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Wait Stats Investigation Expand / Collapse
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Posted Monday, September 10, 2012 11:56 PM
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Hi All

I'm using the following script to assess my highest wait_types ona fairly new SQL Server (+- 2 weeks)

SELECT TOP 15
wait_type ,
wait_time_ms ,
signal_wait_time_ms ,
wait_time_ms - signal_wait_time_ms AS resource_wait_time_ms ,
100.0 * wait_time_ms / SUM(wait_time_ms) OVER ( )
AS percent_total_waits ,
100.0 * signal_wait_time_ms / SUM(signal_wait_time_ms) OVER ( )
AS percent_total_signal_waits ,
100.0 * ( wait_time_ms - signal_wait_time_ms )
/ SUM(wait_time_ms) OVER ( ) AS percent_total_resource_waits
FROM sys.dm_os_wait_stats
WHERE wait_time_ms > 0 -- remove zero wait_time
AND wait_type NOT IN -- filter out additional irrelevant waits
( 'SLEEP_TASK', 'BROKER_TASK_STOP', 'BROKER_TO_FLUSH',
'SQLTRACE_BUFFER_FLUSH','CLR_AUTO_EVENT', 'CLR_MANUAL_EVENT',
'LAZYWRITER_SLEEP', 'SLEEP_SYSTEMTASK', 'SLEEP_BPOOL_FLUSH',
'BROKER_EVENTHANDLER', 'XE_DISPATCHER_WAIT', 'FT_IFTSHC_MUTEX',
'CHECKPOINT_QUEUE', 'FT_IFTS_SCHEDULER_IDLE_WAIT',
'BROKER_TRANSMITTER', 'FT_IFTSHC_MUTEX', 'KSOURCE_WAKEUP',
'LAZYWRITER_SLEEP', 'LOGMGR_QUEUE', 'ONDEMAND_TASK_QUEUE',
'REQUEST_FOR_DEADLOCK_SEARCH', 'XE_TIMER_EVENT', 'BAD_PAGE_PROCESS',
'DBMIRROR_EVENTS_QUEUE', 'BROKER_RECEIVE_WAITFOR',
'PREEMPTIVE_OS_GETPROCADDRESS', 'PREEMPTIVE_OS_AUTHENTICATIONOPS',
'WAITFOR', 'DISPATCHER_QUEUE_SEMAPHORE', 'XE_DISPATCHER_JOIN',
'RESOURCE_QUEUE' )
ORDER BY wait_time_ms DESC

The highest wait type is for PAGEIOLATCH_SH and it shows that this wait_type contributes 35% of the total waits.

Where can I start troubleshooting this wait?

Is this a sign of a slow disk subsystem or should I start looking at my CPU pressure or is it query related?

Any help would be great

Thanks

Post #1357147
Posted Tuesday, September 11, 2012 2:49 AM
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I think you mean its 35% of the wait time after excluding all those other waits.

it *may* be negligible in proportion to all waits.

Before looking at hardware you should really investigate the querys that are causing the waits - you can also look at the missing index stats, which may provide some clues.

If users are experiencing performance problems, what are they? is it only certain queries?, only on one database?, or just generally slow?

Post #1357205
Posted Tuesday, September 11, 2012 2:52 AM


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http://www.simple-talk.com/books/sql-books/troubleshooting-sql-server-a-guide-for-the-accidental-dba/
Start with chapter 1.



Gail Shaw
Microsoft Certified Master: SQL Server 2008, MVP
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

Post #1357210
Posted Tuesday, September 11, 2012 3:10 AM
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Thanks for the free book, Obi-Wan.

Looks pretty comprehensive from a first skim through, and small enough to read it all (*not* a 1200 page monster - which is good)
Post #1357217
Posted Tuesday, September 11, 2012 3:59 AM


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We'd have easily written 1200 pages, but the deadline was against us.


Gail Shaw
Microsoft Certified Master: SQL Server 2008, MVP
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

Post #1357253
Posted Tuesday, September 11, 2012 4:19 AM
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Hi Gail,


Just noticed your name in the sig line - and that you're technical reviewer on the book!

and apologies - yours isn't a picture of Obi-Wan either is it?








Post #1357273
Posted Tuesday, September 11, 2012 4:22 AM


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t.brown 89142 (9/11/2012)
Just noticed your name in the sig line - and that you're technical reviewer on the book!


Yup

and apologies - yours isn't a picture of Obi-Wan either is it?


It's Qui-gon Jinn from Phantom Menace.



Gail Shaw
Microsoft Certified Master: SQL Server 2008, MVP
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

Post #1357279
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