title: What causes the extreme slowness when changing from rails 3.2.12 to 3.2.13
body: <p>This morning, I updated rails from 3.2.12 to 3.2.13, which resulted in a major delay in loading my views.
  This is from loading my home page:</p>
  
  <pre><code>Rails 3.2.12:
  Completed 200 OK in 387ms (Views: 339.0ms | ActiveRecord: 27.1ms)
  
  Rails 3.2.13:
  Completed 200 OK in 4416ms (Views: 4361.2ms | ActiveRecord: 28.7ms)
  </code></pre>
  
  <p>The only difference between the two commits it the Rails version, which of course did also result in a lot of other gems being updated...
  This is the difference in the Gemfile.lock:</p>
  
  <pre><code>GEM
     remote: https://rubygems.org/
     specs:
  -    actionmailer (3.2.12)
  -      actionpack (= 3.2.12)
  -      mail (~&gt; 2.4.4)
  -    actionpack (3.2.12)
  -      activemodel (= 3.2.12)
  -      activesupport (= 3.2.12)
  +    actionmailer (3.2.13)
  +      actionpack (= 3.2.13)
  +      mail (~&gt; 2.5.3)
  +    actionpack (3.2.13)
  +      activemodel (= 3.2.13)
  +      activesupport (= 3.2.13)
         builder (~&gt; 3.0.0)
         erubis (~&gt; 2.7.0)
         journey (~&gt; 1.0.4)
  @@ -14,19 +14,19 @@ GEM
         rack-cache (~&gt; 1.2)
         rack-test (~&gt; 0.6.1)
         sprockets (~&gt; 2.2.1)
  -    activemodel (3.2.12)
  -      activesupport (= 3.2.12)
  +    activemodel (3.2.13)
  +      activesupport (= 3.2.13)
         builder (~&gt; 3.0.0)
  -    activerecord (3.2.12)
  -      activemodel (= 3.2.12)
  -      activesupport (= 3.2.12)
  +    activerecord (3.2.13)
  +      activemodel (= 3.2.13)
  +      activesupport (= 3.2.13)
         arel (~&gt; 3.0.2)
         tzinfo (~&gt; 0.3.29)
  -    activeresource (3.2.12)
  -      activemodel (= 3.2.12)
  -      activesupport (= 3.2.12)
  -    activesupport (3.2.12)
  -      i18n (~&gt; 0.6)
  +    activeresource (3.2.13)
  +      activemodel (= 3.2.13)
  +      activesupport (= 3.2.13)
  +    activesupport (3.2.13)
  +      i18n (= 0.6.1)
         multi_json (~&gt; 1.0)
       airbrake (3.1.7)
         activesupport
  @@ -129,7 +129,7 @@ GEM
       hashr (0.0.22)
       hike (1.2.1)
       honeypot-captcha (0.0.2)
  -    i18n (0.6.4)
  +    i18n (0.6.1)
       journey (1.0.4)
       jquery-rails (2.2.0)
         railties (&gt;= 3.0, &lt; 5.0)
  @@ -146,7 +146,7 @@ GEM
       kgio (2.8.0)
       listen (0.7.2)
       lumberjack (1.0.2)
  -    mail (2.4.4)
  +    mail (2.5.3)
         i18n (&gt;= 0.4.0)
         mime-types (~&gt; 1.16)
         treetop (~&gt; 1.4.8)
  @@ -155,7 +155,7 @@ GEM
       mime-types (1.21)
       mocha (0.10.5)
         metaclass (~&gt; 0.0.1)
  -    multi_json (1.6.1)
  +    multi_json (1.7.1)
       mysql2 (0.3.11)
       nested_form (0.3.1)
       net-scp (1.0.4)
  @@ -180,14 +180,14 @@ GEM
         rack
       rack-test (0.6.2)
         rack (&gt;= 1.0)
  -    rails (3.2.12)
  -      actionmailer (= 3.2.12)
  -      actionpack (= 3.2.12)
  -      activerecord (= 3.2.12)
  -      activeresource (= 3.2.12)
  -      activesupport (= 3.2.12)
  +    rails (3.2.13)
  +      actionmailer (= 3.2.13)
  +      actionpack (= 3.2.13)
  +      activerecord (= 3.2.13)
  +      activeresource (= 3.2.13)
  +      activesupport (= 3.2.13)
         bundler (~&gt; 1.0)
  -      railties (= 3.2.12)
  +      railties (= 3.2.13)
       rails_admin (0.4.3)
         bootstrap-sass (~&gt; 2.2)
         builder (~&gt; 3.0)
  @@ -202,9 +202,9 @@ GEM
         rails (~&gt; 3.1)
         remotipart (~&gt; 1.0)
         sass-rails (~&gt; 3.1)
  -    railties (3.2.12)
  -      actionpack (= 3.2.12)
  -      activesupport (= 3.2.12)
  +    railties (3.2.13)
  +      actionpack (= 3.2.13)
  +      activesupport (= 3.2.13)
         rack-ssl (~&gt; 1.3.2)
         rake (&gt;= 0.8.7)
         rdoc (~&gt; 3.4)
  @@ -212,7 +212,7 @@ GEM
       raindrops (0.10.0)
       rake (10.0.3)
       rb-fsevent (0.9.1)
  -    rdoc (3.12.1)
  +    rdoc (3.12.2)
         json (~&gt; 1.4)
       remotipart (1.0.2)
       rest-client (1.6.7)
  @@ -266,7 +266,7 @@ GEM
         eventmachine (&gt;= 0.12.6)
         rack (&gt;= 1.0.0)
       thor (0.17.0)
  -    tilt (1.3.4)
  +    tilt (1.3.6)
       tire (0.5.4)
         activemodel (&gt;= 3.0)
         hashr (~&gt; 0.0.19)
  @@ -280,7 +280,7 @@ GEM
         actionpack (&gt;= 3.1)
         execjs
         railties (&gt;= 3.1)
  -    tzinfo (0.3.35)
  +    tzinfo (0.3.37)
       uglifier (1.3.0)
         execjs (&gt;= 0.3.0)
         multi_json (~&gt; 1.0, &gt;= 1.0.2)
  @@ -325,7 +325,7 @@ DEPENDENCIES
     nested_form
     newrelic_rpm (~&gt; 3.5.5.38)
     pry
  -  rails (= 3.2.12)
  +  rails (= 3.2.13)
     rails_admin
     rb-fsevent (= 0.9.1)
     rmagick
  </code></pre>
  
  <p>Other then these two files nothing has changed.</p>
  
  <p>From reading <a href="https://stackoverflow.com/questions/15317048/diagnosing-the-cause-of-slow-view-rendering">Diagnosing the cause of slow view rendering</a> I understand that stuff in the asset pipeline can be slowing it down, but I dont see a difference when I change the value of "config.assets.debug = false" inside of development.rb.</p>
  
  <p>I suppose I do have a lot of assets in my asset pipeline I still need to clean up, which I will do before I deploy to production, but I wonder why this has now suddenly caused the lag after updating Rails. Question is: What is causing it and can I do something about it?</p>
  
  <p>Let me know if you need more info. Any help is greatly appreciated.</p>
  
  <p>EDIT: I also created an issue on the github.com/rails/rails, which seems to be picked up as a regression: <a href="https://github.com/rails/rails/issues/9803" rel="nofollow noreferrer">https://github.com/rails/rails/issues/9803</a>.</p>