PERF: Reduce number of topics to filter while querying for unread.

lib/topic_query.rb

@@ -288,8 +288,9 @@ class TopicQuery
 
     list
       .where("tu.last_read_post_number < topics.#{col_name}")
-      .where("COALESCE(tu.notification_level, :regular) >= :tracking",
+      .where("tu.notification_level >= :tracking",
-               regular: TopicUser.notification_levels[:regular], tracking: TopicUser.notification_levels[:tracking])
+        tracking: TopicUser.notification_levels[:tracking]
+      )
   end
 
   def prioritize_pinned_topics(topics, options)
@@ -369,6 +370,10 @@ class TopicQuery
     result
   end
 
+  def unread_results_redis_key
+    "last_unread_result_bumped_at:#{@user.id}"
+  end
+
   def unread_results(options = {})
     result = TopicQuery.unread_filter(
         default_results(options.reverse_merge(unordered: true)),
@@ -380,6 +385,17 @@ class TopicQuery
       result = filter_callback.call(:unread, result, @user, options)
     end
 
+    if !(last_bumped_at = $redis.get(unread_results_redis_key))
+      last_bumped_at = result.unscope(:limit, :order).order(:bumped_at).first&.bumped_at
+
+      $redis.setex(
+        unread_results_redis_key,
+        1.hour.to_i,
+        (last_bumped_at || Time.zone.now).to_s
+      )
+    end
+
+    result = result.where("topics.bumped_at >= ?", last_bumped_at) if last_bumped_at
     suggested_ordering(result, options)
   end
 

spec/components/topic_query_spec.rb

@@ -443,6 +443,9 @@ describe TopicQuery do
   end
 
   context 'unread / read topics' do
+    after do
+      $redis.flushall
+    end
 
     context 'with no data' do
       it "has no unread topics" do
@@ -484,10 +487,15 @@ describe TopicQuery do
 
       context 'list_unread' do
         it 'lists topics correctly' do
-          new_topic = Fabricate(:post, user: creator).topic
+          freeze_time do
+            new_topic = Fabricate(:post, user: creator).topic
 
-          expect(topic_query.list_unread.topics).to eq([])
+            expect(topic_query.list_unread.topics).to eq([])
-          expect(topic_query.list_read.topics).to match_array([fully_read, partially_read])
+            expect(topic_query.list_read.topics).to match_array([fully_read, partially_read])
+
+            expect($redis.get(topic_query.unread_results_redis_key))
+              .to eq(Time.zone.now.to_s)
+          end
         end
       end
 
@@ -495,10 +503,16 @@ describe TopicQuery do
         before do
           user.user_option.auto_track_topics_after_msecs = 0
           user.user_option.save
+          partially_read.update!(bumped_at: 2.days.ago)
         end
 
         it 'only contains the partially read topic' do
-          expect(topic_query.list_unread.topics).to eq([partially_read])
+          freeze_time do
+            expect(topic_query.list_unread.topics).to eq([partially_read])
+
+            expect($redis.get(topic_query.unread_results_redis_key))
+              .to eq(partially_read.bumped_at.to_s)
+          end
         end
       end