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RedHat 9 (Linux i386) - man page for set_transaction (redhat section 7)

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SET TRANSACTION(7)			   SQL Commands 		       SET TRANSACTION(7)

NAME
       SET TRANSACTION - set the characteristics of the current transaction

SYNOPSIS
       SET TRANSACTION ISOLATION LEVEL { READ COMMITTED | SERIALIZABLE }
       SET SESSION CHARACTERISTICS AS TRANSACTION ISOLATION LEVEL
	   { READ COMMITTED | SERIALIZABLE }

DESCRIPTION
       This  command  sets  the transaction isolation level. The SET TRANSACTION command sets the
       characteristics for the current SQL-transaction. It has no effect on any subsequent trans-
       actions.  This command cannot be used after the first query or data-modification statement
       (SELECT, INSERT, DELETE, UPDATE, FETCH, COPY) of a transaction has been executed. SET SES-
       SION CHARACTERISTICS sets the default transaction isolation level for each transaction for
       a session. SET TRANSACTION can override it for an individual transaction.

       The isolation level of a transaction determines what data the  transaction  can	see  when
       other transactions are running concurrently.

       READ COMMITTED
	      A statement can only see rows committed before it began. This is the default.

       SERIALIZABLE
	      The current transaction can only see rows committed before first query or data-mod-
	      ification statement was executed in this transaction.

	      Tip: Intuitively, serializable means that two concurrent	transactions  will  leave
	      the  database  in the same state as if the two has been executed strictly after one
	      another in either order.

NOTES
       The session default transaction isolation level can also be set with the command

       SET default_transaction_isolation = 'value'

       and in the configuration file. Consult the Administrator's Guide for more information.

COMPATIBILITY
   SQL92, SQL99
       SERIALIZABLE is the default level in SQL. PostgreSQL does not provide the isolation levels
       READ  UNCOMMITTED  and  REPEATABLE  READ. Because of multiversion concurrency control, the
       SERIALIZABLE level is not truly serializable. See the User's Guide for details.

       In SQL there are two other transaction characteristics that can be  set	with  these  com-
       mands: whether the transaction is read-only and the size of the diagnostics area.  Neither
       of these concepts are supported in PostgreSQL.

SQL - Language Statements		    2000-11-24			       SET TRANSACTION(7)
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