How to connect to specific session id & serial# ? Blocked sessions
That will not happen. You can kill a session, or cancel the SQL it is currently executing from another session, but you can not end its transaction (with leaving the session alive). Usually such blocking sessions are just simply killed.

For your other question: blocking another transaction in another session that inserts to another table may be blocked through foreign keys. Example:

create table request(c1 number(10, 0) not null primary key);
create table response (c1 number(10, 0) not null,
                       request_c1 number(10, 0) not null references request(c1));


Session 1:

SQL&gt; insert into request values(1);

1 row created.


No commit yet, session 1 is waiting. In session 2:

SQL&gt; insert into response values(1, 1);


And session 2 hangs there until session 1 performs a commit or rollback.