1. ERRORS
How they live, eat and reproduce
Slides at https://bit.ly/gugu-talk-errors

2. ERRORS
How cognitive bias prevent you from using them
Slides at https://bit.ly/gugu-talk-errors

3. How I learned to program

4. What I wish I had been told

5. “Good judgement is the result of experience,
experience is the result of bad judgement.
Fred Brooks

6. Availability
heuristic
We expect things to work, ignoring
the usefulness of error
A biased prediction, due to the
tendency to focus on the most salient
and emotionally-charged outcome.
Gabriel, P. Richard: The Rise of Worse Is Better

7. Treat errors and logs the same
Assert, measure and don’t forget to learn!

8. Log messages have 10 parts

9. 1. Messages
● Choose one:
○ What happened?
○ What didn’t happen?
○ What should be done?
● DDD (the shit out of) them:
○ Make usage of ubiquitous language
○ The same error should always
produce the same message (allowing
to group them)
Not easy to make them good,
impossible if you don’t start using
them

12. Day-to-day vocabulary

13. Error
Emergency, Alert, Critical or Error
A database drop, an update without
“where”, hardware failure, resource
stealing, an attack or an old lady
scraping metal to sell… shit happens.
When they happen, we usually have
contingency. But there is a limit to it,
so we act quickly on those - so they
don’t become defects.
2001. Lonvick, C.: The BSD syslog Protocol (IETF RFC 3164)

14. Defect
What customers should never face
We never want end-users seeing
errors.
We know them as bugs, but using a
more specific term for when end-users
are affected speeds communication
and resolution.
2008. Pryce, Nat: Throw Defect

15. Warning
Notice, Info and Debugs
Fixing bugs is also known as
debugging, logs aid on that.
Remember those `var_dump` calls?
Make them log messages and use the
severity based on the likelihood of
defects happening because of them.
2001. Lonvick, C.: The BSD syslog Protocol (IETF RFC 3164)

16. 2. Contexts
● Important details:
○ When it happened?
○ Where it happened?
■ Application name
■ Environment
■ Hostname
○ Severity
○ Facility
● Details to aid debug:
○ User information
○ Stack trace
○ HTTP call being made
○ What file/line generated it?
○ Request ID
● Usually follow a filterable pattern
The devil is on the details

17. Is this message Good or Bad?

18. Database error

19. @augustohp not found

20. Missing DB_DSN environment variable

21. 404: Page not found

22. Where can you find good error messages?
● Database error messages, care for how variable they are
● HTTP errors are few and precious, not a bingo
● PHP errors are very informative, care for variables as well

23. When to use variable messages?
Be mindful of who they are for

24. 2002. Spolsky, Joel: The Law of Leaky Abstractions
Hardware
OS
I/O
Language
Framework
App
Abstraction level

25. 2002. Spolsky, Joel: The Law of Leaky Abstractions
Hardware
OS
I/O
Language
Framework
App
Errors “leak” from lower
levels

26. If you aggregate every
message....

27. Cry wolf
You must never filter which error
is relevant
Anthropic bias is when evidence is
biased by “observation selection
effects”.
You don’t want to base your
assumptions over someone’s
observation.
2012. Bostrom, Nick: Anthropic Bias - Observation Selection Effects in Science and Philosophy

28. Alert over frequency
Monitorama EU 2013 - Lindsay Holmwood: Psychology of alert design

29. “Abstractions save us time working, not learning.
Joel Spolsky

30. The PHP cookbook for Errors
Dirty tricks for the day to day
2014. Pascutti, Augusto: Logs - O que eles comem, onde vivem e como se reproduzem

31. PHP Configuration

32. Development
You want to see every nasty error
; php.ini
display_errors = On
error_reporting = -1
log_errors = On
error_log = /var/log/php_error.log

33. Production
Make them sexy, and log them
; php.ini
display_errors = Off
error_reporting = -1
log_errors = On
error_log = /var/log/php_error.log

34. Chain exceptions

36. Create 2 base exceptions

37. 2008. Pryce, Nat: Generic Throws

38. Exception ideas

39. 2008. Pryce, Nat: Throw Defect

41. Exceptions are for
exceptional cases
C2 Wiki: Don’t use Exceptions For Flow Control

42. Use monolog (PSR-3)

43. Aggregate using Syslog
2001. Lonvick, C.: The BSD syslog Protocol (IETF RFC 3164)

45. “I would advise students to pay more attention to
the fundamental ideas rather than latest
technology.
The technology will be out-of-date before they
graduate.
Fundamental ideas never get out of date.
David Lorge Parnas

46. Conclusions
● Errors are not problems
● Treat them like logs
● Log eases debugging

47. Can I help you make more
mistakes?
Questions? Suggestions?! Beer time?

48. Credits
● Fonts in use are Ubuntu (Ubuntu) and Gentium Basic (Sil International)
● Theme is based on Solarized color-scheme by Ethan Schoonover