The View is Clear From Here

About view compilation in Rails

Transcript

1. The View Is Clear from Here
   

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2. Aaron Patterson
   

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3. @tenderlove
   

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

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10. Ruby Core Team
    

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11. Rails Core Team
    

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12. G GitHub
    

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13. Le Git
    

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14. git push -f
    

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15. git checkout -b
    

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16. git cherry-pick
    

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18. Happy GPS Rollover Day!
    April 6, 23:59:42 UTC
    I guess this is actually tomorrow……
    

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19. GPS Uses 10 bits!
    

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20. Single Quotes Are 2x Faster
    Than Double Quotes
    

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

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22. Logic
    AND OR
    NOT
    A
    

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23. Гематоген
    

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24. "атоген"
    

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25. gem 'атоген'
    Gemfile
    

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26. The View Is Clear from Here
    

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27. WARNING!@
    There Will Be Code
    

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28. There Will Be Ruby
    

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29. There Will Be Rails
    

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30. Software Engineering Practices
    

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31. Rails is MVC
    

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32. MVC
    Model
    View
    Controller
    

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33. MVC
    Model View
    Controller
    Request
    

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34. MVC
    Model View
    Controller
    Request
    Action Controller
    Action View
    Active Record
    

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35. Action View
    

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36. Action View
    Finds Templates
    Compiles Templates
    Executes Views
    

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37. Finding Templates
    

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38. View Templates
    

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39. ERB
    

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40. Developed by @m_seki
    

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41. ERB Template
    New User
    <%= render_form %>
    <%= link_to 'Back' %>
    new.html.erb
    

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42. 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
    

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43. Compiled Template
    _erbout = +""
    _erbout << "New User\n\n".freeze
    _erbout << render_form.to_s
    _erbout << "\n\n".freeze
    _erbout << link_to("Back").to_s
    _erbout << "\n".freeze
    _erbout
    

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44. Modified Compile Script
    require "erb"
    def render_form
    ""
    end
    def link_to(text)
    "#{text}"
    end
    # Compile the template
    template = ERB.new File.read "test.html.erb"
    # Evaluate the template
    puts template.result(binding)
    

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45. Compiler Output
    $ ruby compiler.rb
    New User
    
    Back
    

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46. ERB Translations
    ERB Source Translated Ruby
    <%= something %> _erbout << something.to_s
    <% something_else %> something_else
    

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47. Capturing Blocks
    
    <%= capture do %>
    Hello!
    <% end %>
    
    require "erb"
    def capture
    yield
    end
    # Compile the template
    template = ERB.new File.read "test.html.erb"
    puts template.result(binding)
    

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48. What is the output?
    Hello!
    
    
    
    Hello!
    
    ERROR!
    

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49. Compiled Source
    _erbout = +''
    _erbout << "\n ".freeze
    _erbout << ( capture do ).to_s
    _erbout << "\n Hello!\n ".freeze
    end
    _erbout << "\n\n".freeze
    _erbout
    
    <%= capture do %>
    Hello!
    <% end %>
    
    

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50. How does this work in Rails?
    

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51. 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
    

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52. ERB in Rails
    

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53. Different ERB Flavors
    Original ERB
    ERubis
    ERubi
    

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54. ERB Performance
    

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55. Rendering Speed
    require "erb"
    require "benchmark/ips"
    class AaronView
    TEMPLATES = { }
    TEMPLATES["index"] = <<-eerb
    
    
    Hello <%= name %>
    
    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
    $ ruby rendering_speed.rb
    Warming up --------------------------------------
    render 2.696k i/100ms
    Calculating -------------------------------------
    render 27.117k (± 5.9%) i/s -
    137.496k in 5.092633s
    

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56. Cache Compilation
    class AaronView
    TEMPLATES = { }
    TEMPLATES["index"] = <<-eerb
    
    
    Hello <%= name %>
    
    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
    $ 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
    

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57. Define a Method
    class AaronView
    TEMPLATES = { }
    TEMPLATES["index"] = <<-eerb
    
    
    Hello <%= name %>
    
    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
    $ 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
    

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58. Method Generation
    require "erb"
    erb_source = <<-erb
    
