我有两个非常简单的表,让我们称它们为[UserData1]和[UserData2].它们都有[UserId]列作为主键.我正在针对这两个表运行两种类型的查询.一个是SELECT语句,它返回特定用户的组合数据:
- SELECT <a subset of columns from both tables>
- FROM [UserData1] ud1
- FULL OUTER JOIN [UserData2] ud2 ON ud1.[UserId] = ud2.[UserId]
- WHERE
- ud1.[UserId] = @UserId OR ud2.[UserId] = @UserId
- BEGIN TRANSACTION
- UPDATE [UserData1]
- SET <new values>
- WHERE [UserId] = @UserId
- UPDATE [UserData2]
- SET <new values>
- WHERE [UserId] = @UserId
- COMMIT TRANSACTION
这里的问题是在SELECT语句中获取共享表锁的顺序是不确定的,如果sql Server决定在[UserData1]之前锁定[UserData2],这可能(并且实际上)会导致传统的死锁情况.在这种情况下,避免死锁的最佳方法是什么?
将这些表合并到一个表中,对吗?我希望这很容易.假设有理由将它们分开.
READ UNCOMMITTED / NOLOCK提示?假设不能容忍脏读.
SNAPSHOT隔离级别?这样可以解决问题,但我不确定所涉及的开销.
所以问题归结为:有没有办法保证获取连接表的锁定顺序?
起初我认为这可以通过FORCE ORDER查询提示来实现,但后来我通过实验发现它不一定强制执行表被锁定的顺序.在这种特殊情况下的另一个解决方案是为每个表发出单独的SELECT查询,然后在应用程序层中组合两个单行记录集,但是如果我需要为多个用户进行查询,我仍然希望得到所有导致一个记录集.
更新:
这是死锁跟踪的摘录:
- Deadlock encountered .... Printing deadlock information
- Wait-for graph
- Node:1
- KEY: 17:72057594039173120 (e21762ccf3dc) CleanCnt:3 Mode:X Flags: 0x1
- Grant List 1:
- Owner:0x00000020F75B0480 Mode: X Flg:0x40 Ref:0 Life:02000000 SPID:72 ECID:0 XactLockInfo: 0x00000020EB13ED68
- SPID: 72 ECID: 0 Statement Type: UPDATE Line #: 1
- Input Buf: Language Event: (@UserId bigint,@DataColumn2 int)update
- Requested by:
- ResType:LockOwner Stype:'OR'Xdes:0x00000020FC98DA40 Mode: S SPID:75 BatchID:0 ECID:0 TaskProxy:(0x00000020DAB38608) Value:0xf75abbc0 Cost:(0/0)
- Node:2
- KEY: 17:72057594039107584 (e21762ccf3dc) CleanCnt:9 Mode:S Flags: 0x1
- Grant List 1:
- Owner:0x00000020EEBFE580 Mode: S Flg:0x40 Ref:1 Life:00000000 SPID:75 ECID:0 XactLockInfo: 0x00000020FC98DA80
- SPID: 75 ECID: 0 Statement Type: SELECT Line #: 1
- Input Buf: Language Event: (@UserId bigint)select [t].[UserId],t.[DataColumn2],t1.[DataColumn1]
- Requested by:
- ResType:LockOwner Stype:'OR'Xdes:0x00000020EB13ED28 Mode: X SPID:72 BatchID:0 ECID:0 TaskProxy:(0x0000001F671C6608) Value:0xf75b5400 Cost:(0/456)
- Victim Resource Owner:
- ResType:LockOwner Stype:'OR'Xdes:0x00000020FC98DA40 Mode: S SPID:75 BatchID:0 ECID:0 TaskProxy:(0x00000020DAB38608) Value:0xf75abbc0 Cost:(0/0)
- deadlock-list
- deadlock victim=process20fda2ccf8
- process-list
- process id=process20fda2ccf8 taskpriority=0 logused=0 waitresource=KEY: 17:72057594039173120 (e21762ccf3dc) waittime=4526 ownerId=3416711 transactionname=SELECT lasttranstarted=2013-07-11T18:42:20.943 XDES=0x20fc98da40 lockMode=S schedulerid=20 kpid=2800 status=suspended spid=75 sbid=0 ecid=0 priority=0 trancount=0 lastbatchstarted=2013-07-11T18:42:20.950 lastbatchcompleted=2013-07-11T18:42:20.950 lastattention=1900-01-01T00:00:00.950 clientapp=.Net sqlClient Data Provider hostname=hostname hostpid=27716 loginname=loginname isolationlevel=read committed (2) xactid=3416711 currentdb=17 lockTimeout=4294967295 clientoption1=671088672 clientoption2=128056
