UPDATE 上的 SQL Server 死锁

Question

我的应用程序中出现死锁问题。
DB 是 SQL Server 2005，当 2 个线程尝试更新同一个表时会发生死锁。
我不明白情况，我希望有人可以帮助我。
这是死锁图:

<deadlock-list> 
   <deadlock victim="process3a0ac58"> 
      <process-list>
         <process id="process3a0ac58" taskpriority="0" logused="5048" waitresource="KEY: 9:72057594078035968 (e100ae2e5d7f)" waittime="4750" ownerId="22329947" transactionname="user_transaction" lasttranstarted="2012-07-20T08:53:33.440" XDES="0x24b429210" lockMode="U" schedulerid="1" kpid="1428" status="suspended" spid="57" sbid="0" ecid="0" priority="0" transcount="2" lastbatchstarted="2012-07-20T08:53:34.753" lastbatchcompleted="2012-07-20T08:53:34.753" clientapp=".Net SqlClient Data Provider" hostname="VMDBSRVCRISPI" hostpid="4012" loginname="sa" isolationlevel="read uncommitted (1)" xactid="22329947" currentdb="9" lockTimeout="4294967295" clientoption1="671088672" clientoption2="128056"> 
             <executionStack> 
                 <frame procname="adhoc" line="1" stmtstart="34" sqlhandle="0x0200000008adf4202a2e77131e147fe8c50b173a5f8d5302"> UPDATE [FreeAvailability] SET Resource_id = null WHERE Resource_id = @p0 AND Id = @p1 </frame> 
                 <frame procname="unknown" line="1" sqlhandle="0x000000000000000000000000000000000000000000000000"> unknown </frame>
             </executionStack> 
             <inputbuf> (@p0 int,@p1 int)UPDATE [FreeAvailability] SET Resource_id = null WHERE Resource_id = @p0 AND Id = @p1 </inputbuf> 
         </process> 
         <process id="process3a28da8" taskpriority="0" logused="8720" waitresource="KEY: 9:72057594078035968 (d0006ab1ca37)" waittime="2734" ownerId="22329913" transactionname="user_transaction" lasttranstarted="2012-07-20T08:53:33.067" XDES="0x28dd4aa40" lockMode="U" schedulerid="4" kpid="3732" status="suspended" spid="58" sbid="0" ecid="0" priority="0" transcount="2" lastbatchstarted="2012-07-20T08:53:36.770" lastbatchcompleted="2012-07-20T08:53:36.737" clientapp=".Net SqlClient Data Provider" hostname="VMDBSRVCRISPI" hostpid="4012" loginname="sa" isolationlevel="read uncommitted (1)" xactid="22329913" currentdb="9" lockTimeout="4294967295" clientoption1="671088672" clientoption2="128056"> 
            <executionStack>
               <frame procname="adhoc" line="1" stmtstart="34" sqlhandle="0x0200000008adf4202a2e77131e147fe8c50b173a5f8d5302"> UPDATE [FreeAvailability] SET Resource_id = null WHERE Resource_id = @p0 AND Id = @p1 </frame> 
               <frame procname="unknown" line="1" sqlhandle="0x000000000000000000000000000000000000000000000000"> unknown </frame> 
            </executionStack> 
            <inputbuf> (@p0 int,@p1 int)UPDATE [FreeAvailability] SET Resource_id = null WHERE Resource_id = @p0 AND Id = @p1 </inputbuf> 
         </process> 
      </process-list> 
      <resource-list> 
        <keylock hobtid="72057594078035968" dbid="9" objectname="SDN.Napoli.dbo.FreeAvailability" indexname="PK__FreeAvailability__3939548A" id="lock4bdb180" mode="X" associatedObjectId="72057594078035968">
            <owner-list> 
               <owner id="process3a28da8" mode="X"/> 
            </owner-list> 
            <waiter-list> 
               <waiter id="process3a0ac58" mode="U" requestType="wait"/> 
            </waiter-list> 
        </keylock> 
        <keylock hobtid="72057594078035968" dbid="9" objectname="SDN.Napoli.dbo.FreeAvailability" indexname="PK__FreeAvailability__3939548A" id="lock4c25680" mode="X" associatedObjectId="72057594078035968"> 
           <owner-list> 
              <owner id="process3a0ac58" mode="X"/> 
           </owner-list> 
           <waiter-list> 
              <waiter id="process3a28da8" mode="U" requestType="wait"/> 
           </waiter-list> 
        </keylock> 
      </resource-list> 
   </deadlock> 
</deadlock-list>

