create sequence SOME_ID start with <номер сервера> increment by  1000 ;

Connected to Oracle Database 10g Express Edition Release  10 . 2 . 0 . 1 . 0  
Connected as test

SQL> set serveroutput on;
SQL> declare
   2     fsize varchar( 15 ) := '(2000 byte)';
   3     pk varchar2( 32000 ) := 'i1';
   4   
   5     procedure exec (stmt varchar2) is
   6     begin
   7       dbms_output.put_line (stmt);
   8       execute immediate stmt;
   9     exception
  10       when others then dbms_output.put_line (sqlerrm);
  11       raise;
  12     end;
  13   
  14   begin
  15     exec ('create table pkmax (i1 char' || fsize || ')');
  16     for i in  2 .. 1000  loop
  17       if i >  2  then exec ('alter table pkmax drop primary key'); end if;
  18       exec ('alter table pkmax add i' || i || ' char' || fsize);
  19       pk := pk || ', i' || i;
  20       begin
  21         exec ('alter table pkmax add primary key (' || pk || ')');
  22       exception
  23         when others then
  24           dbms_output.put_line ('Навернулось на ключе из ' || i || ' полей');
  25           exit;
  26       end;
  27     end loop;
  28     exec ('drop table pkmax');
  29   exception
  30     when others then
  31       exec ('drop table pkmax');
  32       raise;
  33   end;
  34   /
create table pkmax (i1 char( 2000  byte))
alter table pkmax add i2 char( 2000  byte)
alter table pkmax add primary key (i1, i2)
alter table pkmax drop primary key
alter table pkmax add i3 char( 2000  byte)
alter table pkmax add primary key (i1, i2, i3)
alter table pkmax drop primary key
alter table pkmax add i4 char( 2000  byte)
alter table pkmax add primary key (i1, i2, i3, i4)
ORA- 01450 : maximum key length ( 6398 ) exceeded
Навернулось на ключе из  4  полей
drop table pkmax

PL/SQL procedure successfully completed