Add index on mentions status_id

db/migrate/20170405112956_add_index_on_mentions_status_id.rb

@@ -0,0 +1,5 @@
+class AddIndexOnMentionsStatusId < ActiveRecord::Migration[5.0]
+  def change
+    add_index :mentions, :status_id
+  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: 20170403172249) do
+ActiveRecord::Schema.define(version: 20170405112956) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -127,6 +127,7 @@ ActiveRecord::Schema.define(version: 20170403172249) do
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.index ["account_id", "status_id"], name: "index_mentions_on_account_id_and_status_id", unique: true, using: :btree
+    t.index ["status_id"], name: "index_mentions_on_status_id", using: :btree
   end
 
   create_table "mutes", force: :cascade do |t|