But At What Cost?

Aaron Patterson

May 02, 2019

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Transcript

1. Hello!

2. doES iT sCaLe?

3. Jubilee Year

4. Look at all the things I’m NOT doing!

5. Prologue

6. None

7. Ruby Script

8. None

9. But At What Cost?

10. Aaron Patterson

11. Live From Here

12. None
13. None
14. None
15. None
16. None
17. None
18. None

19. I have stickers of my cat! (please say "hello")

20. @tenderlove

21. None
22. None

23. Other == Puns?

24. Speaking of Twitter…

25. "

26. None
27. None
28. None
29. None

30. @buritica

31. ~54% useless

32. March 14, 2019

33. None
34. None

35. "But At What Cost?" Bot

36. Twitter: 100% Useless

37. Facepalm-er

38. Facepalm-ee

39. Response Algorithm Is it a pun? "Aaron" "But At What

    Cost?" Yes No

40. Let’s Practice

41. G GitHub

42. Active Job

43. None

44. G GitHub We’re Hiring!!!!

45. None
46. None

47. http://git.io/sparkles

48. Ruby Core Team

49. 10 Years On Ruby Core! W ow !!!

50. Rails Core Team

51. None

52. I ❤ Ruby

53. None

54. Just Worked™

55. No Boilerplate

56. Java (1.3?) vs Ruby List list = new ArrayList(); list.add("1");

    list.add("2"); list.add("3"); Iterator iter = list.iterator(); List intList = new ArrayList(); while (iter.hasNext()) { String str = (String)iter.next(); intList.add(Integer.parseInt(str)); } list = %w{ 1 2 3 } intList = list.map { |l| l.to_i } Java Ruby

57. My First Ruby Program Serious ^

58. Never Write Infinite Loops

59. I ❤ Rails

60. None

61. Just Worked™

62. No Boilerplate

63. Community Values

64. "I MUST WRITE RAILS!"

65. BUT AT WHAT COST?

66. -25% $114k ➡ $85k (in 2006)

67. More Companies

68. More People

69. Thank You!

70. #ENDGAME

71. None

72. BUT AT WHAT COST?

73. None

74. Game of Thrones

75. Dumbledore Dies

76. None

77. Cool Performance Tips

78. No Parenthesis is Faster

79. Parens vs No Parens def foo1(bar, baz) end def foo2(bar,

    baz) end def foo3(bar, baz) end def foo1 bar, baz end def foo2 bar, baz end def foo3 bar, baz end Parens No Parens

80. "No code is faster than no code"

81. ruby -y

82. Parse States $ ruby --disable-gems -y with-parens.rb | wc -l

    805 $ ruby --disable-gems -y without-parens.rb | wc -l 778

83. Single Quotes Are 2x Faster Than Double Quotes

84. You Have To Hit The Shift Key To Type "

85. Actual Performance Tip Rails 6!

86. Allocation Count Started GET "/users/new" for ::1 at 2019-04-30 16:45:49

    -0500 Processing by UsersController#new as */* Rendering users/new.html.erb within layouts/application Rendered users/_form.html.erb (Duration: 1.4ms | Allocations: 552) Rendered users/new.html.erb within layouts/application (Duration: 1.7ms | Allocations: 640) Completed 200 OK in 6ms (Views: 5.4ms | ActiveRecord: 0.0ms | Allocations: 4140) Started GET "/users/new" for ::1 at 2019-04-30 16:47:02 -0500 Processing by UsersController#new as */* Rendering users/new.html.erb within layouts/application Rendered users/_form.html.erb (Duration: 1.4ms | Allocations: 827) Rendered users/_expensive.html.erb (Duration: 1.6ms | Allocations: 10098) Rendered users/new.html.erb within layouts/application (Duration: 4.3ms | Allocations: 11553) Completed 200 OK in 9ms (Views: 8.5ms | ActiveRecord: 0.0ms | Allocations: 15981)

