SQL> DECLARE
  2      V_C CLOB;
  3  BEGIN
  4      SELECT  C
  5        INTO  V_C
  6        FROM  TBL;
  7      DBMS_LOB.WRITEAPPEND(V_C,3,'DEF');
  8  END;
  9  /
DECLARE
*
ERROR at line 1:
ORA-22920: row containing the LOB value is not locked
ORA-06512: at "SYS.DBMS_LOB", line 1163
ORA-06512: at line 7


SQL> DECLARE
  2      V_C CLOB;
  3  BEGIN
  4      SELECT  C
  5        INTO  V_C
  6        FROM  TBL
  7        FOR UPDATE;
  8      DBMS_LOB.WRITEAPPEND(V_C,3,'DEF');
  9  END;
 10  /

PL/SQL procedure successfully completed.

SQL> 

Іменник
локатор - locator
землемер - surveyor, locator, land-surveyor

SQL> set lines 80
SQL> desc stax_blob
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 ID                                                 NUMBER(38)
 B                                                  BLOB

SQL> declare
  2    v_data raw(32000);
  3    V_bb blob;
  4    v_id int;
  5  begin
  6    commit;
  7    select id,b into v_id,v_bb from stax_blob ; --for update of id;
  8    --получили локатор незаблокированной записи
  9    update stax_blob set id=1;
 10    --заблокировали
 11    v_data := utl_raw.cast_to_raw(rpad('Stax',v_id*10,'!'));
 12    --откуда знает что уже заблакировали?
 13    dbms_lob.write(
 14      lob_loc => v_bb,
 15      amount => utl_raw.length(v_data),
 16      offset => 1,
 17      buffer => v_data
 18      );
 19  end;
 20  /

PL/SQL procedure successfully completed.

SQL> select * from stax_blob;

        ID B
---------- --------------------
         1 53746178212121212121
           21212121212121212121
           21212121212121212121
           21212121212121212121
           21212121212121212121
           21212121212121212121


SQL>