redhat man page for start_transaction

START 
TRANSACTION(7)						   SQL Commands 					      START TRANSACTION(7)

NAME
       START TRANSACTION - start a transaction block

SYNOPSIS
       START TRANSACTION [ ISOLATION LEVEL { READ COMMITTED | SERIALIZABLE } ]

   INPUTS
       None.

   OUTPUTS
       START TRANSACTION
	      Message returned if successful.

       WARNING: BEGIN: already a transaction in progress
	      If there is already a transaction in progress when the command is issued.

DESCRIPTION
       This  command  begins  a  new  transaction. If the isolation level is specified, the new transaction has that isolation level. In all other
       respects, the behavior of this command is identical to the BEGIN [begin(7)] command.

NOTES
       The isolation level of a transaction can also be set with the SET TRANSACTION [set_transaction(7)] command. If no isolation level is speci-
       fied, the default isolation level is used.

COMPATIBILITY
   SQL99
       SERIALIZABLE  is  the  default isolation level in SQL99, but it is not the usual default in PostgreSQL: the factory default setting is READ
       COMMITTED.  PostgreSQL does not provide the isolation levels READ UNCOMMITTED and REPEATABLE READ. Because of lack  of  predicate  locking,
       the SERIALIZABLE level is not truly serializable. See the User's Guide for details.

       In  SQL99  this statement can specify two other properties of the new transaction: whether the transaction is read-only and the size of the
       diagnostics area. Neither of these concepts are currently supported in PostgreSQL.

SQL - Language Statements					    2002-07-26						      START TRANSACTION(7)