12.6 Transaction Isolation Level

In addition to grouping statements, you can use transactions to preserve the integrity of data in a database. Transactions can lock data to prevent concurrent access or modification. The isolation level of a transaction determines how locks are set. Usually, the default isolation level that the driver uses is sufficient and should not be altered.

The custom attribute jdbc:isolation-level allows you to adjust the isolation transaction level if necessary. The java.sql.Connection parameter defines five possible values in the interface. See java.sql.Connection.

The driver’s default transaction isolation level is read committed unless overridden by a descriptor file. In manual transactions, place the jdbc:isolation-level attribute on the first element in the transaction. This attribute is ignored on subsequent elements. In the following example. the attribute is in bold text.

<input xmlns:jdbc="urn:dirxml:jdbc">
    <add class-name="usr" jdbc:transaction-id="0"
                          jdbc:isolation-level="serializable">
        <add-attr name="lname">
            <value>Doe</value>
        </add-attr>
    </add>
    <jdbc:statement jdbc:transaction-type="manual"
                    jdbc:transaction-id="0">
        <jdbc:sql>UPDATE indirect.usr SET fname = 'John'
                  WHERE idu = {$idu}</jdbc:sql>
    </jdbc:statement>
</input>

This XML resolves to:

SET AUTOCOMMIT OFF
SET TRANSACTION ISOLATION LEVEL SERIALIZABLE
INSERT INTO indirect.usr(lname) VALUES('Doe');
UPDATE indirect.usr SET fname = 'John' WHERE idu = 1;
COMMIT; -- explicit commit