The document discusses SQL Server monitoring and troubleshooting. It provides an overview of SQL Server monitoring, including why it is important and common monitoring tools. It also describes the SQL Server threading model, including threads, schedulers, states, the waiter list, and runnable queue. Methods for using wait statistics like the DMVs sys.dm_os_waiting_tasks and sys.dm_os_wait_stats are presented. Extended Events are introduced as an alternative to SQL Trace. The importance of establishing a performance baseline is also noted.

1. C H A P T E R
Troubleshooting
SQL Server
Athens Oct 23, 2015

2. Presenter introduction
 1982 - I have been started with computers.
 1988 - I started my professional carrier in computers industry.
 1996 - I have been started to work with SQL Server version 6.0
 1998 - I earned my first certification at Microsoft as Microsoft Certified
Solution Developer (3rd in Greece) and started my carrier as
Microsoft Certified Trainer (MCT) with more than 25.000 hours
of training until now!
 2010 - I became for first time Microsoft MVP on SQL Server
I created the SQL School Greece (www.sqlschool.gr)
 2012 - I became MCT Regional Lead by Microsoft Learning Program.
 2013 - I was certified as MCSE : Data Platform,
MCSE : Business Intelligence
Antonios
Chatzipavlis
Database Architect
SQL Server Evangelist
MCT, MCSE, MCITP, MCPD, MCSD, MCDBA,
MCSA, MCTS, MCAD, MCP, OCA, ITIL-F

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4. Need help?
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5. Presentation outline
01: SQL Server Monitoring Overview
02: SQL Server Threading Model
03: Using Wait Statistics
04: Using Extended Events
05: Create your Baseline

6. C H A P T E R
01
SQL Server Monitoring Overview
 Why Monitor?
 Guidelines for Monitoring
 Monitoring Tools for SQL Server

7. Why Monitor?
 Diagnosing causes of performance issues
 Response Time
 Throughput of the system
 Detecting and resolving concurrency issues
 SQL Server uses locks to ensure data consistency.
 Identifying changing trends in resource utilization
 Capacity planning to identify the required hardware resources to support the
database workload.
 It is important to monitor resource utilization changes

8. Guidelines for Monitoring
 Understand the workloads you need to support
 Every workload has different requirements
 You need to understand its workloads so that you can identify the relevant metrics to monitor
 Prioritize resources based on the importance of each workload to the business
 Establish a baseline
 A common mistake is to wait until there is a problem before monitoring the SQL Server solution
 A better approach is to identify the key metrics that your workloads rely on, and record baseline
values for these metrics when the system is operating normally
 Monitor regularly to track changes in key metrics.
 It is generally better to proactively monitor the system on a regular basis to identify any trends
that signify changes in the way the workloads consume resources.
 With this approach, you can plan server upgrades or application optimizations before they
become critical.

9. Monitoring Tools for SQL Server
Build in and External Tools
Activity Monitor
A component of SQL Server Management Studio that
enables DBAs to view details of current activity in the
database engine
Dynamic Management
View and Functions
Database objects that provide insight into internal SQL
Server operations
Performance Monitor
A windows administrative tool that you can use to record
values for multiple performance counters over a period of
time, and analyze results in a variety of chart
SQL Server Profiler
A tracing and profiling tool that you can use to record
details of Transact-SQL and other events in a SQL Server
workload. We can replay or use it as a source for tuning
SQL Trace A lightweight, Transact-SQL based programming interface
for tracing SQL Server activity

10. Monitoring Tools for SQL Server
Build in and External Tools
Database Engine Tuning
Advisor
A tool provided with SQL Server for tuning indexes and
statistics based on a known workload
SQL Server Utility Control
Point
A centralized management portal for monitoring server
health for multiple instances based on specific collection
sets
SQL Server Extended
Events
A lightweight eventing architecture.
SQL Server Data
Collection
An automated system for collecting and storing and
reporting performance data for multiple SQL Server
instances
Distributed Replay An advanced tool for replaying workloads across a
potentially distributed set of servers

