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

Introduction
HP NonStop SQL/MX Reference Manual—523725-004
1-19
Transaction Access Modes
Transaction Access Modes
A transaction has an access mode that is either READ ONLY or READ WRITE. You
can set the access mode of a transaction by using a SET TRANSACTION statement.
See SET TRANSACTION Statement on page 2-223.
READ ONLY
If a transaction is executing with the READ ONLY access mode, statements within the
transaction can read, but cannot insert, delete, or update, data in tables. This
restriction means that among the DML statements, only the SELECT statement can
execute within that transaction.
If the transaction isolation level is READ UNCOMMITTED, the default access mode is
READ ONLY. Further, for READ UNCOMMITTED, you can specify only READ ONLY
explicitly by using the SET TRANSACTION statement.
READ WRITE
If a transaction is executing with the READ WRITE access mode, statements within the
transaction can read, insert, delete, or update data in tables. Therefore, any DML
statement can execute within that transaction.
If the transaction isolation level is not READ UNCOMMITTED, the default access
mode is READ WRITE. However, you can specify READ ONLY explicitly by using the
SET TRANSACTION statement.
Utilities that update
data and potentially
change metadata:
FIXUP
DUP (target table only)
IMPORT using fast
load
MODIFY when
dropping a hash
partition
PURGEDATA
RESTORE
Not allowed. Concurrent
operations are not
allowed.
Not allowed.
* There are some exceptions. Dropping a partition from a hash partitioned table or index requires exclusive
access.
** The last phase of these operations requires exclusive access to the table or index, which prevents even
SELECT operations.
*** The last phase of the MODIFY operation requires exclusive access to the table or index, which prevents all
DDL and DML operations.
Table 1-5. Concurrency Limits on Utility Operations (page 2 of 2)
Utility DML operations Other utilities
DDL
operations