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SQLServer中的死锁说明 - 站长搜索
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SQLServer中的死锁说明

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2022-09-23 20:35:16 转载来源: 网络整理/侵权必删

两个进程发生死锁的典型例子是:进程T1中获取锁A,申请锁B;进程T2中获取锁B,申请锁A,我们下面动手来演示一下这种情况:1.创建一个Database,名为InvDB。2.执行下面脚本创建person表并填充两条数据:3.在SQLServerManagementStudio的两个窗口中同时执行下面的查询:这段代码在默认的READCOMMITTED隔离级别下运行,两个进程分别在获取一个排它锁的情况下,申请对方的共享锁从而造成死锁

两个进程发生死锁的典型例子是:进程T1中获取锁A,申请锁B;进程T2中获取锁B,申请锁A,我们下面动手来演示一下这种情况:

1. 创建一个Database,名为InvDB。

2. 执行下面脚本创建person表并填充两条数据:

image

3. 在SQL Server Management Studio的两个窗口中同时执行下面的查询:

image image

这段代码在默认的READ COMMITTED隔离级别下运行,两个进程分别在获取一个排它锁的情况下,申请对方的共享锁从而造成死锁。

可见一个进程可以正常更新并显示结果,而另一个进程已经被回滚:

(1 row(s) affected)
Msg 1205, Level 13, State 45, Line 8
Transaction (Process ID 55) was deadlocked on lock resources with another process and has been chosen as the deadlock victim. Rerun the transaction.

4. 启动 SQL Server Profiler,选择下面4种Events:

image

再执行一次上面的死锁实验,可以看到如下所示的死锁图:

image

 

非常有趣的一点是:第二次执行上述语句不会发生死锁!这是因为此时两个进程中,SQL Server会智能的识别出update语句是不需要做的,所以都不会去获取排它锁,当然也就不会死锁了。SQL Server 2008 的查询优化器还真是非常强大!

标签: SQLServer 中的 死锁 说明


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