模拟死锁及案例分析

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1、模拟死锁

首先创建测试数据，然后开启必要的跟踪，最后执行两个语句模拟死锁。

1.1、创建测试数据

创建测试数据表、创建索引

create table testklup
(
clskey int not null,
nlskey int not null,
cont1  int not null,
cont2  char(3000)
)

create unique clustered index inx_cls on testklup(clskey)

create unique nonclustered index inx_nlcs  on testklup(nlskey) include(cont1)

insert into testklup select 1,1,100,'aaa'
insert into testklup select 2,2,200,'bbb'
insert into testklup select 3,3,300,'ccc'

在测试之前，先开启监视死锁的开关1222，让SQL Server遇到死锁时，在Errorlog文件里打印出死锁的详细内容。

DBCC TRACEON(1222,-1)

也可以同时使用SQL Trace来捕捉和死锁相关的信息。主要选择事件Locks->Daedlock graph

1.2、开启死锁会话

开启一个会话进行修改

----模拟高频update操作
declare @i int
set @i = 100
while 1=1
begin
    update testklup set cont1 = @i where clskey = 1  
    set @i = @i+1
end

开启另外一个会话进行查询

----模拟高频select操作
declare @cont2 char(3000)
while 1=1
begin
    select @cont2=cont2 from testklup where nlskey=1
end

两条语句一起运行，无须多长时间就会有其中一个连接遇到死锁的错误：

2、分析死锁

在开启必要的跟踪并捕获到死锁后，就可以对其进行分析。

2.1、1222标志

这时在Errorlog文件里，就会看到下面的输出

spid16s     deadlock-list
spid16s      deadlock victim=process5f3000
spid16s       process-list
spid16s        process id=process5f3000 taskpriority=0 logused=0 waitresource=KEY: 8:72057594040025088 (8194443284a0) waittime=3300 ownerId=16991311 transactionname=SELECT lasttranstarted=2016-09-28T15:07:26.720 XDES=0xe291448 lockMode=S schedulerid=4 kpid=5748 status=suspended spid=57 sbid=0 ecid=0 priority=0 trancount=0 lastbatchstarted=2016-09-28T15:07:26.717 lastbatchcompleted=2016-09-28T15:02:29.293 clientapp=Microsoft SQL Server Management Studio - 查询 hostname=LIXUANYAO hostpid=7584 loginname=LIXUANYAO\Administrator isolationlevel=read committed (2) xactid=16991311 currentdb=8 lockTimeout=4294967295 clientoption1=671090784 clientoption2=390200
spid16s         executionStack
spid16s          frame procname=adhoc line=5 stmtstart=134 stmtend=232 sqlhandle=0x02000000c3289f0a3b1699a92a155bf6611d1a82d2dbd79a
spid16s     select @cont2=cont2 from testklup where nlskey=1     
spid16s         inputbuf
spid16s     ----模拟高频select操作
spid16s     declare @cont2 char(3000)
spid16s     while 1=1
spid16s     begin
spid16s         select @cont2=cont2 from testklup where nlskey=1
spid16s     end    
spid16s        process id=process5f3558 taskpriority=0 logused=228 waitresource=KEY: 8:72057594040090624 (8194443284a0) waittime=3300 ownerId=16991312 transactionname=UPDATE lasttranstarted=2016-09-28T15:07:26.720 XDES=0xe291860 lockMode=X schedulerid=4 kpid=7240 status=suspended spid=55 sbid=0 ecid=0 priority=0 trancount=2 lastbatchstarted=2016-09-28T15:07:24.843 lastbatchcompleted=2016-09-28T15:07:23.603 clientapp=Microsoft SQL Server Management Studio - 查询 hostname=LIXUANYAO hostpid=7584 loginname=LIXUANYAO\Administrator isolationlevel=read committed (2) xactid=16991312 currentdb=8 lockTimeout=4294967295 clientoption1=671090784 clientoption2=390200
spid16s         executionStack
spid16s          frame procname=adhoc line=6 stmtstart=140 stmtend=248 sqlhandle=0x0200000087695c3ac89c30f0ca649915b3e2cb1c22db1292
spid16s     update testklup set cont1 = @i where clskey = 1     
spid16s         inputbuf
spid16s     ----模拟高频update操作
spid16s     declare @i int
spid16s     set @i = 100
spid16s     while 1=1
spid16s     begin
spid16s         update testklup set cont1 = @i where clskey = 1  
spid16s         set @i = @i+1
spid16s     end    
spid16s       resource-list
spid16s        keylock hobtid=72057594040025088 dbid=8 objectname=Test.dbo.testklup indexname=inx_cls id=locka2bc5c0 mode=X associatedObjectId=72057594040025088
spid16s         owner-list
spid16s          owner id=process5f3558 mode=X
spid16s         waiter-list
spid16s          waiter id=process5f3000 mode=S requestType=wait
spid16s        keylock hobtid=72057594040090624 dbid=8 objectname=Test.dbo.testklup indexname=inx_nlcs id=locka2b8d80 mode=S associatedObjectId=72057594040090624
spid16s         owner-list
spid16s          owner id=process5f3000 mode=S
spid16s         waiter-list
spid16s          waiter id=process5f3558 mode=X requestType=wait

