数据库 发布日期:2024/12/26 浏览次数:1
1 背景
1.1 报警情况
最近整理笔记,打算全部迁移到EVERNOTE。整理到锁这一部分,里边刚好有个自己记录下来的案例,重新整理分享下给大家。
某日中午,收到报警短信,DB死锁异常,单分钟死锁120个。
死锁的xml文件如下:
<deadlock-list> <deadlock victim="process810b00cf8"> <process-list> <process id="process810b00cf8" taskpriority="0" logused="0" waitresource="RID: 13:1:1541136:62" waittime="7682" ownerId="3396587959" transactionname="UPDATE" lasttranstarted="2016-01-08T12:03:51.067" XDES="0xa99746d08" lockMode="U" schedulerid="41" kpid="17308" status="suspended" spid="108" sbid="0" ecid="0" priority="0" trancount="2" lastbatchstarted="2016-01-08T12:03:51.067" lastbatchcompleted="2016-01-08T12:03:51.067" lastattention="1900-01-01T00:00:00.067" clientapp="Microsoft SQL Server Management Studio - 查询" hostname="test-server" hostpid="1433" loginname="xinysu" isolationlevel="read committed (2)" xactid="3396587959" currentdb="13" lockTimeout="4294967295" clientoption1="671098976" clientoption2="390200"> <executionStack> <frame procname="adhoc" line="7" stmtstart="214" stmtend="484" sqlhandle="0x020000003acf4f010561e479685209fb09a7fd15239977c60000000000000000000000000000000000000000"> UPDATE FinanceReceiptNoRule SET NowSeqValue=@ReturnNum,ISRUNNING='0',LastWriteTime=GETDATE() WHERE IsRunning='1' AND SeqCode=@SeqCode </frame> </executionStack> <inputbuf> declare @SeqCode varchar(60) declare @ReturnNum bigint set @SeqCode='CGJS20160106' while(1=1) begin UPDATE FinanceReceiptNoRule SET NowSeqValue=@ReturnNum,ISRUNNING='0',LastWriteTime=GETDATE() WHERE IsRunning='1' AND SeqCode=@SeqCode end </inputbuf> </process> <process id="process18fd5d8cf8" taskpriority="0" logused="248" waitresource="KEY: 13:72057594040090624 (b3ade7c5980c)" waittime="4" ownerId="3396522828" transactionname="user_transaction" lasttranstarted="2016-01-08T12:03:05.310" XDES="0x18c1db63a8" lockMode="U" schedulerid="57" kpid="16448" status="suspended" spid="161" sbid="0" ecid="0" priority="0" trancount="2" lastbatchstarted="2016-01-08T12:03:58.737" lastbatchcompleted="2016-01-08T12:03:33.847" lastattention="2016-01-08T12:03:33.850" clientapp="Microsoft SQL Server Management Studio - 查询" hostname="test-server" hostpid="1433" loginname="xinysu" isolationlevel="read committed (2)" xactid="3396522828" currentdb="13" lockTimeout="4294967295" clientoption1="671090784" clientoption2="390200"> <executionStack> <frame procname="adhoc" line="6" stmtstart="210" stmtend="400" sqlhandle="0x020000001b4f23368af7bba99098c10dec46585804f1b4ce0000000000000000000000000000000000000000"> Update dbo.FinanceReceiptNoRule Set [IsRunning]='1' where SeqCode=@SeqCode and IsRunning='0' </frame> </executionStack> <inputbuf> declare @SeqCode varchar(60) declare @ReturnNum bigint set @SeqCode='CGJS20160106' while(1=1) begin Update dbo.FinanceReceiptNoRule Set [IsRunning]='1' where SeqCode=@SeqCode and