DESC ADP_APPDEFINITION

SELECT LENGTH(xmldef) FROM ADP_APPDEFINITION

SQL> create table x (a clob);

Table created.

SQL>
SQL> declare
  2          c clob;
  3  begin
  4          c := lpad('X', 10000, 'X');
  5          insert into x values(c);
  6  end;
  7  /

PL/SQL procedure successfully completed.

SQL>
SQL> select length(a) from x;

 LENGTH(A)
----------
     10000

create table x (a clob);

declare
  c clob;
begin
  c := lpad('X', 10000, 'X');
  insert into x values(c);
end;
/

select length(a) from x;

drop table x;