- executionStack
- frame procname=adhoc line=1 stmtstart=36 sqlhandle=0x020000001fcbbe1423a0c65cc8411344c6040e879195af3a0000000000000000000000000000000000000000
- select [t].[UserId],t1.[DataColumn1] from [UserData1] t1 full outer join [UserData2] t on t1.[UserId]=t.[UserId] where t.[UserId]=@UserId or t1.[UserId]=@UserId option (force order)
- frame procname=unknown line=1 sqlhandle=0x0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
- unknown
- inputbuf
- (@UserId bigint)select [t].[UserId],t1.[DataColumn1] from [UserData1] t1 full outer join [UserData2] t on t1.[UserId]=t.[UserId] where t.[UserId]=@UserId or t1.[UserId]=@UserId option (force order)
- process id=process20fd055498 taskpriority=0 logused=456 waitresource=KEY: 17:72057594039107584 (e21762ccf3dc) waittime=4525 ownerId=3416764 transactionname=user_transaction lasttranstarted=2013-07-11T18:42:20.960 XDES=0x20eb13ed28 lockMode=X schedulerid=9 kpid=6024 status=suspended spid=72 sbid=0 ecid=0 priority=0 trancount=2 lastbatchstarted=2013-07-11T18:42:20.970 lastbatchcompleted=2013-07-11T18:42:20.970 lastattention=1900-01-01T00:00:00.970 clientapp=.Net sqlClient Data Provider hostname=hostname hostpid=27716 loginname=loginname isolationlevel=read committed (2) xactid=3416764 currentdb=17 lockTimeout=4294967295 clientoption1=671088672 clientoption2=128056
- executionStack
- frame procname=adhoc line=1 stmtstart=508 sqlhandle=0x02000000c0d74a32597ec460559a2d5dbdc92f7746cdce270000000000000000000000000000000000000000
- update UserData2 set [LastModified]=getutcdate(),[DataColumn2]=[DataColumn2]+@DataColumn2Increment where [UserId]=@UserId
- frame procname=unknown line=1 sqlhandle=0x0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
- unknown
- inputbuf
- (@UserId bigint,@DataColumn2Increment int)update UserData2 set [LastModified]=getutcdate(),[DataColumn2]=[DataColumn2]+@DataColumn2Increment where [UserId]=@UserId
- resource-list
- keylock hobtid=72057594039173120 dbid=17 objectname=database_name.dbo.UserData1 indexname=1 id=lock20ec75b380 mode=X associatedObjectId=72057594039173120
- owner-list
- owner id=process20fd055498 mode=X
- waiter-list
- waiter id=process20fda2ccf8 mode=S requestType=wait
- keylock hobtid=72057594039107584 dbid=17 objectname=database_name.dbo.UserData2 indexname=1 id=lock20ec07f600 mode=S associatedObjectId=72057594039107584
- owner-list
- owner id=process20fda2ccf8 mode=S
- waiter-list
- waiter id=process20fd055498 mode=X requestType=wait
显然,在[UserData1]之前,运行SELECT语句的进程在[UserData2]表上获取了一个锁,尽管有FORCE ORDER提示.