Local and global transaction considerations
Applications use resources, such as JDBC data sources or connection factories, that are configured through the Resources view of the WAS Administrative Console. How these resources participate in a global transaction depends on the underlying transaction support of the resource provider.
For example, most JDBC providers can provide either XA or non-XA versions of a data source. A non-XA data source can support only resource manager local transactions (RMLTs), but an XA data source can support two-phase commit coordination, as well as local transactions.
If an application uses two or more resource providers that support only RMLTs, then atomicity cannot be assured because of the one-phase nature of these resources. To ensure atomic behavior, the application should use resources that support XA coordination and should access them within a global transaction.
If an application uses only one RMLT, the atomic behavior can be guaranteed by the resource manager, which can be accessed under a LTC context.
An application can also access a single resource manager under a global transaction context, even if that resource manager does not support the XA coordination. An application can do this, because WAS performs an "only resource optimization" and interacts with the resource manager under a RMLT. Within a global transaction context, any attempt to use more than one resource provider that supports only RMLTs causes the global transaction to be rolled back.
At any moment, an instance of an enterprise bean can have work outstanding in either a global transaction context or a LTC context, but never both. An instance of an enterprise bean can change from running under one type of context to the other (in either direction), if all outstanding work in the original context is complete. Any violation of this principle causes an exception to be thrown when the enterprise bean tries to start the new context.