IsRunning='0' end </inputbuf> </process> </process-list> <resource-list> <ridlock fileid="1" pageid="1541136" dbid="13" objectname="fin_test.dbo.FinanceReceiptNoRule" id="lock51e8a3980" mode="X" associatedObjectId="72057594040025088"> <owner-list> <owner id="process18fd5d8cf8" mode="X" /> </owner-list> <waiter-list> <waiter id="process810b00cf8" mode="U" requestType="wait" /> </waiter-list> </ridlock> <keylock hobtid="72057594040090624" dbid="13" objectname="fin_test.dbo.FinanceReceiptNoRule" indexname="PK_FINANCERECEIPTNORULE" id="lock7b2c6bc80" mode="U" associatedObjectId="72057594040090624"> <owner-list> <owner id="process810b00cf8" mode="U" /> </owner-list> <waiter-list> <waiter id="process18fd5d8cf8" mode="U" requestType="wait" /> </waiter-list> </keylock> </resource-list> </deadlock> </deadlock-list>
表格结构跟模拟数据如下:
--涉及表格: CREATE TABLE [dbo].[FinanceReceiptNoRule]( [SeqCode] [varchar](60) NOT NULL, [NowSeqValue] [bigint] NULL, [SeqDate] [varchar](14) NOT NULL, [IsRunning] [varchar](1) NULL, [LastWriteTime] [datetime] NULL, [Prefix] [varchar](4) NULL ) ON [PRIMARY] GO --数据模拟 INSERT [dbo].[FinanceReceiptNoRule] ([SeqCode], [NowSeqValue], [SeqDate], [IsRunning], [LastWriteTime], [Prefix]) VALUES (N'TEST20150108', 1469, N'20150108', N'0', CAST(N'2015-01-08 05:05:49.163' AS DateTime), N'TEST') GO INSERT [dbo].[FinanceReceiptNoRule] ([SeqCode], [NowSeqValue], [SeqDate], [IsRunning], [LastWriteTime], [Prefix]) VALUES (N'TEST20150109', 1377, N'20150109', N'0', CAST(N'2015-01-09 04:50:26.610' AS DateTime), N'TEST') GO ALTER TABLE [dbo].[FinanceReceiptNoRule] ADD CONSTRAINT [pk_FinanceReceiptNoRule] PRIMARY KEY NONCLUSTERED ( [SeqCode] ASC )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY] GO
1.2 如何监控
捕获死锁有多种方式可以捕获,这里介绍2种:SQL SERVER Profiler工具跟Extended Events。Profiler相对比较耗资源,但是由于只监控死锁这一项,所以性能影响不是很大,其可视化界面较易上手;Extended Events耗费资源较少,实时记录到倒数第二个死锁,同时需要SQL语句来分析查询记录文件。
如何使用 Profiler监控?
打开 SSMS,点击<工具>,选择 <SQL Server Profiler>,如下图。
登录到需要监控的DB实例,填写相应的跟踪属性,首先是<常规>页面,如下图。这里注意2个方面,第一,选择 <TSQL-Locks>模板,这个模板即可以用来监控死锁,也可以拿来观察 锁申请与释放情况,非常详细,有事没事可以多拿来看SELECT UPDATE DELETE等语句对锁的申请及释放情况;第二,监控结果存储,建议可以存放到某个表格中去,方便定期分析与统计。
接着填写<事件选择>项,只需要选择 <deadlock graph> Events,其他都不需要打勾,最后点击运行就可以开始监控了。
可以用一个万年常用的例子来检查是否监控正常,开3个查询窗口,按照以下顺序执行则会发生资源占用及申请互斥导致死锁,执行完第5步,等待1-3s则发生死锁。脚本提供如下:
--session 1 CREATE TABLE Test_DL( id int not null primary key , name varchar(100)); INSERT INTO Test_DL(id,name) select 1,'a'; INSERT INTO Test_DL(id,name) select 2,'b'; --session2 2 2 2 2 2 2 2 2 2 BEGIN TRANSACTION UPDATE Test_DL SET Name='a-test' WHERE ID=1 --session3 3 3 3 3 3 3 3 3 3 BEGIN TRANSACTION UPDATE Test_DL SET Name='b-test' WHERE ID=2 --session2 2 2 2 2 2 2 2 2 2 SELECT * FROM Test_DL WHERE ID=2 --session3 3 3 3 3 3 3 3 3 3 SELECT * FROM Test_DL WHERE ID=1 模拟死锁SQL
监控到的死锁界面如下:
如何使用Extended Events监控?
