死锁的四个必要条件：
互斥条件(Mutual exclusion)：资源不能被共享，只能由一个进程使用。
请求与保持条件(Hold and wait)：已经得到资源的进程可以再次申请新的资源。
非剥夺条件(No pre-emption)：已经分配的资源不能从相应的进程中被强制地剥夺。
循环等待条件(Circular wait)：系统中若干进程组成环路，该环路中每个进程都在等待相邻进程正占用的资源。
仓库拣货卡死，排查了数据库的很多地方，都没有头绪，最后到SQL Server 错误日志里查看，终于发现了蛛丝马迹
EXEC xp_readerrorlog 0,1,NULL,NULL,'2015-09-21','2015-10-10','DESC'
waiter id=process5c30e08 mode=U requestType=wait
waiter-list
owner id=process5c26988 mode=X
owner-list
keylock hobtid=72057597785604096 dbid=33 objectname=stoxxx.dbo.Orderxxx indexname=IX_PricingExpressProductCode_State id=lock17fa96980 mode=X associatedObjectId=72057597785604096
waiter id=process5c26988 mode=U requestType=wait
waiter-list
owner id=process5c30e08 mode=X
owner-list
keylock hobtid=72057597785604096 dbid=33 objectname=stoxxx.dbo.Orderxxx indexname=IX_PricingExpressProductCode_State id=lock87d69e780 mode=X associatedObjectId=72057597785604096
resource-list
(@OperateState money,@HandledByNewWms bit,@State int,@OrderOut int)
UPDATE [Orderxx] SET [OperateState] = @OperateState,[HandledByNewWms] = @HandledByNewWms WHERE (([Orderxxx].[State] = @State) And ([Orderxxx].[OrderOut] = @OrderOut) And ([Orderxxx].[PricingExpressProductCode] IN ('UKNIR')))
inputbuf
unknown
frame procname=unknown line=1 sqlhandle=0x000000000000000000000000000000000000000000000000
UPDATE [Orderxxx] SET [OperateState] = @OperateState,[HandledByNewWms] = @HandledByNewWms WHERE (([Orderxxx].[State] = @State) And ([Orderxxx].[OrderOut] = @OrderOut) And ([Orderxxx].[PricingExpressProductCode] IN ('UKNIR')))
frame procname=adhoc line=1 stmtstart=134 sqlhandle=0x020000009d376d18a17e7ea51289d8caa2fb4de65c976389
executionStack
process id=process5c30e08 taskpriority=0 logused=10320 waitresource=KEY: 33:72057597785604096 (112399c2054a) waittime=4813 ownerId=31578743038 transactionname=user_transaction lasttranstarted=2015-09-24T10:22:58.410 XDES=0x372e95950 lockMode=U schedulerid=17 kpid=8496 status=suspended spid=153 sbid=0 ecid=0 priority=0 trancount=2 lastbatchstarted=2015-09-24T10:22:58.540 lastbatchcompleted=2015-09-24T10:22:58.540 clientapp=.Net SqlClient Data Provider hostname=CK1-WIN-WEB02 hostpid=37992 loginname=ck1.biz isolationlevel=read committed (2) xactid=31578743038 currentdb=33 lockTimeout=4294967295 clientoption1=671088672 clientoption2=128056
(@OperateState money,@HandledByNewWms bit,@State int,@OrderOut int)UPDATE [Orderxxx] SET [OperateState] = @OperateState,[HandledByNewWms] = @HandledByNewWms WHERE (([Orderxxx].[State] = @State) And ([Orderxxx].[OrderOut] = @OrderOut) And ([Orderxxx].[PricingExpressProductCode] IN ('UKNIR')))
inputbuf
unknown
frame procname=unknown line=1 sqlhandle=0x000000000000000000000000000000000000000000000000
UPDATE [Orderxxx] SET [OperateState] = @OperateState,[HandledByNewWms] = @HandledByNewWms WHERE (([Orderxxx].[State] = @State) And ([Orderxxx].[OrderOut] = @OrderOut) And ([Orderxxx].[PricingExpressProductCode] IN ('UKNIR')))
frame procname=adhoc line=1 stmtstart=134 sqlhandle=0x020000009d376d18a17e7ea51289d8caa2fb4de65c976389
executionStack
process id=process5c26988 taskpriority=0 logused=9892 waitresource=KEY: 33:72057597785604096 (70f5b089bb2b) waittime=4813 ownerId=31579268946 transactionname=user_transaction lasttranstarted=2015-09-24T10:27:01.357 XDES=0x98312f950 lockMode=U schedulerid=16 kpid=9184 status=suspended spid=454 sbid=0 ecid=0 priority=0 trancount=2 lastbatchstarted=2015-09-24T10:27:01.490 lastbatchcompleted=2015-09-24T10:27:01.487 clientapp=.Net SqlClient Data Provider hostname=CK1-WIN-WEB02 hostpid=37992 loginname=ck1.biz isolationlevel=read committed (2) xactid=31579268946 currentdb=33 lockTimeout=4294967295 clientoption1=671088672 clientoption2=128056
process-list
deadlock victim=process5c26988
deadlock-list
咋一看上面的错误信息，可以发现两条相同的语句造成的死锁，但是这么短的语句不可能持有排他锁太久
再仔细分析一下错误日志，发现都死锁在同一个非聚集索引上，再问了一下开发，开发那边说，这条语句是在一个大事务里面，这个事务会做7、8件事
索引属性
还有索引里面的数据，发现很多重复值
SQL语句是这样的
(@OperateState money,@HandledByNewWms bit,@State int,@OrderOut int)
@HandledByNewWms=(1) @OperateState=($1.0000) @OrderOut=(4055484) @State=(3)
UPDATE [Orderxxx] SET [OperateState] = $1.0000,[HandledByNewWms] = 1
WHERE (([Orderxxx].[State] = 3) And ([Orderxxx].[OrderOut] = 4055484) And ([Orderxxx].[PricingExpressProductCode] IN ('UKRRM','UKRLE')))
下图为语句生成的执行计划
当时的情况是大量SQL语句被阻塞，而阻塞的语句正是下面这条语句
UPDATE [Orderxxx] SET [OperateState] = $1.0000,[HandledByNewWms] = 1
WHERE (([Orderxxx].[State] = 3) And ([Orderxxx].[OrderOut] = 4055484) And ([Orderxxx].[PricingExpressProductCode] IN ('UKRRM','UKRLE')))
解决方法
上面得出几个症状
1、update语句是在一个大事务里面，事务太大导致其他session等待排他锁的时间变长
2、大家都在使用同一个非聚集索引，并扫描PricingExpressProductCode字段
3、索引里的重复值很多
从上面的症状基本可以判断，这个非聚集索引无啥用，可以禁用之
ALTER INDEX [IX_PricingExpressProductCode_State] ON [dbo].[Orderxxx] DISABLE
禁用之后，死锁消失，问题解决，仓库的怨气也随之消失
这一次排查过程时间有点长，但是很好定位，SQL Server错误日志给出了足够的信息定位死锁问题，所以遇到问题的时候一定要分析清楚日志
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