PERF: deleting a post in huge topics was timing out

- add missing index to user actions for fast retrieval by post
- add missing indexes to users for fast retrieval of staff
- only refresh topic_users liked/bookmarked cache for affected users

app/models/topic_user.rb

@@ -232,6 +232,7 @@ class TopicUser < ActiveRecord::Base
 
   def self.update_post_action_cache(opts={})
     user_id = opts[:user_id]
+    post_id = opts[:post_id]
     topic_id = opts[:topic_id]
     action_type = opts[:post_action_type]
 
@@ -277,6 +278,13 @@ SQL
       builder.where("tu2.topic_id = :topic_id", topic_id: topic_id)
     end
 
+    if post_id
+      builder.where("tu2.topic_id IN (SELECT topic_id FROM posts WHERE id = :post_id)", post_id: post_id)
+      builder.where("tu2.user_id IN (SELECT user_id FROM post_actions
+                                     WHERE post_id = :post_id AND
+                                           post_action_type_id = :action_type_id)")
+    end
+
     builder.exec(action_type_id: PostActionType.types[action_type])
   end
 

db/migrate/20150617233018_add_index_target_post_id_on_user_actions.rb

@@ -0,0 +1,5 @@
+class AddIndexTargetPostIdOnUserActions < ActiveRecord::Migration
+  def change
+    add_index :user_actions, [:target_post_id]
+  end
+end

db/migrate/20150617234511_add_staff_index_to_users.rb

@@ -0,0 +1,6 @@
+class AddStaffIndexToUsers < ActiveRecord::Migration
+  def change
+    add_index :users, [:id], name: 'idx_users_admin', where: 'admin'
+    add_index :users, [:id], name: 'idx_users_moderator', where: 'moderator'
+  end
+end

lib/post_destroyer.rb

@@ -90,7 +90,7 @@ class PostDestroyer
       end
       update_associated_category_latest_topic
       update_user_counts
-      TopicUser.update_post_action_cache(topic_id: @post.topic_id)
+      TopicUser.update_post_action_cache(post_id: @post.id)
     end
 
     feature_users_in_the_topic if @post.topic