SQL/MX Programming Manual for Java

SQL/MX Programming Considerations
HP NonStop SQL/MX Programming Manual for Java—523726-003
4-44
Setting Attributes for Transactions
•
Calling the setAutoCommit() method of the java.sql.Connection interface:
For an implicit connection context:
java.sql.Connection conn =
DefaultContext.getDefaultContext().getConnection();
conn.setAutoCommit(false);
For an explicit connection context named ctx:
ctx.getConnection().setAutoCommit(false);
For information about setAutoCommit(), see the JDBC Driver for SQL/MX
Programmer’s Reference. For information about implicit and explicit connection
contexts, see Connection Contexts on page 3-8.
Isolation Level Setting
The isolation level specifies the level of data consistency defined for the transaction
and the degree of concurrency the transaction has with other transactions that use the
same data. The isolation level of a transaction can be READ UNCOMMITTED, READ
COMMITTED, or SERIALIZABLE (or REPEATABLE READ). For more information, see
the SQL/MX Reference Manual.
In an SQLJ program, avoid using the SET TRANSACTION ISOLATION LEVEL
statement because:
•
It always starts a compiler process.
•
It could cause automatic recompilation.
•
It could adversely affect UPDATE, INSERT, and DELETE statements in
subsequent transactions.
The SET TRANSACTION ISOLATION LEVEL statement, regardless of whether it was
statically compiled, always executes dynamically and applies its setting at run time.
Therefore, this statement always starts a compiler process. To avoid performance
costs, use a CONTROL QUERY DEFAULT ISOLATION_LEVEL statement instead. For
more information about coding CONTROL statements, see CONTROL Statements on
page 4-6.
The SET TRANSACTION ISOLATION LEVEL statement could cause automatic
recompilation of DML statements in the next transaction. If a DML statement is
statically compiled and does not specify an explicit access option (for example, READ
COMMITTED, SERIALIZABLE, and so on), its access option at compile time is
determined by the ISOLATION_LEVEL setting, if present, or by the system-defined
isolation level, which is READ COMMITTED. If SQL/MX executes the DML statement
after executing a SET TRANSACTION ISOLATION LEVEL statement with a different
isolation level setting, the SQL/MX executor automatically recompiles the DML
statement. To avoid automatic recompilation, specify explicit access options in
individual DML statements. The access options in DML statements override the