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'\" t .\" Title: BEGIN .\" Author: The PostgreSQL Global Development Group .\" Generator: DocBook XSL Stylesheets v1.76.1 <http://docbook.sf.net/> .\" Date: 2014 .\" Manual: PostgreSQL 9.3.5 Documentation .\" Source: PostgreSQL 9.3.5 .\" Language: English .\" .TH "BEGIN" "7" "2014" "PostgreSQL 9.3.5" "PostgreSQL 9.3.5 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" BEGIN \- start a transaction block .\" BEGIN .SH "SYNOPSIS" .sp .nf BEGIN [ WORK | TRANSACTION ] [ \fItransaction_mode\fR [, \&.\&.\&.] ] where \fItransaction_mode\fR is one of: ISOLATION LEVEL { SERIALIZABLE | REPEATABLE READ | READ COMMITTED | READ UNCOMMITTED } READ WRITE | READ ONLY [ NOT ] DEFERRABLE .fi .SH "DESCRIPTION" .PP \fBBEGIN\fR initiates a transaction block, that is, all statements after a \fBBEGIN\fR command will be executed in a single transaction until an explicit \fBCOMMIT\fR(7) or \fBROLLBACK\fR(7) is given\&. By default (without \fBBEGIN\fR), PostgreSQL executes transactions in \(lqautocommit\(rq mode, that is, each statement is executed in its own transaction and a commit is implicitly performed at the end of the statement (if execution was successful, otherwise a rollback is done)\&. .PP Statements are executed more quickly in a transaction block, because transaction start/commit requires significant CPU and disk activity\&. Execution of multiple statements inside a transaction is also useful to ensure consistency when making several related changes: other sessions will be unable to see the intermediate states wherein not all the related updates have been done\&. .PP If the isolation level, read/write mode, or deferrable mode is specified, the new transaction has those characteristics, as if SET TRANSACTION (\fBSET_TRANSACTION\fR(7)) was executed\&. .SH "PARAMETERS" .PP WORK, TRANSACTION .RS 4 Optional key words\&. They have no effect\&. .RE .PP Refer to SET TRANSACTION (\fBSET_TRANSACTION\fR(7)) for information on the meaning of the other parameters to this statement\&. .SH "NOTES" .PP START TRANSACTION (\fBSTART_TRANSACTION\fR(7)) has the same functionality as \fBBEGIN\fR\&. .PP Use \fBCOMMIT\fR(7) or \fBROLLBACK\fR(7) to terminate a transaction block\&. .PP Issuing \fBBEGIN\fR when already inside a transaction block will provoke a warning message\&. The state of the transaction is not affected\&. To nest transactions within a transaction block, use savepoints (see \fBSAVEPOINT\fR(7))\&. .PP For reasons of backwards compatibility, the commas between successive \fItransaction_modes\fR can be omitted\&. .SH "EXAMPLES" .PP To begin a transaction block: .sp .if n \{\ .RS 4 .\} .nf BEGIN; .fi .if n \{\ .RE .\} .SH "COMPATIBILITY" .PP \fBBEGIN\fR is a PostgreSQL language extension\&. It is equivalent to the SQL\-standard command START TRANSACTION (\fBSTART_TRANSACTION\fR(7)), whose reference page contains additional compatibility information\&. .PP The DEFERRABLE \fItransaction_mode\fR is a PostgreSQL language extension\&. .PP Incidentally, the BEGIN key word is used for a different purpose in embedded SQL\&. You are advised to be careful about the transaction semantics when porting database applications\&. .SH "SEE ALSO" \fBCOMMIT\fR(7), \fBROLLBACK\fR(7), START TRANSACTION (\fBSTART_TRANSACTION\fR(7)), \fBSAVEPOINT\fR(7)