先来看看这些输出是什么意思，完成下表：

参与者	process5f3000	process5f3558
牺牲者	√
SPID	57	55
连接背景	Microsoft SQL Server Management Studio - 查询 hostname=LIXUANYAO hostpid=7584 loginname=LIXUANYAO\Administrator	Microsoft SQL Server Management Studio - 查询 hostname=LIXUANYAO hostpid=7584 loginname=LIXUANYAO\Administrator
正在申请中资源/类型	KEY: 8:72057594040025088 (8194443284a0)/ Mode:S	KEY: 8:72057594040090624 (8194443284a0)/ Mode:X
当前开启了几层事务	0	2
事务隔离级别	read committed (2)	read committed (2)
当前正在运行的语句	select @cont2=cont2 from testklup where nlskey=1	update testklup set cont1 = @i where clskey = 1
当前正在运行的批处理	--模拟高频select操作 declare @cont2 char(3000) while 1=1 begin     select @cont2=cont2 from testklup where nlskey=1 end	--模拟高频update操作 declare @i int set @i = 100 while 1=1 begin     update testklup set cont1 = @i where clskey = 1       set @i = @i+1 end
死锁资源	资源2	资源1
资源类型	keylock	keylock
具体内容	hobtid=72057594040090624 dbid=8 objectname=Test.dbo.testklup  indexname=inx_nlcs id=locka2b8d80	hobtid=72057594040025088 dbid=8 objectname=Test.dbo.testklup  indexname=inx_cls id=locka2bc5c0
持有资源进程/类型	process5f3000(spid57) / mode:S	process5f3558(spid55) / mode:X
等待资源进程/类型	process5f3558(spid55) / mode:X	process5f3000(spid57) / mode:S

