确定持有锁的查询

项目
06/25/2013

数据库管理员通常需要识别影响数据库性能的锁定来源。

例如，您怀疑服务器的性能问题可能是由阻塞导致的。查询 sys.dm_exec_requests 时，您发现处于挂起模式的若干会话具有等待类型，指示锁定就是等待的资源。

查询 sys.dm_tran_locks 后，结果显示许多锁定处于未完成状态，但是已授予锁定的会话没有任何以 sys.dm_exec_requests 显示的活动请求。

此示例说明如何确定占用锁定的查询、查询的计划以及占用锁定时的 Transact-SQL 堆栈。本示例还说明了在扩展事件会话中如何使用配对目标。

若要完成此任务，需使用 SQL Server Management Studio 中的查询编辑器执行以下过程。

注意
本示例使用 AdventureWorks 数据库。

确定保持锁定的查询

在查询编辑器中发出以下语句：

-- Perform cleanup. 
IF EXISTS(SELECT * FROM sys.server_event_sessions WHERE name='FindBlockers')
    DROP EVENT SESSION FindBlockers ON SERVER
GO
-- Use dynamic SQL to create the event session and allow creating a -- predicate on the AdventureWorks database id.
--
DECLARE @dbid int

SELECT @dbid = db_id('AdventureWorks')

IF @dbid IS NULL
BEGIN
    RAISERROR('AdventureWorks is not installed. Install AdventureWorks before proceeding', 17, 1)
    RETURN
END

DECLARE @sql nvarchar(1024)
SET @sql = '
CREATE EVENT SESSION FindBlockers ON SERVER
ADD EVENT sqlserver.lock_acquired 
    (action 
        ( sqlserver.sql_text, sqlserver.database_id, sqlserver.tsql_stack,
         sqlserver.plan_handle, sqlserver.session_id)
    WHERE ( database_id=' + cast(@dbid as nvarchar) + ' AND resource_0!=0) 
    ),
ADD EVENT sqlserver.lock_released 
    (WHERE ( database_id=' + cast(@dbid as nvarchar) + ' AND resource_0!=0 ))
ADD TARGET package0.pair_matching 
    ( SET begin_event=''sqlserver.lock_acquired'', 
            begin_matching_columns=''database_id, resource_0, resource_1, resource_2, transaction_id, mode'', 
            end_event=''sqlserver.lock_released'', 
            end_matching_columns=''database_id, resource_0, resource_1, resource_2, transaction_id, mode'',
    respond_to_memory_pressure=1)
WITH (max_dispatch_latency = 1 seconds)'

EXEC (@sql)
-- 
-- Create the metadata for the event session
-- Start the event session
--
ALTER EVENT SESSION FindBlockers ON SERVER
STATE = START

在服务器上执行工作负荷后，在查询编辑器中发出以下语句来查找仍保持锁定的查询。

--
-- The pair matching targets report current unpaired events using 
-- the sys.dm_xe_session_targets dynamic management view (DMV)
-- in XML format.
-- The following query retrieves the data from the DMV and stores
-- key data in a temporary table to speed subsequent access and
-- retrieval.
--
SELECT 
objlocks.value('(action[@name="session_id"]/value)[1]', 'int')
        AS session_id,
    objlocks.value('(data[@name="database_id"]/value)[1]', 'int') 
        AS database_id,
    objlocks.value('(data[@name="resource_type"]/text)[1]', 'nvarchar(50)' ) 
        AS resource_type,
    objlocks.value('(data[@name="resource_0"]/value)[1]', 'bigint') 
        AS resource_0,
    objlocks.value('(data[@name="resource_1"]/value)[1]', 'bigint') 
        AS resource_1,
    objlocks.value('(data[@name="resource_2"]/value)[1]', 'bigint') 
        AS resource_2,
    objlocks.value('(data[@name="mode"]/text)[1]', 'nvarchar(50)') 
        AS mode,
    objlocks.value('(action[@name="sql_text"]/value)[1]', 'varchar(MAX)') 
        AS sql_text,
    CAST(objlocks.value('(action[@name="plan_handle"]/value)[1]', 'varchar(MAX)') AS xml) 
        AS plan_handle,    
    CAST(objlocks.value('(action[@name="tsql_stack"]/value)[1]', 'varchar(MAX)') AS xml) 
        AS tsql_stack
INTO #unmatched_locks
FROM (
    SELECT CAST(xest.target_data as xml) 
        lockinfo
    FROM sys.dm_xe_session_targets xest
    JOIN sys.dm_xe_sessions xes ON xes.address = xest.event_session_address
    WHERE xest.target_name = 'pair_matching' AND xes.name = 'FindBlockers'
) heldlocks
CROSS APPLY lockinfo.nodes('//event[@name="lock_acquired"]') AS T(objlocks)

--
-- Join the data acquired from the pairing target with other 
-- DMVs to return provide additional information about blockers
--
SELECT ul.*
    FROM #unmatched_locks ul
    INNER JOIN sys.dm_tran_locks tl ON ul.database_id = tl.resource_database_id AND ul.resource_type = tl.resource_type
    WHERE resource_0 IS NOT NULL
    AND session_id IN 
        (SELECT blocking_session_id FROM sys.dm_exec_requests WHERE blocking_session_id != 0)
    AND tl.request_status='wait'
    AND REPLACE(ul.mode, 'LCK_M_', '' ) = tl.request_mode

识别问题后，删除所有临时表和事件会话。

DROP TABLE #unmatched_locks
DROP EVENT SESSION FindBlockers ON SERVER

请参阅

参考

CREATE EVENT SESSION (Transact-SQL)

ALTER EVENT SESSION (Transact-SQL)

DROP EVENT SESSION (Transact-SQL)

sys.dm_xe_session_targets (Transact-SQL)

sys.dm_xe_sessions (Transact-SQL)

通过

确定持有锁的查询

确定保持锁定的查询

请参阅

参考

其他资源