Can a trigger be locked; how would one determine that it is?

Question

In answering Will I miss any changes if I replace an oracle trigger while my application is running?, I went looking to see if the trigger was locked by an INSERT statement.

Answer 1

To determine if a trigger(as well as any other stored procedure) is locked or not, the V$ACCESS dynamic performance view can be queried.

Session #1

insert into test_trigger
 select level
   from dual
connect by level <= 1000000; 

Session #2

SQL> select *
  2    from v$access
  3   where object = upper('test_trigger_t')
  4  ;


Sid  Owner  Object         Type    Con_Id 
--------------------------------------
441  HR     TEST_TRIGGER_T TRIGGER  3 

Those kinds of locks are library cache pins(library cache locks are resource(TM type of lock) locks), needed to ensure that an object is protected from being modified while session is executing it.

--session sid # 441
insert into test_trigger
  select level
    from dual
 connect by level <= 1000000;


-- session sid #24
create or replace trigger test_trigger_t 
after insert on test_trigger for each row
begin
  insert into test_trigger_h (id) values (:new.id);
end;  

-- Session # 3
select vs.sid
     , vs.username
     , vw.event
  from v$session       vs
  join v$session_wait  vw
    on (vw.sid = vs.sid)
  join v$access        va
    on (va.owner = vs.username)
 where vs.username = 'HR'

Result:

Sid Username Event 
--------------------------
24 HR library cache pin 
....
441 HR log file switch (checkpoint incomplete) 

Here we can see that the session #441 waits for a log file switching and session #24 waits for library cache pin.