SQL> create table my_table as
  2  select rownum id, lpad('*', 4000, '*') padding
  3  from dual
  4  connect by rownum <= 1e4;

Table created.

SQL> begin
  2    for i in (select id, row_number() over(order by id desc) as rn from my_table) loop
  3      dbms_output.put_line(i.id || '   ' || i.rn); exit;
  4    end loop;
  5  end;
  6  /
10000   1

PL/SQL procedure successfully completed.

SQL> alter table my_table parallel (degree 2);

Table altered.

SQL> begin
  2    for i in (select id, row_number() over(order by id desc) as rn from my_table) loop
  3      dbms_output.put_line(i.id || '   ' || i.rn); exit;
  4    end loop;
  5  end;
  6  /
5095   4906

PL/SQL procedure successfully completed.