You can watch the replay for this Geek Sync webcast, Performance Tune Like an MVP, in the IDERA Resource Center, http://ow.ly/aDE250A4qdF. The life of a DBA is evolving and your tuning skills should always be sharp. Tuning is one of the key components of a great DBA and developer. In this demo rich session we'll deep dive into performance tuning for on-premises, PaaS (platform as a service), and IaaS (infrastructure as a service). We'll discuss tips and techniques for troubleshooting bottlenecks and how to remediate them for hardware, OS, and the database. Speaker: Daniel Janik has been supporting SQL Server for over 18 years. Six of those years were at Microsoft Corporation supporting SQL Server as a Senior Premier Field Engineer (PFE) where he supported over 287 different clients with both reactive and proactive database needs. Daniel has presented at many community events and SQL Saturdays.

1. Performance Tune
Like a Microsoft MVP

2. • Microsoft Field Engineer (PFE) for 6 years
• Working with SQL since 6.5 in ~1998
• @SQLSME, Daniel Janik on LinkedIn, Daniel@SQLDataPros.com
www.SQLTechBlog.com
About Me

3. About this Webinar
• We’ll discuss performance tuning on a mix of
On-Prem SQL Server and Azure data platform
solutions.

4. Troubleshooting Flow
O/S Issue?
Taskman
Resmon
Research Error
Message
sys.messages
Storage
ISSUE
?
Specific
Error?
General
Slowness?
Single
Query?

5. SQL Server’s #1 Bottleneck: Disk Latency
• Caused by a bottleneck in the disk or fabric
– Disk is the physical spindle where the data is stored.
– Fabric is the communication path from the application to
the physical disk (HBA, switch, Fiber Adapter ports, …)
• Can be observed from
– DMVs (Dynamic Management Views)
– Windows tools (Perfmon, Resmon, Storport, …)
– SAN tools
– Azure Portal

6. Latency causing blocking

7. XPERF Example

8. What about Azure SQL Database?

9. PaaS DMVs
sys.dm_db_resource_stats (per db)
– Collects every 15 seconds
– Stored for 1 hour
– Shows resource utilization
sys.resource_stats (in master)
– Collects every 5 minutes

10. Storage Limitations in Azure
Small databases
may require a lot of
storage depending
on IOP and
throughput needs
https://docs.microsoft.com/en-us/azure/sql-database/sql-database-managed-
instance-resource-limits#file-io-characteristics-in-general-purpose-tier

11. Troubleshooting Flow
O/S Issue?
Taskman
Resmon
Research Error
Message
sys.messages
Storage
ISSUE
?
Specific
Error?
General
Slowness?
Single
Query?
Memory

12. RAM Considerations in Azure
RAM depends on
VCORE count
(adding more VCORES
increases RAM).
4 VCORES may be
enough compute but
20 GB RAM for a 500
GB db may be too little
https://azure.microsoft.com/en-us/pricing/details/sql-database/managed/

13. Troubleshooting Flow
O/S Issue?
Taskman
Resmon
SQL Issue?
Research Error
Message
sys.messages
Storage Processor
Memory Network
Blocking?
Exec_requests
ISSUE
?
Specific
Error?
General
Slowness?
Single
Query?

14. Viewing Blocking by Using DMVs
• sys.dm_tran_locks
– Replaces syslockinfo and sp_lock
– Each row has information about both the resource and the request
– request_status = WAIT implies blocking
• sys.dm_os_waiting_tasks
– blocking_session_id > 0
• sys.dm_exec_requests
– status = suspended
– blocking_session_id > 0
• sys.dm_exec_sessions
– Join with each of the above for session details (join on session_id)

15. DEMO
Lock resource %%lockres%%

16. Retrieving Query Text
• SQL 2005+
– SYS.DM_EXEC_SQL_TEXT()
• SQL 2014 SP2+
– SYS.DM_EXEC_INPUT_BUFFER()
16

17. Monitoring Query Performance
Script on GitHub to help monitor query
performance:
https://github.com/DanielJanik/DBAHelpers

18. Troubleshooting Flow
O/S Issue?
Taskman
Resmon
SQL Issue?
Research Error
Message
sys.messages
Storage Processor
Memory Network
Blocking?
Exec_requests
ISSUE
?
Specific
Error?
General
Slowness?
Single
Query?
Query Stats

19. Query Statistics
• SQL 2005+
– sys.dm_exec_query_stats
– sys.dm_exec_trigger_stats
– sys.dm_exec_procedure_stats
• SQL 2014+
– sys.dm_exec_query_profiles
• Requires use of SET STATISTICS PROFILE ON;
• Monitors real time query progress while the query is in execution. For example, use
this DMV to determine which part of the query is running slow.
• SQL 2016+
– sys.dm_exec_function_stats
19

