Veselin Nikolov shared lessons he learned from working on WordPress.com. He discussed stories about adding a new ID which led to legacy code issues and no unit tests. Another story involved sending millions of emails and coupons that broke things due to large queries and offsets. An A/B test story highlighted keeping code simple. Simple queries, atomic commits, testing, and avoiding large launches on Fridays were some of the key lessons learned.

1. Lessons from working on
WordPress.com
WordCamp Romania 2014

2. About me
●
Veselin Nikolov
● @dzver
● WordPress.com

3. About me
●
Background as MS SQL
DBA
● Currently trying to
keep things simple in
a team of 10

4. What happened with the MySQL talk

5. One month ago

6. The reception

7. The questions
● How do I make WordPress secure
● What are your tips for secure WordPress
● How do I chose save plugins and themes
● How do you manage to work remotely?
● Are there any other Bulgarians at Automattic?

8. ! MySQL

9. There are no mistakes,
only lessons.

10. Lesson learned
● Another set of lessons this time and we'll see
which one worked better :-)

12. Story #1 The ID
● 7 year old legacy code
● Entire table described in the code
● We have items with ids 5 and 6. We need to
add 7.

13. Story #1 The ID
● One new object
● A few helpers
● 135 removed magic numbers
● One changeset
● 0 unit tests
● What could possibly go wrong?

14. Story #1 Lessons
● Pleasepleaseplease, no magic numbers
● Atomic commits, please!
● Long functions are hard to understand
● Stats monitoring
● Legacy is code for which we don't have tests

15. Story #2 The Notification
● Montreal
● 1+ million emails
● 1+ million discount coupons (10-ish previously)
● Friday
● What could possibly go wrong?

16. Story #2 The Notification
● Queries that work with small tables:
SELECT * FROM table
SELECT * FROM table ORDER BY whatever
LIMIT 200, 100

17. Story #2 The Notification
● Queries that don't work with large tables:
SELECT * FROM table
SELECT * FROM table ORDER BY whatever
LIMIT 200, 100

18. Story #2 The Notification
● Fetching big amounts of data breaks things
● Offsetting breaks things
● The coupons weren't really used in the past
● Repeating millions of anything means a lot of
time

19. Launching big things on Friday

20. Offsets
SELECT * FROM ...
WHERE `id` > 1093029
ORDER BY `id` LIMIT 20
SELECT `deadline` FROM ...
WHERE `date` BETWEEN '2014-06-20'
AND ...

21. Offsets
SELECT * FROM ...
WHERE `id` > 1093029
ORDER BY `id` LIMIT 20
SELECT `deadline` FROM ...
WHERE `date` BETWEEN '2014-06-20'
AND ...

22. Offsets
SELECT * FROM `table` JOIN (
SELECT `id` FROM `table`
ORDER BY `whatever`
LIMIT 5000,50
) as `b` USING `id`

23. Story #3 The A/B Test
● A/B test is showing different things to users and
measuring effect
● We use Kissmetrics
● We've had 5 different A/B testing classes

24. Story #3 The A/B Test
● Feature-rich classes
● Many levels of abstraction
● Expressive names
● Many filters and actions
● What could possibly go wrong?

25. Story #3 The A/B Test
● Wrong results, no one knows why.

26. Story #3 Lessons Learned
● KISS. Simplest solution worked
● Kissmetrics rocks
● A/B test everything

27. Story #4 Barry
<bazza> howdy
<dzver> hi, did I break anything?
<bazza> your blog looks hacked

28. Story #4
● Unique passwords
● 2-factor auth
● Come to WordCamp Europe and maybe watch
Barry live :-)
● #praythatbarrycomestowceurope

29. Summary
● KISS. Simple queries. Simple code.
● DRY. Repetition fails.
● A/B test. Unit test. Test!
● Launch your next project on Friday at 7pm.

30. My name is Veselin
I code for food.
Ask me anything!