oracle - 是否可以锁定触发器；如何确定它是？

Question

在回答 Will I miss any changes if I replace an oracle trigger while my application is running? ，我去看看触发器是否被 INSERT 语句锁定。不是，我在互联网上找不到任何建议可以锁定触发器的内容。

如果我在一个 session 中运行以下内容:

create table test_trigger (id number);
create table test_trigger_h (id number);

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;    
/

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

然后在第二个 session 中尝试找出发生了什么锁，我得到以下信息:

select object_name, object_type
     , case l.block
            when 0 then 'Not Blocking'
            when 1 then 'Blocking'
            when 2 then 'Global'
       end as status
     , case v.locked_mode
            when 0 then 'None'
            when 1 then 'Null'
            when 2 then 'Row-S (SS)'
            when 3 then 'Row-X (SX)'
            when 4 then 'Share'
            when 5 then 'S/Row-X (SSX)'
            when 6 then 'Exclusive'
            else to_char(lmode)
       end as mode_held
  from v$locked_object v
  join dba_objects d
    on v.object_id = d.object_id
  join v$lock l
    on v.object_id = l.id1
  join v$session s
    on v.session_id = s.sid
       ;

OBJECT_NAME          OBJECT_TYPE          STATUS          MODE_HELD
-------------------- -------------------- --------------- ---------------
TEST_TRIGGER         TABLE                Not Blocking    Row-X (SX)
TEST_TRIGGER_H       TABLE                Not Blocking    Row-X (SX)

根据 Oracle 的说法，触发器没有被锁定。

但是，如果我在 INSERT 语句运行时尝试替换触发器，则直到语句完成(不包括提交)后才会替换触发器，这意味着触发器已锁定。

在这种情况下，触发器是否被锁定，如果是，如何确定它是？

Answer 1

要确定触发器(以及任何其他存储过程)是否被锁定，V$ACCESS可以查询动态性能 View 。

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 

那些类型的锁是库缓存引脚(库缓存锁是资源( TM 类型的锁)锁)，需要确保在 session 执行时保护对象不被修改。

--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'

结果:

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

在这里我们可以看到 session #441 等待日志文件切换， session #24 等待库缓存 pin。