Discussion on caching in WordPress from Maura Teal of Pagely

1. @mlteal | #loopconf | 2018
The Balancing Act of
Caching in WordPress
“[Cache] rules everything around me”

2. @mlteal | #loopconf | 2018
Maura Teal (@mlteal)
Software Engineer at Pagely.
Previously Sr Dev at Time Inc.
Emoji and meme enthusiast:
github.com/mlteal/custom-emoji

3. @mlteal | #loopconf | 2018

4. @mlteal | #loopconf | 2018
Caching?
• Data stored “closer” to the end user*
• *or closer to where it will be utilized often

5. @mlteal | #loopconf | 2018
Caching?
• Object Caching (storage in memory):
• Memcached
• Redis
• …

6. @mlteal | #loopconf | 2018
Caching what?
• Object Caching (storage in memory):
• Memcached
• Redis
• Alternative storage mechanisms:
• Database storage (Transients)
• Custom tables/meta
• Local (browser level) storage

7. @mlteal | #loopconf | 2018
Data is not forever

8. @mlteal | #loopconf | 2018
Quick Win
*
*Basic blogs 💻

9. @mlteal | #loopconf | 2018
*Except logged-in content

10. @mlteal | #loopconf | 2018
*Except frequently-changing content

11. @mlteal | #loopconf | 2018

12. @mlteal | #loopconf | 2018
What to Cache

13. @mlteal | #loopconf | 2018
WP’s Caching API’s
• wp_cache_set( $key, $data, $group, $expire );
• wp_cache_get( $key, $group, $force, $found );

14. @mlteal | #loopconf | 2018
Transients API
• get_transient( $key );
• set_transient( $key, $value, $expires );
• delete_transient( $key );

15. @mlteal | #loopconf | 2018
WP’s Caching API’s
get_my_data() {
$data = get_transient( ‘my_transient_name’ );
if ( false === $data ) { // Transient was expired/hasn’t been set.
$data = fetch_my_data(); // Pull data from original source.
set_transient( ‘my_transient_name’, $data,
2 * HOUR_IN_SECONDS );
}
return $data;
}

16. @mlteal | #loopconf | 2018
Do I need to cache more?

17. @mlteal | #loopconf | 2018
Do I need to cache more?
• Performance indicators
(Speed, CPU & memory use)
• Traffic indicators
(Any expected upticks?)
• Use of external API’s
• Content and access goals

18. @mlteal | #loopconf | 2018
Do I need to cache more?
• Performance indicators
(Speed, CPU & memory use)

19. @mlteal | #loopconf | 2018
Do I need to cache more?
• Traffic indicators
(Any expected upticks?)

20. @mlteal | #loopconf | 2018
Do I need to cache more?
• Use of external API’s

21. @mlteal | #loopconf | 2018
Browser Cache API

22. @mlteal | #loopconf | 2018
Browser Cache API
• Fully frontend-focused solution.
• Store data directly in browser's cache.
• Use sparingly. With great power…
• Depending on the API, not fully supported across
browsers.

23. @mlteal | #loopconf | 2018
Browser Cache API
caches.open('my-cache').then((cache) => {
// do something with cache...
});

24. @mlteal | #loopconf | 2018
Browser Cache API:
Further Reading
• https://developer.mozilla.org/en-US/docs/Web/API/
Cache
• https://developers.google.com/web/fundamentals/
instant-and-offline/web-storage/cache-api
• https://davidwalsh.name/cache

25. @mlteal | #loopconf | 2018
Lessons Learned at Scale
• Cache warming is real
• There is such a thing as caching too much
• Significantly reducing load is great, but still need
to handle clearing or refreshing data without
bringing the site down!

26. @mlteal | #loopconf | 2018
Lessons Learned at Scale
• Load test before big events
• Knowledge is power—anyone working at scale
should load test

27. @mlteal | #loopconf | 2018
Lessons Learned at Scale
• Expired != deleted
• Unless there’s a specific garbage collection
process in place, cached data, especially transients
in the DB, have a way of hanging around.

28. @mlteal | #loopconf | 2018
Lessons Learned at Scale
• Cache all you want, but you still need to write
performant code

29. @mlteal | #loopconf | 2018
Maura Teal
@mlteal