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 transactions. 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 SESSION 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-modification statement was executed in this  transac-
	      tion.

	      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 commands: 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)