我有关于死锁的数据,但我不明白它们为什么会发生

Question

我在我的大型Web应用程序中收到了很多死锁.

如何自动重新运行死锁事务？(ASP.NET MVC/SQL Server)

在这里,我想重新运行死锁事务,但我被告知摆脱死锁 - 它比试图赶上死锁要好得多.

所以我花了整整一天的时间用SQL Profiler,设置跟踪键等等.这就是我得到的.

有一张Users桌子.我有一个非常高的可用页面与以下查询(它不是唯一的查询,但它是导致麻烦的那个)

UPDATE Users
SET views = views + 1
WHERE ID IN (SELECT AuthorID FROM Articles WHERE ArticleID = @ArticleID)

然后在所有页面中都有以下查询:

User = DB.Users.SingleOrDefault(u => u.Password == password && u.Name == username);

这就是我从cookie中获取用户的地方.

通常会发生死锁,并且第二个Linq-to-SQL查询被选为受害者,因此它不会运行,并且我的站点用户会看到错误屏幕.

这是来自SQL事件探查器捕获的.XDL图形的信息(它只是第一个死锁,它不是唯一的.整个列表都是巨大的.):

<deadlock-list>
    <deadlock victim="process824df048">
        <process-list>
            <process id="process824df048" taskpriority="0" logused="0" waitresource="PAGE: 7:1:13921" waittime="1830" ownerId="91418" transactionname="SELECT" lasttranstarted="2010-05-31T12:17:37.663" XDES="0x868175e0" lockMode="S" schedulerid="2" kpid="5076" status="suspended" spid="72" sbid="0" ecid="2" priority="0" trancount="0" lastbatchstarted="2010-05-31T12:17:37.663" lastbatchcompleted="2010-05-31T12:17:37.663" clientapp=".Net SqlClient Data Provider" hostname="WIN-S41KV2CLS67" hostpid="6920" isolationlevel="read committed (2)" xactid="91418" currentdb="7" lockTimeout="4294967295" clientoption1="671088672" clientoption2="128056">
                <executionStack>
                    <frame procname="adhoc" line="1" stmtstart="74" sqlhandle="0x02000000de1cb30b5b2e40e31ffb345af3c7529430b559c2">
*password-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------     </frame>
                    <frame procname="unknown" line="1" sqlhandle="0x000000000000000000000000000000000000000000000000">
unknown     </frame>
                </executionStack>
                <inputbuf>
                </inputbuf>
            </process>
            <process id="process8765fb88" taskpriority="0" logused="216" waitresource="PAGE: 7:1:14196" waittime="1822" ownerId="91408" transactionname="UPDATE" lasttranstarted="2010-05-31T12:17:37.640" XDES="0x86978e90" lockMode="IX" schedulerid="2" kpid="5216" status="suspended" spid="73" sbid="0" ecid="0" priority="0" trancount="2" lastbatchstarted="2010-05-31T12:17:37.557" lastbatchcompleted="2010-05-31T12:17:37.557" clientapp=".Net SqlClient Data Provider" hostname="WIN-S41KV2CLS67" hostpid="6920" loginname="sdfkj93jks9sl" isolationlevel="read committed (2)" xactid="91408" currentdb="7" lockTimeout="4294967295" clientoption1="671088672" clientoption2="128056">
                <executionStack>
                    <frame procname="database.dbo.UpdateUserStats" line="31" stmtstart="1794" stmtend="2088" sqlhandle="0x03000700bac8836333e58f00879d00000100000000000000">
UPDATE Users
    SET Views = Views + 1
    WHERE ID IN (SELECT AuthorID FROM Articles WHERE ArticleID = @ArticleID)     </frame>
                    <frame procname="adhoc" line="1" stmtstart="84" sqlhandle="0x01000700b7c78e0760dd3f81000000000000000000000000">
EXEC @RETURN_VALUE = [dbo].[UpdateUserStats] @UserID = @p0    </frame>
                    <frame procname="unknown" line="1" sqlhandle="0x000000000000000000000000000000000000000000000000">
unknown     </frame>
                </executionStack>
                <inputbuf>
(@p0 int,@RETURN_VALUE int output)EXEC @RETURN_VALUE = [dbo].[UpdateUserStats] @UserID = @p0   </inputbuf>
            </process>
            <process id="process86ce0988" taskpriority="0" logused="10000" waittime="1806" schedulerid="1" kpid="2604" status="suspended" spid="72" sbid="0" ecid="0" priority="0" trancount="0" lastbatchstarted="2010-05-31T12:17:37.663" lastbatchcompleted="2010-05-31T12:17:37.663" clientapp=".Net SqlClient Data Provider" hostname="WIN-S41KV2CLS67" hostpid="6920" loginname="sdfkj93jks9sl" isolationlevel="read committed (2)" xactid="91418" currentdb="7" lockTimeout="4294967295" clientoption1="671088672" clientoption2="128056">
                <executionStack>
                    <frame procname="adhoc" line="1" stmtstart="74" sqlhandle="0x02000000de1cb30b5b2e40e31ffb345af3c7529430b559c2">
*password-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------     </frame>
                    <frame procname="unknown" line="1" sqlhandle="0x000000000000000000000000000000000000000000000000">
unknown     </frame>
                </executionStack>
                <inputbuf>
*password--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------    </inputbuf>
            </process>
        </process-list>
        <resource-list>
            <pagelock fileid="1" pageid="13921" dbid="7" objectname="database.dbo.Users" id="lock85535c80" mode="IX" associatedObjectId="72057594046382080">
                <owner-list>
                    <owner id="process8765fb88" mode="IX"/>
                </owner-list>
                <waiter-list>
                    <waiter id="process824df048" mode="S" requestType="wait"/>
                </waiter-list>
            </pagelock>
            <pagelock fileid="1" pageid="14196" dbid="7" objectname="database.dbo.Users" id="lock8469f980" mode="SIU" associatedObjectId="72057594046382080">
                <owner-list>
                    <owner id="process86ce0988" mode="S"/>
                </owner-list>
                <waiter-list>
                    <waiter id="process8765fb88" mode="IX" requestType="convert"/>
                </waiter-list>
            </pagelock>
            <exchangeEvent id="Pipe894b0680" WaitType="e_waitPipeGetRow" nodeId="0">
                <owner-list>
                    <owner id="process824df048"/>
                </owner-list>
                <waiter-list>
                    <waiter id="process86ce0988"/>
                </waiter-list>
            </exchangeEvent>
        </resource-list>
    </deadlock>