87. Allocation Count Started GET "/users/new" for ::1 at 2019-04-30 16:45:49

    -0500 Processing by UsersController#new as */* Rendering users/new.html.erb within layouts/application Rendered users/_form.html.erb (Duration: 1.4ms | Allocations: 552) Rendered users/new.html.erb within layouts/application (Duration: 1.7ms | Allocations: 640) Completed 200 OK in 6ms (Views: 5.4ms | ActiveRecord: 0.0ms | Allocations: 4140) Started GET "/users/new" for ::1 at 2019-04-30 16:47:02 -0500 Processing by UsersController#new as */* Rendering users/new.html.erb within layouts/application Rendered users/_form.html.erb (Duration: 1.4ms | Allocations: 827) Rendered users/_expensive.html.erb (Duration: 1.6ms | Allocations: 10098) Rendered users/new.html.erb within layouts/application (Duration: 4.3ms | Allocations: 11553) Completed 200 OK in 9ms (Views: 8.5ms | ActiveRecord: 0.0ms | Allocations: 15981)

88. Rails at GitHub

89. Template Pre-Compilation Method Name Generation

90. Template Pre- Compilation

91. Method Name Generation

92. Build a Template Renderer!

93. Rails is MVC

94. MVC Model View Controller Request

95. Modal View Controller

96. MVC Model View Controller Request Action Controller Action View Active

    Record

97. Action View

98. Action View Finds Templates Compiles Templates Executes Views

99. View Templates

100. ERB

101. Developed by @m_seki

102. ERB Template <h1>New User</h1> <%= render_form %> <%= link_to 'Back'

     %> new.html.erb

103. ERB Compiler require "erb" # Compile the template template =

     ERB.new File.read "test.html.erb" # Print the template source puts template.src # Evaluate the template puts template.result(binding) compile.rb

104. Compiled Template _erbout = +"" _erbout << "<h1>New User</h1>\n\n".freeze _erbout

     << render_form.to_s _erbout << "\n\n".freeze _erbout << link_to("Back").to_s _erbout << "\n".freeze _erbout

105. Modified Compile Script require "erb" def render_form "<form></form>" end def

     link_to(text) "<a href=\"#\">#{text}</a>" end # Compile the template template = ERB.new File.read "test.html.erb" # Evaluate the template puts template.result(binding)

106. Compiler Output $ ruby compiler.rb <h1>New User</h1> <form></form> <a href="#">Back</a>

107. ERB Translations ERB Source Translated Ruby <%= something %> _erbout

     << something.to_s <% something_else %> something_else

108. Capturing Blocks <div> <%= capture do %> Hello! <% end

     %> </div> require "erb" def capture yield end # Compile the template template = ERB.new File.read "test.html.erb" puts template.result(binding)

109. What is the output? Hello! <div> </div> <div> Hello! </div>

     ERROR!

110. Compiled Source _erbout = +'' _erbout << "<div>\n ".freeze _erbout

     << ( capture do ).to_s _erbout << "\n Hello!\n ".freeze end _erbout << "\n</div>\n".freeze _erbout <div> <%= capture do %> Hello! <% end %> </div>

111. Compiled Source _erbout = +'' _erbout << "<div>\n ".freeze _erbout

     << ( capture do ).to_s _erbout << "\n Hello!\n ".freeze end _erbout << "\n</div>\n".freeze _erbout <div> <%= capture do %> Hello! <% end %> </div>

112. How does this work in Rails?

113. ERB Compiler BLOCK_EXPR = /\s*((\s+|\))do|\{)(\s*\|[^|]*\|)?\s*\Z/ def add_expression(indicator, code) flush_newline_if_pending(src) if

     (indicator == "==") || @escape src << "@output_buffer.safe_expr_append=" else src << "@output_buffer.append=" end if BLOCK_EXPR.match?(code) src << " " << code else src << "(" << code << ");" end end

114. ERB in Rails

115. Different ERB Flavors Original ERB ERubis ERubi

116. ERB Performance

117. Rendering Speed require "erb" require "benchmark/ips" class AaronView TEMPLATES =

     { } TEMPLATES["index"] = <<-eerb <html> <body> <h1>Hello <%= name %><h1> </html> eerb def name; "Aaron"; end def render(template) ERB.new(TEMPLATES[template]).result(binding) end end view = AaronView.new Benchmark.ips do |x| x.report("render") { view.render("index") } end

118. Rendering Speed $ ruby rendering_speed.rb Warming up -------------------------------------- render 2.696k

     i/100ms Calculating ------------------------------------- render 27.117k (± 5.9%) i/s - 137.496k in 5.092633s

