SQL/MX 2.x Reference Manual (G06.24+, H06.03+)

Metadata Tables

HP NonStop SQL/MX Reference Manual—523725-004

10-44

Isolation Level

This attribute determines how NonStop SQL/MX assigns transaction isolation levels:

Transaction isolation levels are determined according to rules applied in this order:

1. If you specify an access option explicitly in a DML statement, the SQL/MX compiler

compiles the statement with the access option. This access option overrides the

isolation level of any containing transactions.

2. If there are no individual statement access options and you issue a SET

TRANSACTION ISOLATION LEVEL statement, the SQL/MX compiler uses the

setting determined by this SET TRANSACTION statement as the isolation level for

the next transaction. See SET TRANSACTION Statement on page 2-223.

3. If you do not specify a SET TRANSACTION statement and you issue a CONTROL

QUERY DEFAULT ISOLATION_LEVEL statement, the CONTROL QUERY

DEFAULT statement determines the isolation level.

4. If you do not issue a CONTROL QUERY DEFAULT ISOLATION_LEVEL

statement, NonStop SQL/MX uses the ISOLATION_LEVEL setting in the

SYSTEM_DEFAULTS table if it exists.

5. If you do not specify isolation-level settings, NonStop SQL/MX uses the system-

defined isolation level, which is READ COMMITTED.

Attribute Setting

ISOLATION_LEVEL The isolation level for a transaction. Set to:

READ UNCOMMITTED

READ COMMITTED

REPEATABLE READ

SERIALIZABLE

The default is READ COMMITTED. See Transaction Isolation

Levels on page 1-20.