Transactions

A transaction is a logical unit of work. To complete a logical unit of work, several actions may have to be taken against a database.

Transactional support allows applications to ensure the following:

• All the steps to complete a logical unit of work are followed.
• When one of the steps to the unit of work files fails, all the work done as part of that logical unit of work can be undone and the database can return to its previous state before the transaction began.

Transactions are used to provide data integrity, correct application semantics, and a consistent view of data during concurrent access. All Java™ Database Connectivity (JDBC) compliant drivers must support transactions.

All transactional work is handled at the Connection object level. When the work for a transaction completes, it can be finalized by calling the commit method. If the application aborts the transaction, the rollback method is called.

All Statement objects under a connection are a part of the transaction. This means is that if an application creates three Statement objects and uses each object to make changes to the database, when a commit or rollback call happens, the work for all three statements either becomes permanent or is discarded.

The commit and rollback SQL statements are used to finalize transactions when working purely with SQL. These SQL statements cannot be dynamically prepared and you should not attempt to use them in your JDBC applications to complete transactions.

• Auto-commit mode
  By default, JDBC uses an operation mode called auto-commit. This means that every update to the database is immediately made permanent.
• Transaction isolation levels
  Transaction isolation levels specify what data is visible to statements within a transaction. These levels directly impact the level of concurrent access by defining what interaction is possible between transactions against the same target data source.
• Savepoints
  Savepoints allow the setting of "staging points" in a transaction. Savepoints are checkpoints that the application can roll back to without throwing away the entire transaction. Savepoints are new in JDBC 3.0, meaning that the application must run on Java Development Kit (JDK) 1.4 or a subsequent release to use them. Moreover, savepoints are new to the Developer Kit for Java, meaning that savepoints are not supported if JDK 1.4 or a subsequent release is not used with previous releases of the Developer Kit for Java.