Question

我在oracle触发器中有关于OF，IF和WHEN子句性能的查询。请考虑以下触发器-

CREATE OR REPLACE TRIGGER WeightChange

   AFTER UPDATE ON Person

   FOR EACH ROW

BEGIN 

   IF :new.Weight > 250 AND new:Weight > old:Weight THEN 

      LogWeightChange(:new.PersonId, :new.Weight, :old.Weight); 

   END IF;

END WeightChange;

现在，如果我进行以下更改，

喜欢增加体重 -WHEN（：new.Weight> 250 AND new：Weight> old：Weight）
返回整数

以上任何一项或全部内容是否会大大改善触发条件？

Answer 1

WHEN (condition)和OF column触发功能可以显着提高触发性能。触发器的大部分性能损失是SQL和PL / SQL上下文切换，通过将更多的逻辑转移到SQL中，可以避免这些切换。

例如，让我们从一个简单的模式开始：

--Sample schema with 100K simple PERSON rows.
create table person
(
    id number not null primary key,
    name varchar2(100),
    weight number
);

insert into person
select level, level, 100 from dual connect by level <= 100000;
commit;

启用或禁用不同的触发功能：

--Create trigger that fires for all rows.
CREATE OR REPLACE TRIGGER WeightChange
   AFTER UPDATE ON Person
   FOR EACH ROW
BEGIN 
   IF :new.Weight > 250 AND :new.Weight > :old.Weight THEN 
      null;
   END IF;
END WeightChange;
/

--Create trigger that only fires for relevant rows.
CREATE OR REPLACE TRIGGER WeightChange
   AFTER UPDATE ON Person
   FOR EACH ROW
   WHEN (new.Weight > 250 AND new.Weight > old.Weight)
BEGIN 
   null;
END WeightChange;
/

--Create trigger that fires for all updates of WEIGHT.
CREATE OR REPLACE TRIGGER WeightChange
   AFTER UPDATE OF weight ON person
   FOR EACH ROW
   WHEN (new.Weight > 250 AND new.Weight > old.Weight)
BEGIN 
   null;
END WeightChange;
/

--No trigger.
drop trigger WeightChange;

WHEN (condition)和OF column功能可以使UPDATE语句在最佳情况下的运行速度几乎快一倍。

--With no trigger - FAST:
--0.749, 0.670, 0.733
update person set weight = 100;
rollback;

--With normal trigger - SLOW:
--1.295, 1.279, 1.264 seconds
update person set weight = 100;
rollback;

--With WHEN condition trigger - FAST:
--0.687, 0.686, 0.687
update person set weight = 100;
rollback;

--With WHEN condition, using a value that satisfies conditions - SLOW:
--1.233, 1.232, 1.233
update person set weight = 500;
rollback;

--With normal trigger, update irrelevant column - SLOW:
--1.263, 1.248, 1.248
update person set name = name;
rollback;

--With OF column trigger, update irrelevant column - FAST:
--0.624, 0.624, 0.609
update person set name = name;
rollback;

有关调整Oracle触发器的查询

1 个答案: