A caching pie

"Peeling off the cache layers of a Ruby on Rails application"

This is an internal talk I gave to the Codegram team. It's a brief exploration of most of the mechanism and strategies the Rails stack gives us.

Transcript

1. A Caching Pie Peeling off the cache layers of a Ruby on Rails application Friday, September 27, 13
2. /kæʃ/ Friday, September 27, 13
3. A fast temporary storage where recently or frequently used information is stored to avoid having to reload it from a slower storage medium. Friday, September 27, 13
4. Being naive: memoization Friday, September 27, 13
5. 1 def ed 2 Balls.new 3 end Friday, September 27, 13
6. 1 def ed 2 @ed ||= Balls.new 3 end Friday, September 27, 13
7. What’s good Friday, September 27, 13
8. •OMG so simple What’s good Friday, September 27, 13
9. •OMG so simple •Any kind of ruby object What’s good Friday, September 27, 13
10. •OMG so simple •Any kind of ruby object •Low impact, no dependencies What’s good Friday, September 27, 13
11. What isn’t Friday, September 27, 13
12. •Caching with arguments What isn’t Friday, September 27, 13
13. •Caching with arguments •Expiration mechanisms What isn’t Friday, September 27, 13
14. •Caching with arguments •Expiration mechanisms •Sharing across processes What isn’t Friday, September 27, 13
15. Leveraging Memcached Friday, September 27, 13
16. What the heck is it? Friday, September 27, 13
17. •Standalone network service What the heck is it? Friday, September 27, 13
18. •Standalone network service •Simple API (get, set, delete) What the heck is it? Friday, September 27, 13
19. •Standalone network service •Simple API (get, set, delete) •Uber fast key-value store What the heck is it? Friday, September 27, 13
20. •Standalone network service •Simple API (get, set, delete) •Uber fast key-value store •Persistent storage What the heck is it? Friday, September 27, 13
21. •Standalone network service •Simple API (get, set, delete) •Uber fast key-value store •Persistent storage •LRU expiration (maximum size) What the heck is it? Friday, September 27, 13
22. •Standalone network service •Simple API (get, set, delete) •Uber fast key-value store •Persistent storage •LRU expiration (maximum size) •Open source, mature & stable What the heck is it? Friday, September 27, 13
23. A Ruby gem: dalli Friday, September 27, 13
24. 1 require 'dalli' 2 dalli = Dalli::Client.new Friday, September 27, 13
25. 1 require 'dalli' 2 dalli = Dalli::Client.new 3 Friday, September 27, 13
26. 1 require 'dalli' 2 dalli = Dalli::Client.new 3 4 def ed 5 return balls if balls = dalli.get('ed') 6 7 balls = Balls.new 8 dalli.set('ed', balls) 9 10 balls 11 end Friday, September 27, 13
27. 1 # With Rails 2 # 3 def ed 4 Rails.cache.fetch 'ed' do 5 Balls.new 6 end 7 end Friday, September 27, 13
28. 1 # Parameters 2 # 3 def ed(color = 'red') 4 Rails.cache.fetch "ed-#{color}" do 5 Balls.new(color) 6 end 7 end Friday, September 27, 13
29. 1 # Expiration 2 # 3 def ed 4 Rails.cache.fetch "ed", expires_in: 1.hour do 5 Balls.new 6 end 7 end Friday, September 27, 13
30. What’s cool Friday, September 27, 13
31. •Shared across processes, persistent What’s cool Friday, September 27, 13
32. •Shared across processes, persistent •Time expiration What’s cool Friday, September 27, 13
33. •Shared across processes, persistent •Time expiration •Centralized cache store What’s cool Friday, September 27, 13
34. Not so cool... Friday, September 27, 13
35. •Beware: Serialization Not so cool... Friday, September 27, 13
36. •Beware: Serialization •Higher cost (still pretty low) Not so cool... Friday, September 27, 13
37. •Beware: Serialization •Higher cost (still pretty low) •Global key scope Not so cool... Friday, September 27, 13
38. Rails: Other implementations Friday, September 27, 13
39. Rails: Other implementations • ActiveSupport::Cache::Store (abstract) Friday, September 27, 13
40. Rails: Other implementations • ActiveSupport::Cache::Store (abstract) • ActiveSupport::Cache::MemoryStore Friday, September 27, 13
