Two-Phase Commit

What Does Two-Phase Commit Mean?

A two-phase commit is a standardized protocol that ensures that a database commit is implementing in the situation where a commit operation must be broken into two separate parts.


In database management, saving data changes is known as a commit and undoing changes is known as a rollback. Both can be achieved easily using transaction logging when a single server is involved, but when the data is spread across geographically-diverse servers in distributed computing (i.e., each server being an independent entity with separate log records), the process can become more tricky.

Techopedia Explains Two-Phase Commit

A special object, known as a coordinator, is required in a distributed transaction. As its name implies, the coordinator arranges activities and synchronization between distributed servers. The two-phase commit is implemented as follows:

Phase 1 – Each server that needs to commit data writes its data records to the log. If a server is unsuccessful, it responds with a failure message. If successful, the server replies with an OK message.

Phase 2 – This phase begins after all participants respond OK. Then, the coordinator sends a signal to each server with commit instructions. After committing, each writes the commit as part of its log record for reference and sends the coordinator a message that its commit has been successfully implemented. If a server fails, the coordinator sends instructions to all servers to roll back the transaction. After the servers roll back, each sends feedback that this has been completed.


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Margaret Rouse
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Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.