Database Two Phase Commit

Since the 1980s, two phase commit technology has been used to automatically control and monitor commit and/or rollback activities for transactions in a distributed database system. Two phase commit technology is used when data updates need to occur simultaneously at multiple databases within a distributed system. Two phase commits are done to maintain data integrity and accuracy within the distributed databases through synchronized locking of all pieces of a transaction.

Two phase commit is a proven solution when data integrity in a distributed system is a requirement. Two phase commit technology is mostly used for hotel and airline reservations, stock market transactions, banking applications, and credit card systems.

Applying two phase commit protocols ensures that execution of data transactions are synchronized, either all committed or all rolled back (not committed) to each of the distributed databases.

When dealing with distributed databases, such as in the client/server architecture, distributed transactions need to be coordinated throughout the network to ensure data integrity for the users. Distributed databases using the two phase commit technique update all participating databases simultaneously.

Two phase commit has two distinct processes that are accomplished in less than a fraction of a second:

1. The Prepare Phase, where the global coordinator (initiating database) requests that all participants (distributed databases) will promise to commit or rollback the transaction. (Note: Any database could serve as the global coordinator, depending on the transaction.)
2. The Commit Phase, where all participants respond to the coordinator that they are prepared, then the coordinator asks all nodes to commit the transaction. If all participants cannot prepare or there is a system component failure, the coordinator asks all databases to roll back the transaction.