119. Cache Compilation class AaronView TEMPLATES = { } TEMPLATES["index"] =

     <<-eerb <html> <body> <h1>Hello <%= name %><h1> </html> eerb def name; "Aaron"; end def render(template) ERB.new(TEMPLATES[template]).result(binding) end COMPILED_TEMPLATES = { } def render_compiled(template) erb = COMPILED_TEMPLATES[template] ||= ERB.new(TEMPLATES[template]) erb.result(binding) end end view = AaronView.new Benchmark.ips do |x| x.report("render") { view.render("index") } x.report("render compiled") { view.render_compiled("index") } x.compare! end

120. Cache Compilation $ ruby rendering_speed.rb Warming up -------------------------------------- render 2.709k

     i/100ms render compiled 6.293k i/100ms Calculating ------------------------------------- render 27.115k (± 2.6%) i/s - 138.159k in 5.098881s render compiled 63.645k (± 3.9%) i/s - 320.943k in 5.050544s Comparison: render compiled: 63645.5 i/s render: 27114.8 i/s - 2.35x slower

121. Define a Method class AaronView TEMPLATES = { } TEMPLATES["index"]

     = <<-eerb <html> <body> <h1>Hello <%= name %><h1> </html> eerb def name; "Aaron"; end def render(template) ERB.new(TEMPLATES[template]).result(binding) end COMPILED_TEMPLATES = { } def render_compiled(template) erb = COMPILED_TEMPLATES[template] ||= ERB.new(TEMPLATES[template]) erb.result(binding) end METHODS_DEFINED = { } def render_with_method(template) unless METHODS_DEFINED.key? template erb = ERB.new(TEMPLATES[template]) self.class.class_eval "def render_#{template}; #{erb.src}; end" METHODS_DEFINED[template] = true end send "render_#{template}" end end

122. Define a Method $ ruby rendering_speed.rb Warming up -------------------------------------- render

     2.750k i/100ms render compiled 6.462k i/100ms render method 114.420k i/100ms Calculating ------------------------------------- render 28.389k (± 2.7%) i/s - 143.000k in 5.041158s render compiled 65.860k (± 2.4%) i/s - 329.562k in 5.006962s render method 1.477M (± 1.7%) i/s - 7.437M in 5.038304s Comparison: render method: 1476591.3 i/s render compiled: 65860.1 i/s - 22.42x slower render: 28388.6 i/s - 52.01x slower

123. Method Generation require "erb" erb_source = <<-erb <html> <body> <h1>Hello

     <%= name %><h1> </html> erb erb = ERB.new erb_source template = "index" self.class.class_eval "def render_#{template}; #{erb.src}; end" send "render_#{template}" Template Source Compile Source Define a m ethod Render the Template

124. Method Generation def render_index _erbout = +'' _erbout << "<html>\n

     <body>\n <h1>Hello ".freeze _erbout << name.to_s _erbout << "<h1>\n</html>\n".freeze _erbout end Compiled Source

125. Templates Are Translated to Methods

126. Rails Template Methods <h1> This is an inner template <%

     puts methods.grep(/_app/) %> </h1> Template in Rails

127. Rails Template Methods Console Output _app_views_users_index_html_erb___4485674087862414886_70282093274980 _app_views_users__first_ja_html_erb__657974686689484881_70282053324000 _app_views_users__second_html_erb___3508242123539422948_70282053523460

128. Memory Size def render_index _erbout = +'' _erbout << "<html>\n

     <body>\n <h1>Hello ".freeze _erbout << name.to_s _erbout << "<h1>\n</html>\n".freeze _erbout end require "objspace" iseq = RubyVM::InstructionSequence.of( method(:render_index)) p ObjectSpace.memsize_of iseq $ ruby test.rb 1264

129. Template Handling In Rails

130. Instance Variable Visibility <h1>This is template Foo!</h1> <%= @some_ivar %>

     <h1>This is template Bar!</h1> <%= @some_ivar %> _foo.html.erb _bar.html.erb

131. Compiled Templates class ActionView::Base def render_foo _erbout = +'' _erbout

     << "<h1>This is template Foo!</h1>\n".freeze _erbout << @some_ivar.to_s _erbout << "\n".freeze _erbout end def render_bar _erbout = +'' _erbout << "<h1>This is template Barr!</h1>\n".freeze _erbout << @some_ivar.to_s _erbout << "\n".freeze _erbout end end _foo.html.erb _bar.html.erb Same Instance Same Instance

