SQL SERVER ->> Wait Stats

等待状态是隔离SQL SERVER性能问题的一个重要手段，从实例级别入手。可以大概看出SQL SERVER在过去某段时间内是否处于某种资源的吃紧状态。不过取决于你是否有建立有效的性能数据收集机制。sys.dm_os_wait_stats这张DMV的数据是从实例上次启动起收集的。

WITH Waits AS
 (
 SELECT
   wait_type,
   wait_time_ms / 1000. AS wait_time_s,
   100. * wait_time_ms / SUM(wait_time_ms) OVER() AS pct,
   ROW_NUMBER() OVER(ORDER BY wait_time_ms DESC) AS rn
 FROM sys.dm_os_wait_stats
 WHERE wait_type
   NOT IN
     ('CLR_SEMAPHORE', 'LAZYWRITER_SLEEP', 'RESOURCE_QUEUE',
   'SLEEP_TASK', 'SLEEP_SYSTEMTASK', 'SQLTRACE_BUFFER_FLUSH', 'WAITFOR',
   'CLR_AUTO_EVENT', 'CLR_MANUAL_EVENT')
   ) -- filter out additional irrelevant waits 

SELECT W1.wait_type,
 CAST(W1.wait_time_s AS DECIMAL(12, 2)) AS wait_time_s,
 CAST(W1.pct AS DECIMAL(12, 2)) AS pct,
 CAST(SUM(W2.pct) AS DECIMAL(12, 2)) AS running_pct
FROM Waits AS W1
 INNER JOIN Waits AS W2 ON W2.rn <= W1.rn
GROUP BY W1.rn,
 W1.wait_type,
 W1.wait_time_s,
 W1.pct
HAVING SUM(W2.pct) - W1.pct < 95; -- percentage threshold;

可以通过下面命令reset数据收集

DBCC SQLPERF ('sys.dm_os_wait_stats', CLEAR);
GO

参考：

https://msdn.microsoft.com/en-us/library/ms179984.aspx