问题引入

在过去很长一段时间，不断有客人会问道：“在事先没有任何跟踪或者监控部署的情况下，阿里云RDS SQL Server有没有办法获取到历史死锁信息，供我们分析？”。在写到RDS SQL Server死锁系列文章之五时，我们就可以使用Extended Events来解决这个问题。

分析问题

Extended Events是微软从SQL Server 2008版本开始引入的，其中有一个默认事件会话是system_health，它的作用是用来收集SQL Server发生的错误信息，以XML格式存储在一个名为sys.dm_xe_session_targets的DMV中，这其中就包含了死锁信息。所以，我们可以利用这个DMV关联另外一个名为sys.dm_xe_sessions的DMV来获取死锁信息。
注意：存储在这两个DMV中的信息会伴随SQL Server服务重启而消失。也就是说，我们无法获取到SQL Server服务重启之前的历史死锁信息。

获取历史死锁信息

为了描述清楚如何获取历史死锁信息，我们可以选择其中任意一条死锁信息加以分析，代码如下：

USE master
GO-- analysis Extend Event for deadlock
DECLARE@deadlock_graph_nvarchar nvarchar(max),@deadlock_graph_xml xml
;;WITH RingBufferTarget
AS
(SELECT CAST (target_data AS XML) AS target_xmlFROM sys.dm_xe_session_targets stINNER JOIN sys.dm_xe_sessions s ON s.address = st.event_session_addressWHERE s.[name] = 'system_health' and st.target_name = 'ring_buffer'
)
SELECT TOP 1 @deadlock_graph_nvarchar = CAST(T.C.query('.') AS NVARCHAR(MAX))
FROM RingBufferTarget AS ACROSS APPLY target_xml.nodes('./RingBufferTarget/event') AS T(C)
WHERE T.C.value('./@name','varchar(200)') = 'xml_deadlock_report'SELECT @deadlock_graph_xml = CAST(REPLACE(REPLACE(@deadlock_graph_nvarchar, '&lt;', '<'),'&gt;', '>') as xml)
;select @deadlock_graph_xml.query('event/data/value/deadlock');WITH deadlock
AS
(SELECT OwnerID = T.C.value('@id', 'varchar(50)'),SPid = T.C.value('(./@spid)[1]','int'),status = T.C.value('(./@status)[1]','varchar(10)'),Victim = case when T.C.value('@id', 'varchar(50)') = T.C.value('(./../../victim-list/victimProcess/@id)[1]','varchar(50)') then 1 else 0 end,LockMode = T.C.value('@lockMode', 'varchar(20)'),Inputbuf = T.C.value('(./inputbuf/text())[1]','varchar(max)'),SPName = T.C.value('(./executionStack/frame/@procname)[1]','sysname'),Hostname = T.C.value('(./@hostname)[1]','sysname'),Clientapp = T.C.value('(./@clientapp)[1]','varchar(max)'),LoginName = T.C.value('@loginname', 'varchar(20)'),Action = T.C.value('(./@transactionname)[1]','varchar(max)'),TransactionTime = T.C.value('@lasttranstarted', 'datetime')--,* FROM @deadlock_graph_xml.nodes('./event/data/value/deadlock/process-list/process') AS T(C)
)
,
keylock
AS
(SELECTOwnerID = T.C.value('./owner[1]/@id', 'varchar(50)'),KeylockObject = T.C.value('./../@objectname', 'varchar(200)'),Indexname = T.C.value('./../@indexname', 'varchar(200)'),IndexLockMode = T.C.value('./../@mode', 'varchar(20)')FROM @deadlock_graph_xml.nodes('./event/data/value/deadlock/resource-list/keylock/owner-list') AS T(C)
)
SELECT A.SPid,A.TransactionTime,is_Vitim = A.Victim,A.SPName,A.LockMode,B.Indexname,B.KeylockObject,B.IndexLockMode,A.Inputbuf,A.Hostname,A.LoginName,A.Clientapp,A.Action,status
FROM deadlock AS ALEFT JOIN keylock AS BON A.OwnerID = B.OwnerID

