Your users complain about the bad performance of your app or website? Developers blame the database? How can we find the cause for the performance hotspot? Far too often the database is held responsible for performance or scalability problems. It seems to be main contributor to the overall web request response time. However, in many cases it’s not the database itself, but the way, how the application is using the database! Too many database statements, inefficient queries and poor index selection are among the common problem patterns. Based on real life examples, you will learn how to approach performance problems, how to figure out if the database is really to blame and how to end the finger pointing between developers and DBAs. Slides from my talk at PHP conference Asia 2016 in Singapore

1. Slow database in your PHP stack?
Don’t blame the DBA!
harald.zeitlhofer@dynatrace.com
@HZeitlhofer

4. Let the blame game start!
Web Server Application Server Database
DEV Team DBA Team
Blame the database for
all performance issues
Blame the SW/HW or
system administrators
Network?

5. function roomReservationReport($room)
{
$reservations = loadDataForRoom($room->id);
return generateReport($room, $reservations);
}
Slow Report

6. function roomReservationReport($room)
{
$tstart = microtime(true);
$reservations = loadDataForRoom($room->id);
$dataLoadTime = microtime(true) - $tstart;
return generateReport($room, $reservations);
}
DEV team add log output

7. 45s
DEV team result

9. < 1ms
DBA team looks at DB stats per query

12. Excessive SQL: 24889!
Calls to Database
Database Heavy:
66.51% (40.27s)
Time Spent in SQL Execs

13. Server /
Infrastructure
DB Queries
Application design
DB Design
Database
Performance
hotspots

14. Database Performance Hotspots
Application Design Database Infrastructure

16. http://apmblog.dynatrace.com/2015/06/25/when-old-jira-tickets-killed-our-productivityuser-experience/
Too many database queries

17. Exercise:
create list of courses

18. Create list of courses
$schools = new SchoolEntities();
foreach ($schools as $school) {
foreach ($school->departments as $department) {
foreach ($department->courses as $course) {
echo $department->name . ": " . $course->title;
}
}
} • 10 schools
• 20 departments per school
• 50 curses per department

19. N+1 problem
• 10 schools
• 20 departments per school
• 50 curses per department
=> 10 x 20 x 50 = 10001 single database statements !!!

20. Use a JOIN query
$rows = $db->query ("
select department.name as department, course.title as course
from school
join department on school_id = school.id
join course on department_id = department.id
");
foreach ($rows as $row) {
echo $row->department . ": " . $row->course;
}
=> ONE database statement !!!

21. Retrieving too many records

22. Retrieving too many records
$schools = new SchoolEntities();
foreach ($schools->departments as $department) {
foreach ($department->courses as $course) {
if ($course->category == "SQL" &&
$course->level == "expert") {
echo $department->name . ": " . $course->title);
}
}
}
=> 3 records, still 10001 queries

23. Use a JOIN query
$rows = $db->query ("
select department.name as department, course.title as course
from school
join department on school_id = school.id
join course on department_id = department.id
where course.category = 'SQL' and course.level = 'expert'
");
foreach ($rows as $row) {
echo $department . ": " . $course);
}
=> ONE database statement !!!

24. Caching

25. MySQL Query Cache
• Caches query results in memory

26. Oracle SQL Cache
• Oracle SQL cache stores the execution plan for a SQL statement
• Even different plans a stored for different bind variable values
• No parsing required
• Parsing is the most CPU consuming process
• Cache key is full SQL query text
select * from country where code = 'AT'
!=
SELECT * from country where code = 'AT'

27. Oracle SQL Cache
<?php
$db = new PDO('oci:dbname=sid', 'username', 'password');
$data = Array();
$data[] = $db->query("select * from country where code = 'AT'");
$data[] = $db->query("select * from country where code = 'AU'");
$data[] = $db->query("select * from country where code = 'NZ'");
$data[] = $db->query("select * from country where code = 'ES'");
?>

29. Oracle SQL Cache
<?php
$db = new PDO('oci:dbname=sid', 'username', 'password');
$data = Array();
$ps = $db->prepare("select * from country where code = :code");
$data[] = $ps->exec(array("code" => "AT"));
$data[] = $ps->exec(array("code" => "AU"));
$data[] = $ps->exec(array("code" => "NZ"));
$data[] = $ps->exec(array("code" => "ES"));
?>

30. Database Health

31. Indexes

32. Indexes are data structures for
referencing a search value (in an
indexed column) to (a) row(s) in
the target table

34. Indexes are used to find records in a
table when a where clause is used

36. Indexes are also used to join tables in
a query, where multiple tables are
used

38. Useful commands in MySQL
explain select ...
show indexes for table_name

39. I'm a developer for business
logic! I don't have to
understand what the
database does and I do not
care at all!
I'm a developer for business
logic! My code can be much
more efficient if I understand
what the database does and
how it works!

40. Make developers self-sufficient

41. Make developers self-sufficient

42. Make developers self-sufficient

43. Slow Single SQL query –
tuning/indexing might be required
Make developers self-sufficient

44. Takeaways
• Much time spent in database does not necessarily mean database is slow!
• Performance hotspots
• Too many SQL statements
• Missing caching
• Bad query design
• Index (mis)usage
• Undersized database server
• Let developers know what’s happening in the database
• The DBA is our friend!

45. Harald Zeitlhofer
Performance Advocate
@HZeitlhofer
harald.zeitlhofer@dynatrace.com
http://blog.dynatrace.com
Dynatrace Free Trial
Free Personal License
http://bit.ly/monitoring-2016