Make an Event of It! (CodeMash 2014)

The upsurge in asynchronous programming has brought event-driven patterns to the forefront. But even if you aren't re-writing your app in Node.js, evented patterns can improve your application. This talk demonstrates concrete examples of how events can benefit the various layers of your application. It shows how events can pitch in the fight against fat controllers (and fat models too!) It applies eventing to simplify testing and decouple our app from external dependencies. It even reveals how eventing can help shape data to provide flexibility and auditing.

Transcript

1. Jason Clark
   @jasonrclark
   Ruby Agent Engineer
   Make an Event of It!
   Evented Patterns in Ruby
   Thursday, January 9, 14
   

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2. Where Are We Going?
   • The Pattern
   • Internal Coupling
   • External Coupling
   • Adding Eventing
   • ActiveSupport::Notifications
   • Notifiers
   • Subscribers
   • Events as Data
   2
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3. The Pattern
   http://flic.kr/p/6K9jC4
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4. 4
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5. 5
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6. 5
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7. 5
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8. Events Aren't
   (Necessarily)
   6
   • Asynchronous
   • IO related
   • Distributed
   • Complicated
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9. 7
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10. 7
    Notifier
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11. 7
    Notifier
    Subscriber
    Subscriber
    Subscriber
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12. 7
    Notifier
    Subscriber
    Subscriber
    Subscriber
    Eventing
    System
    Thursday, January 9, 14
    

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13. 7
    Notifier
    Subscriber
    Subscriber
    Subscriber
    Eventing
    System
    Thursday, January 9, 14
    

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14. 7
    Notifier
    Subscriber
    Subscriber
    Subscriber
    Eventing
    System
    Thursday, January 9, 14
    

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15. 8
    Why Not Methods?
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16. 9
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17. 9
    Notifier
    Subscriber
    Subscriber
    Subscriber
    Eventing
    System
    Thursday, January 9, 14
    

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18. 9
    Notifier
    Subscriber
    Subscriber
    Subscriber
    Eventing
    System
    Thursday, January 9, 14
    

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19. Why Not Callbacks?
    10
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20. 11
    class Subscription < ActiveRecord::Base
    before_create :record_signup
    private
    def record_signup
    self.signed_up_on = Date.today
    end
    end
    Thursday, January 9, 14
    

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21. 11
    class Subscription < ActiveRecord::Base
    before_create :record_signup
    private
    def record_signup
    self.signed_up_on = Date.today
    end
    end
    Thursday, January 9, 14
    

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22. Where Have We Been?
    • The Pattern
    • Internal Coupling
    • External Coupling
    • Adding Eventing
    • ActiveSupport::Notifications
    • Notifiers
    • Subscribers
    • Events as Data
    12
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23. 13
    Internal Coupling
    http://flic.kr/p/KikA9
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24. 14
    newrelic_rpm
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25. 14
    app start
    newrelic_rpm
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26. 14
    app start connect
    New Relic
    Server
    newrelic_rpm
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27. {server config}
    14
    app start connect
    New Relic
    Server
    newrelic_rpm
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28. {server config}
    14
    app start connect
    New Relic
    Server
    ?
    newrelic_rpm
    Thursday, January 9, 14
    

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29. 15
    def connect()
    config = config_from_server()
    finish_setup(config)
    end
    newrelic_rpm
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30. 16
    def finish_setup(config)
    add_naming_rule(config['rules'])
    @cross_app_tracing.set_key(config)
    @js_instrumentor.log_config(config)
    @beacon = Beacon.new
    end
    newrelic_rpm
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31. 17
    def test_finish_setup_naming_rules
    config = { 'rules' => [...] }
    @agent.finish_setup(config)
    assert_equal 2, @agent.transaction_rules.size
    end
    newrelic_rpm
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32. 18
    def test_finish_setup_naming_rules
    @agent.cross_app_tracing.stub(:set_key)
    @agent.js_instrumentor.stub(:log_config)
    config = { 'rules' => [...] }
    @agent.finish_setup(config)
    assert_equal 2, @agent.transaction_rules.size
    end
    newrelic_rpm
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33. 19
    def finish_setup(config)
    add_naming_rule(config['rules'])
    @cross_app_tracing.set_key(config)
    @js_instrumentor.log_config(config)
    @beacon = Beacon.new
    end
    newrelic_rpm
    Thursday, January 9, 14
    

