SQLServer数据库优化与管理——锁，阻塞，死锁篇

1侦测阻塞问题
阻塞会发生在很多情况下，它会引起终端用户的响应时间变长。而且由于锁住了数据，
可能会得不到想要的结果，甚至会产生连接超时等问题。
sQL Server提供了–些工具来侦测基于锁的阻塞，比如相关的DMVs、性能监视器、
SQLDiag等。下面来简要介绍一下。
.1) PerfMon counters为性能监视器，其中SQL Server:General Statistics事件中的
Processes blocked计数器，显示被阻塞进程的数量。还可以在SQL Server:Wait Statistics事
件的Lock Waits计数器中查看锁的数量和锁的持续时间。但是得到的只是概要信息。
2 ) DMVs:可以使用sys.dm_os_waiting_tasks来返回当前正在等待的任务信息。对于
这个DMV的说明，请查阅联机丛书。注意DMV 返回的是任务级别的信息，而不是会话级
别的，如果-个查询是并行运行，其中一个线程被阻塞，这个DMV只会显示这个线程的信
息。某些情况下，sys.dm_os_waiting_tasks中 blocking_session_id可能为null，因为没有正
在阻塞的会话，或者SQL Server无法标识这个会话。但是在以下情形下blocking_session_.
id会出现负数。
-2:被锁定的资源属于一个孤立的分布式事务。
…
-3:被锁定的资源属于–个延迟恢复事务。
.
-4:门锁等待。
下面是查看阻塞持续时间超过5000ms的会话。

SELECT  W.session_id AS waiting_session_id , 
        W.waiting_task_address , 
        W.wait_duration_ms , 
        W.wait_type , 
        W.blocking_session_id , 
        W.resource_description 
FROM    sys.dm_os_waiting_tasks AS W 
WHERE   W.wait_duration_ms > 5000 
        AND blocking_session_id IS NOT NULL;

也可以用下面的语句查看库内所有在WAIT状态的锁，并了解它们在等待什么锁。

USE AdventureWorks2008R2
GO 
SELECT  L1.resource_type ,
        DB_NAME(L1.resource_database_id) AS DatabaseName ,
        CASE L1.resource_type
          WHEN 'OBJECT'
          THEN OBJECT_NAME(L1.resource_associated_entity_id,
                           L1.resource_database_id)
          WHEN 'DATABASE' THEN 'DATABASE'
          ELSE CASE WHEN L1.resource_database_id = DB_ID()
                    THEN ( SELECT   OBJECT_NAME(object_id,
                                                L1.resource_database_id)
                           FROM     sys.partitions
                           WHERE    hobt_id = L1.resource_associated_entity_id
                         )
                    ELSE NULL
               END
        END AS ObjectName ,
        L1.resource_description ,
        L1.request_session_id ,
        L1.request_mode ,
        L1.request_status
FROM    sys.dm_tran_locks AS L1
        JOIN sys.dm_tran_locks AS L2 ON L1.resource_associated_entity_id = L2.resource_associated_entity_id
WHERE   L1.request_status <> L2.request_status
        AND ( L1.resource_description = L2.resource_description
              OR ( L1.resource_description IS NULL
                   AND L2.resource_description IS NULL
                 )
            )
ORDER BY L1.resource_database_id ,
        L1.resource_associated_entity_id ,
        L1.request_status ASC;

