add index_notifications_on_id_and_account_id_and_activity_type on notifications table (#4750)

db/migrate/20170905044538_add_index_id_account_id_activity_type_on_notifications.rb

+class AddIndexIdAccountIdActivityTypeOnNotifications < ActiveRecord::Migration[5.1]
+  def change
+    add_index :notifications, [:id, :account_id, :activity_type], order: { id: :desc }
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20170901142658) do
+ActiveRecord::Schema.define(version: 20170905044538) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -180,6 +180,7 @@ ActiveRecord::Schema.define(version: 20170901142658) do
     t.integer "from_account_id"
     t.index ["account_id", "activity_id", "activity_type"], name: "account_activity", unique: true
     t.index ["activity_id", "activity_type"], name: "index_notifications_on_activity_id_and_activity_type"
+    t.index ["id", "account_id", "activity_type"], name: "index_notifications_on_id_and_account_id_and_activity_type", order: { id: :desc }
   end
 
   create_table "oauth_access_grants", id: :serial, force: :cascade do |t|