132. Don’t use instance variables in your templates

133. "Don’t use instance variables in your templates" - Aaron

134. Instance Variable Visibility <h1>This is template Foo!</h1> <%= @some_ivar %>

     <h1>This is template Bar!</h1> <%= @some_ivar %> _foo.html.erb _bar.html.erb

135. Local Variables

136. Rendering With Locals <body> <%= render "content", locals: { name:

     "Gorby" } %> </body>

137. Compiling With Locals <h1> Hello, <%= name %> </h1> def

     render_content _erbout = +'' _erbout << "<h1>\n Hello, ".freeze _erbout << name.to_s _erbout << "\n</h1>\n".freeze _erbout end content.html.erb Compiled Method Method Call

138. Preamble With Locals

139. Compiling With Locals <h1> Hello, <%= name %> </h1> def

     render_content(locals) # Locals preamble name = locals[:name] _erbout = +'' _erbout << "<h1>\n Hello, ".freeze _erbout << name.to_s _erbout << "\n</h1>\n".freeze _erbout end content.html.erb Compiled Method

140. Templates Require Context <body> <%= render "content", locals: { name:

     "Gorby" } %> <%= render "content" %> </body> <h1> Hello, <%= name %> </h1> main.html.erb content.html.erb Method call or local variable? local variable method call

141. Templates Can’t Be Compiled In Advance* *(FORESHADOWING)

142. Compiled Too Many Times

143. Too Many Compilations <body> <%= render "content", locals: { name:

     "Gorby" } %> <%= render "content", locals: { name: "Gorby", friend: "Aaron" } %> </body> def render_content_1(locals) # Locals preamble name = locals[:name] _erbout = +'' _erbout << "<h1>\n Hello, ".freeze _erbout << name.to_s _erbout << "\n</h1>\n".freeze _erbout end def render_content_2(locals) # Locals preamble name = locals[:name] friend = locals[:friend] _erbout = +'' _erbout << "<h1>\n Hello, ".freeze _erbout << name.to_s _erbout << "\n</h1>\n".freeze _erbout end main.html.erb Compiled "content" Unique Preambles

144. "This is nice, but what should I do?"

145. Always pass the same locals to individual templates.

146. The render function

147. Finds a Template Compiles the Template Calculates a Method Name

     Calls the Method

148. Find a Template (from the cache) Compiled? Compile the Template

     Call the method Calculate a Method Name

149. Finding a Template

150. Template Rendering Depends on "Requested Format"

151. Users Controller class UsersController < ApplicationController # GET /users #

     GET /users.json def index @users = User.all render "index" end end $ tree app/views/users app/views/users !"" index.html.erb #"" index.xml.erb Controller app/views/users/*

152. Template Source <h1>XML template</h1> <h1>Users</h1> index.xml.erb index.html.erb

153. Requests and Rendering Request Response Template Rendered curl -H 'Accept:

     application/xml' http:// localhost:3000/users <h1>XML template</h1> index.xml.erb curl http://localhost: 3000/users <h1>Users</h1> index.html.erb curl -H 'Accept: text/ html' http://localhost: 3000/users <h1>Users</h1> index.html.erb

154. Template Cache Keys • Local variables • Format • Locale

     • Variant (iPhone, etc)

155. Strange Render Behavior

156. Users Controller class UsersController < ApplicationController # GET /users #

     GET /users.json def index @users = User.all render "index" end end $ tree app/views/users app/views/users !"" _my_template.png.erb !"" _my_template.xml.erb #"" index.html.erb Controller app/views/users/*

157. Template Contents <h1>Users</h1> <%= render "my_template" %> I guess this

     is a png? index.html.erb _my_template.png.erb <cool> XML is cool! </cool> _my_template.xml.erb

158. Requests and Rendering Request Response Template Rendered curl -H 'Accept:

     application/xml' http://localhost:3000/users Missing XML template Error None curl -H 'Accept: text/html' http://localhost:3000/users Missing HTML partial Error None Browser Missing HTML partial Error None curl http://localhost:3000/users <h1>Users</h1> I guess this is a png? index.html.erb _my_template.png.erb

