Add index to milestone_id on boards table

db/migrate/20170306180725_add_index_to_milestone_id_on_boards.rb

+class AddIndexToMilestoneIdOnBoards < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_index(:boards, :milestone_id)
+  end
+
+  def down
+    remove_index(:boards, :milestone_id)
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20170224075132) do
+ActiveRecord::Schema.define(version: 20170306180725) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -188,6 +188,7 @@ ActiveRecord::Schema.define(version: 20170224075132) do
     t.integer "milestone_id"
   end
 
+  add_index "boards", ["milestone_id"], name: "index_boards_on_milestone_id", using: :btree
   add_index "boards", ["project_id"], name: "index_boards_on_project_id", using: :btree
 
   create_table "broadcast_messages", force: :cascade do |t|