11. Monitoring Tools for SQL Server
Build in and External Tools
Microsoft System Center
Operations Manager
An enterprise-wide infrastructure management solution
that uses management packs to collect performance and
health data from Windows and application services
SqlDiag Tool
The SQLdiag utility is a general purpose diagnostics
collection utility that can be run as a console application or
as a service
sp_WhoIsActive
Provides detailed information about all of the sessions
running on your SQL Server system, including what they’re
doing and how they’re impacting server behavior
sp_Blitz SQL Server health and warning check
Performance Monitor
Windows Performance Monitor is an operating system
tool that brings together several previously disparate
performance and monitoring tool

12. Monitoring Tools for SQL Server
SQL Server 2016
Query Store
An enterprise-wide infrastructure management solution
that uses management packs to collect performance and
health data from Windows and application services
Live Query Stats
Windows Performance Monitor is an operating system
tool that brings together several previously disparate
performance and monitoring tool

13. C H A P T E R
02
SQL Server Threading Model
 Introduction
 What a thread is
 Thread Scheduling
 SQL Server Schedulers
 Thread States
 The Waiter List
 The Runnable Queue

14. Introduction
 SQL Server is an OS on Windows OS
 It performs and controls its own:
 Memory management
 I/O
 Scheduling

15. What a thread is
 A thread is unit of execution within a process
 Multiple threads can exist within a process
 Each is given small amount of processor time
 Waits while other threads execute (called scheduling)
 SQL Server uses OS threads to perform its work
 Called worker threads
 Dedicated threads exists
 Such as for performing checkpoints, deadlock monitoring, and ghost record cleanup
 Most are in a pool of threads that SQL Server uses to process user requests
(Working Threads)

16. Thread Scheduling
 SQL Server has its own thread scheduling
 Called non-preemptive scheduling
 Is more efficient than Windows scheduling
 Performed by the SQLOS layer of the Storage Engine
 Each processor core (logical or physical) has a scheduler
 A scheduler is responsible for managing the execution of work by threads
 Schedulers exist for user threads and for internal operations
 Use the sys.dm_os_schedulers DMV to view schedulers

17. SQL Server Schedulers
Processor
Runnable
Queue
Waiter List
One scheduler per logical or physical processor core
Plus some extra ones for internal tasks and the DAC

18. Thread States
 RUNNING
 The thread is currently executing on the processor
 SUSPENDED
 The thread is currently on the Waiter List waiting for a resource
 RUNNABLE
 The thread is currently on the Runnable Queue waiting to execute on the
processor

19. The Waiter List
 Is an unordered list of threads that are suspended
 Any thread can be notified at any time that the resource it is waiting for is now
available
 No time limit for a thread on the waiter list
 Although execution timeouts or lock timeouts may take effect
 No limit on the number of threads on waiter list
 The sys.dm_os_waiting_tasks DMV
 Shows which threads are currently waiting and what they are waiting for

20. The Runnable Queue
 Is a strict First-In-First-Out (FIFO) queue
 Resource Governor exception
 The sys.dm_os_schedulers DMV shows the size of the
Runnable Queue in Runnable_tasks_count column

21. Examine Schedulers
02
Examine Schedulers
Examine Waiting Tasks

22. C H A P T E R
03
Using Wait Statistics
 Waits and Queues
 Wait Times
 DMVs for Waits

23. Waits and Queues
 Waits
 Wait is when a thread that's running on the processor cannot proceed because
it needs a resource and the resource that it needs is not available
 The thread state changed from RUNNING to SUSPENDED
 Moved to Waiter List and remains on the list until it became available
 Queues
 Is a generic term and means what's stopping the thread being able to get its
resource
 PAGEIOLATCH_XX : The I/O subsystem need to complete the I/O
 LCK_M_XX : Another thread holding an incompatible lock
 CXPACKET : Another thread needs to complete its portion of work

