The document discusses wait statistics and wait types in SQL Server. It provides an overview of defining, viewing, collecting and reviewing wait data using dynamic management views and wait statistics. It also simplifies the SQL Server execution model using a grocery store checkout line analogy. Specific wait types are explained such as CXPACKET, OLEDB, PAGEIOLATCH_X, PAGELATCH_X and LATCH_X. Guidelines and potential resolutions are provided for analyzing and addressing top wait events.

1. WHAT ARE YOU Jason Strate
Database Architect
Pragmatic Works, Inc.
WAITING FOR?

2. WHAT ARE YOU WAITING FOR?
You…
SQL Server
Developers
DBAs

3. AGENDA
Defining Viewing Collecting Reviewing

4. AGENDA Defining
Defining Viewing Collecting Reviewing

5. WAIT, WAIT… I’LL TELL YOU
Waits & Queues Methodology

6. SO WHAT?!

7. WAIT STATISTICS
Identity
Prioritize Measure

8. EXECUTION MODEL (SIMPLIFIED)
Grocery Store
 Cashier
 Scheduler
 Customer
 Query
 Checkout Line
 Queue
 Running
 Runnable
 Suspended

9. EXECUTION MODEL (SIMPLIFIED)
RUNNING

10. EXECUTION MODEL (SIMPLIFIED)
RUNNABLE RUNNING

11. EXECUTION MODEL (SIMPLIFIED)
RUNNABLE RUNNING
WAIT
SUSPENDED

12. EXECUTION MODEL (SIMPLIFIED)
RUNNABLE RUNNING
SUSPENDED

13. EXECUTION MODEL (SIMPLIFIED)
RUNNABLE RUNNING
WAIT TIME
SUSPENDED

14. EXECUTION MODEL (SIMPLIFIED)
RUNNABLE RUNNING
SUSPENDED

15. EXECUTION MODEL (SIMPLIFIED)
RUNNABLE RUNNING
SUSPENDED

16. EXECUTION MODEL (SIMPLIFIED)
RUNNABLE RUNNING
SIGNAL WAIT SUSPENDED
TIME

17. AGENDA Viewing
Defining Viewing Collecting Reviewing

18. WAIT DMVS
 sys.dm_os_wait_stats
 Accumulated statistics on tasks that have waited for resources
 sys.dm_os_waiting_tasks
 Information on queued tasks waiting for resources

19. WAITS STATS

20. WAITS STATS
Name of the wait type.

21. WAITS STATS
Number of waits on this wait type. This counter is
incremented at the start of each wait.

22. WAITS STATS
Total wait time for this wait type in milliseconds. This
time is inclusive of signal_wait_time_ms.

23. WAITS STATS
Maximum wait time on this wait type.

24. WAITS STATS
Difference between the time that the waiting thread
was signaled and when it started running.

25. WAITING TASKS

26. WAITING TASKS

27. WAITING TASKS
ID of the session associated with the task.

28. WAITING TASKS
Total wait time for this wait type, in milliseconds. This
time is inclusive of signal_wait_time.

29. WAITING TASKS
Name of the wait type.

30. WAITING TASKS
ID of the session that is blocking the request. If this
column is NULL, the request is not blocked, or the
session information of the blocking session is not
available

31. WAITING TASKS
Difference between the time that the waiting thread
was signaled and when it started running.

32. VIEWING WAIT STATS Demo

33. AGENDA Collecting
Defining Viewing Collecting Reviewing

34. DMV STATS

35. MANAGEMENT DATA WAREHOUSE

36. DO-IT-YOURSELF
Collect Summarize Analyze

37. DO-IT-YOURSELF Demo

38. AGENDA Reviewing
Defining Viewing Collecting Reviewing

39. WAIT T YPES
 Tied to process
 Audit
 Buffer
 I/O
 Indexing
 Lock
 SQLOS
 Categories
 Background
 External
 Queue

40. BACKGROUND WAITS
CLR_SEMAPHORE CHECKPOINT_QUEUE
LAZYWRITER_SLEEP XE_TIMER_EVENT
RESOURCE_QUEUE BROKER_TO_FLUSH
Not all inclusive
SLEEP_TASK BROKER_TASK_STOP
SLEEP_SYSTEMTASK CLR_MANUAL_EVENT
WAITFOR CLR_AUTO_EVENT
LOGMGR_QUEUE XE_DISPATCHER_WAIT

41. CXPACKET
Translation
•Contention with queries the at are executing in parallel; across multiple CPUs.
Generally due to unbalanced execution across CPUs or tasks ahead of query
executing longer than expected.
Guideline
•>5% for OLTP
•>10% for data warehouses
Resolution
•Review indexing
•Tune queries
•Adjust Max Degree of parallelism
•Research cost threshold for parallelism

42. OLEDB
Translation
• Occurs when SQL Server calls the Microsoft SQL Native Client OLE DB
Provider. It indicates the duration of calls to the OLE DB provider.
Guideline
• Examine when it is a top wait and exceeds background waits. (TOP 5)
Resolution
• Identify queries with OLE DB waits with extended events or
sys.dm_os_waiting_tasks
• Check application placement and Disk secs/Read and Disk secs/Write
• Tune transactions using RPC, Distributed (Linked Server), and Full Text
Search

43. PAGEIOLATCH_X
Translation
• Contention caused by disk to memory transfer. Typically suggests disk IO
subsystem issues.
Guideline
• Examine when it is a top wait and exceeds background waits. (TOP 5)
Resolution
• Review Physical disk: disk seconds/read and Physical disk: disk
seconds/write and SQL Server Buffer Manager: Page Life Expectancy
• Review information for virtual file stats
• Reconfigure disk to improve IO throughput
• Analyze indexes to reduce need to move data to memory
• Increase memory to increase data available to SQL Server

44. PAGELATCH_X
Translation
• Contention between short term light weight synchronization objects.
Latches are not held for the duration of a transaction. Occur in the
buffer pool but unrelated to IO requests.
Guideline
• Examine when it is a top wait and exceeds background waits. (TOP 5)
Resolution
• Check tempdb configuration
• Additional data files
• Trace Flag 1118
• Troubleshoot memory pressure

45. LATCH_X
Translation
• Contention between short term light weight synchronization objects.
Latches are not held for the duration of a transaction. Non buffer
pool related.
Guideline
• Examine when it is a top wait and exceeds background waits. (TOP 5)
Resolution
• Review T-SQL generating LATCH waits using extended events.
• Examine memory items in sys.dm_os_latch_stats
• Partition table across multiple files

46. SQL SERVER MVP DEEP DIVES, VOLUME 2
 www.operationsmile.org
 www.manning.com/delaney

47. RESOURCES
Jason e: jstrate@pragmaticworks.com
Strate
e: jasonstrate@gmail.com
b: www.jasonstrate.com
t: StrateSQL
Resources jasonstrate.com/go/Waits2013/