Add indices to improve loading of labels page

changelogs/unreleased/sh-add-labels-index.yml

+---
+title: Add indices to improve loading of labels page
+merge_request:
+author:

db/migrate/20170210062829_add_index_to_labels_for_title_and_project.rb

+class AddIndexToLabelsForTitleAndProject < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def change
+    add_concurrent_index :labels, :title
+    add_concurrent_index :labels, :project_id
+  end
+end

db/schema.rb

@@ -581,6 +581,8 @@ ActiveRecord::Schema.define(version: 20170210075922) do
   add_index "labels", ["group_id", "project_id", "title"], name: "index_labels_on_group_id_and_project_id_and_title", unique: true, using: :btree
   add_index "labels", ["type", "project_id"], name: "index_labels_on_type_and_project_id", using: :btree
+  add_index "labels", ["project_id"], name: "index_labels_on_project_id", using: :btree
+  add_index "labels", ["title"], name: "index_labels_on_title", using: :btree
   create_table "lfs_objects", force: :cascade do |t|
     t.string "oid", null: false