Distributed transaction

A distributed transaction is a database transaction in which two or more network hosts are involved. Usually, hosts provide transactional resources, while a transaction manager creates and manages a global transaction that encompasses all operations against such resources. Distributed transactions, as any other transactions, must have all four ACID (atomicity, consistency, isolation, durability) properties, where atomicity guarantees all-or-nothing outcomes for the unit of work (operations bundle).

The Open Group, a vendor consortium, proposed the X/Open Distributed Transaction Processing Model (X/Open XA), which became a de facto standard for the behavior of transaction model components.

Databases are common transactional resources and, often, transactions span a couple of such databases. In this case, a distributed transaction can be seen as a

strong strict two phase locking (SS2PL) for concurrency control

, which ensures global serializability, if all the participating databases employ it.

A common

two-phase commit (2PC). This algorithm is usually applied for updates able to commit

in a short period of time, ranging from couple of milliseconds to couple of minutes.

There are also long-lived distributed transactions, for example a transaction to book a trip, which consists of booking a flight, a rental car and a hotel. Since booking the flight might take up to a day to get a confirmation, two-phase commit is not applicable here, it will lock the resources for this long. In this case more sophisticated techniques that involve multiple undo levels are used. The way you can undo the hotel booking by calling a desk and cancelling the reservation, a system can be designed to undo certain operations (unless they are irreversibly finished).

In practice, long-lived distributed transactions are implemented in systems based on

web services. Usually these transactions utilize principles of compensating transactions, Optimism and Isolation Without Locking. The X/Open standard does not cover long-lived distributed transactions.^{[citation needed}

]

Several technologies, including

Jakarta Enterprise Beans and Microsoft Transaction Server

fully support distributed transaction standards.

References

"Web-Services Transactions". Archived from the original on May 11, 2008. Retrieved May 2, 2005.
"Nuts And Bolts Of Transaction Processing". Article about Transaction Management. Archived from the original on July 13, 2018. Retrieved May 3, 2005.
"A Detailed Comparison of Enterprise JavaBeans (EJB) & The Microsoft Transaction Server (MTS) Models".

Distributed transaction

See also

References

Further reading