41. Rails: Other implementations • ActiveSupport::Cache::Store (abstract) • ActiveSupport::Cache::MemoryStore • ActiveSupport::Cache::FileStore Friday, September 27, 13
42. Rails: Other implementations • ActiveSupport::Cache::Store (abstract) • ActiveSupport::Cache::MemoryStore • ActiveSupport::Cache::FileStore • ActiveSupport::Cache::NullStore Friday, September 27, 13
43. Rails: Other implementations • ActiveSupport::Cache::Store (abstract) • ActiveSupport::Cache::MemoryStore • ActiveSupport::Cache::FileStore • ActiveSupport::Cache::NullStore • ActiveSupport::Cache::RedisStore Friday, September 27, 13
44. Rails: Other implementations • ActiveSupport::Cache::Store (abstract) • ActiveSupport::Cache::MemoryStore • ActiveSupport::Cache::FileStore • ActiveSupport::Cache::NullStore • ActiveSupport::Cache::RedisStore • ActiveSupport::Cache::CouchbaseStore Friday, September 27, 13
45. Caching representations Friday, September 27, 13
46. 1 class StuffController < ActionController::Base 2 def show 3 thing = Thing.find(params[:id]) 4 5 render json: thing.to_json 6 end 7 end Friday, September 27, 13
47. 1 class StuffController < ActionController::Base 2 def show 3 thing = Thing.find(params[:id]) 4 json = Rails.cache.fetch(thing){ thing.to_json } 5 6 render json: json 7 end 8 end Friday, September 27, 13
48. 1 # Only with Rails 2 thing.cache_key 3 => "thing/1-20130919103345" Friday, September 27, 13
49. 1 # Only with Rails 2 thing.cache_key 3 => "thing/1-20130919103345" class Friday, September 27, 13
50. 1 # Only with Rails 2 thing.cache_key 3 => "thing/1-20130919103345" class ID Friday, September 27, 13
51. 1 # Only with Rails 2 thing.cache_key 3 => "thing/1-20130919103345" class ID updated_at Friday, September 27, 13
52. 1 # app/views/stuff/show.json.erb 2 <%= cache @thing do %> 3 { 4 thing: <%= render partial: 'thing', object: @thing %> 5 } 6 <%= end %> Friday, September 27, 13
53. 1 # app/views/stuff/show.json.erb 2 <%= cache @thing do %> 3 { 4 thing: <%= render partial: 'thing', object: @thing %> 5 } 6 <%= end %> Problem: What if the template changes? Friday, September 27, 13
54. cache_digests (gem) views/stuff/1-20130919103345/d9fb66b120b61f46707c67ab41d93cb2 1 $ rake cache_digests:nested_dependencies TEMPLATE=stuff/show 2 [ 3 { 4 "stuff/thing": [ 5 "stuff/moar" 6 ] 7 } 8 ] Friday, September 27, 13
55. What’s good Friday, September 27, 13
56. •Easy, straightforward DSL What’s good Friday, September 27, 13
57. •Easy, straightforward DSL •Nested caching (russian doll) What’s good Friday, September 27, 13
58. •Easy, straightforward DSL •Nested caching (russian doll) •Auto-expiration when representation changes What’s good Friday, September 27, 13
59. Be careful! Friday, September 27, 13
60. •Beware of time-sensitive cached data Be careful! Friday, September 27, 13
61. •Beware of time-sensitive cached data •Partial support of templating engines Be careful! Friday, September 27, 13
62. •Beware of time-sensitive cached data •Partial support of templating engines •`updated_at` touching can lead to rabbit holes Be careful! Friday, September 27, 13
63. Caching in HTTP Friday, September 27, 13
64. 1 # HTTP Expiration caching 2 # 3 class StuffController < ActionController::Base 4 def show 5 @thing = Thing.find(params[:id]) 6 expires_in 2.hours, public: true 7 end 8 end Friday, September 27, 13
65. 1 # HTTP Expiration caching 2 # 3 class StuffController < ActionController::Base 4 def show 5 @thing = Thing.find(params[:id]) 6 expires_in 2.hours, public: true 7 end 8 end HTTP/1.1 200 OK Cache-Control: max-age=3600, public Friday, September 27, 13
66. 1 # HTTP Validation caching 2 # 3 class StuffController < ActionController::Base 4 def show 5 @thing = Thing.find(params[:id]) 6 7 fresh_when( 8 last_modified: @thing.updated_at.utc, 9 etag: Digest::MD5.hexdigest(@thing.cache_key) 10 ) 11 end 12 end Friday, September 27, 13
