add indexes so counting topics and posts is faster

db/migrate/20130320012100_add_user_indexes_to_posts_and_topics.rb

@@ -0,0 +1,14 @@
+class AddUserIndexesToPostsAndTopics < ActiveRecord::Migration
+  def up
+    execute "CREATE INDEX idx_posts_user_id_deleted_at 
+              ON posts(user_id) WHERE deleted_at IS NULL"
+    
+    execute "CREATE INDEX idx_topics_user_id_deleted_at 
+              ON topics(user_id) WHERE deleted_at IS NULL"
+  end
+
+  def down
+    execute "DROP INDEX idx_posts_user_id_deleted_at"
+    execute "DROP INDEX idx_topics_user_id_deleted_at"
+  end
+end