Add post_id index to topic_links

db/migrate/20140617193351_add_post_id_index_on_topic_links.rb

@@ -0,0 +1,9 @@
+class AddPostIdIndexOnTopicLinks < ActiveRecord::Migration
+  def up
+    add_index :topic_links, :post_id
+  end
+
+  def down
+    remove_index :topic_links, :post_id
+  end
+end