sys.dm_os_wait_stats 查看数据库等待信息

当用户告诉你数据库很慢的时候，你要怎么开始Narrowdown问题呢？SQL Server提供了sys.dm_os_wait_stats可以帮助我们查看CPU,内存或者IO的等待状况。SQL
Server执行过程中中等待信息会被记录到这个View中。

通过下面的语句我们可以抓取一段时间内SQL Server等待的累积信息，通过对这些信息进行排序可以找出资源瓶颈。

先看一下各个Wait等待的占比：

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

WHEREwait_type

NOT IN

('CLR_SEMAPHORE',
'LAZYWRITER_SLEEP',
'RESOURCE_QUEUE',

'SLEEP_TASK',
'SLEEP_SYSTEMTASK',
'SQLTRACE_BUFFER_FLUSH',
'WAITFOR',

'CLR_AUTO_EVENT',
'CLR_MANUAL_EVENT','BROKER_TASK_STOP')

) -- 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;

由于这个View是累积的，所以我们需要定期的收集统计信息，通过前后两次数据的比较获得这一段时间的等待状况。

--Create table topersist wait stats information:

CREATE TABLE ColWaitInfo

(

[wait_type] [nvarchar](60)
NOT NULL,

[waiting_tasks_count] [bigint] NOT
NULL,

[wait_time_ms] [bigint] NOT
NULL,

[max_wait_time_ms] [bigint] NOT
NULL,

[signal_wait_time_ms] [bigint] NOT
NULL,

[capture_time] [datetime] NOT
NULL,

[increment_id] [int] NOTNULL

);

ALTER TABLE ColWaitInfo ADD DEFAULT
(GETDATE())
FOR [capture_time];

--Insert waitstats info in a datestamped format for later querying:

DECLARE @DT DATETIME
;

SET @DT =
GETDATE() ;

DECLARE@increment_id
INT;

SELECT@increment_id =
MAX(increment_id)
+ 1 FROM ColWaitInfo

SELECT@increment_id =
ISNULL(@increment_id, 1)

INSERT INTO ColWaitInfo

([wait_type], [waiting_tasks_count],[wait_time_ms], [max_wait_time_ms],

[signal_wait_time_ms],[capture_time], [increment_id])

SELECT[wait_type], [waiting_tasks_count], [wait_time_ms],[max_wait_time_ms],

[signal_wait_time_ms],@DT, @increment_id

FROM sys.dm_os_wait_stats;

下面的语句用来查询间隔内的累积信息：

DECLARE@max_increment_id
INT

------------------------------------------------------------------

--Determinemost-recent increment_id

------------------------------------------------------------------

SELECT@max_increment_id
= MAX(increment_id)

FROM ColWaitInfo

------------------------------------------------------------------

--Present Waitsresults for period

------------------------------------------------------------------

SELECT DOWS1.wait_type,

(DOWS1.waiting_tasks_count
-DOWS2.waiting_tasks_count)
AS[waiting_tasks_count],

(DOWS1.wait_time_ms
- DOWS2.wait_time_ms)
AS [wait_time_ms],

DOWS1.max_wait_time_ms,

(DOWS1.signal_wait_time_ms
-DOWS2.signal_wait_time_ms)
AS[signal_wait_time_ms],

DATEDIFF(ms, DOWS2.capture_time, DOWS1.capture_time)
AS [elapsed_time_ms],

DOWS1.capture_timeAS [last_time_stamp],DOWS2.capture_time
AS[previous_time_stamp]

FROM

(

SELECT wait_type,waiting_tasks_count, wait_time_ms, max_wait_time_ms,

signal_wait_time_ms, capture_time,increment_id

FROMColWaitInfo

WHEREincrement_id = @max_increment_id

)AS DOWS1

INNER JOIN

(

SELECT wait_type,waiting_tasks_count, wait_time_ms, max_wait_time_ms,

signal_wait_time_ms, capture_time,increment_id

FROMColWaitInfo

WHEREincrement_id =(@max_increment_id
-1)

)AS DOWS2
ON DOWS1.wait_type
= DOWS2.wait_type

WHERE (DOWS1.wait_time_ms
- DOWS2.wait_time_ms)
> 0

AND DOWS1.wait_type
NOT IN

('CLR_SEMAPHORE',
'LAZYWRITER_SLEEP',
'RESOURCE_QUEUE',

'SLEEP_TASK',
'SLEEP_SYSTEMTASK',
'SQLTRACE_BUFFER_FLUSH',
'WAITFOR',

'CLR_AUTO_EVENT',
'CLR_MANUAL_EVENT','BROKER_TASK_STOP')
-- filter out additional irrelevant waits

ORDER BY (DOWS1.wait_time_ms
- DOWS2.wait_time_ms)
DESC;