1. Wait Stats and You

2. Bio – Greg Celentano
SQL DBA – Manufacturing ERP and MES Systems Reporting (SSRS, PowerBI, etc.) Wife, 2yo daughter, and grey hair Active CrossFit’er RI SQL User Group

3. https://safetyismygoal. files. wordpress

4. What are they? Well…..Its what SQL is waiting on
An insight into the stress or lack there of in the system
Tell the best story over a span of time
Ad hoc server wait stats queries are as good as your last reboot or manually cleared out
To Clear them out - DBCC SQLPERF('sys.dm_os_wait_stats', CLEAR);
To see wait stat counters - SELECT * FROM sys.dm_os_wait_stats
To see when SQL was last started - SELECT sqlserver_start_time from sys.dm_os_sys_info

5. MSFT BOL Definition – Wait Stats
Resource waits - occur when a worker requests access to a resource that is not available because the resource is being used by some other worker or is not yet available. Examples of resource waits are locks, latches, network and disk I/O waits. Lock and latch waits are waits on synchronization objects
Queue waits - occur when a worker is idle, waiting for work to be assigned. Queue waits are most typically seen with system background tasks such as the deadlock monitor and deleted record cleanup tasks. These tasks will wait for work requests to be placed into a work queue. Queue waits may also periodically become active even if no new packets have been put on the queue.
External waits - occur when a SQL Server worker is waiting for an external event, such as an extended stored procedure call or a linked server query, to finish. When you diagnose blocking issues, remember that external waits do not always imply that the worker is idle, because the worker may actively be running some external code.

6. How to track them
sys.dm_os_wait_stats (comes with some overhead out of the box)
Active transaction queries – Adam Mechanic’s WhoIsActive
3rd party monitoring tools
Paul Randal Tell Me Where It Hurts Script – Good overall assement

7. What to do with wait stat data
Grab top x wait stats in intervals
Every hour, Every 10 minutes, etc.
Write that data to a table
Create reports off that table to trend over time
Use SSRS, PowerBI, or excel to make it look pretty
Mangers and Executives love pretty graphs
Trend with 3rd party utilities
Red Gate, Spotlight, Database Health Monitor (FREE)

9. https://www. brentozar

10. Wait Stat, Extra weight You don’t need all the wait stats
Some wait stats are system related
SQLTRACE_INCREMENTAL_FLUSH_SLEEP; SQLTRACE_BUFFER_FLUSH; LAZYWRITER_SLEEP; XE_TIMER_EVENT; XE_DISPATCHER_WAIT; FT_IFTS_SCHEDULER_IDLE_WAIT; LOGMGR_QUEUE; CHECKPOINT_QUEUE; BROKER_TO_FLUSH; BROKER_TASK_STOP; BROKER_EVENTHANDLER; SLEEP_TASK; WAITFOR; DBMIRROR_DBM_MUTEXDBMIRROR_EVENTS_QUEUEDBMIRRORING_CMD; DISPATCHER_QUEUE_SEMAPHORE; BROKER_RECEIVE_WAITFOR; CLR_AUTO_EVENT; DIRTY_PAGE_POLL; HADR_FILESTREAM_IOMGR_IOCOMPLETION; ONDEMAND_TASK_QUEUE; FT_IFTSHC_MUTEX; CLR_MANUAL_EVENT; SP_SERVER_DIAGNOSTICS_SLEEP; REQUEST_FOR_DEADLOCK_SEARCH;

11. Top Waits to watch for CXPACKET and SOS_Scheduler_Yield – CPU
BackIO – backup thread waiting complete
Async Network IO – application/network related wait
LCK_M_xxx – Lock waits
PAGExxx – Latch waits
OLEDB – Remote calls to return data, Linked servers, Bulk Inserts, etc
WriteLog – Logged transactions
Any PREEMTIVE – OS interruptions

12. Lock Waits Popular Lock Types LCK_M_(type) Shared (S) Update (U)
Exclusive (X)
Intent (I)
Schema (Sch)

13. Latch Waits Often confused with Locks
A latch can be defined as an object that ensures data integrity on other objects in SQL Server memory, particularly pages.
Buffer class waits PAGELATCH_(type)
IO Class waits PAGEIOLATCH_(type)
Popular types include SHARED (SH), UPDATE (UP), EXCLUSIVE (EX)
sys.dm_os_latch_stats to monitor Latches
Another nice DMV to collect over time

14. Popular Async and Backup Wait types
Async Network IO – Waiting on the application/network
Async IO Completion – Waiting on Disk
BackupIO/BackupBuffer– The backup is waiting data to write backup data
3rd party utilities (tape drives, disk staging, etc)
BackupThread – Backup is waiting to finish
Check out

15. Wait Stat Case Study AsyncNetworkIO was always at the top
CPU and other resources were not maxed out
All best practices from the vendor were followed to the letter
User environment was a mix of VDI virtual clients and physical PC’s or laptops
VDI clients saw the slowest performance (majority of the users)
Physical machines saw the best performance
Production servers were on the worst OS – Win2012 (non R2)

16. Case Study – continued
TCPING times were high 5 – 7ms on average from Applications servers to SQL Server
Normal should be sub 1 – 2ms
Used a utility supplied by the software vendor to test latency
SQL test had a round trip of 5 secs for the test operation preformed
No glaring issues on the SQL side
Some re-indexing was done
Statistics were looked at
Again, all CPU, IO, Memory looked fine and no signs of stress

17. What was done to fix this
After many, many, consulting hours we figured it out internally
A best practice was broken
Replaced the VM Ware VM3 NIC with the Intel
Tuned the NIC settings
Trial and Error

18. What does breaking the rules do to wait stats?

19. Database Health Monitor Tool – Steve Stedman

21. Training the team
Make your development group aware of how you (the DBA) monitor traffic
Have a single pane of glass to monitor different scenarios
Firefighting, in the moment troubleshooting
Long term trends
Response kits
Work towards better solutions to reduce problems

22. Resources Used Tonight
Steve Stedman Database Health Monitor (Free)
Bing - Paul Randal Wait Stats
Bing – Brent Ozar Waits
Waitopedia

23. SOS Scheduler Waits on VM
waits-on-virtual-machines/
Capturing Baslines w/ Erin
Lock and Latches
difference-between-latches-and-locks/