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+'\" t
+.\"     Title: PREPARE TRANSACTION
+.\"    Author: The PostgreSQL Global Development Group
+.\" Generator: DocBook XSL Stylesheets vsnapshot <http://docbook.sf.net/>
+.\"      Date: 2023
+.\"    Manual: PostgreSQL 15.5 Documentation
+.\"    Source: PostgreSQL 15.5
+.\"  Language: English
+.\"
+.TH "PREPARE TRANSACTION" "7" "2023" "PostgreSQL 15.5" "PostgreSQL 15.5 Documentation"
+.\" -----------------------------------------------------------------
+.\" * Define some portability stuff
+.\" -----------------------------------------------------------------
+.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+.\" http://bugs.debian.org/507673
+.\" http://lists.gnu.org/archive/html/groff/2009-02/msg00013.html
+.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+.ie \n(.g .ds Aq \(aq
+.el       .ds Aq '
+.\" -----------------------------------------------------------------
+.\" * set default formatting
+.\" -----------------------------------------------------------------
+.\" disable hyphenation
+.nh
+.\" disable justification (adjust text to left margin only)
+.ad l
+.\" -----------------------------------------------------------------
+.\" * MAIN CONTENT STARTS HERE *
+.\" -----------------------------------------------------------------
+.SH "NAME"
+PREPARE_TRANSACTION \- prepare the current transaction for two\-phase commit
+.SH "SYNOPSIS"
+.sp
+.nf
+PREPARE TRANSACTION \fItransaction_id\fR
+.fi
+.SH "DESCRIPTION"
+.PP
+\fBPREPARE TRANSACTION\fR
+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\&.
+.PP
+Once prepared, a transaction can later be committed or rolled back with
+\fBCOMMIT PREPARED\fR
+or
+\fBROLLBACK PREPARED\fR, respectively\&. Those commands can be issued from any session, not only the one that executed the original transaction\&.
+.PP
+From the point of view of the issuing session,
+\fBPREPARE TRANSACTION\fR
+is not unlike a
+\fBROLLBACK\fR
+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\&.)
+.PP
+If the
+\fBPREPARE TRANSACTION\fR
+command fails for any reason, it becomes a
+\fBROLLBACK\fR: the current transaction is canceled\&.
+.SH "PARAMETERS"
+.PP
+\fItransaction_id\fR
+.RS 4
+An arbitrary identifier that later identifies this transaction for
+\fBCOMMIT PREPARED\fR
+or
+\fBROLLBACK PREPARED\fR\&. 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\&.
+.RE
+.SH "NOTES"
+.PP
+\fBPREPARE TRANSACTION\fR
+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\*(Aqre writing a transaction manager, you probably shouldn\*(Aqt be using
+\fBPREPARE TRANSACTION\fR\&.
+.PP
+This command must be used inside a transaction block\&. Use
+\fBBEGIN\fR
+to start one\&.
+.PP
+It is not currently allowed to
+\fBPREPARE\fR
+a transaction that has executed any operations involving temporary tables or the session\*(Aqs temporary namespace, created any cursors
+WITH HOLD, or executed
+\fBLISTEN\fR,
+\fBUNLISTEN\fR, or
+\fBNOTIFY\fR\&. Those features are too tightly tied to the current session to be useful in a transaction to be prepared\&.
+.PP
+If the transaction modified any run\-time parameters with
+\fBSET\fR
+(without the
+LOCAL
+option), those effects persist after
+\fBPREPARE TRANSACTION\fR, and will not be affected by any later
+\fBCOMMIT PREPARED\fR
+or
+\fBROLLBACK PREPARED\fR\&. Thus, in this one respect
+\fBPREPARE TRANSACTION\fR
+acts more like
+\fBCOMMIT\fR
+than
+\fBROLLBACK\fR\&.
+.PP
+All currently available prepared transactions are listed in the
+pg_prepared_xacts
+system view\&.
+.if n \{\
+.sp
+.\}
+.RS 4
+.it 1 an-trap
+.nr an-no-space-flag 1
+.nr an-break-flag 1
+.br
+.ps +1
+\fBCaution\fR
+.ps -1
+.br
+.PP
+It is unwise to leave transactions in the prepared state for a long time\&. This will interfere with the ability of
+\fBVACUUM\fR
+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\&.
+.PP
+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\&.
+.sp .5v
+.RE
+.SH "EXAMPLES"
+.PP
+Prepare the current transaction for two\-phase commit, using
+foobar
+as the transaction identifier:
+.sp
+.if n \{\
+.RS 4
+.\}
+.nf
+PREPARE TRANSACTION \*(Aqfoobar\*(Aq;
+.fi
+.if n \{\
+.RE
+.\}
+.SH "COMPATIBILITY"
+.PP
+\fBPREPARE TRANSACTION\fR
+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\&.
+.SH "SEE ALSO"
+COMMIT PREPARED (\fBCOMMIT_PREPARED\fR(7)), ROLLBACK PREPARED (\fBROLLBACK_PREPARED\fR(7))