    
    Hello <%= name %>
    
    erb
    erb = ERB.new erb_source
    template = "index"
    self.class.class_eval "def render_#{template}; #{erb.src}; end"
    send "render_#{template}"
    def render_index
    _erbout = +''
    _erbout << "\n \n Hello ".freeze
    _erbout << name.to_s
    _erbout << "\n\n".freeze
    _erbout
    end
    Template
    Source
    Compile
    Source
    Define
    a
    m
    ethod
    Render the
    Tem
    plate
    Compiled Source
    

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59. Templates Are Translated to
    Methods
    

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60. Rails Template Methods
    
    This is an inner template
    <% puts methods.grep(/_app/) %>
    
    Template in Rails 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
    

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61. Memory Size
    def render_index
    _erbout = +''
    _erbout << "\n \n Hello ".freeze
    _erbout << name.to_s
    _erbout << "\n\n".freeze
    _erbout
    end
    require "objspace"
    iseq = RubyVM::InstructionSequence.of(
    method(:render_index))
    p ObjectSpace.memsize_of iseq
    $ ruby test.rb
    1264
    Measuring Memory Console Output
    

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62. Template Handling
    In Rails
    

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63. Instance Variable Visibility
    This is template Foo!
    <%= @some_ivar %>
    This is template Bar!
    <%= @some_ivar %>
    _foo.html.erb _bar.html.erb
    

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64. Compiled Templates
    class ActionView::Base
    def render_foo
    _erbout = +''
    _erbout << "This is template Foo!\n".freeze
    _erbout << @some_ivar.to_s
    _erbout << "\n".freeze
    _erbout
    end
    def render_bar
    _erbout = +''
    _erbout << "This is template Barr!\n".freeze
    _erbout << @some_ivar.to_s
    _erbout << "\n".freeze
    _erbout
    end
    end
    _foo.html.erb
    _bar.html.erb
    Same Instance
    Same Instance
    

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65. Don’t use instance variables in
    your templates
    

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

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67. Instance Variable Visibility
    This is template Foo!
    <%= @some_ivar %>
    This is template Bar!
    <%= @some_ivar %>
    _foo.html.erb _bar.html.erb
    

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68. Local Variables
    

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69. Rendering With Locals
    
    <%= render "content", locals: { name: "Gorby" } %>
    
    

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70. Compiling With Locals
    
    Hello, <%= name %>
    
    def render_content
    _erbout = +''
    _erbout << "\n Hello, ".freeze
    _erbout << name.to_s
    _erbout << "\n\n".freeze
    _erbout
    end
    content.html.erb Compiled Method
    Method Call
    

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71. Preamble With Locals
    

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

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73. Templates Require Context
    
    <%= render "content",
    locals: { name: "Gorby" } %>
    <%= render "content" %>
    
    
    Hello, <%= name %>
    
    main.html.erb content.html.erb
    Method call or
    local variable?
    local variable
    method call
    

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74. Templates Can’t Be Compiled
    In Advance
    

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75. Compiled Too Many Times
    

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

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

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78. Always pass the same locals to
    individual templates.
    

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79. The render function
    

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80. Finds a Template
    Compiles the Template
    Calculates a Method Name
    Calls the Method
    

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81. Find a Template
    (from the cache)
    Compiled?
    Compile the Template
    Call the method
    Calculate a Method
    Name
    

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82. Finding a Template
    

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83. Template Rendering Depends
    on "Requested Format"
    

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84. 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/*
    

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85. Template Source
    XML template Users
    index.xml.erb index.html.erb
    

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86. Requests and Rendering
    Request Response Template Rendered
    curl -H 'Accept: application/xml'
    http://localhost:3000/users
    XML template index.xml.erb
    curl http://localhost:3000/users Users index.html.erb
    curl -H 'Accept: text/html' http://
    localhost:3000/users
    Users index.html.erb
    

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87. Template Cache Keys
    • Local variables
    • Format
    • Locale
    • Variant (iPhone, etc)
    

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88. Strange Render Behavior
    

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89. 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/*
    

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90. Template Contents
    Users
    <%= render "my_template" %>
    I guess this is a png?
    index.html.erb _my_template.png.erb
    
    XML is cool!
    
    _my_template.xml.erb
    

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91. Requests and Rendering
    Request Response Template Rendered
    curl -H 'Accept: application/xml'
    http://localhost:3000/users
    Missing XML template Error None
    curl http://localhost:3000/users
    Users
    
    I guess this is a png?
    index.html.erb
    
    _my_template.png.erb
    curl -H 'Accept: text/html' http://
    localhost:3000/users
    Missing HTML partial Error None
    Browser Missing HTML partial Error None
    

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92. Error!!
    