159. Error!!

160. Requests and Rendering Request Response Template Rendered curl -H 'Accept:

     application/xml' http://localhost:3000/users Missing XML template Error None curl -H 'Accept: text/html' http://localhost:3000/users Missing HTML partial Error None Browser Missing HTML partial Error None curl http://localhost: 3000/users <h1>Users</h1> I guess this is a png? index.html.erb _my_template.png.erb

161. We Can’t Predict <h1>Users</h1> <%= render "my_template" %>

162. respond_to Controller class UsersController < ApplicationController # GET /users #

     GET /users.json def index @users = User.all render "index" end end class UsersController < ApplicationController # GET /users # GET /users.json def index @users = User.all respond_to do |format| format.html do render "index" end end end end "Bare" render respond_to render

163. Requests and Rendering Request Response Template Rendered curl -H 'Accept:

     application/ xml' http://localhost:3000/ users Missing XML template Error None curl -H 'Accept: text/html' http://localhost:3000/users Missing HTML partial Error None Browser Missing HTML partial Error None curl http://localhost:3000/ users Missing HTML partial Error None

164. Context Dependent <h1>Users</h1> <%= render "my_template" %> class UsersController <

     ApplicationController # GET /users # GET /users.json def index @users = User.all render "index" end end class UsersController < ApplicationController # GET /users # GET /users.json def index @users = User.all respond_to do |format| format.html do render "index" end end end end index.html.erb

165. Templates are not "Context Free"

166. Prediction and Consistency

167. Find a Template (from the cache) Compiled? Compile the Template

     Call the method Calculate a Method Name Cheap! Cheap! Expensive!

168. What Method Will This Call? <h1>Users</h1> <%= render "my_template" %>

     <h1>Users</h1> <%= render_my_template_00011123abf %> index.html.erb translated template Calls a unique method. But what method?

169. Find a Template (from the cache) Compiled? Compile the Template

     Call the method Calculate a Method Name Cheap! Cheap! Expensive!

170. #SPOILER

171. Slower Production Boot (but could be eliminated by BootSnap)

172. Lower Memory

173. Faster Runtime No More "Cache Check" Penalty

174. DETOUR!

175. Three Templates <ul> <%= render partial: "customer", collection: customers %>

     </ul> <ul> <%= render partial: "customer", collection: customers, cached: true %> </ul> _col.html.erb _cached_col.html.erb <li> Hello: <%= customer.name %> </li> _customer.html.erb

176. Benchmark https://github.com/rails/rails/issues/35257

177. Results $ be ruby render_benchmark.rb -- create_table(:customers, {:force=>true}) -> 0.0108s

     <#ActiveSupport::Cache::MemoryStore entries=1000, size=333893, options={}> Warming up -------------------------------------- collection render: no cache 6.000 i/100ms collection render: with cache 1.000 i/100ms Calculating ------------------------------------- collection render: no cache 65.319 (± 7.7%) i/s - 330.000 in 5.080651s collection render: with cache 11.504 (± 8.7%) i/s - 58.000 in 5.071030s Comparison: collection render: no cache: 65.3 i/s collection render: with cache: 11.5 i/s - 5.68x slower

178. I was convinced the cache didn’t work

179. I was convinced the cache didn’t work

180. I was convinced the cache didn’t work

181. I was convinced the cache didn’t work

182. But, there were entries in the cache

183. BUT AT WHAT COST?

184. Profiled The Cache ================================== Mode: wall(1000) Samples: 4690 (0.00% miss

     rate) GC: 207 (4.41%) ================================== TOTAL (pct) SAMPLES (pct) FRAME 594 (12.7%) 594 (12.7%) ActiveModel::LazyAttributeHash#[] 387 (8.3%) 387 (8.3%) ActiveRecord::Transactions#update_attributes_from_transaction_state 1199 (25.6%) 246 (5.2%) ActiveSupport::Cache::Store#expanded_key 301 (6.4%) 218 (4.6%) AbstractController::Caching::Fragments#combined_fragment_cache_key 207 (4.4%) 207 (4.4%) (garbage collection) 932 (19.9%) 196 (4.2%) ActionView::CollectionCaching#collection_by_cache_keys 450 (9.6%) 181 (3.9%) ActiveSupport::Cache::Store#expanded_version

