PERF: Don't calculate the same query twice.

app/controllers/list_controller.rb

@@ -327,14 +327,20 @@ class ListController < ApplicationController
     exclude_category_ids.pluck(:id)
   end
 
-  def self.best_period_for(previous_visit_at, category_id=nil)
+  def self.best_period_with_topics_for(previous_visit_at, category_id=nil)
     best_periods_for(previous_visit_at).each do |period|
       top_topics = TopTopic.where("#{period}_score > 0")
       top_topics = top_topics.joins(:topic).where("topics.category_id = ?", category_id) if category_id
-      return period if top_topics.count >= SiteSetting.topics_per_period_in_top_page
+      top_topics = top_topics.limit(SiteSetting.topics_per_period_in_top_page)
+      return period if top_topics.count == SiteSetting.topics_per_period_in_top_page
     end
-    # default period is yearly
-    SiteSetting.top_page_default_timeframe.to_sym
+
+    false
+  end
+
+  def self.best_period_for(previous_visit_at, category_id=nil)
+    best_period_with_topics_for(previous_visit_at, category_id) ||
+      SiteSetting.top_page_default_timeframe.to_sym
   end
 
   def self.best_periods_for(date)

app/models/site_setting.rb

@@ -99,8 +99,8 @@ class SiteSetting < ActiveRecord::Base
   end
 
   def self.min_redirected_to_top_period(duration)
-    period = ListController.best_period_for(duration)
-    return period if TopTopic.topics_per_period(period) >= SiteSetting.topics_per_period_in_top_page
+    period = ListController.best_period_with_topics_for(duration)
+    return period if period
 
     # not enough topics
     nil

app/models/top_topic.rb

@@ -4,12 +4,6 @@ class TopTopic < ActiveRecord::Base
 
   belongs_to :topic
 
-  def self.topics_per_period(period)
-    DistributedMemoizer.memoize("#{Discourse.current_hostname}_topics_per_period_#{period}", 1.day) do
-      TopTopic.where("#{period}_score > 0").count
-    end.to_i
-  end
-
   # The top topics we want to refresh often
   def self.refresh_daily!
     transaction do

spec/models/site_setting_spec.rb

@@ -76,7 +76,11 @@ describe SiteSetting do
       before do
         SiteSetting.topics_per_period_in_top_page = 2
         SiteSetting.top_page_default_timeframe = 'daily'
-        TopTopic.stubs(:topics_per_period).with(:daily).returns(3)
+
+        2.times do
+          TopTopic.create!(daily_score: 2.5)
+        end
+
         TopTopic.refresh!
       end
 
@@ -91,7 +95,6 @@ describe SiteSetting do
       before do
         SiteSetting.topics_per_period_in_top_page = 20
         SiteSetting.top_page_default_timeframe = 'daily'
-        TopTopic.stubs(:topics_per_period).with(:daily).returns(1)
         TopTopic.refresh!
       end