24. Wait Times
Wait time=Resource Wait time + Signal Wait time
 Wait time
 Is the time spent from when a thread is running on the processor (RUNNING)
moved to the Waiter List (SUSPENDED) and is being signaled and moving back
onto the runnable queue (RUNNABLE) and is going back to running
 Resource Wait time
 Time spent on the Waiter List with state SUSPENDED
 Signal Wait time
 Time spent on the Runnable Queue with state RUNNABLE

25. DMVs for Waits
 sys.dm_os_waiting_tasks
 Shows all threads that are currently suspended
 Think of it as the ‘what is happening right now?’ view of a server
 The first thing to run when approaching a ‘slow’ server
 sys.dm_os_wait_stats
 Shows aggregated wait statistics for all wait types
 Aggregated since the server started or the wait statistics were cleared
 Some math is required to make the results useful
 Calculating the resource wait time
 Calculating the average times rather than the total times

26. Using Waits DMVs
03

27. C H A P T E R
04
Using Extended Events
 Why Extended Events?
 Switch from SQL Trace to Xevents
 Extended Events Architecture
 Event Life Cycle
 Targets

28. Why Extended Events?
 It’s the FUTURE
 SQL Trace is a deprecated feature in SQL Server 2012
 This makes understanding XE crucial to supporting SQL Server in the future
 Less overhead
 Lightweight to minimize impact
 Provides minimum schema of data that is specific to the event being fired
 Events are filtered early in the firing lifecycle based on the predicates
 Flexibility and Power
 Allows complex configurations for event collection that simplify problem identification.
 Many events in more recent releases

29. Switch from SQL Trace to XEvents
 Events Mapping Query
 Column to Action Mapping Query
select xe.xe_event_name,st.name
from sys.trace_xe_event_map as xe
inner join sys.trace_events as st
on xe.trace_event_id = st.trace_event_id;
select xe.xe_action_name, tc.name
from sys.trace_xe_action_map as xe
inner join sys.trace_columns as tc
on xe.trace_column_id = tc.trace_column_id;

30. Extended Events Architecture
 Sessions
 Are a functional boundary for configuration of events
 Events
 Correspond to well-know points of code
 Predicates
 Boolean expressions that define the conditions required for an event to actually fire
 Actions
 Actions only execute after predicate evaluation determines the event will fire
 Targets
 Targets are event consumers

31. Event Life Cycle
Event point
encountered in code
Is Event Enabled
in a session Code Continues
Buffer Data for
Asynchronus Targets
Send to Synchronous
Targets Immediately
Execute Actions and
Collect data
(if applicable)
Are there
configurable
columns
Collect
non-configurable
column data
Passes Filter
Criteria (Predicate)
Collect Configurable
Column data
No
No
Yes
Yes
Yes

32. Targets
 Event counter
 Counts all specified events that occur during an Extended Events session.
 Use to obtain information about workload characteristics without adding the
overhead of full event collection.
 This is a synchronous target.
 Event file
 Use to write event session output from complete memory buffers to disk.
 This is an asynchronous target.

33. Targets
 Event pairing
 Many kinds of events occur in pairs, such as lock acquires and lock releases.
 Use to determine when a specified paired event does not occur in a matched
set.
 This is an asynchronous target.
 Event Tracing for Windows (ETW)
 Use to correlate SQL Server events with Windows operating system or
application event data.
 This is a synchronous target.

34. Targets
 Histogram
 Use to count the number of times that a specified event occurs, based on a
specified event column or action.
 This is an asynchronous target.
 Ring buffer
 Use to hold the event data in memory on a first-in first-out (FIFO) basis, or on a
per-event FIFO basis.
 This is an asynchronous target.

35. Use case scenarios of
Extended Events
04

36. C H A P T E R
05
Create your Baseline

37. Create Baseline
05

38. Summary
 SQL Server Monitoring Overview
 SQL Server Threading Model
 Using Wait Statistics
 Using Extended Events
 Create your Baseline

39. Questions?
Thank you!

40. SELECT
KNOWLEDGE
FROM
SQL SERVER
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