Search performance optimization

* Add basic trigram indexes
* Change search query to use unions for better index use
* Remove duplicate query execution in search result display

Author: dutow

Gemfile

@@ -6,6 +6,8 @@ gem "rails", "~> 8.0.2"
 gem "propshaft"
 # Use postgresql as the database for Active Record
 gem "pg", "~> 1.1"
+# PostgreSQL-specific ActiveRecord extensions (UNION, CTE, etc.)
+gem "active_record_extended"
 # Use the Puma web server [https://github.com/puma/puma]
 gem "puma", ">= 5.0"
 # Use JavaScript with ESM import maps [https://github.com/rails/importmap-rails]

Gemfile.lock

@@ -44,6 +44,9 @@ GEM
       erubi (~> 1.11)
       rails-dom-testing (~> 2.2)
       rails-html-sanitizer (~> 1.6)
+    active_record_extended (3.4.0)
+      activerecord (>= 5.2, < 8.1)
+      pg (< 3.0)
     activejob (8.0.4)
       activesupport (= 8.0.4)
       globalid (>= 0.3.6)
@@ -472,6 +475,7 @@ PLATFORMS
   x86_64-linux-musl
 
 DEPENDENCIES
+  active_record_extended
   bcrypt (~> 3.1)
   bootsnap
   brakeman

app/controllers/topics_controller.rb

@@ -82,9 +82,13 @@ def search
     @search_query = params[:q].to_s.strip
 
     base_query = if @search_query.present?
-                   Topic.joins(:messages)
-                        .where("topics.title ILIKE ? OR messages.body ILIKE ?", "%#{@search_query}%", "%#{@search_query}%")
-                        .distinct
+                   search_pattern = "%#{ActiveRecord::Base.sanitize_sql_like(@search_query)}%"
+
+                   title_sql = Topic.select(:id).where("title ILIKE ?", search_pattern).to_sql
+                   message_sql = Message.select(:topic_id).where("body ILIKE ?", search_pattern).to_sql
+                   union_sql = "(#{title_sql}) UNION (#{message_sql})"
+
+                   Topic.where("topics.id IN (#{union_sql})")
                         .includes(:creator)
                  else
                    Topic.none
@@ -237,6 +241,7 @@ def apply_cursor_pagination(base_query)
 
     @topics = @topics.order('MAX(messages.created_at) DESC, topics.id DESC')
                      .limit(25)
+                     .load
 
     @new_topics_count = base_query.joins(:messages)
                                    .group('topics.id')

db/migrate/20251215150057_add_trigram_indexes_for_search.rb

@@ -0,0 +1,16 @@
+class AddTrigramIndexesForSearch < ActiveRecord::Migration[8.0]
+  def up
+    # Enable pg_trgm extension for trigram-based text search
+    enable_extension 'pg_trgm'
+
+    # Add GIN trigram indexes for efficient ILIKE searches
+    add_index :topics, :title, using: :gin, opclass: :gin_trgm_ops, name: 'index_topics_on_title_trgm'
+    add_index :messages, :body, using: :gin, opclass: :gin_trgm_ops, name: 'index_messages_on_body_trgm'
+  end
+
+  def down
+    remove_index :topics, name: 'index_topics_on_title_trgm'
+    remove_index :messages, name: 'index_messages_on_body_trgm'
+    # Note: Not disabling pg_trgm extension as it might be used elsewhere
+  end
+end