关于mysql事务行锁forupdate实现写锁的功能
在电子商务里,经常会出现库存数量少,购买的人又特别多,大并发情况下如何确保商品数量不会被多次购买. 其实很简单,利用事务+for update就可以解决. 我们都知道for update实际上是共享锁,是可以被读取的.但是如何在执行时,不被读取呢. 简单来说:假设现在库存为
在电子商务里,经常会出现库存数量少,购买的人又特别多,大并发情况下如何确保商品数量不会被多次购买.
其实很简单,利用事务+for update就可以解决.
我们都知道for update实际上是共享锁,是可以被读取的.但是如何在执行时,不被读取呢.
简单来说:假设现在库存为1,现在有A和B同时购买
先开启一个事务
begin;
select stock from good where id=1 for update;//查询good表某个商品中stock的数量
查出来后,在程序里在判断这个stock是否为0(你用什么语言,不关我事)
最后在执行
update good set stock=stock-1 where id=1
最后在
commit
但是这个时候B也是select stock from good where id=1 for update;注意:for update不能省略..这个时候会出现被锁住,无法被读取.
所以这就能够保证了商品剩余数量为1的一致性.
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