Web Services Atomic Transaction support in WAS
The Web Services Atomic Transaction support in WebSphere Application Server provides transactional quality of service to the Web services environment. This enables distributed Web service applications, and the resources they use, to take part in distributed global transactions.
The Web Services Atomic Transaction (WS-AT) support is an implementation of the following specifications on WAS. These specifications define a set of Web services that enable Web service applications to participate in global transactions distributed across the heterogeneous Web service environment.
- Web Services Atomic Transaction (WS-AT)
WS-AT is a specific coordination type that defines protocols for atomic transactions.
- Web Service Coordination (WS-COOR)
WS-COOR specifies a CoordinationContext and a Registration service with which Participant web services may enlist to take part in the protocols offered by specific coordination types.
The WS-AT support is an interoperability protocol that introduces no new programming interfaces for transactional support. Global transaction demarcation is provided by standard J2EE use of the JTA UserTransaction interface. If a Web service request is made by an application component running under a global transaction, then a WS-AT CoordinationContext is implicitly propagated to the target Web service, but only if the appropriate application deployment descriptors have been set.
If WAS is the system hosting the target endpoint for a Web service request that contains a WS-AT CoordinationContext, then WebSphere automatically establishes a subordinate JTA transaction in the target runtime environment that becomes the transactional context under which the target Web service application executes.
The following figure, Transaction context shared between two WebSphere appservers., shows a transaction context shared between two WebSphere appservers for a Web service request that contains a WS-AT CoordinationContext.
Figure 1. Transaction context shared between two WebSphere appservers.
WS-AT support restrictions
In this version of WAS, WS-AT contexts cannot be started from a non-recoverable client process.
Application design considerations
WS-AT is a two-phase commit transaction protocol and is suitable for short duration transactions only.
Because the purpose of an atomic transaction is to coordinate resource managers that isolate transactional updates by holding transactional locks on resources, it is generally not recommended that WS-AT transactions be distributed across enterprise domains. Inter-enterprise transactions typically require a looser semantic than two-phase commit and, in such scenarios, it can be more appropriate to use a compensating business transaction, for example a Web Services Business Activity or as part of a BPEL process.
WS-AT is most appropriate for distributing transaction context across Web services deployed within a single enterprise. Only request-response message exchange patterns carry transaction context since the originator (application or container) of a transaction needs to be sure that all business tasks executed under that transaction have finished before requesting the completion of a transaction. Web services invoked by a one-way request never run under the transaction of the requesting client.
Application development considerations
There are no specific development tasks required for Web service applications to take advantage of WS-AT. There are some application deployment descriptors that need to be set appropriately.
Application developers do not need to explicitly register WS-AT participants. The WAS runtime takes responsibility for the registration of WS-AT participants, in the same way as the registration of XAResources in the JTA transaction to which the WS-AT transaction is federated. At transaction completion time, all XAResources and WS-AT participants are atomically coordinated by the WebSphere Application Server transaction service.
If a JTA transaction is active on the thread when a Web service Application request is made, the transaction is propagated across on the Web service request and established in the target 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.
Related concepts
Support for Web Services protocols