建立扩展事件监控的脚本如下:(扩展事件很赞,2012版支持可视化操作,感兴趣的可以上 MSDN了解:https://msdn.microsoft.com/zh-cn/library/bb630282.aspx,本文就不分析语法等知识点了)
CREATE EVENT SESSION [DeadLock] ON SERVER ADD EVENT sqlserver.xml_deadlock_report ADD TARGET package0.event_file(SET filename=N'F:\events\deadlock\deadlock.xel',max_file_size=(20)), ADD TARGET package0.ring_buffer(SET max_events_limit=(100),max_memory=(10240),occurrence_number=(50)) WITH (MAX_MEMORY=4096 KB,EVENT_RETENTION_MODE=ALLOW_SINGLE_EVENT_LOSS,MAX_DISPATCH_LATENCY=30 SECONDS,MAX_EVENT_SIZE=0 KB,MEMORY_PARTITION_MODE=NONE,TRACK_CAUSALITY=OFF,STARTUP_STATE=ON) GO
查询SQL如下,这里需要注意:查询是基于buffer还是基于filer分析,一般buffer存储的个数都是有限的,比如上文我们只分配了4M存储,file分析则是完整的,但是要看保留的文件个数。这里我们给出buffer的查询SQL如下,file的查询大家感兴趣的可以动手写下。
DECLARE @deadlock_xml XML SELECT @deadlock_xml=( SELECT ( SELECT CONVERT(XML, target_data) FROM sys.dm_xe_session_targets st JOIN sys.dm_xe_sessions s ON s.address = st.event_session_address WHERE s.name = 'deadlock' AND st.target_name = 'ring_buffer' ) AS [x] FOR XML PATH('') , TYPE ) SELECT dateadd(hour,+6,tb.col.value('@timestamp[1]','varchar(max)')) TimePoint, tb.col.value('(data/value/deadlock/process-list/process/executionStack/frame)[1]','VARCHAR(MAX)') statement_parameter_k, tb.col.value('(data/value/deadlock/process-list/process/executionStack/frame)[2]','VARCHAR(MAX)') statement_k, tb.col.value('(data/value/deadlock/process-list/process/executionStack/frame)[3]','VARCHAR(MAX)') statement_parameter, tb.col.value('(data/value/deadlock/process-list/process/executionStack/frame)[4]','VARCHAR(MAX)') [statement], tb.col.value('(data/value/deadlock/process-list/process/@waitresource)[1]','VARCHAR(MAX)') waitresource_k, tb.col.value('(data/value/deadlock/process-list/process/@waitresource)[2]','VARCHAR(MAX)') waitresource, tb.col.value('(data/value/deadlock/process-list/process/@isolationlevel)[1]','VARCHAR(MAX)') isolationlevel_k, tb.col.value('(data/value/deadlock/process-list/process/@isolationlevel)[2]','VARCHAR(MAX)') isolationlevel, tb.col.value('(data/value/deadlock/process-list/process/@waittime)[1]','VARCHAR(MAX)') waittime_k, tb.col.value('(data/value/deadlock/process-list/process/@waittime)[2]','VARCHAR(MAX)') waittime, tb.col.value('(data/value/deadlock/process-list/process/@clientapp)[1]','VARCHAR(MAX)') clientapp_k, tb.col.value('(data/value/deadlock/process-list/process/@clientapp)[2]','VARCHAR(MAX)') clientapp, tb.col.value('(data/value/deadlock/process-list/process/@hostname)[1]','VARCHAR(MAX)') hostname_k, tb.col.value('(data/value/deadlock/process-list/process/@hostname)[2]','VARCHAR(MAX)') hostname FROM @deadlock_xml.nodes('//event') as tb(col)
这个SQL可以查询的出非常详细的资源争夺情况,如果想要有效的使用扩展事件,建议大家详细查看下官网的xml语法(SQL SERVER对xml的支持也是棒棒哒,期待2016版中的json支持)
是不是很清晰,一目了然,有了这个就可以去分析拉!
2 分析
根据xml文件内容或者扩展事件的监控内容,都可以整理为以下信息(开头的那个死锁分析):
查看事务1及事务2的执行计划如下:
结合表格及执行计划,可以大致推测死锁过程:
会话1:
这个过程中,刚好会话2进行这样的锁申请:
假设这个时候,会话1 中又执行了一次update操作(同一个事务中):
根据主键SeqCode查找到键值所在的 索引页 Index_Page,找到该页上面的 键值行 Index_key,对Index_Page持有IU锁,准备对Index_key持有U锁,但是发现 Index_key被会话2持有了U锁。
那么这个时候死锁就产生了(详见下图):
3 解决
想法子除去RID查找,直接index就找到数据,就不会发生这个死锁,也就是,在主键上面重新建立聚集索引,丢弃原先的非聚集索引主键。因为这样排除了RID的U锁申请与持有,直接是保持X锁 直至事务结束,同时可以直接根据主键来修改键值所在的数据页,减少的RID查询行的时间。
修改后的执行计划如下:
其锁申请释放的流程如下(详见截图):
以上就是本文的全部内容,希望本文的内容对大家的学习或者工作能带来一定的帮助,同时也希望多多支持!