clearstatcache

• In both PHP and Ruby, various file operations result in the interpreter calling down to the underlying operating system’s stat function to query information about the filesystem.

  The architecture of PHP is built around the notion of a PHP program living only for the lifetime of a single HTTP request. With this assumption, various performance optimizations can be made. One of these optimizations is that when you use PHP filesystem functions that result in stat calls to the OS, PHP will cache the result. If another stat on the same file is needed during the request, PHP will pull the information from its cache, avoiding the expense of another call down to the operating system.

  This is usually what you want, but sometimes even within a single request, a PHP script needs to ensure the stat of a file is not stale. The clearstatcache function is used to clear the cache for this use case.

  Ruby doesn’t stat cache

  Ruby, being a more general purpose language than PHP, is not built around the notion of a HTTP request and as such does not have some optimizations like this one. Calls to methods like File.exist? will result in a stat call every time. This is true even with the Rails framework, with one exception noted below.

  As a consequence, Ruby can be less performant in this regard and does not have an equivalent of PHP’s clearstatecache function.

  Rails sometimes stat caches

  The two most expensive filesystem operations that Rails performs are loading your classes (primarily models and controllers) and rendering your views.

  In the production environment mode, your classes are only loaded once. This means that a stat is only performed once, when the file is loaded for the first time. For subsequent requests, the file is not reloaded from the filesystem, and thus the stat is not performed.

  In Rails versions prior to 2.0.2, rendering ActionView templates resulted in stat calls on those files on every request. However, Rails 2.0.2 added a new default in config/environments/production.rb:

  Rails

  config.action_view.cache_template_loading = true

  This results in stat calls on the views occuring only once, just like models and controllers. For all other filesystem operations within the context of Rails, there is no stat cache and the behavior is the same as standalone Ruby.

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