PERF: only require the rss library if used

Before:

Total allocated: 257909321 bytes (2514134 objects)
Total retained:  39681579 bytes (343387 objects)

allocated memory by gem
-----------------------------------
  42875979  rss

retained memory by gem
-----------------------------------
   2080188  rss

retained objects by gem
-----------------------------------
     13052  rss

After:

Total allocated: 210562047 bytes (2252030 objects)
Total retained:  37433816 bytes (328635 objects)

----

So, 2 less megabytes on boot and 13000 objects stuck in ruby heaps forever.

Gemfile.lock

@@ -165,7 +165,7 @@ GEM
     lru_redux (1.1.0)
     mail (2.6.6)
       mime-types (>= 1.16, < 4)
-    memory_profiler (0.9.8)
+    memory_profiler (0.9.10)
     message_bus (2.1.2)
       rack (>= 1.1.3)
     metaclass (0.0.4)

app/jobs/scheduled/poll_feed.rb

@@ -3,9 +3,6 @@
 #
 require 'digest/sha1'
 require 'excon'
-require 'rss'
-require_dependency 'feed_item_accessor'
-require_dependency 'feed_element_installer'
 require_dependency 'final_destination'
 require_dependency 'post_creator'
 require_dependency 'post_revisor'
@@ -27,12 +24,23 @@ module Jobs
     end
 
     def poll_feed
+      ensure_rss_loaded
+      # defer loading rss
       feed = Feed.new
       import_topics(feed.topics)
     end
 
     private
 
+    # rss lib is very expensive memory wise, no need to load it till it is needed
+    def ensure_rss_loaded
+      return if @@rss_loaded
+      require 'rss'
+      require_dependency 'feed_item_accessor'
+      require_dependency 'feed_element_installer'
+      @@rss_loaded
+    end
+
     def not_polled_recently?
       $redis.set(
         'feed-polled-recently',

script/boot_mem.rb

@@ -0,0 +1,21 @@
+# simple script to measure memory at boot
+
+if ENV['RAILS_ENV'] != "production"
+  exec "RAILS_ENV=production ruby #{__FILE__}"
+end
+
+require 'memory_profiler'
+
+MemoryProfiler.report do
+  require File.expand_path("../../config/environment", __FILE__)
+
+  Rails.application.routes.recognize_path('abc') rescue nil
+
+  # load up the yaml for the localization bits, in master process
+  I18n.t(:posts)
+
+  # load up all models and schema
+  (ActiveRecord::Base.connection.tables - %w[schema_migrations versions]).each do |table|
+    table.classify.constantize.first rescue nil
+  end
+end.pretty_print