What is the AUTONOMOUS_TRANSACTION pragma in Oracle PL/SQL?

PRAGMA's are simply directives (instructions) for the Oracle PL/SQL compiler. The pragma AUTONOMOUS_TRANSACTION instructs the compiler to treat the pl/sql block following the pragma as autonomous (independent) from the calling transaction. This means that any changes made to the database in the autonomous transaction are independent of the main transaction and are either committed or rolled back without affecting the main transaction.

Oracle pl/sql autonomous transactions must explicitly either roll back or commit any changes before exiting and can be:-

• stand alone procedures or functions
• procedures/functions defined in a package (but not nested)
• triggers
• or schema-level anonymous pl/sql blocks

Autonomous transactions are often used for logging errors in Oracle PL/SQL applications. By making the error logging procedure autonomous you ensure that the error message itself is logged in the error log table and is committed whilst the transaction that encountered the error is rolled back. Then when the application has fini9shed (or indeed whilst it's still running) error messages can be examined and corrective action potentially applied.

Let's look at a brief example.

First we declare an anonymous transaction

CREATE OR REPLACE PROCEDURE log_details
(msg IN VARCHAR2) IS
PRAGMA AUTONOMOUS_TRANSACTION
BEGIN

    INSERT INTO log(msg_id         ,log_msg,time_of_msg)
    VALUES         (log_seq.NEXTVAL,msg    ,SYSDATE);

    COMMIT; -- must commit or rollback

END;

Next, we have another transaction that calls this procedure.

BEGIN

    DELETE employees;
    log_msg('Deleting all employees');
    ROLLBACK;
    log_msg('after rollback of delete employees');

END;