Local transaction containment considerations


 

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IBM WAS supports local transaction containment (LTC), which we can configure using local transaction extended deployment descriptors. This page describes the advantages that this support provides to application programmers, and the relevant settings to use. It also lists points to consider when deciding the best way to configure transaction support for local transactions.

The following sections describe the advantages that LTC support provides, and how to set the local transaction extended deployment descriptors in each situation.

We can develop an enterprise bean or servlet that accesses one or more databases that are independent and require no coordination.

If an enterprise bean does not have to use global transactions, it is often more efficient to deploy the bean with the deployment descriptor for the container transaction type set to NotSupported instead of Required.

With the extended local transaction support of the appserver, applications can perform the same business logic in an unspecific transaction context as they can in a global transaction. An enterprise bean, for example, runs in an unspecified transaction context if it is deployed with a container transaction type of NotSupported or Never.

The extended local transaction support provides a container-managed, implicit local transaction boundary, within which the container commits application updates and cleans up their connections. We can design applications with more independence from deployment concerns. This makes using a container transaction type of Supports much simpler, for example, when the business logic might be called either with or without a global transaction context.

An application can follow a get-use-close pattern of connection usage, regardless of whether the application runs in a transaction. The application can depend on the close action behaving in the same way in all situations, that is, the close action does not cause a rollback to occur on the connection if there is no global transaction.

There are many scenarios where ACID coordination of multiple resource managers is not needed. In such scenarios, running business logic in a Transaction policy of NotSupported performs better than in a policy of Required. This benefit is applied through setting the deployment descriptor, in the Local Transactions section, of the Resolver attribute to ContainerAtBoundary. With this setting, application interactions with resource providers, such as databases, are managed within implicit resource manager local transactions (RMLT) that the container both starts and ends. The container commits RMLTs at the containment boundary specified by the Boundary attribute in the Local Transactions section; for example, at the end of a method. If the application returns control to the container by an exception, the container rolls back any RMLTs that it has started.

This usage applies to both servlets and enterprise beans.

Use local transactions in a managed environment that guarantees cleanup.

Applications that want to control RMLTs, by starting and ending them explicitly, can use the default setting of Application for the Resolver extended deployment descriptor in the Local Transactions section. In this situation, the container ensures connection cleanup at the boundary of the local transaction context.

Java platform for enterprise apps specifications that describe application use of local transactions do so in the manner provided by the default settings of Application for the Resolver extended deployment descriptor, and Rollback for the Unresolved action extended deployment descriptor, in the Local Transactions section. When the Unresolved action extended deployment descriptor in the Local Transactions section is set to Commit, the container commits any RMLTs that the application starts but that do not complete when the local transaction containment ends (for example, when the method ends). This usage applies to both servlets and enterprise beans.

We can extend the duration of a local transaction beyond the duration of an EJB component method.

The EJB specifications restrict the use of RMLTs to single EJB methods. This restriction is because the specifications have no scoping device, beyond a container-imposed method boundary, to which an RMLT can be extended. Use the Boundary extended deployment setting in the Local Transactions section to give the following advantages:

  • Significantly extend the use cases of RMLTs.

  • Make conversational interactions with one-phase resource managers possible through ActivitySession support.

Use an ActivitySession to provide a distributed context with a boundary that is longer than a single method. We can extend the use of RMLTs over the longer ActivitySession boundary, which a client can control. The ActivitySession boundary reduces the need to use distributed transactions where ACID operations on multiple resources are not needed. This benefit is applied through the Boundary extended deployment setting, in the Local transactions section, of ActivitySession. Such extended RMLTs can remain under the control of the application, or be managed by the container, depending on the setting of the Resolver deployment descriptor in the Local Transactions section.

We can coordinate multiple one-phase resource managers.

For resource managers that do not support XA transaction coordination, a client can use ActivitySession-bounded local transaction contexts. Such contexts give a client the same ability to control the completion direction of the resource updates by the resource managers as the client has for transactional resource managers. A client can start an ActivitySession and call its entity beans in that context. Those beans can perform their RMLTs within the scope of that ActivitySession and return without completing the RMLTs. The client can later complete the ActivitySession in a commit or rollback direction and cause the container to drive the ActivitySession-bounded RMLTs in that coordinated direction.

Use shareable LTCs to reduce the number of connections you require.

Application components can share LTCs. If components obtain connections to the same resource manager, they can share that connection if they run under the same global transaction or shareable LTC. To configure two components to run under the same shareable LTC, set the Shareable attribute of the Local Transactions section in the deployment descriptor of each component. Make sure that the resource reference in the deployment descriptor for each component uses the default value of Shareable for the res-sharing-scope element, if this element is specified. A shareable LTC can reduce the numbers of RMLTs an application uses. For example, an application that makes frequent use of Web module include calls can share resource manager connections between those Web modules, exploiting either shareable LTCs, or a global transaction, reducing lock contention for resources.

 

Examples of local transaction support configurations

The following list gives scenarios that use local transactions, and points to consider when deciding the best way to configure the transaction support for an application.




 

Related concepts

Local transaction containment (LTC)
Local and global transaction considerations
Transaction support in WAS

 

Related tasks

Use component-managed transactions
Use one-phase and two-phase commit resources in the same transaction
Use the ActivitySession service
Set transactional deployment attributes