1. ©2011 Hewlett-Packard Development Company, L.P.
The information contained herein is subject to change without
notice
SQL Server 2008 WAITS
Miroslav Dimitrov

2. How SQL Server works ?!
• SQL Server OS
– Schedulers
– Workers
Lists to which workers can be assigned:
worker
waiter
runnable
I/O
timer

3. WAITS – What are they ?!
• SQL Server 2000
– DBCC SQLPERF
– ”sysprocesses” system view (waittype column)
• SQL Server 2005 - DMVs
– sys.dm_os_wait_stats – wait statistics
– sys.dm_os_waiting_tasks – task-level wait information
• SQL Server 2008
– new waits
– Solve the problem with fine-grained analysis of wait statistics in SQL Server 2005

4. Types of WAITS
• Resource waits
• Queue waits
• External waits
A SQL Server worker thread is not considered to be waiting if any of the
following is true:
• A resource becomes available.
• A queue is nonempty.
• An external process finishes.

5. Waits
• Memory Waits
– CMEMTHREAD
– RESOURCE_SEMAPHORE
• Disk I/O Waits
– IO_COMPLETION
– ASYNC_IO_COMPLETION
– WRITELOG
– PAGEIOLATCH_*
• Blocking waits
– LCK_*

6. Waits (continued)
• CPU
– CXPACKET
– SOS_SCHEDULER_YIELD
• Network Waits
– ASYNC_NETWORK_IO
– DBMIRROR_SEND
• System waits
– LAZYWRITER_SLEEP
– REQUEST_FOR_DEADLOCK_SEARCH
– SQLTRACE_BUFFER_FLUSH
– XE_TIMER_EVENT
– FT_IFTS_SCHEDULER_IDLE_WAIT
– LOGMGR_QUEUE
– CHECKPOINT_QUEUE
– SLEEP_TASK
– BROKER_TO_FLUSH

7. Waits (continued)
• Preemptive Wait Types
• SQL Server extended events

8. Demo time

9. References
• http://msdn.microsoft.com/en-
us/library/ms179984%28v=SQL.90%29.aspx
• http://msdn.microsoft.com/en-
us/library/ms179984%28v=SQL.100%29.aspx
• http://msdn.microsoft.com/en-
us/library/ms179984%28v=SQL.105%29.aspx