Failures in communications, operating systems, or resource or transaction managers can interrupt the two-phase commit process. The point at which the failure occurs determines whether a transaction's changes are ultimately committed or backed out. If the failure occurs during the first phase in the process, changes are backed out. If the failure occurs during the second phase, changes are committed.
Recovery from failure during a two-phase commit involves a process called resynchronization, in which messages are exchanged between a coordinator and a participant in order to complete the transaction. To facilitate resynchronization, both the coordinator and the participant write additional journal records at critical points during the two-phase commit process.
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