Why I don't need to COMMIT in database trigger?

We can't COMMIT/ROLLBACK in DML triggers because transaction is handled manually after DML statement. However, database triggers seems to be an exception. For example, suppose there's a database trigger:

SQL> CREATE TABLE log (timestamp DATE, operation VARCHAR2(2000));

Table created.

SQL>  CREATE TABLE  honnikery (col1 NUMBER);

Table created.

SQL> create or replace trigger honni_trig
  2      after insert on honnikery
  3      begin
  4      insert into log values(sysdate,'insert on tab1');
  5      commit;
  6      end;
  7  /

Trigger created.

SQL> INSERT INTO honnikery VALUES (1);
INSERT INTO honnikery VALUES (1)
            *
ERROR at line 1:
ORA-04092: cannot COMMIT in a trigger
ORA-06512: at "SCOTT.HONNI_TRIG", line 3
ORA-04088: error during execution of trigger 'SCOTT.HONNI_TRIG'


As workaround, one can use autonomous transactions. Autonomous transactions execute separate from the current transaction.


create or replace trigger honnikery_trig
    after insert on honnikery
declare
  PRAGMA AUTONOMOUS_TRANSACTION;
    begin
    insert into log values(sysdate,'insert on honnikery');
    commit;
    end;

Trigger created.

SQL> INSERT INTO honnikery VALUES (1);
1 row created.