返回阻塞的信息及相关语句。

SELECT  T.session_id AS waiting_session_id ,
        DB_NAME(L.resource_database_id) AS DatabaseName ,
        T.wait_duration_ms / 60000. AS duration_in_minutes ,
        T.waiting_task_address ,
        L.request_mode ,
        ( SELECT    SUBSTRING(Q.text, ( R.statement_start_offset / 2 ) + 1,
                              ( ( CASE R.statement_end_offset
                                    WHEN -1 THEN DATALENGTH(Q.text)
                                    ELSE R.statement_end_offset
                                  END - R.statement_start_offset ) / 2 ) + 1)
          FROM      sys.dm_exec_requests AS R
                    CROSS APPLY sys.dm_exec_sql_text(R.sql_handle) AS Q
          WHERE     R.session_id = L.request_session_id
        ) AS waiting_query_text ,
        L.resource_type ,
        L.resource_associated_entity_id ,
        T.wait_type ,
        T.blocking_session_id ,
        T.resource_description AS blocking_resource_description ,
        CASE WHEN T.blocking_session_id > 0
             THEN ( SELECT  ST2.text
                    FROM    sys.sysprocesses AS P
                            CROSS APPLY sys.dm_exec_sql_text(P.sql_handle) AS ST2
                    WHERE   P.spid = T.blocking_session_id
                  )
             ELSE NULL
        END AS blocking_query_text
FROM    sys.dm_os_waiting_tasks AS T
        JOIN sys.dm_tran_locks AS L ON T.resource_address = L.lock_owner_address
WHERE   T.wait_duration_ms > 5000
        AND T.session_id > 50;

在 Extended Events中，默认的事件会话是system_health，用于收集 SQL Server发生
的错误，包括死锁信息。system_health会话使用-个名为ring_buffer的目标，来收集内存
中的事件信息，然后以XML格式存储在sys.dm_xe_session_targets 这个DMV中。另外可
以把这个DMV通过关联另外-个DMV: sys.dm_xe_sessions，获取相关信息。下面是查询
死锁信息的语句:

USE Master
GO
SELECT  xed.value('@timestamp', 'datetime') AS Creation_Date ,
        xed.query('.') AS Extend_Event
FROM    ( SELECT    CAST([target_data] AS XML) AS Target_Data
          FROM      sys.dm_xe_session_targets AS xt
                    INNER JOIN sys.dm_xe_sessions AS xs ON xs.address = xt.event_session_address
          WHERE     xs.name = N'system_health'
                    AND xt.target_name = N'ring_buffer'
        ) AS XML_Data
        CROSS APPLY Target_Data.nodes('RingBufferTarget/event[@name="xml_deadlock_report"]')
        AS XEventData ( xed )
ORDER BY Creation_Date DESC

下面的DMV代码可以用来捕获阻塞信息。

SELECT  dtl.request_session_id AS WaitingSessionID ,
        der.blocking_session_id AS BlockingSessionID ,
        dowt.resource_description ,
        der.wait_type ,
        dowt.wait_duration_ms ,
        DB_NAME(dtl.resource_database_id) AS DatabaseName ,
        dtl.resource_associated_entity_id AS WaitingAssociatedEntity ,
        dtl.resource_type AS WaitingResourceType ,
        dtl.request_type AS WaitingRequestType ,
        dest.[text] AS WaitingTSql ,
        dtlbl.request_type BlockingRequestType ,
        destbl.[text] AS BlockingTsql
FROM    sys.dm_tran_locks AS dtl
        JOIN sys.dm_os_waiting_tasks AS dowt ON dtl.lock_owner_address = dowt.resource_address
        JOIN sys.dm_exec_requests AS der ON der.session_id = dtl.request_session_id
        CROSS APPLY sys.dm_exec_sql_text(der.sql_handle) AS dest
        LEFT JOIN sys.dm_exec_requests derbl ON derbl.session_id = dowt.blocking_session_id
        OUTER APPLY sys.dm_exec_sql_text(derbl.sql_handle) AS destbl
        LEFT JOIN sys.dm_tran_locks AS dtlbl ON derbl.session_id = dtlbl.request_session_id;

其中resource_description列的值如下(不同的机器值会不-一样):
ridlock fileid=1 pageid=411 dbid=2 id=lock368aab480 mode=X associatedObject-
Id–4395513238772318208
对于dbid=2，通过SELECT Db_name(2)可以知道是在TempDB中运行。mode=-X，证明
加上了排他锁，因为已经在实际 UPDATE，所以已经从U锁升级到X锁。至于associatedObj
ectld=4395513238772318208.前而已经提讨，可用以下代码查看：

SELECT OBJECT_MAME(i.objectid),
.i.name
FROM-sys.partitions AS p
·
INNER JoIN sys.indexes As i ON i.object_id=p.object_id 
AND i.index_id=p.index_id
wHERE p.partition_id - 4395513238772318208，