How Transactions Guard Your Database
The transaction is a sequence of SQL data manipulation statements which does a logical unit of work. The Oracle treats the sequence of SQL statements as a unit so that all the changes brought about by the statements are either committed (made permanent) or rolled back (undone) at similar time. If your program fails in the center of a transaction, then the database is automatically restored to its previous state.
The first SQL statements in your program begin a transaction. Whenever a transaction ends, the next SQL statement automatically begins the other transaction. And hence, every SQL statement is part of the transaction. The distributed transaction involves at least one SQL statement which updates the data at multiple nodes in a distributed database.
The COMMIT and ROLLBACK statements assures that all the database changes brought about by the SQL operations are either made permanent or undone at similar time. All the SQL statements executed as the last commit or rollback make up the present transaction. The SAVEPOINT statement names and marks the present point in the processing of a transaction.