Live Query Statistics & Query Store in SQL Server 2016

2. SQL Server 2016
Live Query Statistics
& Query Store

3. PresenterInfo
1976 Born. The world is now a safer place to be :P
1987 My first computer was a Sinclair ZX Spectrum
1995 I started my professional career in computers
industry as an all-around-all-weather IT-guy while
studying.
Later that year I got introduced to SQL Server 6.5
2000
.
.
.
Microsoft Certified Professional and MCT on 2005.
Staff happening…
I got older and wiser while still educating myself on
SQL Server and other staff that made me what I am
today
2007 I became father to a wonderful boy! 
.
.
.
Staff happening…
2016 Here we are now looking at me saying about
myself (recursion-alert)
Vassilis IOANNIDIS a.k.a. “Bull”
SQL Server Geek
MCT, MCSD, MCDBA, MCSA, MCTS, MCPS

4. SQLschool.gr
Team
Antonios Chatzipavlis
SQL Server Evangelist • Trainer
Vassilis Ioannidis
SQL Server Expert • Trainer
Fivi Panopoulou
System Engineer • Speaker
Sotiris Karras
System Engineer • Speaker

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7. Presentation
Content
 Live Query Statistics
 Query Store

8. Live Query Statistics
 Let’s lay the basis
 Say hello world to Query Optimizer!
 High-level bits of the engine running, under the hood of SQL Server
 Procedure Cache
 Buffer Pool
 Execution Plans
 Live Query Statistics (LQS)
 Definition and aim
 When and why
 Meanwhile, behind the scenes…
 Limitations and permissions
 Demo
 Summary

9.  Say hello world to Query Optimizer!
The Query Optimizer of SQL Server is a cost-based optimizer. Its work is to
analyze candidate execution plans, and based on the cost each one produce, to
choose the one with lowest estimated cost. It is part of the Query Processor which
one of the two main components of the Relational Engine of SQL Server, with the
other one being the Storage Engine.
LQS: Let’s lay the basis

10.  Say hello world to Query Optimizer! (cont.)
….This means that this tiny part of the engine holds a gigantic affect on the
performance of your instance!
So keep it happy and feed it regularly! With what??
Statistics of course!
LQS: Let’s lay the basis

11. When the Jr. DBA tells me he fixed the parameter sniffing issue by setting up a
job to update statistics every 2 hours. (HT @SQLsoldier)
Bonus slide!

12.  High-level bits of the engine running under the hood
 Procedure cache
A place in memory, where all your execution plans reside. Well, at least one for
each query.
To clear the plan cache use: DBCC FREEPROCCACHE
Governed by the Query Processor.
 Buffer pool
A place in memory, also, where the cached data resides, and is first checked before
hitting on the disk and producing physical I/O.
To clear the buffer pool use: DBCC DROPCLEANBUFFERS
Governed by the Storage Engine.
LQS: Let’s lay the basis

13.  High-level bits of the engine running under the hood (cont.)
 Execution Plans
Two kinds of executions plans: Estimated and Actual
Even in Actual plans, exists estimate numbers based on …statistics 
Tip: Try not to have the following iterator: lookup, hash, sort, spool, nested (serial) loop and
scans …maybe.
LQS: Let’s lay the basis

14. Live Query Statistics, are a brand new feature of the latest
SQL Server Management Studio namely “2016”, which
allows you to witness the live execution of the plan chosen
by the Query Optimizer for the running query!
Sounds awesome, right? …right!
LQS: Definition and aim

15. Warning! This feature is primarily intended for troubleshooting purposes. Using this feature can moderately slow the overall query performance.
You’ve been warned! 
So, LQS is great for troubleshooting and debugging mainly long running queries or queries
that are never ending or overflowing the poor old-tempdb! Timeout issues could be also a
thingy to investigate with QLS.
…or it you could just run it because you like to see data flow around from operator to
operator and fancy yourself as the almighty “data whisperer”.
LQS: When, Why, How

16. LQS: When, Why, How (cont.)
 Can be activated in one of 3 ways:

17. Tada…. enters sys.dm_exec_query_profiles DMV!
So, what we see as Live Query Statistics is a very nice and visual interpretation of the
sys.dm_exec_query_profiles DMV
Nonetheless you gotta love the easiness it provides for quick execution insight!
Just love it! Debug-debug-debug! New tools under your belt! Use them wisely!
LQS: Meanwhile, behindthe scenes…

18. LQS: Meanwhile, behindthe scenes…
 Limitations
 The live windows will not show up if the query:
 is using column store indexes
 Is using memory optimized tables
 Native Stored Procedures are not supported
 The good thing is that you can utilize it from SQL Server 2014 SP1 and onwards by
installing the latest SSMS, which now is not included in the initial setup of SQL
Server.
 Permissions
 Requires the database level SHOWPLAN permission to populate the Live Query
Statistics results page, the server level VIEW SERVER STATE permission to see the
live statistics, and requires any permissions necessary to execute the query.

