Alter trigger Oracle Does alter trigger hang if a table is locked by some DML operation
? 
What kind of exception does it throw? Resource busy 0054 or some other exception...?  I have tried to reproduce this scenario but in vain.
Test case.

Open 2 sqlplus sessions, run the following in the first to set the test up:

create table stall_table
(
  a number
);

create or replace trigger stall_session
before insert on stall_table
begin
  DBMS_LOCK.sleep(10000);
end;


Then, execute in session 1:

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


Execute in session 2:

SQL&gt; create or replace trigger stall_session
before insert on stall_table
begin
  DBMS_LOCK.sleep(10000);
end;
/


You'll get, after some time:

create or replace trigger stall_session
                          *
ERROR at line 1:
ORA-04021: timeout occurred while waiting to lock object


SQL&gt;


... which answers your question.