You seem to have a slow database in your PHP stack? Don’t blame the DBA!

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

2. Harald Zeitlhofer – who's that?
• Technology Strategist at Dynatrace
• Database and Web Development
• Father of 2
• Love climbing, music, cooking, photography
• Love to discover new things

3. PHP and databases
• Connectivity
• Abstraction Layers
• Caching
• Access Patterns
• Performance
-> Relational SQL databases

4. Connectivity via DB extensions
• mysql (deprecated in 5.5, removed in 7.0)
• mysqli
• oracle
• PDO
• …

5. Connectivity via ORM layer
• Object Relational Mapper
• Doctrine
• Propel, RedBeanPHP, Spot
• Complete abstraction of persistence layer
• Caching
• Limited flexibility

8. 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?

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

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

11. 45s
DEV team result

13. < 1ms
DBA team looks at DB stats per query

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

17. Database Performance Hotspots
Application Design Database Infrastructure

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

20. Entity Framework lazy loading
$schools = new SchoolEntities();
foreach ($schools as $school) {
foreach ($school->departments as $department) {
foreach ($department->courses as $course) {
echo $department->name . ": " . $course->title);
}
}
}

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

22. 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 !!!

23. Traditional code
$author_id = get_author_id( 'Jack London' );
$books = get_books( $author_id );
foreach ($books as $book_id) {
$book = get_book( $book_id );
var_dump( $book );
}
=> N+1 Problem !!!

24. Traditional code
function get_author_id( $name ){
global $db;
$res = $db->query( "SELECT id FROM authors WHERE name=?", array( $name ) );
$id = null;
while( $res->fetchInto( $row ) ) { $id = $row[0]; }
return $id;
}
function get_books( $id ){
global $db;
$res = $db->query( "SELECT id FROM books WHERE author_id=?", array( $id ) );
$ids = array();
while( $res->fetchInto( $row ) ) { $ids []= $row[0]; }
return $ids;
}
function get_book( $id ){
global $db;
$res = $db->query( "SELECT * FROM books WHERE id=?", array( $id ) );
while( $res->fetchInto( $row ) ) { return $row; }
return null;
}
=> N+1 Problem !!!

25. Retrieving too many records

26. 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

27. 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 !!!

28. Reduce the number of queries
Reduce the amount of data retrieved
Profile the generated queries!

29. 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!

30. Make developers self-sufficient

31. Make developers self-sufficient

32. Make developers self-sufficient

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

34. Indexes

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

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

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

42. Index Killer
where … in (…)

43. Better
• Join tables
• Use where exists (…)

44. What’s the overall Execution
Time of different SQL Types
(SELECT, INSERT, DELETE, …)
Indexing – Read v/s Write

45. Analyzing SQLs by Type (SELECT, INSERT,
UPDATE,DELETE)
Which Types take how long? When do you have spikes?
When do we see # of SQL spikes? Spikes related to
INSERT, UPDATE, DELETE? Any job running?

46. Different databases
for read and write???

47. Different databases for read and write
• Data Warehouse
• Document oriented NoSQL
• Separate logic for data transfer needed

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

49. Caching

50. Application Data Cache
• Caching layer inside the application
• Application logic required to get data from and store in cache

51. MySQL Query Cache
• Caches query results in memory

52. 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

53. 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'");
?>

54. Oracle SQL Cache
<?php
$db = new PDO('oci:dbname=sid', 'username', 'password');
$data = Array();
$ps = $db->prepare("select * from emp 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"));
?>

56. Database Health

57. Horizontally scaled environments

60. Performance problem after upscaling

64. Database Access
• Size server (cluster) appropriately for maximum number of connected
instances
• Reduce connections
• Reduce SQL statements
• Leverage caching

66. Working together, looking at the same data
Web Server Application Server Database

67. 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!

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