PostgreSQL supports a two-phase commit (2PC) protocol that allows multiple distributed systems to work together in a transactional manner. The commands are
COMMIT PREPARED and
ROLLBACK PREPARED. Two-phase transactions are intended for use by external transaction management systems. PostgreSQL follows the features and model proposed by the X/Open XA standard, but does not implement some less often used aspects.
When the user executes
PREPARE TRANSACTION, the only possible next commands are
COMMIT PREPARED or
ROLLBACK PREPARED. In general, this prepared state is intended to be of very short duration, but external availability issues might mean transactions stay in this state for an extended interval. Short-lived prepared transactions are stored only in shared memory and WAL. Transactions that span checkpoints are recorded in the
pg_twophase directory. Transactions that are currently prepared can be inspected using
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