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34. 20
    class Beacon
    def initialize
    # Your code is bad and you should feel bad
    Net::HTTP.get("http://...")
    end
    end
    newrelic_rpm
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35. 21
    def test_finish_setup_naming_rules
    @agent.cross_app_tracing.stub(:set_key)
    @agent.js_instrumentor.stub(:log_config)
    Beacon.stub(:new).return(stub("fake beacon"))
    config = { 'rules' => [...] }
    @agent.finish_setup(config)
    assert_equal 2, @agent.transaction_rules.size
    end
    newrelic_rpm
    Thursday, January 9, 14
    

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36. 22
    def finish_setup(config)
    add_naming_rule(config['rules'])
    @cross_app_tracing.set_key(config)
    @js_instrumentor.log_config(config)
    @beacon = Beacon.new
    end
    newrelic_rpm
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37. 23
    def finish_setup(config)
    events.notify(:configured)
    end
    newrelic_rpm
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38. 24
    class Beacon
    def initialize
    events.subscribe(:configured) do
    Net::HTTP.get("http://...")
    end
    end
    end
    newrelic_rpm
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39. 25
    def test_finish_setup_notifies
    called = false
    @events.subscribe(:configured) do
    called = true
    end
    @agent.finish_setup({})
    assert called
    end
    newrelic_rpm
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40. 26
    def test_add_naming_rules
    config = { 'rules' => [...] }
    @agent.add_naming_rules(config)
    assert_equal 2, @agent.transaction_rules.size
    end
    newrelic_rpm
    Thursday, January 9, 14
    

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41. More Focused
    Tests
    27
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42. More Independent
    Classes
    28
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43. Implicit Ordering
    29
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44. Debugging
    30
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45. Performance
    31
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46. Where Have We Been?
    • The Pattern
    • Internal Coupling
    • External Coupling
    • Adding Eventing
    • ActiveSupport::Notifications
    • Notifiers
    • Subscribers
    • Events as Data
    32
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47. http://flic.kr/p/euQpT
    External Coupling
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48. 34
    newrelic_rpm
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49. 34
    Javascript insertion
    newrelic_rpm
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50. 34
    Javascript insertion
    Error collection
    newrelic_rpm
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51. 34
    Javascript insertion
    Cross application tracing
    Error collection
    newrelic_rpm
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52. 35
    No Setup Please!
    newrelic_rpm
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53. 36
    module NewRelic::Rack
    class AgentHooks
    def call(env)
    notify(:before_call, env)
    result = @app.call(env)
    notify(:after_call, env, result)
    result
    end
    end
    end
    newrelic_rpm
    Thursday, January 9, 14
    

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54. 37
    class CrossAppTracing
    def initialize
    events.subscribe(:before_call) do |e|
    process_request(e)
    end
    ...
    end
    end
    newrelic_rpm
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55. Ever Heard of
    Composition?
    38
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56. Looser Coupling
    39
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57. Compatibilty
    Layer
    40
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58. Where Have We Been?
    • The Pattern
    • Internal Coupling
    • External Coupling
    • Adding Eventing
    • ActiveSupport::Notifications
    • Notifiers
    • Subscribers
    • Events as Data
    41
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59. http://flic.kr/p/dYor95
    Adding Eventing
    Thursday, January 9, 14
    

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60. 43
    Thursday, January 9, 14
    

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61. 43
    Notifier
    Subscriber
    Subscriber
    Subscriber
    Eventing
    System
    Thursday, January 9, 14
    

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62. 43
    Notifier
    Subscriber
    Subscriber
    Subscriber
    Eventing
    System
    Thursday, January 9, 14
    

