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

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 trans- action 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 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 serial- izable. See the User's Guide for details. In SQL there are two other transaction characteristics that can be set with these commands: whether the trans- action is read-only and the size of the diagnostics area. Neither of these concepts are supported in Post- greSQL. SQL - Language Statements 2000-11-24 SET TRANSACTION(7)


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