lifecycles that are influenced by ActivitySession context, as an alternative to transaction context. An application can then interact with a resource manager for the period of a client-scoped ActivitySession, rather than only the duration of an EJB method, and have the resource manager's local transaction outcome directed by the ActivitySession. For more information about ActivitySessions, see Using the ActivitySession service.

Related concepts
Coordinating access to one-phase and two-phase commit resources within the same transaction
The ActivitySession service

Related information
The Java transaction service (JTS), http://java.sun.com/products/jts/
The Java transaction API (JTA), http://java.sun.com/products/jta/
Web Service Atomic Transactions (WS-AtomicTransactions)
J2EE Connector Architecture 1.5
CORBA Object Transaction Service (OTS)