begin(7)
NAME
BEGIN - start a transaction block
SYNOPSIS
BEGIN [ WORK | TRANSACTION ] [ transaction_mode [, ...] ]
where transaction_mode is one of:
ISOLATION LEVEL { SERIALIZABLE | REPEATABLE READ | READ COMMITTED | READ UNCOMMITTED }
READ WRITE | READ ONLY
DESCRIPTION
BEGIN initiates a transaction block, that is, all statements after a
BEGIN command will be executed in a single transaction until an
explicit COMMIT [commit(7)] or ROLLBACK [rollback(l)] is given. By
default (without BEGIN), PostgreSQL executes transactions in ``autocommit'' 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).
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.
If the isolation level or read/write mode is specified, the new transaction has those characteristics, as if SET TRANSACTION [set_transaction(7)] was executed.
PARAMETERS
WORK
- TRANSACTION
- Optional key words. They have no effect.
- Refer to SET TRANSACTION [set_transaction(7)] for information on the meaning of the other parameters to this statement.
NOTES
START TRANSACTION [start_transaction(7)] has the same functionality as
BEGIN.
Use COMMIT [commit(7)] or ROLLBACK [rollback(7)] to terminate a transaction block.
Issuing BEGIN 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 SAVEPOINT
[savepoint(7)]).
For reasons of backwards compatibility, the commas between successive
transaction_modes may be omitted.
EXAMPLES
To begin a transaction block:
BEGIN;
COMPATIBILITY
BEGIN is a PostgreSQL language extension. It is equivalent to the SQLstandard command START TRANSACTION [start_transaction(7)], which see
for additional compatibility information.
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.
SEE ALSO
- COMMIT [commit(7)], ROLLBACK [rollback(l)], START TRANSACTION [start_transaction(l)], SAVEPOINT [savepoint(l)]