Handling Transactions

By default, all new Connection objects are in autocommit mode. When autocommit mode is on, a COMMIT statement is automatically executed after each statement that is sent to the database server. To turn autocommit mode off, explicitly call Connection.setAutoCommit(false).

When autocommit mode is off, IBM Informix JDBC Driver implicitly starts a new transaction when the next statement is sent to the database server. This transaction lasts until the user issues a COMMIT or ROLLBACK statement. If the user has already started a transaction by executing setAutoCommit(false) and then calls setAutoCommit(false) again, the existing transaction continues unchanged. The Java program must explicitly terminate the transaction by issuing either a COMMIT or a ROLLBACK statement before it drops the connection to the database or the database server.

If the Java program sets autocommit mode on during a transaction, IBM Informix JDBC Driver commits the current transaction if the JDK is version 1.4 and later, otherwise the driver rolls back the current transaction before turning on autocommit.

In a database that has been created with logging, if a COMMIT statement is sent to the database server and autocommit mode is on, the error -255: Not in transaction is returned by the database server because there is currently no user transaction started. This occurs whether the COMMIT statement was sent with the Connection.commit() method or directly with an SQL statement.

In a database created in ANSI mode, explicitly sending a COMMIT statement to the database server commits an empty transaction. No error is returned because the database server automatically starts a transaction before it executes the statement if there is no user transaction currently open.

For an XAConnection object, autocommit mode is off by default and must remain off while a distributed transaction is occurring. The transaction manager performs commit and rollback operations; therefore, you should avoid performing these operations directly.