JDBC Type 4 Driver Programmer's Reference for SQL/MX Release 3.2.1

• The Type 4 driver assumes that any SQL CONTROL statements in effect at the time of execution
or reuse are the same as those in effect at the time of SQL/MX compilation. If this condition
is not true, reuse of a PreparedStatement object might result in unexpected behavior.
• You should avoid SQL/MX recompilation to yield performance improvements from statement
pooling. The SQL/MX executor automatically recompiles queries when certain conditions are
met. Some of these conditions are:
◦ A run-time version of a table has a different redefinition timestamp than the compile-time
version of the same table.
◦ An existing open operation on a table was eliminated by a DDL or SQL utility operation.
◦ The transaction isolation level and access mode at execution time is different from that
at the compile time.
For more information on SQL/MX recompilation, see the HP NonStop SQL/MX Release 3.2.1
Programming Manual for C and COBOL or the SQL/MX Programming Manual for Java.
• When a query is recompiled, the SQL/MX executor stores the recompiled query; therefore,
the query is recompiled only once until any of the previous conditions are met again.
• The Type 4 driver pools CallableStatement objects in the same way as
PreparedStatement objects when the statement pooling is activated.
• The Type 4 driver does not cache Statement objects.
Thread-safe SQL/MX Access
In the Type 4 driver, API layer classes are implemented as instance-specific objects to ensure thread
safety:
• SQLMXDataSource.getConnection() is implemented as a synchronized method to
ensure thread safety in getting a connection.
• After a connection is made, the connection object is instance-specific.
• If multiple statements are run on different threads in a single connection, statement objects are
serialized to prevent data corruption.
"Update ... Where Current of" Operations
When performing an update ... where current of cursor SQL statement, the fetch size
on a ResultSet must be 1.
If the value of the fetch size is greater than 1, the result of the update ... where current of
operation might be one of the following:
• An incorrect row might be updated based on the actual cursor position.
• An SQLException might occur, because the cursor being updated might have already been
closed.
NOTE: By default, the fetch size is 1.
The following is an example of setting a result set fetch size to 1 and executing an update ...
where current of cursor SQL statement.
ResultSet rs;
... rs.setFetchSize(1);
String st1 = rs.getCursorName();
Statement stmt2 = connection.createStatement( ResultSet.TYPE_FORWARD_ONLY
, ResultSet.CONCUR_UPDATABLE );
stmt2.executeUpdate("UPDATE cat2.sch2.table1
set j = 'update row' WHERE CURRENT OF " + st1);
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