SQL/MX 2.x Reference Manual (H06.04+)

Metadata Tables
HP NonStop SQL/MX Reference Manual—540440-003
10-45
Isolation Level
For more information about histogram statistics, see the SQL/MX Query Guide.
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 2-218.
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.
HIST_SECURITY_WARNINGS Controls whether MXCMP displays a warning if the user
does not have access permissions to statistics tables and
the user table's estimated rowcount is greater than the
HIST_ROWCOUNT_REQUIRING_STATS value.
If set to ON, the compiler reports this warning.
If set to OFF, the compiler does not report a warning.
The default is ON.
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 1-21.
Attribute Setting