A common request sent from your web browser to a web server goes quite a long way and it can take a great deal of time until the data your browser can display are fetched back. I will talk about making this great deal of time significantly less great by caching things on different levels, starting with client-side caching for faster display and minimizing transferred data, storing results of already performed operations and computations and finishing with lowering the load of database servers by caching result sets. Cache expiration and invalidation is the hardest part so I will cover that too. Presentation will be focused mainly on PHP, but most of the principles are quite general work elsewhere too.

1. Caching Strategies Michal Špaček, Skype; WebExpo 2011 , Prague @spazef0rze, www.michalspacek.cz

2. What the... Cache ? HDD cache, CPU cache, DNS cache, web cache, geocache

3. What the... Cache ? HDD cache, CPU cache, DNS cache, web cache , geocache

4. CLIENT (BROWSER) WEB SERVER DATABASE SERVER

5. HTTP level caching

6. Client local disk/memory cache CLIENT (BROWSER) WEB SERVER

7. Response headers: Expires Last-Modified ETag Cache-Control Pragma CLIENT (BROWSER) WEB SERVER

8. Expires: HTTP-date Expires: Sat, 24 Sep 2011 12:00:00 GMT < Expires CLIENT (BROWSER)

9. Expires: HTTP-date Expires: Sat, 24 Sep 2011 12:00:00 GMT > Expires CLIENT (BROWSER) WEB SERVER

10. Last-Modified: HTTP-date Following request: If-Modified-Since: HTTP-date

11. Last-Modified: HTTP-date Following request: If-Modified-Since: HTTP-date Response: Entity modified: HTTP 200 OK Not modified: HTTP 304 Not Modified

12. Last-Modified: HTTP-date Saves bandwidth!

13. ETag: quoted-string Following request: If-None-Match: quoted-string

14. ETag: quoted-string Following request: If-None-Match: quoted-string Response: No match : HTTP 200 OK A match: HTTP 304 Not Modified

15. Saves bandwidth, too! ETag: quoted-string

16. If-Modified-Since If-Unmodified-Since If-None-Match If-Match

17. ETag × Last-Modified hash (GUID) × HTTP-date (seconds)

18. ETag × Last-Modified hash (GUID) × HTTP-date (seconds) weak+strong validation × strong

19. ETag × Last-Modified hash (GUID) × HTTP-date (seconds) weak+strong validation × strong needs content × needs date

20. Request+Response header Cache-Control: whatever

21. Request+Response header whatever = max-age , no-cache , public , must-revalidate (response only), ... Cache-Control: whatever

22. Pragma: no-cache Request+Response header

23. Pragma: no-cache Request+Response header Request: HTTP 1.0 variant of Cache-Control: no-cache

24. Pragma: no-cache Request+Response header Request: HTTP 1.0 variant of Cache-Control: no-cache Response: meaning undefined, wtf

25. Proxy cache CLIENT (BROWSER) WEB SERVER

26. Proxy cache CLIENT (BROWSER) WEB SERVER

27. Application level caching

28. Configuration Does not change often

29. Configuration Does not change often Parse (files)/read (from db) and store to APC

30. APC: The Alternative PHP Cache PHP extension Data store (also opcode cache)

31. APC: The Alternative PHP Cache Data persist between requests

32. APC: The Alternative PHP Cache Data persist between requests … until deleted or cache cleared or server restarted

33. Database connection cache Persistent connections (don't work) Connection pooler

34. Database query cache Some systems have query cache

35. Database query cache Some systems have query cache Some don't

36. Result set cache Some data don't change

37. Result set cache Some data don't change Fetch and store to memcached

38. Memcached Client-server architecture Key-value in memory store for strings and objects

39. Problems with caching

40. Data change sometimes but not often enough Employee list of a company

41. Data change sometimes but not often enough Employee list of a company Invalidate cache when adding or removing employees

42. Data change sometimes and delay is okay Translations from database

43. Data change sometimes and delay is okay Translations from database Introduce cache lifetime

44. Moar cache keys for the same data Sorted employee list (asc, desc)

45. Moar cache keys for the same data Sorted employee list (asc, desc) Cache groups

46. Cache groups Keys: list-sorted-asc, list-sorted-desc

47. Cache groups Keys: list-sorted-asc, list-sorted-desc Group „list“: list-sorted-asc, list-sorted-desc, list-unsorted

48. Cache groups Keys: list-sorted-asc, list-sorted-desc Group „list“: list-sorted-asc, list-sorted-desc, list-unsorted Delete group „list“ when adding/removing

49. Cache wherever and whatever

50. … but delete your whatever when needed

51. Caching is magic

52. Caching is magic but not automagic

53. Caching is magic but not automagic until now