cur_1        Sys_Refcursor;

   cur_2        Sys_Refcursor;

   v_1          VARCHAR2(30);

   v_2          VARCHAR2(30);

   v_3          VARCHAR2(30);

   v_4          VARCHAR2(30);

OPEN cur_1 for Select * from tab1@dblink1;

   Loop

       Fetch cur_1 into v_1, v_2;

       EXIT WHEN cur_1%NOTFOUND;

       OPEN cur_2 for Select * from tab2@dblink1 where col1 = v_1 and col2 = v2;

       Loop

           Fetch cur2 into v_3, v_4;

           Exit when cur_2%notfound;

           INSERT INTO local.tab3 values (v_1,v_2, v_3, v_4);

       END Loop;

       close cur_2;

   End Loop;

   close cur_1;

.

         .

         .

         .

insert into local.tab3(col1, col2, col3, col4)
select tab1.col1, tab1.col2, tab2.col1, tab2.col2
from tab1@dblink1 tab1
join tab2@dblink1 tab2
    on tab1.col1 = tab2.col1
    and tab1.col2 = tab2.col2;