(1) A two-step process by which recoverable resources and an external subsystem are committed. During the first step, the database manager subsystems are polled to ensure that they are ready to commit. If all subsystems respond positively, the database manager instructs them to commit. See also distributed transaction.
(2) The process used by resource managers to coordinate changes in an atomic, consistent, isolated, and durable (ACID) transaction. In the first phase, all resource managers confirm that a transaction has been received and that it is possible to process it. In the second phase, the changes are committed if all the resource managers agreed to them. If any resource manager fails to confirm that it is able to process the transaction, then no databases are updated. Using the two-phase commit process, multiple changes across multiple resource managers can be treated as a single ACID transaction.