Explain what a hash function is and how it is used to transform data.

Autonomous transactions are transactions that are executed independently of the main transaction in which they were called. They allow operations to be performed that do not depend on the success or rollback of the external transaction.

For example, in Oracle PL/SQL, an autonomous transaction can be used for logging or auditing, even if the main transaction is rolled back.

Data exchange between a regular and an autonomous transaction is limited, as the autonomous transaction operates in a separate context. It does not see uncommitted changes of the main transaction and vice versa. Data is usually transferred using parameters or temporary tables, but it is important to remember that changes in an autonomous transaction are committed independently.

Example in PL/SQL:

DECLARE
  PRAGMA AUTONOMOUS_TRANSACTION;
BEGIN
  INSERT INTO audit_log VALUES ('Log entry');
  COMMIT; -- mandatory commit inside the autonomous transaction
END;

Thus, autonomous transactions are useful for isolating operations that need to be committed independently of the main transaction's outcome.