Question

在回答Will I miss any changes if I replace an oracle trigger while my application is running?时，我去查看触发器是否被INSERT语句锁定。它不是，我无法在互联网上找到任何可以锁定触发器的内容。

如果我在一个会话中运行以下内容：

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;

然后在第二个会话中尝试找出正在发生的锁定，我得到以下内容：

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，触发器不被锁定。

但是，如果我在INSERT语句运行时尝试替换触发器，则在语句完成（不包括提交）之前不会替换它，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，那么如何判断它是什么？

Answer 1

要确定是否锁定了触发器（以及任何其他存储过程），可以查询V$ACCESS动态性能视图。

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

这些 lock 是库缓存引脚（库缓存锁是资源（TM类型的锁）），需要确保在会话期间保护对象不被修改正在执行它。

--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，我们可以看到会话＃441等待日志文件切换，会话＃24等待库缓存引脚。

可以锁定触发器;怎么会确定它是？

1 个答案: