Slow Database in your PHP stack? Don't blame the DBA!
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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
![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'");
?>](https://image.slidesharecdn.com/phpanddatabases-160825054815/85/Slow-Database-in-your-PHP-stack-Don-t-blame-the-DBA-27-320.jpg)
![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[] = $ps->exec(array("code" => "ES"));
?>](https://image.slidesharecdn.com/phpanddatabases-160825054815/85/Slow-Database-in-your-PHP-stack-Don-t-blame-the-DBA-29-320.jpg)
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Slow Database in your PHP stack? Don't blame the DBA!
- 4. Let the blame game start! Web Server Application Server Database DEV Team DBA Team Blame the database for all performance issues Blame the SW/HW or system administrators Network?
- 5. function roomReservationReport($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
- 14. Database Performance Hotspots Application Design Database Infrastructure
- 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 !!!
- 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
- 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
- 38. Useful commands in MySQL explain select ... show indexes for table_name
- 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!