我读了很多关于死锁的内容......我不明白为什么这会导致死锁.

很明显,这两个查询都经常运行.至少每秒一次.可能更频繁(在线300-400名用户).所以它们可以很容易地在同一时间运行,但为什么会导致死锁呢？请帮忙.

谢谢

Answer 1

您需要捕获死锁图.附加Profiler并捕获死锁图事件类.保存.XDL图表并将该信息添加到您的帖子中.

在此之前,很明显你的DB.Users.SingleOrDefault查询至少要求Name上的索引,如果没有名称和密码:

CREATE INDEX idxUsersNamePassword on Users(Name,Password);

我希望用户已经拥有ID的索引,而Article还有一个ArticleID索引,它也涵盖了AuthorID.假设Users.ID和Articles.ArticleID是它们各自的表中的PK,它们可能是各自的聚簇键,所以它是真的.值得仔细检查一下.

而且,由于我已经在您之前的帖子中回答了您的问题,因此您决定继续前进并保持未回答,您应该考虑打开快照隔离:

ALTER DATABASE ... SET READ_COMMITTED_SNAPSHOT ON

除此之外,以明文形式存储密码是一个主要的#fail.

死锁信息后更新

有三个进程(请求):

• A)...正在运行的F048 SELECT ... FROM Users WHERE Password = ... and Name = ...
• B)...... 0988正在运行 SELECT ... FROM Users WHERE Password = ... and Name = ...
• C)...正在运行的FB88 UPDATE ...

死锁周期是:

1. C等待第IX页锁定,被A的S锁定阻止
2. B等待Page S锁定,被C的IX锁定阻止
3. 等待并行交换资源,被B阻止

因此循环是C-> A-> B-> C.

从涉及的两个SELECT决定1)使用并行计划和2)使用页面锁定显然他们对整个Users表进行端到端扫描的事实.所以问题是,正如我预测的那样,用户上缺少索引(名称,密码)会导致查询扫描过多的数据.添加索引会将SELECT转换为Nc索引上的直接SEEK和Clustered索引上的查找,这将大大减少与UPDATE重叠的窗口.现在UPDATE几乎可以保证与所有 SELECT 冲突,因为每个SELECT都保证读取每一行.

添加索引将缓解当前的问题.使用快照隔离将掩盖问题,因为除非添加(名称,密码)索引,否则仍将发生端到端扫描.或者只有(姓名)可能也会起作用.

为了将来的可扩展性,更新每个页面视图上的"视图"列将不起作用.延迟更新,批量聚合计数更新,垂直分区Users表和取出Views列是可行的替代方案.