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Example of a Global Transaction
An e-retailer uses a service called CUST_ORDER. When a customer places an order through the company's Web site, the CUST_ORDER service performs two operations:
The company wants to be sure that the CUST_ORDER service adheres to the principle of atomicity: whenever CUST_ORDER is executed, both the database update and the enqueueing of the customer request on the shipping department queue must be completed successfully. To make sure that the CUST_ORDER service always handles customer orders with atomicity, the client that invokes CUST_ORDER associates its request with a global transaction.
To associate a service with a global transaction, a client:
As part of a global transaction, the operation is performed as a single unit of work. When the CUST_ORDER service is invoked, the server is propagated with the client's transaction. The two resulting operations, accessing the order database and enqueuing the order to the shipping queue, become part of the client's transaction.
If either operation fails for any reason, whether due to a system error or an application error, the work of the transaction is undone or rolled back. In other words, the transaction is returned to its initial state.
If both operations succeed, however, the client commits the transaction. In other words, it formally signals that the effects of the transaction should be made permanent: the order database is updated permanently and the order sent to the shipping department is kept in that department's queue.
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