Improve performance of User.by_login

CHANGELOG

@@ -2,6 +2,7 @@ Please view this file on the master branch, on stable branches it's out of date.
 
 v 8.1.0 (unreleased)
   - Make diff file view easier to use on mobile screens (Stan Hu)
+  - Improved performance of finding users by username or Email address
   - Add support for creating directories from Files page (Stan Hu)
   - Allow removing of project without confirmation when JavaScript is disabled (Stan Hu)
   - Support filtering by "Any" milestone or issue and fix "No Milestone" and "No Label" filters (Stan Hu)

app/models/user.rb

@@ -68,6 +68,7 @@ class User < ActiveRecord::Base
   include Referable
   include Sortable
   include TokenAuthenticatable
+  include CaseSensitivity
 
   default_value_for :admin, false
   default_value_for :can_create_group, gitlab_config.default_can_create_group
@@ -273,8 +274,13 @@ class User < ActiveRecord::Base
     end
 
     def by_login(login)
-      where('lower(username) = :value OR lower(email) = :value',
-            value: login.to_s.downcase).first
+      return nil unless login
+
+      if login.include?('@'.freeze)
+        unscoped.iwhere(email: login).take
+      else
+        unscoped.iwhere(username: login).take
+      end
     end
 
     def find_by_username!(username)

db/migrate/20151008110232_add_users_lower_username_email_indexes.rb

+class AddUsersLowerUsernameEmailIndexes < ActiveRecord::Migration
+  disable_ddl_transaction!
+
+  def up
+    return unless Gitlab::Database.postgresql?
+
+    execute 'CREATE INDEX CONCURRENTLY index_on_users_lower_username ON users (LOWER(username));'
+    execute 'CREATE INDEX CONCURRENTLY index_on_users_lower_email ON users (LOWER(email));'
+  end
+
+  def down
+    return unless Gitlab::Database.postgresql?
+
+    remove_index :users, :index_on_users_lower_username
+    remove_index :users, :index_on_users_lower_email
+  end
+end

lib/tasks/migrate/setup_postgresql.rake

 require Rails.root.join('db/migrate/20151007120511_namespaces_projects_path_lower_indexes')
+require Rails.root.join('db/migrate/20151008110232_add_users_lower_username_email_indexes')
 
 desc 'GitLab | Sets up PostgreSQL'
 task setup_postgresql: :environment do
   NamespacesProjectsPathLowerIndexes.new.up
+  AddUsersLowerUsernameEmailIndexes.new.up
 end

spec/benchmarks/models/user_spec.rb

@@ -11,7 +11,9 @@ describe User, benchmark: true do
       end
     end
 
-    let(:iterations) { 1000 }
+    # The iteration count is based on the query taking little over 1 ms when
+    # using PostgreSQL.
+    let(:iterations) { 900 }
 
     describe 'using a capitalized username' do
       benchmark_subject { User.by_login('Alice') }