SQL Server2000使用行锁解决并发库存为负超卖问题

作者:袖梨 2022-06-29

假设库存表结构及数据如下:

 代码如下 复制代码


create table Stock
(
    Id int identity(1,1) primary key,
    Name nvarchar(50),
    Quantity int
)
--insert
insert into Stock select 'orange',10

在秒杀等高并发情况下,使用下面的存储过程会导致库存为负产生超卖问题:

 代码如下 复制代码


create procedure [dbo].Sale
    @name nvarchar(50),
    @number int,
    @result bit output
as
begin tran
declare @Quantity int
select @Quantity=Quantity from Stock where Name=@name
if @Quantity>=@number begin
    waitfor delay '00:00:10' --todo
    update Stock set Quantity=Quantity-@number where Name=@name
end
if @@rowcount>0 begin
    select @result=1
    commit
end
else begin
    select @result=0
    rollback
end
go

这种情况下,我们可以对行使用排他锁(X锁)来解决:

 代码如下 复制代码


create procedure [dbo].Sale
    @name nvarchar(50),
    @number int,
    @result bit output
as
begin tran
declare @Quantity int
select @Quantity=Quantity from Stock with(ROWLOCK,XLOCK) where Name=@name
if @Quantity>=@number begin
    waitfor delay '00:00:10' --todo
    update Stock set Quantity=Quantity-@number where Name=@name
end
if @@rowcount>0 begin
    select @result=1
    commit
end
else begin
    select @result=0
    rollback
end
go

补充说明

[1].不用行锁时,减库存用Quantity=@Quantity-@number问题更严重,不仅仅是为负的问题了;
[2].XLOCK的作用有两点:一是说明锁模式为排他锁,二是延长行锁时间至事务结束。若省略XLOCK仍会产生超卖问题;
[3].锁模式有共享锁(HOLDLOCK)、更新锁(UPDLOCK)和排他锁(XLOCK),考虑将上边XLOCK改为HOLDLOCK结果会怎样?

--------------------------------------------------------------------------------------------------------
有网友提供了另外一种方法,由于update语句本身具有排他锁,因而用下边方法也是可以的:

 

 代码如下 复制代码
create procedure [dbo].Sale
    @name nvarchar(50),
    @number int,
    @result bit output
as
begin tran
declare @Quantity int
select @Quantity=Quantity from Stock where Name=@name
if @Quantity>=@number begin
    waitfor delay '00:00:10' --todo
    update Stock set Quantity=Quantity-@number where Name=@name and Quantity>=@number
end
if @@rowcount>0 begin
    select @result=1
    commit
end
else begin
    select @result=0
    rollback
end
go

相关文章

精彩推荐