PERF: Preload only gists when including summaries in topic list

app/models/ai_summary.rb

@@ -51,5 +51,6 @@ def outdated
 #
 # Indexes
 #
-#  index_ai_summaries_on_target_type_and_target_id  (target_type,target_id)
+#  idx_on_target_id_target_type_summary_type_3355609fbb  (target_id,target_type,summary_type) UNIQUE
+#  index_ai_summaries_on_target_type_and_target_id       (target_type,target_id)
 #

config/settings.yml

@@ -368,6 +368,7 @@ discourse_ai:
     default: 0
     min: 0
     max: 1000
+    hidden: true
   ai_hot_topic_gists_allowed_groups:
     type: group_list
     list_type: compact

db/migrate/20241125132452_unique_ai_summaries.rb

@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+class UniqueAiSummaries < ActiveRecord::Migration[7.1]
+  def up
+    execute <<~SQL
+      DELETE FROM ai_summaries ais1
+      USING ai_summaries ais2
+      WHERE ais1.id < ais2.id
+        AND ais1.target_id = ais2.target_id
+        AND ais1.target_type = ais2.target_type
+        AND ais1.summary_type = ais2.summary_type
+    SQL
+
+    add_index :ai_summaries, %i[target_id target_type summary_type], unique: true
+  end
+
+  def down
+    remove_index :ai_summaries, column: %i[target_id target_type summary_type]
+  end
+end

lib/summarization/entry_point.rb

@@ -20,7 +20,7 @@ def inject_into(plugin)
         plugin.register_modifier(:topic_query_create_list_topics) do |topics, options|
           if Discourse.filters.include?(options[:filter]) && SiteSetting.ai_summarization_enabled &&
                SiteSetting.ai_summarize_max_hot_topics_gists_per_batch > 0
-            topics.includes(:ai_summaries)
+            topics.includes(:ai_gist_summary)
           else
             topics
           end
@@ -32,11 +32,7 @@ def inject_into(plugin)
           include_condition: -> { scope.can_see_gists? },
         ) do
           return if !Discourse.filters.include?(options[:filter])
-          summaries = object.ai_summaries.to_a
-
-          # Summaries should always have one or zero elements here.
-          # This is an extra safeguard to avoid including regular summaries.
-          summaries.find { |s| s.summary_type == "gist" }&.summarized_text
+          object.ai_gist_summary&.summarized_text
         end
 
         # To make sure hot topic gists are inmediately up to date, we rely on this event

lib/topic_extensions.rb

@@ -4,6 +4,13 @@ module DiscourseAi
   module TopicExtensions
     extend ActiveSupport::Concern
 
-    prepended { has_many :ai_summaries, as: :target }
+    prepended do
+      has_many :ai_summaries, as: :target
+
+      has_one :ai_gist_summary,
+              -> { where(summary_type: AiSummary.summary_types[:gist]) },
+              class_name: "AiSummary",
+              as: :target
+    end
   end
 end