2.2、死锁图

在跟踪文件里，可以看到这样的死锁图形：

我们可以从跟踪文件中，提取死锁事件数据，将死锁图保存为死锁XML文件(.xdl)。然后针对.xdl文件使用记事本打开，整个死锁的内容一目了然。

/** 死锁事件数据是后期提取的，与原死锁图稍有不同 **/
-- 第一部分
<deadlock-list>
    <deadlock victim="process2b6b000">
        -- 第二部分
        <process-list>
            <process id="process2b6b000" taskpriority="0" logused="0" waitresource="KEY: 8:72057594040025088 (8194443284a0)" waittime="636" ownerId="758239" transactionname="SELECT" lasttranstarted="2016-10-26T09:59:00.300" XDES="0x5dba408" lockMode="S" schedulerid="1" kpid="4008" status="suspended" spid="57" sbid="0" ecid="0" priority="0" trancount="0" lastbatchstarted="2016-10-26T09:59:00.300" lastbatchcompleted="2016-10-26T09:58:55.807" clientapp="Microsoft SQL Server Management Studio - 查询" hostname="LIXUANYAO" hostpid="5872" loginname="LIXUANYAO\Administrator" isolationlevel="read committed (2)" xactid="758239" currentdb="8" lockTimeout="4294967295" clientoption1="671090784" clientoption2="390200">
                <executionStack>
                    <frame procname="adhoc" line="5" stmtstart="134" stmtend="232" sqlhandle="0x02000000c3289f0a3b1699a92a155bf6611d1a82d2dbd79a">
                        select @cont2=cont2 from testklup where nlskey=1     
                    </frame>
                </executionStack>
                <inputbuf>
                    ----模拟高频select操作
                    declare @cont2 char(3000)
                    while 1=1
                    begin
                        select @cont2=cont2 from testklup where nlskey=1
                    end    
                </inputbuf>
            </process>
            <process id="process2dc2aa8" taskpriority="0" logused="228" waitresource="KEY: 8:72057594040090624 (8194443284a0)" waittime="636" ownerId="758240" transactionname="UPDATE" lasttranstarted="2016-10-26T09:59:00.307" XDES="0x5bf6c08" lockMode="X" schedulerid="4" kpid="5832" status="suspended" spid="55" sbid="0" ecid="0" priority="0" trancount="2" lastbatchstarted="2016-10-26T09:58:59.470" lastbatchcompleted="2016-10-26T09:58:58.073" lastattention="2016-10-26T09:58:58.073" clientapp="Microsoft SQL Server Management Studio - 查询" hostname="LIXUANYAO" hostpid="5872" loginname="LIXUANYAO\Administrator" isolationlevel="read committed (2)" xactid="758240" currentdb="8" lockTimeout="4294967295" clientoption1="671090784" clientoption2="390200">
                <executionStack>
                    <frame procname="adhoc" line="6" stmtstart="140" stmtend="248" sqlhandle="0x0200000087695c3ac89c30f0ca649915b3e2cb1c22db1292">
                        update testklup set cont1 = @i where clskey = 1     
                    </frame>
                </executionStack>
                <inputbuf>
                    ----模拟高频update操作
                    declare @i int
                    set @i = 100
                    while 1=1
                    begin
                        update testklup set cont1 = @i where clskey = 1  
                        set @i = @i+1
                    end    
                </inputbuf>
            </process>
        </process-list>
        -- 第三部分
        <resource-list>
            <keylock hobtid="72057594040025088" dbid="8" objectname="Test.dbo.testklup" indexname="inx_cls" id="locka49e800" mode="X" associatedObjectId="72057594040025088">
                <owner-list>
                    <owner id="process2dc2aa8" mode="X"/>
                </owner-list>
                <waiter-list>
                    <waiter id="process2b6b000" mode="S" requestType="wait"/>
                </waiter-list>
            </keylock>
            <keylock hobtid="72057594040090624" dbid="8" objectname="Test.dbo.testklup" indexname="inx_nlcs" id="locka47ab40" mode="S" associatedObjectId="72057594040090624">
                <owner-list>
                    <owner id="process2b6b000" mode="S"/>
                </owner-list>
                <waiter-list>
                    <waiter id="process2dc2aa8" mode="X" requestType="wait"/>
                </waiter-list>
            </keylock>
        </resource-list>
    </deadlock>
</deadlock-list>

SPID=57：查询语句使用非聚集索引inx_nlcs查找nlskey=1的记录，持有inx_nlcs上的S锁；由于索引未覆盖列cont2，需通过键查询得到cont2，于是申请inx_cls上的S锁。
SPID=55：更新语句使用聚集索引inx_cls查找clskey=1的记录，持有inx_cls上的X锁；由于非聚集索引inx_nlcs包含列cont1，在更新表中记录后，还需更新非聚集索引中的数值，于是申请inx_ncls上的X锁。

--hobtid
SELECT OBJECT_NAME(p.object_id) AS TableName,
       i.name AS IndexName
FROM sys.partitions AS p
     INNER JOIN sys.indexes AS i ON p.object_id = i.object_id
                                    AND p.index_id = i.index_id
WHERE p.hobt_id = 72057594040090624
--associatedObjectId
SELECT OBJECT_NAME(p.object_id) AS TableName,
       i.name AS IndexName
FROM sys.partitions AS p
     INNER JOIN sys.indexes AS i ON p.object_id = i.object_id
                                    AND p.index_id = i.index_id
WHERE p.partition_id = 72057594040025088

--case when type = 1|3 then container_id = sys.partitions.hobt_id
--case when type = 2 then container_id = sys.partitions.partition_id
SELECT * FROM sys.allocation_units WHERE container_id=72057594040090624
SELECT * FROM sys.allocation_units WHERE container_id=72057594040025088

SELECT %%lockres%% AS keyhashvalue,* FROM testklup WHERE %%lockres%% ='(8194443284a0)'

3、Deadlocks-Example

SQL Server上的一个奇怪的Deadlock及其分析方法：https://blogs.msdn.microsoft.com/apgcdsd/2012/02/27/sql-serverdeadlock/
SQL Server Deadlocks by Example：https://www.simple-talk.com/sql/performance/sql-server-deadlocks-by-example/