Add index to notifications to optimize query (#5921) [deploy]

- Index notifications on notifiable_id, notifiable_type, and action

db/migrate/20200205225813_add_notifiable_id_notifiable_type_action_index_to_notifications.rb

@@ -0,0 +1,10 @@
+class AddNotifiableIdNotifiableTypeActionIndexToNotifications < ActiveRecord::Migration[5.2]
+  disable_ddl_transaction!
+
+  def change
+    add_index :notifications, %i[notifiable_id notifiable_type action],
+              unique: false,
+              name: "index_notifications_on_notifiable_id_notifiable_type_and_action",
+              algorithm: :concurrently
+  end
+end

db/schema.rb

@@ -10,7 +10,8 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 2020_01_20_053525) do
+ActiveRecord::Schema.define(version: 2020_02_05_225813) do
+
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
 
@@ -581,6 +582,7 @@ ActiveRecord::Schema.define(version: 2020_01_20_053525) do
     t.integer "user_id"
     t.index ["created_at"], name: "index_notifications_on_created_at"
     t.index ["json_data"], name: "index_notifications_on_json_data", using: :gin
+    t.index ["notifiable_id", "notifiable_type", "action"], name: "index_notifications_on_notifiable_id_notifiable_type_and_action"
     t.index ["notifiable_id"], name: "index_notifications_on_notifiable_id"
     t.index ["notifiable_type"], name: "index_notifications_on_notifiable_type"
     t.index ["notified_at"], name: "index_notifications_on_notified_at"