XA overview

A global transaction is a recoverable unit of work performed by one or more resource managers in a distributed transaction processing environment, coordinated by an external transaction manager.

The resources that are updated by the transaction can take many forms, such as a database table, a messaging queue, or the resources updated by running a CICS® transaction. Each of these resources is managed by a resource manager. Where the recoverable resources updated by the global transaction are all managed by the same resource manager, a one-phase commit protocol is adequate to ensure that all resources are updated in an atomic manner.

However, where the resources updated by a global transaction are managed by multiple resource managers, a two-phase commit protocol is required. With this protocol the atomic nature of the transaction is maintained by ensuring that all resource managers update their resources in a consistent manner. The cicseci.rar supports the two-phase commit XA protocol and enables JEE applications to include CICS resources in such global transactions.

In both the one-phase commit and XA scenarios, a transaction manager is responsible for controlling the running of the transaction and for coordinating the resource managers to ensure that the transaction works in an atomic manner.

An example of where this behavior is required is an online flight booking, which uses one resource manager to debit a customer's bank account and another to reserve the customer a flight. The customer's account must be updated only if the flight is booked; and vice versa.

If a timeout occurs during an XA transaction it is recommended that the EJB sets the transaction to be rolled back.

For information on using XA transactions with JEE applications see Redpaper: Transactions in J2EE (REDP-3659-00).