似乎在主键上发生了死锁，但是这怎么可能，我该如何解决这个问题？

提前致谢

编辑:

这是表结构:

CREATE TABLE [dbo].[FreeAvailability](
    [Id] [int] IDENTITY(1,1) NOT NULL,
    [Date] [datetime] NULL,
    [StartTime] [datetime] NULL,
    [EndTime] [datetime] NULL,
    [BookOnlyIfRequired] [bit] NULL,
    [Free48HsBefore] [bit] NULL,
    [Private] [bit] NULL,
    [F48HBGroup] [bit] NULL,
    [Resource_id] [int] NULL,
    [Sedi_id] [int] NULL,
    [Skill_id] [int] NULL,
    [BOIRGroup_id] [int] NULL,
    [Private48HBGroup] [bit] NULL,
    [Free24HsBefore] [bit] NULL,
    [Free72HsBefore] [bit] NULL,
    [F24HBGroup] [bit] NULL,
    [F72HBGroup] [bit] NULL,
    [Private24HBGroup] [bit] NULL,
    [Private72HBGroup] [bit] NULL,
PRIMARY KEY CLUSTERED 
(
    [Id] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]

GO
ALTER TABLE [dbo].[FreeAvailability]  WITH CHECK ADD  CONSTRAINT [FK4D396931200F9F6C] FOREIGN KEY([Skill_id])
REFERENCES [dbo].[Skill] ([Id])
GO
ALTER TABLE [dbo].[FreeAvailability] CHECK CONSTRAINT [FK4D396931200F9F6C]
GO
ALTER TABLE [dbo].[FreeAvailability]  WITH CHECK ADD  CONSTRAINT [FK4D3969313F693A26] FOREIGN KEY([BOIRGroup_id])
REFERENCES [dbo].[BOIRGroup] ([Id])
GO
ALTER TABLE [dbo].[FreeAvailability] CHECK CONSTRAINT [FK4D3969313F693A26]
GO
ALTER TABLE [dbo].[FreeAvailability]  WITH CHECK ADD  CONSTRAINT [FK4D396931C92BB494] FOREIGN KEY([Resource_id])
REFERENCES [dbo].[Resource] ([Id])
GO
ALTER TABLE [dbo].[FreeAvailability] CHECK CONSTRAINT [FK4D396931C92BB494]
GO
ALTER TABLE [dbo].[FreeAvailability]  WITH CHECK ADD  CONSTRAINT [FK556546F95E61B626] FOREIGN KEY([BOIRGroup_id])
REFERENCES [dbo].[BOIRGroup] ([Id])
GO
ALTER TABLE [dbo].[FreeAvailability] CHECK CONSTRAINT [FK556546F95E61B626]
GO
ALTER TABLE [dbo].[FreeAvailability]  WITH CHECK ADD  CONSTRAINT [FK556546F95ECA95DC] FOREIGN KEY([Skill_id])
REFERENCES [dbo].[Skill] ([Id])
GO
ALTER TABLE [dbo].[FreeAvailability] CHECK CONSTRAINT [FK556546F95ECA95DC]
GO
ALTER TABLE [dbo].[FreeAvailability]  WITH CHECK ADD  CONSTRAINT [FK556546F9E6E3AAC4] FOREIGN KEY([Resource_id])
REFERENCES [dbo].[Resource] ([Id])
GO
ALTER TABLE [dbo].[FreeAvailability] CHECK CONSTRAINT [FK556546F9E6E3AAC4]

我不能说 2 个线程传递的值，因为我没有记录它:(

Answer 1

要识别此死锁中涉及的行，请运行查询

SELECT id, %%lockres%% 作为 LockResource
从 dbo.FreeAvailability
WHERE %%lockres%% IN('(e100ae2e5d7f)','(d0006ab1ca37)')

在这个死锁中，进程 process3a0ac58 在与资源对应的行(e100ae2e5d7f)上持有 X 锁，并在与资源(d0006ab1ca37)对应的行上等待 U 锁(用于 UPDATE 的读取阶段)。

同时，进程 process3a28da8 在对应于资源 (d0006ab1ca37) 的行上持有 X 锁并等待 (e100ae2e5d7f) 上的 U 锁。

死锁跟踪不会告诉您哪些语句获得了锁。我的猜测是您在同一个事务中执行多个 UPDATE。同样在这种情况下，更新以相反的顺序执行。

使用键级锁的两个独立 UPDATE 语句(由于 PK 上的 WHERE 子句)不会彼此死锁。所以这应该是一个经典的循环死锁案例。