title: Rails cache Permission Denied when cache is very large
body: <p>My app uses extensive rails caching, and all the cache keys are created and used by the same application, which has full rights to the cache folder.  </p>
  
  <p>However, occasionally when the cache gets particularly large (large uptick in use within the cache expiration window), I start getting permissions errors when accessing the cache fragments using Rails.cache.fetch:  </p>
  
  <pre><code>Permission denied @ unlink_internal
  </code></pre>
  
  <p>Clearing the cache "fixes" the problem, until it gets large again.  Is there a theoretical limit to the size such a cache can be, or could there be some other cause?  </p>