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63. 44
    gem install
    simple_events
    http://github.com/jasonrclark/simple_events
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64. 45
    class SimpleEvents::Notifier
    def initialize
    @events = {}
    ...
    end
    end
    simple_events
    Thursday, January 9, 14
    

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65. 46
    class SimpleEvents::Notifier
    ...
    def subscribe(event, &handler)
    @events[event] ||= []
    @events[event] << handler
    check_for_runaway_subscriptions(event)
    end
    ...
    end
    simple_events
    Thursday, January 9, 14
    

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66. 47
    class SimpleEvents::Notifier
    ...
    def notify(event, *args)
    return unless @events.has_key?(event)
    @events[event].each do |handler|
    begin
    handler.call(*args)
    rescue => err
    logger.debug("Fail #{@event}", err)
    end
    end
    end
    end
    simple_events
    Thursday, January 9, 14
    

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67. 48
    class SimpleEvents::Notifier
    ...
    def notify(event, *args)
    return unless @events.has_key?(event)
    @events[event].each do |handler|
    begin
    handler.call(*args)
    rescue => err
    logger.debug("Fail #{@event}", err)
    end
    end
    end
    end
    simple_events
    Thursday, January 9, 14
    

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68. 49
    class SimpleEvents::Notifier
    ...
    def notify(event, *args)
    return unless @events.has_key?(event)
    @events[event].each do |handler|
    begin
    handler.call(*args)
    rescue => err
    logger.debug("Fail #{@event}", err)
    end
    end
    end
    end
    simple_events
    Thursday, January 9, 14
    

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69. 50
    class SimpleEvents::Notifier
    ...
    def notify(event, *args)
    return unless @events.has_key?(event)
    @events[event].each do |handler|
    begin
    handler.call(*args)
    rescue => err
    logger.debug("Fail #{@event}", err)
    end
    end
    end
    end
    simple_events
    Thursday, January 9, 14
    

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70. 51
    class SimpleEvents::Notifier
    ...
    def notify(event, *args)
    return unless @events.has_key?(event)
    @events[event].each do |handler|
    begin
    handler.call(*args)
    rescue => err
    logger.debug("Fail #{@event}", err)
    end
    end
    end
    end
    simple_events
    Thursday, January 9, 14
    

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71. Where Have We Been?
    • The Pattern
    • Internal Coupling
    • External Coupling
    • Adding Eventing
    • ActiveSupport::Notifications
    • Notifiers
    • Subscribers
    • Events as Data
    52
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72. ActiveSupport::
    Notifications
    http://flic.kr/p/aWNwU2
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73. 54
    AS::Notifications
    =
    ActiveSupport::Notifications
    activesupport
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74. Rails Request
    55
    •action_dispatch.request
    •start_processing.action_controller
    •process_action.action_controller
    •sql.active_record
    •render_template.action_view
    • ... and more!
    Thursday, January 9, 14
    

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75. 56
    events = []
    AS::Notifications.subscribe("event") do |*args|
    events << *args
    end
    activesupport
    Thursday, January 9, 14
    

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76. 57
    AS::Notifications.subscribe("event") do |*args|
    events << *args
    end
    ["render_template.action_view",
    "e2a1e92a3c613576c2b0"
    {:identifier=>"/file/path/here"}]
    activesupport
    Thursday, January 9, 14
    

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77. 58
    e = AS::Notifications::Event.new(*args)
    e.name # => "render_template..."
    e.duration # => 10 (in milliseconds)
    e.payload # => { :identifier => ... }
    activesupport
    Thursday, January 9, 14
    

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78. 59
    activesupport
    AS::Notifications.instrument("evt", :data => 1)
    Thursday, January 9, 14
    

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79. 60
    AS::Notifications.instrument("evt", :data => 1) do
    #... your timed code here
    end
    activesupport
    Thursday, January 9, 14
    

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80. • Regexp on Notifications.subscribe
    • Event#parent_of?
    • Temporary subscription
    • Unsubscribe
    • LogSubscriber
    61
    activesupport
    Thursday, January 9, 14
    

