Everyone hates seeing the White Screen of Death, especially if it’s discovered by the client calling to tell you their site is down. Even more frustrating can be intermittent error and/or slow response times, as these can be much harder to diagnose. Aimed at newer WordPress developers and advanced users, this talk will start with the basic diagnostics tools available and go all the way through to advanced debugging. Attendees should be able to leave this talk with an informed diagnostic approach to errors, rather than just panic. Presented by Tim Butler @timbutler at WordCamp Sydney 2018

1. Diagnosing WordPress
Presented by Tim Butler
What do to when things go wrong

2. Who am I?
● IT professional with 20 years experience
● Head of infrastructure at Conetix
● NGINX Cookbook author
● Certified beer judge
Infrequent ramblings on Twitter: @timbutler
Probably seen more errors than Stack Overflow!

3. About this talk….
Aimed at developers and agencies
Just as applicable to business owners
Start with the basics and work our way up

4. Before we get started…..

5. One quick takeaway….
Make sure you have a backup!!

6. How you usually find out there’s a
problem...

7. “WHY IS MY WEBSITE DOWN!!!!”

8. Additional management “assistance”

9. Software equivalent of what you’re facing

10. What you actually need….

11. The path to Zen
Where we’ll be focussing

12. Preparation

13. Preparation
● Having a known state to compare to
○ Known plugins and versions installed
○ Known errors or PHP warnings
https://en-au.wordpress.org/plugins/stream/
● Ability to track changes

14. Preparation

15. Monitoring

16. Monitoring
Forearmed is forewarned

17. Monitoring
● You want to know of issues before your clients
● System MUST have a point of presence in Australia
https://statuscake.com https://www.panopta.com/

18. Monitoring

19. Diagnostics

20. Diagnostics
OR
Catastrophic error…..

21. Diagnostics - Server Logs

22. Diagnostics - Server Logs
Let's look in the logs...

23. Diagnostics - Server Logs
80% of your issues will be identified in the logs
wp-content/plugins/tims-shady-plugin/tims-shady-plugin.php

24. Diagnostics - Server Logs
Consider centralised logging
SaaS Open Source
(host yourself)
https://papertrailapp.com/ https://www.graylog.org/

25. Diagnostics - Server Logs
24 hour snapshot

26. Diagnostics
Hard failures = easy to find
“Sometimes the site is slow to load”
“Two out of the 5,000 products in my store have an issue”
“My site seems slower this month”
“My site works perfectly for my customers but wp-admin takes forever”
Soft failures = harder...

27. WordPress Debugging

28. Diagnostics - WordPress Debugging
Great way to see more info on soft failures eg,
“Two out of the 5,000 products in my store have an issue”

29. Diagnostics - WordPress Debugging
PHP / WordPress Log levels
Normal Debug enabled

30. Diagnostics - WordPress Debugging
Enable via management tools:
Or in the wp-config.php:
define('WP_DEBUG', true);
define('WP_DEBUG_LOG', true);
define('WP_DEBUG_DISPLAY', false);

31. Diagnostics - WordPress Debugging
By default: wp-content/debug.log
[23-Jul-2018 06:32:09 UTC] PHP Notice: Undefined index: country in
/var/www/vhosts/wcsyd2.conetixtest.com/httpdocs/wp-content/plugins/woocommerce/includes/class-wc-geolite-integration.php on line 60
[23-Jul-2018 06:32:09 UTC] PHP Stack trace:
[23-Jul-2018 06:32:09 UTC] PHP 1. {main}() /var/www/vhosts/wcsyd2.conetixtest.com/httpdocs/index.php:0
[23-Jul-2018 06:32:09 UTC] PHP 2. require() /var/www/vhosts/wcsyd2.conetixtest.com/httpdocs/index.php:17
[23-Jul-2018 06:32:09 UTC] PHP 3. require_once() /var/www/vhosts/wcsyd2.conetixtest.com/httpdocs/wp-blog-header.php:13
[23-Jul-2018 06:32:09 UTC] PHP 4. require_once() /var/www/vhosts/wcsyd2.conetixtest.com/httpdocs/wp-load.php:37
[23-Jul-2018 06:32:09 UTC] PHP 5. require_once() /var/www/vhosts/wcsyd2.conetixtest.com/httpdocs/wp-config.php:80
[23-Jul-2018 06:32:09 UTC] PHP 6. do_action() /var/www/vhosts/wcsyd2.conetixtest.com/httpdocs/wp-settings.php:450
[23-Jul-2018 06:32:09 UTC] PHP 7. WP_Hook->do_action() /var/www/vhosts/wcsyd2.conetixtest.com/httpdocs/wp-includes/plugin.php:453
[23-Jul-2018 06:32:09 UTC] PHP 8. WP_Hook->apply_filters() /var/www/vhosts/wcsyd2.conetixtest.com/httpdocs/wp-includes/class-wp-hook.php:310
[23-Jul-2018 06:32:09 UTC] PHP 9. WooCommerce->init() /var/www/vhosts/wcsyd2.conetixtest.com/httpdocs/wp-includes/class-wp-hook.php:286
[23-Jul-2018 06:32:09 UTC] PHP 10. WC_Customer->__construct()
/var/www/vhosts/wcsyd2.conetixtest.com/httpdocs/wp-content/plugins/woocommerce/includes/class-woocommerce.php:480
[23-Jul-2018 06:32:09 UTC] PHP 11. WC_Data_Store->read()
/var/www/vhosts/wcsyd2.conetixtest.com/httpdocs/wp-content/plugins/woocommerce/includes/class-wc-customer.php:116
[23-Jul-2018 06:32:09 UTC] PHP 12. WC_Customer_Data_Store_Session->read()
/var/www/vhosts/wcsyd2.conetixtest.com/httpdocs/wp-content/plugins/woocommerce/includes/class-wc-data-store.php:156
[23-Jul-2018 06:32:09 UTC] PHP 13. WC_Customer_Data_Store_Session->set_defaults()
…...