19. Live Query Statistics in Action

20. Live Query Statistics
 View CPU/memory usage, execution time, query progress, and more
 Enables rapid identification of potential bottlenecks for troubleshooting
query performance issues
 Allows drill down to live
operator level statistics
 Number of generated rows
 Elapsed time
 Operator progress
 Live warnings
LQS: Summary

21. Query Store
 Definition and aim
 Architecture-wise where does it stand?
 How QS collects data
 Upgrading to SQL 2016
 Ways to manage and monitor QS
 Best practices
 Demo
 Summary

22. “The SQL Server Query Store feature provides you with insight on query plan
choice and performance.
It simplifies performance troubleshooting by helping you quickly find performance
differences caused by query plan changes.
Query Store automatically captures a history of queries, plans, and runtime
statistics, and retains these for your review.
It separates data by time windows so you can see database usage patterns and
understand when query plan changes happened on the server.”
Query Store: Definition and aim

23. With the power vested to you by the Query Store you, the
DBA, are in control now!
 Dedicated store for query workload performance data
 Captures the history of plans for each query
 Captures the performance of each plan over time
 Persists the data to disk (works across restarts, upgrades, and recompiles)
 Significantly reduces TTD/TTM
 Find regressions and other issues in seconds
 Allows you to force previous plans from history
Query Store: Definition and aim (cont.)

24. Remember this?
Query Store: Architecture-wise where does it stand?

25. …now Query Store enabled! 
Query Store: Architecture-wise where does it stand?

26. Query Store works as a flight data recorder. The information is stored in tables and the
following views are used to display the info to the users:
Query Store: How QS collects data (Part 1/5)
Exposed views
Query
text
Query Plan
Runtime
stats
Context
settings
Runtime
stats
interval
One row per query text per plan
affecting option
(example: ANSI NULLS on/off)
One row per
plan (for
each query)
One row per plan
per time interval
(example: 5 min)
1 - n
Compile stats:
query_store_query_text
query_context_settings
query_store_query
query_store_plan
Runtime stats:
query_store_runtime_stats_interval
query_store_runtime_stats
sys.
Internal tables
1 - n

27. .
Query Store: How QS collects data (Part 2/5)
What happens after you hit “F5”… or you know what I mean.

28. Nuts and bolts of QS continues…
Query Store: How QS collects data (Part 3/5)

29. Nuts and bolts of QS continues…
Query Store write architecture
Query Store: How QS collects data (Part 4/5)
Query Store
Query
Execution
Internal
tables
Query and
Plan Store
Runtime stats
store
Query exec. stats
Compile
Execute
async
Query text and plan

30. Nuts and bolts of QS continues…
Query Store read architecture
Query Store: How QS collects data (Part 5/5)
Query StoreQuery Execution
Internal
tables
Query and
Plan Store
Runtime stats
store
Query exec. stats
Compile
Execute
async
Query text and plan
Query Store views

31. Keeping stability while upgrading to SQL Sever 2016
Query Store: Upgrading to SQL 2016
Install bits
Keep existing
compat. level
Run Query Store
(create a
baseline)
Move to vNext
CompatLevel
Fix
regressions
with plan
forcing

32.  Enable/disable Query Store
ALTER DATABASE <database_name> SET QUERY_STORE = {ON|OFF};
 Is Query Store currently active?
SELECT actual_state, actual_state_desc, readonly_reason,
current_storage_size_mb, max_storage_size_mb
FROM sys.database_query_store_options;
 Get Query Store options
SELECT * FROM sys.database_query_store_options;
 Set all Query Store options
ALTER DATABASE <database name>
SET QUERY_STORE (
OPERATION_MODE = READ_WRITE,
CLEANUP_POLICY =
(STALE_QUERY_THRESHOLD_DAYS = 30),
DATA_FLUSH_INTERVAL_SECONDS = 3000,
MAX_STORAGE_SIZE_MB = 500,
INTERVAL_LENGTH_MINUTES = 15,
SIZE_BASED_CLEANUP_MODE = AUTO,
QUERY_CAPTURE_MODE = AUTO,
MAX_PLANS_PER_QUERY = 1000
);
LQS: Ways to manage and monitor QS

33.  Use the latest SSMS
 Use Query Performance Insight in Azure SQL Databases
 Using Query Store with Elastic Pool Databases
 Keep Query Store adjusted to your workload
 How to start with query performance troubleshooting
 Verify Query Store is collecting data continuously
 Set the optimal Query Capture Mode
 Check the status of Forced Plans regularly
 Avoid renaming databases if you have plans forced
 Keep the Most Relevant Data in Query Store
Query Store: Best practices

34. Query Store in Action

35.  Capability
 Query Store helps customers quickly find and fix query performance issues
 Query Store is a ‘flight data recorder’ for database workloads
 Benefits
 Greatly simplifies query performance troubleshooting
 Provides performance stability across SQL Server upgrades
 Allows deeper insight into workload performance
Query Store: Summary

36. Apart from my passion for SQL, other sources
were used to make this presentation a reality:
 MSDN
 TechNet
 BOL
 Many blogs from around the web
…and of course our very own sqlschool.gr 

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