COMMIT PREPARED(7) PostgreSQL 9.2.7 Documentation COMMIT PREPARED(7)NAME
COMMIT_PREPARED - commit a transaction that was earlier prepared for two-phase commit
SYNOPSIS
COMMIT PREPARED transaction_id
DESCRIPTION
COMMIT PREPARED commits a transaction that is in prepared state.
PARAMETERS
transaction_id
The transaction identifier of the transaction that is to be committed.
NOTES
To commit a prepared transaction, you must be either the same user that executed the transaction originally, or a superuser. But you do not
have to be in the same session that executed the transaction.
This command cannot be executed inside a transaction block. The prepared transaction is committed immediately.
All currently available prepared transactions are listed in the pg_prepared_xacts system view.
EXAMPLES
Commit the transaction identified by the transaction identifier foobar:
COMMIT PREPARED 'foobar';
COMPATIBILITY
COMMIT PREPARED is a PostgreSQL extension. It is intended for use by external transaction management systems, some of which are covered by
standards (such as X/Open XA), but the SQL side of those systems is not standardized.
SEE ALSO
PREPARE TRANSACTION (PREPARE_TRANSACTION(7)), ROLLBACK PREPARED (ROLLBACK_PREPARED(7))
PostgreSQL 9.2.7 2014-02-17 COMMIT PREPARED(7)
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PREPARE TRANSACTION(7) PostgreSQL 9.2.7 Documentation PREPARE TRANSACTION(7)NAME
PREPARE_TRANSACTION - prepare the current transaction for two-phase commit
SYNOPSIS
PREPARE TRANSACTION transaction_id
DESCRIPTION
PREPARE TRANSACTION prepares the current transaction for two-phase commit. After this command, the transaction is no longer associated with
the current session; instead, its state is fully stored on disk, and there is a very high probability that it can be committed
successfully, even if a database crash occurs before the commit is requested.
Once prepared, a transaction can later be committed or rolled back with COMMIT PREPARED (COMMIT_PREPARED(7)) or ROLLBACK PREPARED
(ROLLBACK_PREPARED(7)), respectively. Those commands can be issued from any session, not only the one that executed the original
transaction.
From the point of view of the issuing session, PREPARE TRANSACTION is not unlike a ROLLBACK command: after executing it, there is no active
current transaction, and the effects of the prepared transaction are no longer visible. (The effects will become visible again if the
transaction is committed.)
If the PREPARE TRANSACTION command fails for any reason, it becomes a ROLLBACK: the current transaction is canceled.
PARAMETERS
transaction_id
An arbitrary identifier that later identifies this transaction for COMMIT PREPARED or ROLLBACK PREPARED. The identifier must be written
as a string literal, and must be less than 200 bytes long. It must not be the same as the identifier used for any currently prepared
transaction.
NOTES
PREPARE TRANSACTION is not intended for use in applications or interactive sessions. Its purpose is to allow an external transaction
manager to perform atomic global transactions across multiple databases or other transactional resources. Unless you're writing a
transaction manager, you probably shouldn't be using PREPARE TRANSACTION.
This command must be used inside a transaction block. Use BEGIN(7) to start one.
It is not currently allowed to PREPARE a transaction that has executed any operations involving temporary tables, created any cursors WITH
HOLD, or executed LISTEN or UNLISTEN. Those features are too tightly tied to the current session to be useful in a transaction to be
prepared.
If the transaction modified any run-time parameters with SET (without the LOCAL option), those effects persist after PREPARE TRANSACTION,
and will not be affected by any later COMMIT PREPARED or ROLLBACK PREPARED. Thus, in this one respect PREPARE TRANSACTION acts more like
COMMIT than ROLLBACK.
All currently available prepared transactions are listed in the pg_prepared_xacts system view.
Caution
It is unwise to leave transactions in the prepared state for a long time. This will interfere with the ability of VACUUM to reclaim
storage, and in extreme cases could cause the database to shut down to prevent transaction ID wraparound (see Section 23.1.5,
"Preventing Transaction ID Wraparound Failures", in the documentation). Keep in mind also that the transaction continues to hold
whatever locks it held. The intended usage of the feature is that a prepared transaction will normally be committed or rolled back as
soon as an external transaction manager has verified that other databases are also prepared to commit.
If you have not set up an external transaction manager to track prepared transactions and ensure they get closed out promptly, it is
best to keep the prepared-transaction feature disabled by setting max_prepared_transactions to zero. This will prevent accidental
creation of prepared transactions that might then be forgotten and eventually cause problems.
EXAMPLES
Prepare the current transaction for two-phase commit, using foobar as the transaction identifier:
PREPARE TRANSACTION 'foobar';
COMPATIBILITY
PREPARE TRANSACTION is a PostgreSQL extension. It is intended for use by external transaction management systems, some of which are covered
by standards (such as X/Open XA), but the SQL side of those systems is not standardized.
SEE ALSO
COMMIT PREPARED (COMMIT_PREPARED(7)), ROLLBACK PREPARED (ROLLBACK_PREPARED(7))
PostgreSQL 9.2.7 2014-02-17 PREPARE TRANSACTION(7)