The application programmer's model of transactions is simple: applications either succeed or fail. The application begins a transaction by getting a transaction object. All subsequent work by that application is associated with that transaction object.
When the program reaches a consistent state, it calls the Commit transaction method. If the commit succeeds, the transaction is durably committed. If the commit fails, the transaction is aborted. If the program finds that it cannot complete the transaction, it may call the Abort transaction method to undo the transaction's effects. This is a simple way to clean up complex failure cases.
If the application fails before it calls Commit, the transaction manager will abort the transaction and tell each enlisted resource manager to undo the transaction's effects. If a computer or resource manager fails, the transaction will also be aborted. Once the transaction has successfully committed, the resource managers and the transaction manager will ensure that the transaction's effects are durable, even if there are subsequent failures.
The following figure shows the three possible outcomes of a transaction.
