По большому счёту, вариантов почему запрос работает медленно всего два: или запрос сам по себе работает долго (CPU Time) или ждёт определённого ресурса (Wait Time). Все остальные причины медленной работы запросов являются производными этих двух вариантов. В ходе доклада мы научимся чётко определять, что является причиной долгой работы запроса, посмотрим чего может запрос ждать и как можно его ускорить

1. Why my query is slow and how to fix this
t WITH PASSION TO TECHNOLOGY
Denis Reznik
.NET CONFERENCE #1 IN UKRAINE, KYIV 2018

2. t .NET LEVEL UP
KYIV 2018
About Me
• Denis Reznik
• Kyiv, Ukraine
• Data Architect at Intapp, Inc.
• Microsoft Data Platform MVP
• Co-Founder of Ukrainian Data Community Kyiv
• PASS Regional Mentor, CEE
• Co-author of “SQL Server MVP Deep Dives 2”

3. t .NET LEVEL UP
KYIV 2018
Agenda
• Query Execution Time
• Slow Queries
• Optimization Algorithm
• First-Level Root Cause(s)
• Second-Level Root Cause(s)
• Query/Server/Database/Application Optimization

4. t .NET LEVEL UP
KYIV 2018
Query Execution Time
Duration (Elapsed Time)
CPU (CPU Time) Wait (Wait Time)

5. Query Execution
Thread Pool
Running
Suspended
Runnable
Sleeping
Scheduler
Logical CPU
Worker (Thread)
Connection

6. CPU – Cooperative Multitasking
0
CPUsQueries
1
2
3
Time Quantum Length for each Scheduler is 4 ms

7. Тема доклада
Тема доклада
Тема доклада
KYIV 2018
High CPU – High Duration
.NET CONFERENCE #1 IN UKRAINE
Demo

8. Тема доклада
Тема доклада
Тема доклада
KYIV 2018
Various Waits
.NET CONFERENCE #1 IN UKRAINE
Waits

9. SOS_SCHEDULER_YIELD Wait
0
SchedulersRunnable Queue
1
2
3
Suspended Queue
Time Quantum Length for each Scheduler is 4 ms

10. LCK_M_* Waits
0
SchedulersRunnable Queue
1
2 1
Suspended Queue
2
SELECT * FROM Users
WHERE Name LIKE 'K%'
UPDATE Users
SET Name = 'Jesse Pinkman'
WHERE Id = 3
Id Name
1 John Snow
2 Peter Partner
3 Kirill Nenahov
4 Jane Dow
1
Users
2
3
2
Id Name
1 John Snow
2 Peter Partner
3 Jesse Pinkman
4 Jane Dow
LCK_M_X
LCK_M_X
2
X S

11. PAGEIOLATCH_* Waits
0
SchedulersRunnable Queue
1
2
3
1
Suspended Queue
1
SELECT * FROM Users
WHERE Name LIKE 'P%'
1
1
PAGEIOLATCH_SH
PAGEIOLATCH_SH
1
Buffer Pool
Database File
…
A .. Z
A .. C C .. Q X .. Z
Non-Clustered Index
(Name)
?

12. ASYNC_NETWORK_IO Wait
0
SchedulersRunnable Queue
1
2
3
1
Suspended Queue
1
SELECT * FROM Users1
1
ASYNC_NETWORK_IO
ASYNC_NETWORK_IO
1
Client
Id Name
1 John Snow
2 Darth Vader
3 Peter Parker
4 Andriy Yarmolenko
Users
var command = new SqlCommand("SELECT * FROM Users", connection);
connection.Open();
var reader = command.ExecuteReader();
while (reader.Read())
{
// Do some logic (e.g. Thread.Sleep(1000); )
}

13. CX_PACKET
Thread 1
Thread 2
Thread 3
Thread 4
1s2s
Thread 0CXPACKET WaitCXPACKET Wait
CXPACKET Wait
CXPACKET Wait
CXPACKET Wait

14. THREADPOOL Wait
Runnable Queue
Suspended Queue
Thread Pool
Connection

15. Тема доклада
Тема доклада
Тема доклада
KYIV 2018
Low CPU – High Duration
.NET CONFERENCE #1 IN UKRAINE
Demo

16. Тема доклада
Тема доклада
Тема доклада
KYIV 2018
High CPU – Low Duration
.NET CONFERENCE #1 IN UKRAINE
Demo

17. Тема доклада
Тема доклада
Тема доклада
KYIV 2018
High CPU – High Duration
.NET CONFERENCE #1 IN UKRAINE
Demo

18. t .NET LEVEL UP
KYIV 2018
Summary
• Query Execution Time
• Slow Queries
• Optimization Algorithm
• First-Level Root Cause(s)
• Second-Level Root Cause(s)
• Query/Server/Database/Application Optimization

19. Тема доклада
Тема доклада
Тема доклада
KYIV 2018
.NET LEVEL UP
.NET CONFERENCE #1 IN UKRAINE
Denis Reznik
Twitter: @denisreznik
Email: denisreznik@gmail.com
Blog: http://reznik.uneta.com.ua
Facebook:
https://www.facebook.com/denis.reznik.5
LinkedIn: http://ua.linkedin.com/pub/denis-reznik/3/502/234
Thank You!