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93. We Can’t Predict
    Users
    <%= render "my_template" %>
    

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94. 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
    

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95. Requests and Rendering
    Request Response Template Rendered
    curl -H 'Accept: application/xml'
    http://localhost:3000/users
    Missing XML template Error None
    curl http://localhost:3000/users Missing HTML partial Error None
    curl -H 'Accept: text/html' http://
    localhost:3000/users
    Missing HTML partial Error None
    Browser Missing HTML partial Error None
    

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96. Context Dependent
    Users
    <%= 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
    

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97. Templates are not
    "Context Free"
    

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98. Prediction and Consistency
    

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99. Find a Template
    (from the cache)
    Compiled?
    Compile the Template
    Call the method
    Calculate a Method
    Name
    Cheap!
    Cheap!
    Expensive!
    

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100. What Method Will This Call?
     Users
     <%= render "my_template" %>
     Users
     <%= render_my_template_00011123abf %>
     index.html.erb translated template
     Calls a unique method.
     But what method?
     

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101. Find a Template
     (from the cache)
     Compiled?
     Compile the Template
     Call the method
     Calculate a Method
     Name
     Cheap!
     Cheap!
     Expensive!
     

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

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103. Lower Memory
     

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104. Faster Runtime
     No More "Cache Check" Penalty
     

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105. DETOUR!
     

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106. Three Templates
     
     <%= render partial: "customer",
     collection: customers %>
     
     
     <%= render partial: "customer",
     collection: customers,
     cached: true %>
     
     _col.html.erb _cached_col.html.erb
     
     Hello: <%= customer.name %>
     
     _customer.html.erb
     

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

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108. 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
     

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109. I was convinced
     the cache didn’t work
     

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110. I was convinced
     the cache didn’t work
     

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111. I was convinced
     the cache didn’t work
     

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112. I was convinced
     the cache didn’t work
     

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113. But, there were entries
     in the cache
     

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114. 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
     

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115. Cache Key Calculation
     Was More Expensive
     Than Template Execution
     

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116. Cache Payoff
     
     Hello: <%= customer.name %>
     
     Hello: <%= customer.name %>
     Hello: <%= customer.name %>
     Hello: <%= customer.name %>
     Hello: <%= customer.name %>
     Hello: <%= customer.name %>
     Hello: <%= customer.name %>
     Hello: <%= customer.name %>
     Hello: <%= customer.name %>
     Hello: <%= customer.name %>
     Hello: <%= customer.name %>
     Hello: <%= customer.name %>
     Hello: <%= customer.name %>
     Hello: <%= customer.name %>
     Hello: <%= customer.name %>
     Hello: <%= customer.name %>
     Hello: <%= customer.name %>
     Hello: <%= customer.name %>
     Hello: <%= customer.name %>
     Hello: <%= customer.name %>
     Hello: <%= customer.name %>
     Hello: <%= customer.name %>
     Hello: <%= customer.name %>
     Old Template New Template
     

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117. 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
     

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118. "Cache" doesn’t mean "fast"
     

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119. Making Render Fast
     

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120. Make Render Usually Fast
     

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121. "Same Format Assumption"
     Users
     <%= 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
     

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122. Ambiguous Render Problem
     Users
     <%= 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
     

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123. "Always Optimize"
     Users
     <%= render "my_template" %>
     <%= render "my_template", format: :html %>
     Users
     <%= render "my_template", format: :png %>
     <%= render "my_template", format: :html %>
     index.html.erb index.html.erb
     

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124. "Same Format Assumption"
     Users
     <%= 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
     

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125. "Same Format Assumption"
     Users
     <%= render "my_template" %>
     <%= render "my_template", format: :png %>
     Users
     <%= render_my_template_html_00123abc %>
     <%= render_my_template_png_00123abc %>
     index.html.erb Optimized Template
     

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126. Ambiguous Render Problem
     Users
     <%= 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
     

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127. Ambiguous Render Problem
     Users
     <%= render "my_template" %>
     <%= render "my_template", format: :html %>
     Users
     <%= render "my_template" %>
     <%= raise MissingTemplateError %>
     index.html.erb Optimized Template
     

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128. Wrap It Up
     

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

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130. Be Consistent
     

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131. Cache != Fast
     

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132. Benchmark First!
     

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133. Make Your Locals Match
     

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134. Thank You!!!
     

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