20. Query Optimizer
• The query optimizer
– attempts to find the fastest plan
– validates the query
– parses a query into tree representation
– evaluates possible query plans until a ‘good enough’ plan is found
– can abort optimization due to timeout
– sometimes makes a poor choice

21. Optimization
Process
Trivial
Plan?
Produce
Query
Plan
Simplification
Phase 0
Phase 1
Phase 2
Cost < 0.2
Cost < 1.0
Cost > Cost
Threshold?
Parallel
Optimization

22. Query Optimizer DMV
• sys.dm_exec_query_optimizer_info
– Helps understand workloads
– View stats by phase
– Hints
– Statement types
– Cursor info

23. Real-time Query Analysis
Azure Data Studio extension project on GitHub
https://github.com/DanielJanik/tsqlchecker_adsextension

24. Graphical Plan
Outer Table
Inner table
Branches

25. Query Plan Myths
• Estimated plans give me all the facts
• Estimated cost is in “seconds”
• Estimated cost changes if the data is in cache
or if I have faster storage
• Costs are always accurate

26. Query Optimizer IO cost
• Query Plan IO costs
– Random IO = 0.003125
– Sequential IO = 0.000740741

27. Incorrect Operator Cost
Never fully trust cost in a query plan.
Use SET STATISTICS IO and SET STATISTICS TIME

28. Where to start
• Estimated plan
• Graphical plan
• Seeks vs Scans
• Key or RID lookups
• High cost operators

29. Noteworthy investigation
Look for
• Missing Indexes
• Estimated row count vs actual row count
• Required Memory vs Desired Memory
• Warnings
• Predicate Pushes (Probe Residual, Filter, …)
• Spools, Sorts, and other ‘blocking’ operators

30. ‘Bad’ Plans & Query Performance
• Stats
• Be careful using trace flag 2371
• Ascending Stats
• “@param = is null OR column = @param”

31. Memory – Runtime data
Example of large grant
<MemoryGrantInfo SerialRequiredMemory="46720"
SerialDesiredMemory="9198680"
RequiredMemory="104880"
DesiredMemory="9256848"
RequestedMemory="5133928" GrantWaitTime="0"
GrantedMemory="5133928"
MaxUsedMemory="322736" />
Example of large grant
<MemoryGrantInfo SerialRequiredMemory="46720"
SerialDesiredMemory="9198680"
RequiredMemory="104880"
DesiredMemory="9,256,848 KB" (9.2 GB!!!)
RequestedMemory="5133928" GrantWaitTime="0"
GrantedMemory="5,133,928 KB" (5.1 GB!!!)
MaxUsedMemory="322,736 KB" /> (322 MB used)

32. Adaptive Query Plans and IQP
• Microsoft has done a lot of work to help with
these memory grant issues. For more info
refer to the following:
• https://docs.microsoft.com/en-us/sql/relational-
databases/performance/intelligent-query-
processing?view=sql-server-ver15

33. SARGability
• SARG = Search Argument (aka Predicate)
• SARGable expressions can utilize and index
• Non-SARGable expressions force scans and
can kill performance

34. Query Operators
• Describe how SQL Server executes the query
• Blocking operators such as Sort, Hash, Spool, & Filter reduce
concurrency
– Data must be fully retrieved before an output is produced

35. Probe Residual
• Predicate push
• Can reduce performance significantly

36. Filter
 Predicate Push
 Blocking operator
 Filters output of another operator

37. Spool
• Blocking operator
• Query Optimizer usage
• Halloween protection
• Dumps data from another operator into a
worktable in TempDB.

38. Data type conversion
• Often serious bottleneck
• Can be caused by joining two columns
that do not match data types in a join
or union
• Demo

39. Performance via Constraints
• Trusted constraints can help eliminate joins
• UNIQUE constraint can allow DISTINCT to be
ignored

40. Troubleshooting Flow
O/S Issue?
Taskman
Resmon
SQL Issue?
Research Error
Message
sys.messages
Storage Processor
Memory Network
Blocking?
Exec_requests
Query Stats
ISSUE
?
Specific
Error?
General
Slowness?
Single
Query?
Wait Stats

41. Wait Statistics
• SQL 2005+
– sys.dm_os_wait_stats
• SQL 2016+
– sys.dm_exec_session_wait_stats
• Returns information about all the waits encountered
by threads that executed for each session.
41

42. SQL Server Wait Types
• Typical types seen using the SYS.DM_OS_WAIT_STATS DMV
• Waiting for I/Os to
complete
• Generally not data
pages
• Often associated with
file growth or other
non-read/write
operations
• Waiting for a log flush
operation to complete
• Generally due to disk
latency, although high
activity can contribute
• Waiting for a buffer
(data page) that is in
an I/O operation
• Generally due to disk
latency, although high
I/O queries and lack
of buffer space can
contribute
WRITELOG PAGEIOLATCH_xxASYNC_IO_COMPLETION
IO_COMPLETION

43. Thank You!