What Is Two-Phase Commit?

Two-phase commit is a distributed protocol where a coordinator first asks every participant to prepare and vote on whether it can commit, then in a second phase tells them all to commit or all to abort based on the votes. It guarantees that the participants reach the same outcome. The trade-off is that participants must hold locks while waiting, and a coordinator failure can leave them blocked.

Why it matters

Two-phase commit provides atomicity across separate databases or services, but its blocking nature and coordinator dependency make it heavy. Many systems prefer sagas or eventual consistency to avoid that cost.

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