2. minimalmedia.com/debugging-drupal
DrupalCamp Ohio
December 13, 2013
David Trainer
Minimal Media
@minimalmedia
minimalmedia.com/debugging-drupal

3. What's Debugging?

4. What we won't cover
Interactive debugging and profiling tools like Xdebug, NetBeans, xhprof
xdebug.org
github.com/facebook/xhprof
They are too platform-specific

5. Who does debugging? Not just developers Not just code Not just errors
Anyone who ever needs to dig into the system to figure out how something works
Sometimes requires teamwork
Debugging doesn't necessarily mean development
You don't need to be writing code in order to experience a need to dig into the system and figure out how stuff works
Any situation where the expected behavior doesn't match the expected behavior
Importance of reproducing/replicating the issue: Sales/PMs take note: You can't really start debugging until you can reproduce the problem
Should end with “The result was x, when I expected to see y”

6. When do we need to do debugging?
When the behavior of a system does not match the expected behavior
Need complete knowledge of both, in order to study the gap between them
What if you're not the one encountering the behavior?

7. “It's not coming up”

8. “It's not coming up”

9. “It's not coming up”

10. “It's not coming up”

11. Reproducibility Need a good description of the steps to reproduce
Test by inducing the problem behavior, while observing conditions inside the system
On a complex issue, you can't start debugging until you can reproduce it

12. How to think What's Debugging?
1. Gather information
2. Form a hypothesis; devise a test
3. Test
4. goto 1
What's Debugging?

13. Gather Information

14. Tools and Resources api.drupal.org Chrome Developer tools, Firebug
Drush
Devel
devel_demo
Coder
curl
find

15. Logging Understand how different parts of the system report problems
PHP Logging
php.ini
display_errors
log_errors
error_log
Drupal dblog
Syslog
/var/log/syslog
YMMV
Understand how different parts of the system report problems

16. Understand how different pieces of the architecture fit together
Instrumentation
Understanding what Drupal actually does when it builds a page
Bootstrap
Menu callback
Examine response headers using Chrome and curl
Understand how different pieces of the architecture fit together

17. Know how to use the tools to reveal what's going on inside
Instrumentation
Understanding node hooks
Using dpm() you can peer inside the node object during every phase
You can use dpm() in the theme layer too
ddebug_backtrace()
Hack drupal_set_message()
Know how to use the tools to reveal what's going on inside

18. Strategies Be prepared Dev environment Access to live environment
Tools necessary to create an entire copy of your site, quickly
Divide and conquer, process of elimination
Turn off your theme
Turn off modules

19. Common Problems WSOD: http://drupal.org/node/158043 Caching
Reverse proxy cache
Page cache
Block cache
Permissions
Look out for field permissions
Cron
Performance related
Make a list

20. Uncommon Problems
Teaser trimming
Menu cache

21. Thanks
Robert Ristroph and-lamp/index.html
Angie Byron
Randy Fay
Morten Wulff

22. minimalmedia.com/debugging-drupal
Q&A
@minimalmedia
minimalmedia.com/debugging-drupal