185. Cache Key Calculation Was More Expensive Than Template Execution

186. Cache Payoff <li> Hello: <%= customer.name %> </li> <li>Hello: <%=

     customer.name %></li> <li>Hello: <%= customer.name %></li> <li>Hello: <%= customer.name %></li> <li>Hello: <%= customer.name %></li> <li>Hello: <%= customer.name %></li> <li>Hello: <%= customer.name %></li> <li>Hello: <%= customer.name %></li> <li>Hello: <%= customer.name %></li> <li>Hello: <%= customer.name %></li> <li>Hello: <%= customer.name %></li> <li>Hello: <%= customer.name %></li> <li>Hello: <%= customer.name %></li> <li>Hello: <%= customer.name %></li> <li>Hello: <%= customer.name %></li> <li>Hello: <%= customer.name %></li> <li>Hello: <%= customer.name %></li> <li>Hello: <%= customer.name %></li> <li>Hello: <%= customer.name %></li> <li>Hello: <%= customer.name %></li> <li>Hello: <%= customer.name %></li> <li>Hello: <%= customer.name %></li> <li>Hello: <%= customer.name %></li> Old Template New Template

187. Benchmark Results $ be ruby render_benchmark.rb -- create_table(:customers, {:force=>true}) ->

     0.0075s <#ActiveSupport::Cache::MemoryStore entries=1000, size=900893, options={}> Warming up -------------------------------------- collection render: no cache 4.000 i/100ms collection render: with cache 4.000 i/100ms Calculating ------------------------------------- collection render: no cache 41.066 (± 2.4%) i/s - 208.000 in 5.070051s collection render: with cache 43.192 (± 4.6%) i/s - 216.000 in 5.012803s Comparison: collection render: with cache: 43.2 i/s collection render: no cache: 41.1 i/s - same-ish: difference falls within error

188. "Cache" doesn’t mean "fast"

189. Speeding Up Templates

190. Template Static Analysis

191. Pre-Compiling Templates https://github.com/jhawthorn/actionview_precompiler/

192. ActionviewPrecompiler.precompile

193. Static Analysis <%= render "no_locals" %> <%= render "static_locals", locals:

     { foo: bar } %> <%= render "dynamic_locals", locals: { foo: bar }.merge(baz) %> Can Precompile! Can Precompile! Nope!

194. Predicting "Render" Methods

195. "Same Format Assumption" <h1>Users</h1> <%= render "my_template" %> <%= render

     "my_template", format: :png %> $ tree app/views/users app/views/users !"" _my_template.html.erb !"" _my_template.png.erb !"" _my_template.xml.erb #"" index.html.erb index.html.erb templates

196. Ambiguous Render Problem <h1>Users</h1> <%= render "my_template" %> <%= render

     "my_template", format: :html %> $ tree app/views/users app/views/users !"" _my_template.png.erb !"" _my_template.xml.erb #"" index.html.erb index.html.erb templates Sometimes an exception Sometimes a PNG Always an exception

197. "Always Optimize" <h1>Users</h1> <%= render "my_template" %> <%= render "my_template",

     format: :html %> <h1>Users</h1> <%= render "my_template", format: :png %> <%= render "my_template", format: :html %> index.html.erb index.html.erb

198. "Same Format Assumption" <h1>Users</h1> <%= render "my_template" %> <%= render

     "my_template", format: :png %> $ tree app/views/users app/views/users !"" _my_template.html.erb !"" _my_template.png.erb !"" _my_template.xml.erb #"" index.html.erb index.html.erb templates

199. "Same Format Assumption" <h1>Users</h1> <%= render "my_template" %> <%= render

     "my_template", format: :png %> <h1>Users</h1> <%= render_my_template_html_00123abc %> <%= render_my_template_png_00123abc %> index.html.erb Optimized Template

200. Ambiguous Render Problem <h1>Users</h1> <%= render "my_template" %> <%= render

     "my_template", format: :html %> $ tree app/views/users app/views/users !"" _my_template.png.erb !"" _my_template.xml.erb #"" index.html.erb index.html.erb templates

201. Ambiguous Render Problem <h1>Users</h1> <%= render "my_template" %> <%= render

     "my_template", format: :html %> <h1>Users</h1> <%= render "my_template" %> <%= raise MissingTemplateError %> index.html.erb Optimized Template

202. Wrap It Up

203. Be "Context Free" Don’t depend on side effects

204. Be Consistent

205. Cache != Fast

206. Benchmark First!

207. Keep Building Apps!

208. Thank You!!!