A database transaction comprises of the operations performed against the data in one or more databases. It is an atomic unit that contains one or more SQL statements which are executed as a whole for retrieving or updating data in the database. It may contain the operations such as SELECT, INSERT, UPDATE or DELETE singly or as a whole, or it may be an operation which alters the physical structure of the database. The outcome of the statements in the transaction may be any of the following
1. all committed – all saved permanently in database
2. all rolled back
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  • When one uses a COMMIT or ROLLBACK statement.
  • When executes a DDL statement ( like CREATE, ALTER, RENAME or DROP ). If the transaction involves any DML statement, Oracle commits the transaction first and then executes and commits the DDL statement as a single, new transaction.
  • When exits from Oracle database.
  • When a process terminates exceptionally.
    • If the transaction is completed successfully, it ends with COMMIT and the results will be permanently recorded in the database. Otherwise if it is a failed and terminated transaction, it ends with ROLLBACK to revert the transaction effects on the database.
    State of the data before COMMIT or ROLLBACK
  • The previous state of the data can be recovered.
  • The operations of the DML statements can be recovered by the current user using SELECT statement.
  • The results of the DML statements by the current user cannot be viewed by other users.
  • The data in the affected rows cannot be changed by other users since these rows are locked.
    • Commit Transactions
    This includes making the modifications which are executed by the statements in the transaction permanent.
    COMMIT ;
    State of the data after COMMIT
  • The locks on the affected rows are released.
  • It erases all savepoints

    • Rollback of Transactions
  • Undone the data changes.
  • Previous state of the data ( before transaction ) is restored.
  • The locks on the affected rows are released
    • Savepoints in Transactions
    These are intermediate markers in the transaction which divide the entire transaction into smaller units. Its application is in long transaction where we can mark the work at any intermediate point. So if we make an error in the midst of a complex transaction, we can rollback the operations performed after this declared savepoint and before the current point in the transaction.
    The savepoints can be declared using the statement
    SAVEPOINT name;

    Also the names of the savepoints within a single transaction must be distinct. Thus if a second savepoint with the same name as the earlier is created, the first savepoint will be erased. We can rollback to the savepoint by using the statement :
    ROLLBACK TO SAVEPOINT name;

    State of the data after ROLLBACK TO SAVEPOINT
  • Rolls back the statements that run after the specified savepoint.
  • Preserves the specified savepoint and all the savepoints declared before this point will be erased.
  • Releases the locks on the affected rows after this savepoint and retains the locks before this savepoint.