Sun Microsystems 3 manual Monitoring and Managing Two-Phase Commit

Monitoring and Managing Two-Phase Commit

Because of this two-phase commit capability, an iIS engine transaction and an application transaction can be combined into a higher level distributed transaction. The constituent transactions are placed in a PREPARE phase before either can commit. If either of the constituent transactions cannot be placed in a PREPARE phase, then the other is rolled back to its original state. In other words, the distributed transaction only commits if both constituent transactions commit, guaranteeing that application state and process state are synchronized.

The iIS two-phase commit protocol also facilitates synchronization between different activities—or sessions—in a given process instance. For example, if Client Application A (session A) has already prepared an AbortProcess for the process instance, and Client Application B (session B) tries to complete or abort an activity belonging to that process instance, an exception is raised on session B indicating that session A is going to abort the same process instance.

The iIS two-phase commit protocol makes it possible to include the following iIS engine operations in a transactional context:

•creating a process

•aborting a process

•starting an activity

•completing an activity

•aborting an activity

When included in a transactional context, these operations are automatically placed in a PREPARE phase before being explicitly committed or rolled back. For example, any StartActivity or CompleteActivity operation would be automatically placed in a PREPARE phase.

By being placed in a transactional context, these iIS transactions can be synchronized, as described above, with application update transactions. The client application simply prepares any application (database update) operations it needs to make. If the application transaction can be successfully placed in a PREPARE phase, then the client application can commit both the application transaction and the iIS engine transaction. If the application transaction cannot be successfully placed in a PREPARE phase, then the client application should roll back the iIS engine transaction.

All iIS objects associated with a prepared transaction are unavailable for further operations until the client application explicitly commits or rolls back the transaction.

Chapter 6 Managing Process Execution 201