AUTONOMOUS_TRANSACTION Pragma

The AUTONOMOUS_TRANSACTION pragma instructs the PL/SQL compiler to mark a routine as autonomous (independent). An autonomous transaction is an independent transaction started by another transaction, the main transaction. Autonomous transactions let you suspend the main transaction, do SQL operations, commit or roll back those operations, then resume the main transaction. For more information, see "Doing Independent Units of Work with Autonomous Transactions".

Syntax

Text description of the illustration autonomous_transaction_pragma.gif

Keyword and Parameter Description

PRAGMA

This keyword signifies that the statement is a pragma (compiler directive). Pragmas are processed at compile time, not at run time. They do not affect the meaning of a program; they simply convey information to the compiler.

Usage Notes

In this context, the term routine includes

• Top-level (not nested) anonymous PL/SQL blocks
• Local, standalone, and packaged functions and procedures
• Methods of a SQL object type
• Database triggers

You cannot use the pragma to mark all subprograms in a package (or all methods in an object type) as autonomous. Only individual routines can be marked autonomous. You can code the pragma anywhere in the declarative section of a routine. But, for readability, code the pragma at the top of the section.

Once started, an autonomous transaction is fully independent. It shares no locks, resources, or commit-dependencies with the main transaction. So, you can log events, increment retry counters, and so on, even if the main transaction rolls back.

Unlike regular triggers, autonomous triggers can contain transaction control statements such as COMMIT and ROLLBACK. Also, unlike regular triggers, autonomous triggers can execute DDL statements (such as CREATE and DROP) using native dynamic SQL.

Changes made by an autonomous transaction become visible to other transactions when the autonomous transaction commits. The changes also become visible to the main transaction when it resumes, but only if its isolation level is set to READ COMMITTED (the default).

If you set the isolation level of the main transaction to SERIALIZABLE, as follows, changes made by its autonomous transactions are not visible to the main transaction when it resumes:

When in the main transaction, rolling back to a savepoint marked before you started an autonomous transaction does not roll back the autonomous transaction. Remember, autonomous transactions are fully independent of the main transaction.

If an autonomous transaction attempts to access a resource held by the main transaction (which cannot resume until the autonomous routine exits), a deadlock can occur. In that case, Oracle raises an exception in the autonomous transaction, which is rolled back if the exception goes unhandled.

If you try to exit an active autonomous transaction without committing or rolling back, Oracle raises an exception. If the exception goes unhandled, the transaction is rolled back.

Examples

In the following example, you mark a packaged function as autonomous:

CREATE PACKAGE banking AS
   ...
   FUNCTION balance (acct_id INTEGER) RETURN REAL;
END banking;

CREATE PACKAGE BODY banking AS
   ...
   FUNCTION balance (acct_id INTEGER) RETURN REAL IS
      PRAGMA AUTONOMOUS_TRANSACTION;
      my_bal REAL;
   BEGIN
      ...
   END;
END banking;

In the example below, you mark a database trigger as autonomous. Unlike regular triggers, autonomous triggers can contain transaction control statements.

CREATE TRIGGER parts_trigger
BEFORE INSERT ON parts FOR EACH ROW
DECLARE
   PRAGMA AUTONOMOUS_TRANSACTION;
BEGIN
   INSERT INTO parts_log VALUES(:new.pnum, :new.pname);
   COMMIT;  -- allowed only in autonomous triggers
END;

Related Topics

EXCEPTION_INIT Pragma, RESTRICT_REFERENCES Pragma, SERIALLY_REUSABLE Pragma