67. 1 # HTTP Validation caching 2 # 3 class StuffController < ActionController::Base 4 def show 5 @thing = Thing.find(params[:id]) 6 7 fresh_when( 8 last_modified: @thing.updated_at.utc, 9 etag: Digest::MD5.hexdigest(@thing.cache_key) 10 ) 11 end 12 end HTTP/1.1 200 OK Last-Modified: Sat Sep 21 11:09:56 UTC 2013 ETag: "686897696a7c876b7e" Friday, September 27, 13
68. The browser knows its stuff Friday, September 27, 13
69. •Will send if-modified-since and etag to each request The browser knows its stuff Friday, September 27, 13
70. •Will send if-modified-since and etag to each request •Can combine expiration caching and validation caching: http://stackoverflow.com/a/6351738/871401 The browser knows its stuff Friday, September 27, 13
71. •Will send if-modified-since and etag to each request •Can combine expiration caching and validation caching: http://stackoverflow.com/a/6351738/871401 •Will use the previously stored document when 302 is returned The browser knows its stuff Friday, September 27, 13
72. What’s good Friday, September 27, 13
73. •Rails can skip rendering (and return 302) What’s good Friday, September 27, 13
74. •Rails can skip rendering (and return 302) •Saves bandwith What’s good Friday, September 27, 13
75. •Rails can skip rendering (and return 302) •Saves bandwith •Pure HTTP semantics What’s good Friday, September 27, 13
76. Caveats Friday, September 27, 13
77. •Expiration-caching responses won’t be shared across clients Caveats Friday, September 27, 13
78. •Expiration-caching responses won’t be shared across clients •HTTP caching is hard: http://tools.ietf.org/html/ rfc2616#section-13 Caveats Friday, September 27, 13
79. a gem: rack-cache Friday, September 27, 13
80. config.middleware.use Rack::Cache Friday, September 27, 13
81. •Comes with the Rails stack config.middleware.use Rack::Cache Friday, September 27, 13
82. •Comes with the Rails stack •Watches HTTP cache headers and stores them config.middleware.use Rack::Cache Friday, September 27, 13
83. •Comes with the Rails stack •Watches HTTP cache headers and stores them •Will return cached response to prevent app to be hit config.middleware.use Rack::Cache Friday, September 27, 13
84. Dragons ahead! Friday, September 27, 13
85. Use caching wisely Friday, September 27, 13
86. Or better don’t use it at all Friday, September 27, 13
87. Or use all techniques! Friday, September 27, 13
88. In a typical Rails app... Friday, September 27, 13
89. In a typical Rails app... •Method calls are cached ||= Friday, September 27, 13
90. In a typical Rails app... •Method calls are cached ||= •Database queries are cached Friday, September 27, 13
91. In a typical Rails app... •Method calls are cached ||= •Database queries are cached •Entire views are cached Friday, September 27, 13
92. In a typical Rails app... •Method calls are cached ||= •Database queries are cached •Entire views are cached •Layers and layers of partials are cached Friday, September 27, 13
93. In a typical Rails app... •Method calls are cached ||= •Database queries are cached •Entire views are cached •Layers and layers of partials are cached •Decorator methods are cached Friday, September 27, 13
94. In a typical Rails app... •Method calls are cached ||= •Database queries are cached •Entire views are cached •Layers and layers of partials are cached •Decorator methods are cached •Assets are cached Friday, September 27, 13
95. In a typical Rails app... •Method calls are cached ||= •Database queries are cached •Entire views are cached •Layers and layers of partials are cached •Decorator methods are cached •Assets are cached •External API calls are cached Friday, September 27, 13
96. Yo’mama’s arse is cached Friday, September 27, 13
97. Yo’mama’s arse is cached ...cause it’s so big it takes too much request time LOL Friday, September 27, 13
98. There are only two hard things in Computer Science: cache invalidation and naming things. Phil Karlton (Netscape) Friday, September 27, 13
99. Just remember: Caches won’t help you scale. Friday, September 27, 13
100. Good architecture is. Just remember: Caches won’t help you scale. Friday, September 27, 13
101. Dubbity-doubts? Friday, September 27, 13