SYS> create user u1 identified by u1;

User created.

Elapsed: 00:00:00.30
SYS> grant create session,create job to u1;

Grant succeeded.

Elapsed: 00:00:00.03
SYS> begin
  for i in 1..200 loop
    execute immediate 'create role testrole'||i;
    execute immediate 'grant testrole'||i||' to u1';
  end loop;
end;
/


PL/SQL procedure successfully completed.

Elapsed: 00:01:01.70
11:35:06 SYS> alter user u1 default role none;

User altered.

Elapsed: 00:00:00.03
SYS> conn u1/u1
Connected.
U1> exec dbms_scheduler.create_job(job_name=>'u1.testjob', job_type=>'PLSQL_BLOCK', job_action=>'null;', repeat_interval=>'FREQ=minutely; INTERVAL=1');

PL/SQL procedure successfully completed.

Elapsed: 00:00:00.05

--пользователь может включить джоб
U1> exec dbms_scheduler.enable('u1.testjob');

PL/SQL procedure successfully completed.

Elapsed: 00:00:00.04
U1> exec dbms_scheduler.disable('u1.testjob');

PL/SQL procedure successfully completed.

Elapsed: 00:00:00.02
U1> conn / as sysdba
Connected.

--а вот SYS не может
SYS> exec dbms_scheduler.enable('u1.testjob');
BEGIN dbms_scheduler.enable('u1.testjob'); END;

*
ERROR at line 1:
ORA-28031: maximum of  enabled roles exceeded
ORA-06512: at "SYS.DBMS_ISCHED", line 4790
ORA-06512: at "SYS.DBMS_SCHEDULER", line 3020
ORA-06512: at line 1