# PREPARE_TRANSACTION(7) - man - phpMan

PREPARE [TRANSACTION(7)](https://www.chedong.com/phpMan.php/man/TRANSACTION/7/markdown)             PostgreSQL 14.23 Documentation             PREPARE [TRANSACTION(7)](https://www.chedong.com/phpMan.php/man/TRANSACTION/7/markdown)



## 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** or
       **ROLLBACK** **PREPARED**, 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** to start one.

       It is not currently allowed to **PREPARE** a transaction that has executed any operations
       involving temporary tables or the session's temporary namespace, created any cursors WITH
       HOLD, or executed **LISTEN**, **UNLISTEN**, or **NOTIFY**. 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 25.1.5). 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)](https://www.chedong.com/phpMan.php/man/PREPARED/7/markdown)), ROLLBACK PREPARED (**ROLLBACK**___**[PREPARED**(7)](https://www.chedong.com/phpMan.php/man/PREPARED/7/markdown))



PostgreSQL 14.23                                2026                          PREPARE [TRANSACTION(7)](https://www.chedong.com/phpMan.php/man/TRANSACTION/7/markdown)