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What is Web Services Atomic Transaction for WebSphere Application Server (WS-AT for WAS)?
The WS-AT for WAS is a technology preview that provides transactional support for Web service application requests that are compliant with JSR 109 and made using SOAP/HTTP. It allows distributed Web Service applications, and the resources they use, to take part in distributed global transactions. A transaction is a set of operations that must be executed as a single unit, often called a logical unit of work. A transaction is either completed in its entirety or not at all; it is indivisible or "atomic."
This technology preview is an implementation of the Web Services Atomic Transaction (WS-AT) and the Web Service Coordination (WS-COOR) specifications, published in September 2003, on the WebSphere Application Server. This technology preview contains a sample application that demonstrates its use.
How does it work?
WS-AT for WAS uses the standard JTA support in the J2EE programming model to scope transactions. JTA transactions are interpreted by the WS-AT for WAS run-time environment into CoordinationContexts such that a WS-AT representation of the current JTA transaction is made to flow upon Web service application requests.
If WS-AT for WAS is the system hosting the target endpoint, it automatically establishes a JTA transaction in the target's run-time environment, which becomes the transactional context under which the target Web service application will run. When the Web service request enters the target server, WS-COOR is used to register for participation in the 2PC protocol. The 2PC protocol is driven by the caller's WS-AT Coordinator at completion of transaction.
No explicit registration of participants is required by the application developer. The WAS run-time environment takes responsibility for the registration of WS-AT participants, in the same way as it does the registration of XAResources in the JTA transaction to which the WS-AT transaction is federated. When the transaction is completed, all XAResources and WS-AT participants are atomically coordinated by the WAS Transaction Manager.
If a JTA transaction is active on the thread when a Web Service Application request is made, the transaction is propagated across on the SOAP/HTTP request and established in the target's environment. This is analogous to the distribution of transaction context over IIOP as described in the EJB specification. Any transactional work performed in the target environment becomes part of the same global transaction.
Note: This technical preview does not implement recoverability for WS-AT transactions in the event of a server failure. Therefore, it is recommended that when servers are shutdown, the WAS administrative console or the stopServer command line utility is used to perform a clean shutdown.
For further information, please read the document WSATInformation.doc included in the WSAT.zip file.
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