32. Diagnostics - Diving a little deeper

33. Diagnostics
Make sure you have a backup!
Next items - run on staging / dev copy

34. Diagnostics - Diving a little deeper
https://en-au.wordpress.org/plugins/query-monitor/
What if there’s no errors in the logs?

35. Diagnostics - Query Monitor
● Shows database queries
● See WordPress hooks
● See Theme templates used
● See HTTP calls
● … And more!

36. Diagnostics - Query Monitor
0.06 second page load
3.8MB peak memory
0.003 second db queries
19 database queries

37. Diagnostics - Query Monitor
Database

38. Diagnostics - Query Monitor
Templates

39. Diagnostics - Query Monitor
HTTP Calls

40. Diagnostics - Query Monitor
“Something’s loading JQuery twice….”

41. Diagnostics - Query Monitor
What’s the impact of WooCommerce?

42. Diagnostics - Query Monitor
“Admin is slower..”
Some premium plugins can have issues refreshing,
with a 30 second timeout
HTTP Calls

43. We need to go deeper

44. Diagnostics - Query Monitor

45. Diagnostics
Warning: These examples require root access to a server
(your dev server!) or a localised, development install.

46. Diagnostics - Digging Deeper
Option 1 - XDebug
“Xdebug is an extension for PHP to assist with debugging and development. It contains a
single step debugger to use with IDEs; it upgrades PHP's var_dump() function; it adds
stack traces for Notices, Warnings, Errors and Exceptions; it features functionality for
recording every function call and variable assignment to disk; it contains a profiler; and
it provides code coverage functionality for use with PHPUnit.”
https://xdebug.org/

47. Diagnostics - XDebug
Debugging WordPress with xDebug
2:10 pm - Alex Bishop

48. Diagnostics - XDebug
If it’s compiled in:
zend_extension=xdebug.so
xdebug.profiler_enable_trigger=1
xdebug.profiler_enable_trigger_value=wordcamptest

49. Diagnostics - XDebug
“My website is slow”
Not database queries…. Must be code

50. Diagnostics - XDebug
Creates /tmp/cachegrind.out.26139.07d29e

51. Diagnostics - XDebug KCachegrind / QCachegrind
Webgrind
IDE (PHPStorm)
72.45% time was in apply_filters
This was a single call to excellent_coding
In this function was 100 calls to
password_hash

52. Diagnostics - XDebug
z
Really shouldn’t let this developer near an editor
wp-content/plugins/tims-shady-plugin/tims-shady-plugin.php

53. Diagnostics - XDebug
Debugging WordPress with xDebug
2:10 pm - Alex Bishop

54. Diagnostics - Digging Deeper
Option 2 - New Relic / APM
https://newrelic.com/
“A complete view of your applications and operating environment”
APM = Application Performance Management

55. Diagnostics - New Relic
WordPress specific Tools
Other APM’s also available

56. Diagnostics - New Relic (Lite)
Option 2 - New Relic

57. Diagnostics - New Relic (Lite)

58. Diagnostics - New Relic (Lite)

59. Diagnostics - New Relic (Essentials)
Hooks

60. Diagnostics - New Relic (Essentials)
Plugins and Themes

61. Diagnostics - New Relic (Essentials)
Database

62. Two quick, get out of jail free cards

63. Get out of Jail free cards
Check wp_options table for expired transients
Check WordPress core files via WP-CLI
wp core verify-checksums

64. Summary

65. Summary
1. Remember your path to Zen
2. Find your server log locations
3. Familiarise yourself with the tools before you need them

66. One final reminder...
Make sure you have a backup!!

67. Questions?
Feel free to ask in person
or via @timbutler