Chapter 4: Data visualization

app/controllers/active_monitoring/dashboard_controller.rb

@@ -0,0 +1,9 @@
+require_dependency "active_monitoring/application_controller"
+
+module ActiveMonitoring
+  class DashboardController < ApplicationController
+    def show
+      @dashboard = Dashboard.new
+    end
+  end
+end

app/models/active_monitoring/dashboard.rb

@@ -0,0 +1,33 @@
+module ActiveMonitoring
+  class Dashboard
+    LIMIT = 10
+
+    def initialize(date = Date.current)
+      @date = date
+    end
+
+    def percentile(value)
+      response_metrics.percentile(value)
+    end
+
+    def slow_sql_queries
+      sql_metrics.order(:value).limit(LIMIT)
+    end
+
+    private
+
+      attr_reader :date
+
+      def sql_metrics
+        metrics.where(name: "sql.active_record")
+      end
+
+      def response_metrics
+        metrics.where(name: "process_action.action_controller")
+      end
+
+      def metrics
+        Metric.where(created_at: date.beginning_of_day..date.end_of_day)
+      end
+  end
+end

app/models/active_monitoring/metric.rb

@@ -1,4 +1,7 @@
 module ActiveMonitoring
   class Metric < ApplicationRecord
+    def self.percentile(value)
+      order(:value).offset(count * value / 10 - 1).limit(1).pluck(:value).first
+    end
   end
 end

app/views/active_monitoring/dashboard/show.html.erb

@@ -0,0 +1,23 @@
+<h1>Dashboard</h1>
+
+<h2>Response time</h2>
+<ul>
+  <li>90th Percentile: <%= @dashboard.percentile(9) %><li>
+  <li>50th Percentile: <%= @dashboard.percentile(5) %><li>
+</ul>
+
+<h2>Slow queriess</h2>
+<table>
+  <tr>
+    <th>SQL</th>
+    <th>Location</th>
+    <th>Time</th>
+  </tr>
+  <% @dashboard.slow_sql_queries.each do |metric| %>
+  <tr>
+    <td><%= metric.sql_query %></td>
+    <td><%= metric.location %></td>
+    <td><%= metric.value %></td>
+  </tr>
+  <% end %>
+<table>

config/routes.rb

@@ -1,2 +1,3 @@
 ActiveMonitoring::Engine.routes.draw do
+  resource :dashboard, controller: :dashboard, only: :show
 end

spec/requests/dashboard_spec.rb

@@ -0,0 +1,35 @@
+require "rails_helper"
+
+RSpec.describe "ActiveMonitoring Dashboard", type: :request do
+  scenario "renders percentile" do
+    create_metrics("process_action.action_controller", 10)
+
+    get active_monitoring.dashboard_path
+
+    expect(response.body).to include("90th Percentile: 9")
+    expect(response.body).to include("50th Percentile: 5")
+  end
+
+  scenario "renders percentile" do
+    ActiveMonitoring::Metric.create!(
+      value: 100,
+      name: "sql.active_record",
+      sql_query: "SELECT * FROM books;",
+      location: "BooksController#show"
+    )
+
+    get active_monitoring.dashboard_path
+
+    expect(response.body).to include("SELECT * FROM books;")
+    expect(response.body).to include("BooksController#show")
+    expect(response.body).to include("100")
+  end
+
+  private
+
+    def create_metrics(name, count)
+      1.upto(count) do |i|
+        ActiveMonitoring::Metric.create!(value: i, name: name)
+      end
+    end
+end