PERF: Remove N+1 queries on user messages page.

app/controllers/application_controller.rb

@@ -293,13 +293,15 @@ class ApplicationController < ActionController::Base
     Middleware::AnonymousCache.anon_cache(request.env, time_length)
   end
 
-  def fetch_user_from_params(opts=nil)
+  def fetch_user_from_params(opts=nil, eager_load = [])
     opts ||= {}
     user = if params[:username]
       username_lower = params[:username].downcase.chomp('.json')
       find_opts = { username_lower: username_lower }
       find_opts[:active] = true unless opts[:include_inactive] || current_user.try(:staff?)
-      User.find_by(find_opts)
+      result = User
+      (result = result.includes(*eager_load)) if !eager_load.empty?
+      result.find_by(find_opts)
     elsif params[:external_id]
       external_id = params[:external_id].chomp('.json')
       SingleSignOnRecord.find_by(external_id: external_id).try(:user)

app/controllers/list_controller.rb

@@ -109,7 +109,7 @@ class ListController < ApplicationController
   [:topics_by, :private_messages, :private_messages_sent, :private_messages_unread, :private_messages_archive, :private_messages_group, :private_messages_group_archive].each do |action|
     define_method("#{action}") do
       list_opts = build_topic_list_options
-      target_user = fetch_user_from_params(include_inactive: current_user.try(:staff?))
+      target_user = fetch_user_from_params({ include_inactive: current_user.try(:staff?) }, [:user_stat, :user_option])
       guardian.ensure_can_see_private_messages!(target_user.id) unless action == :topics_by
       list = generate_list_for(action.to_s, target_user, list_opts)
       url_prefix = "topics" unless action == :topics_by

app/serializers/topic_list_item_serializer.rb

@@ -67,6 +67,7 @@ class TopicListItemSerializer < ListableTopicSerializer
   def include_tags?
     SiteSetting.tagging_enabled
   end
+
   def tags
     object.tags.map(&:name)
   end

app/serializers/topic_list_serializer.rb

@@ -26,6 +26,7 @@ class TopicListSerializer < ApplicationSerializer
   def include_tags?
     SiteSetting.tagging_enabled && SiteSetting.show_filter_by_tag
   end
+
   def tags
     Tag.top_tags
   end

lib/topic_query.rb

@@ -355,10 +355,10 @@ class TopicQuery
       options = @options
       options.reverse_merge!(per_page: per_page_setting)
 
-      result = Topic
+      result = Topic.includes(:tags)
 
       if type == :group
-        result = result.includes(:allowed_groups)
+        result = result.includes(:allowed_users)
         result = result.where("topics.id IN (SELECT topic_id FROM topic_allowed_groups
                                               WHERE group_id IN (
                                                   SELECT group_id FROM group_users WHERE user_id = #{user.id.to_i}) AND