从执行查询后的结果来看，我们成功拿到了历史死锁信息（从时间字段来看，死锁发生在8天以前），这些有用的信息包含：锁进程，死锁进程，锁的类型，执行的语句，登录用户等信息，如下截图所示：

我们也可以打开这个死锁信息的xml，如下：

<deadlock><victim-list><victimProcess id="process15ee08" /></victim-list><process-list><process id="process15ee08" taskpriority="0" logused="0" waitresource="KEY: 14:72057594038910976 (8194443284a0)" waittime="3906" ownerId="23597" transactionname="user_transaction" lasttranstarted="2017-04-19T21:28:11.050" XDES="0x87141730" lockMode="X" schedulerid="1" kpid="4784" status="suspended" spid="64" sbid="0" ecid="0" priority="0" trancount="2" lastbatchstarted="2017-04-19T21:28:11.050" lastbatchcompleted="2017-04-19T21:28:11.027" clientapp="Microsoft SQL Server Management Studio - Query" hostname="CHERISH-PC" hostpid="4284" loginname="Cherish-PC\Cherish" isolationlevel="read committed (2)" xactid="23597" currentdb="14" lockTimeout="4294967295" clientoption1="671090784" clientoption2="390200"><executionStack><frame procname="" line="8" stmtstart="58" sqlhandle="0x020000008902b6141ee31ae1865c893c9823c9cf5d55fafb" /><frame procname="" line="8" stmtstart="156" stmtend="276" sqlhandle="0x020000008e0a8d0d015ffe0258d01a670c6864df6370c807" /></executionStack><inputbuf>BEGIN TRAN
UPDATE dbo.test_deadlock2
SET name = &amp;apos;CC&amp;apos;
WHERE id = 1
;UPDATE dbo.test_deadlock1
SET name = &amp;apos;CC&amp;apos;
WHERE id = 1
;
COMMIT</inputbuf></process><process id="process15f048" taskpriority="0" logused="0" waitresource="KEY: 14:72057594038976512 (8194443284a0)" waittime="503" ownerId="23574" transactionname="user_transaction" lasttranstarted="2017-04-19T21:28:09.450" XDES="0x87140e80" lockMode="X" schedulerid="1" kpid="4864" status="suspended" spid="63" sbid="0" ecid="0" priority="0" trancount="2" lastbatchstarted="2017-04-19T21:28:09.443" lastbatchcompleted="2017-04-19T21:28:09.440" clientapp="Microsoft SQL Server Management Studio - Query" hostname="CHERISH-PC" hostpid="4284" loginname="Cherish-PC\Cherish" isolationlevel="read committed (2)" xactid="23574" currentdb="14" lockTimeout="4294967295" clientoption1="671090784" clientoption2="390200"><executionStack><frame procname="" line="9" stmtstart="58" sqlhandle="0x0200000070cad20bef4ae5ada9481eea2eb28415cd7e0c04" /><frame procname="" line="9" stmtstart="208" stmtend="328" sqlhandle="0x020000008b7a380c6bf24758d2b29f0eeb276e4f0aa76d8f" /></executionStack><inputbuf>BEGIN TRAN
UPDATE dbo.test_deadlock1
SET name = &amp;apos;CC&amp;apos;
WHERE id = 1
;
WAITFOR DELAY &amp;apos;00:00:05&amp;apos;UPDATE dbo.test_deadlock2
SET name = &amp;apos;CC&amp;apos;
WHERE id = 1
;
ROLLBACK   </inputbuf></process></process-list><resource-list><keylock hobtid="72057594038910976" dbid="14" objectname="" indexname="" id="lock80153480" mode="X" associatedObjectId="72057594038910976"><owner-list><owner id="process15f048" mode="X" /></owner-list><waiter-list><waiter id="process15ee08" mode="X" requestType="wait" /></waiter-list></keylock><keylock hobtid="72057594038976512" dbid="14" objectname="" indexname="" id="lock80154580" mode="X" associatedObjectId="72057594038976512"><owner-list><owner id="process15ee08" mode="X" /></owner-list><waiter-list><waiter id="process15f048" mode="X" requestType="wait" /></waiter-list></keylock></resource-list>
</deadlock>