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81. Where Have We Been?
    • The Pattern
    • Internal Coupling
    • External Coupling
    • Adding Events
    • ActiveSupport::Notifications
    • Notifiers
    • Subscribers
    • Events as Data
    62
    Thursday, January 9, 14
    

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82. http://flic.kr/p/a1dEec
    Notifiers
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83. 64
    Thursday, January 9, 14
    

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84. 64
    Notifier
    Subscriber
    Subscriber
    Subscriber
    Eventing
    System
    Thursday, January 9, 14
    

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85. 64
    Notifier
    Subscriber
    Subscriber
    Subscriber
    Eventing
    System
    Thursday, January 9, 14
    

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86. Naming
    65
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87. Flexible Payload
    66
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88. Primitives at
    Boundaries
    67
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89. Where Have We Been?
    • The Pattern
    • Internal Coupling
    • External Coupling
    • Adding Events
    • ActiveSupport::Notifications
    • Notifiers
    • Subscribers
    • Events as Data
    68
    Thursday, January 9, 14
    

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90. 69
    http://flic.kr/p/8w9PyF
    Subscribers
    Thursday, January 9, 14
    

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91. 70
    Thursday, January 9, 14
    

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92. 70
    Notifier
    Subscriber
    Subscriber
    Subscriber
    Eventing
    System
    Thursday, January 9, 14
    

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93. 70
    Notifier
    Subscriber
    Subscriber
    Subscriber
    Eventing
    System
    Thursday, January 9, 14
    

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94. != self.only
    71
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95. 72
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96. 73
    class UserSignup < Mutations::Command
    def execute
    user = User.create!(inputs)
    NewsletterSubscriptions.create(user.id)
    UserMailer.async(:deliver_welcome, user.id)
    user
    end
    end
    Thursday, January 9, 14
    

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97. 74
    class SomeSubscriber
    def initialize
    events.subscribe(:configured) do
    log_config
    end
    end
    def log_config
    ...
    end
    end
    Thursday, January 9, 14
    

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98. Memory Leaks
    75
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99. Where Have We Been?
    • The Pattern
    • Internal Coupling
    • External Coupling
    • Adding Events
    • ActiveSupport::Notifications
    • Notifiers
    • Subscribers
    • Events as Data
    76
    Thursday, January 9, 14
    

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100. http://flic.kr/p/ndraB
     Events as Data
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101. 78
     Opened Account $100
     Check 0001 -$15
     Deposit $20
     Check 0002 -$21
     Total $84
     Bank Transactions
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102. 79
     Customer Pricing
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103. 79
     customer_id date plan
     1 1/1/2013 basic
     1 1/2/2013 premium
     1 2/1/2013 basic
     1 2/2/2013 premium
     Customer Pricing
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104. 79
     customer_id date plan
     1 1/1/2013 basic
     1 1/2/2013 premium
     1 2/1/2013 basic
     1 2/2/2013 premium
     Customer Pricing
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105. Event Sourcing
     80
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106. 81 http://flic.kr/p/4LTNc9
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107. 82
     Metrics
     10:00AM
     CPU/Utilization
     0.85
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108. 83
     Metrics
     10:01AM
     CPU/Utilization
     0.24
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109. 84
     Metrics
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110. 85
     Metrics
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111. 86
     Metrics
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112. 87
     Metric Data
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113. 87
     Metric Data
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114. 87
     Metric Data
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115. Other Examples
     88
     • Database replication
     • Log files
     • PubSub
     • Immutable data structures
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116. Upsides
     89
     ★No Updates
     ★Automatic Audits
     ★Summarize/Transform/
     Cache
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117. Downsides
     -So Much Data!
     -Hard to Query Efficiently
     -More Complex Code
     90
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118. Jason Clark
     @jasonrclark
     Ruby Agent Engineer
     • The Pattern
     • Internal Coupling
     • External Coupling
     • Adding Eventing
     • ActiveSupport::Notifications
     • Notifiers
     • Subscribers
     • Events as Data
     ?
     Thursday, January 9, 14
     

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