Support for transactions is provided by the transaction service within WebSphere® Application Server. The way that applications use transactions depends on the type of application component.
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, during the processing of an SQL COMMIT statement, the database manager atomically commits multiple SQL statements to a relational database. 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, an external transaction manager is required to coordinate the individual resource managers. A transaction that spans multiple resource managers is referred to as a global transaction. WebSphere Application Server is a transaction manager that can coordinate global transactions, can be a participant in a received global transaction, and can also provide an environment in which resource manager local transactions can run.
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 or Web Service Atomic Transaction (WS-AtomicTransaction) protocol. WebSphere Application Server also participates in transactions imported through Java™ EE Connector 1.5 resource adapters. You can also configure WebSphere applications to interact with databases, JMS queues, and JCA connectors through their local transaction support, when you do not require distributed transaction coordination.
In addition to supporting the coordination of XAResource-based resource managers, WebSphere Application Server for z/OS® supports the coordination of resource managers through RRS (z/OS resource recovery services). RRS-compliant resource managers include DB2®, WebSphere MQ, IMS™, and CICS®. IBM® WebSphere Application Server for z/OS can coordinate a mix of RRSTransactional resource managers and XA capable resource managers under the same global transaction.
Resource managers that offer transaction support can be categorized into those that support two-phase coordination (by offering an XAResource interface or by supporting RRS) 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.
You can use transaction classes to classify client workload for workload management. The workload is different WebSphere transactions targeted to separate servant regions, each with goals defined by appropriate service classes. Each transaction is dispatched in its own WLM enclave in a servant region process, and is managed according to the goals of its service class. The server controller, which workload management views as a queue manager, uses the enclave associated with a client request to manage the priority of the work. If the work has a high priority, workload management can direct the work to a high-priority servant in the server. If the work has a low priority, workload management can direct the work to a low-priority servant. The effect is to partition the work according to priority within the same server.