This blog is part of our Rails 5 series.

In Rails 4 if I’m doing work related to caching then first I need to turn caching “on” by opening file config/environments/development.rb and changing following line.

config.action_controller.perform_caching = false

After changing the value from false to true, I need to restart the server.

This means that if I am testing caching behavior locally then every time I turn caching “on” or “off” I need to restart the server.

New command to create development cache in Rails 5

Rails 5 has introduced a new command to create development cache and help us test how caching behaves in development mode. Here is the issue and here is the pull request.

$ rails dev:cache
Development mode is now being cached.

Execution of the above command creates file caching-dev.txt in tmp directory.

How does it work?

In Rails 5 when a brand new Rails app is created then config/environments/development.rb file will have the following snippet of code.

if Rails.root.join('tmp/caching-dev.txt').exist?
  config.action_controller.perform_caching = true
  config.static_cache_control = "public, max-age=172800"
  config.cache_store = :mem_cache_store
  config.action_controller.perform_caching = false
  config.cache_store = :null_store

In the above code we are checking if the file tmp/caching-dev.txt is present and then use :mem_cache_store to enable caching only if the file is found.

Also, here is a snippet from the dev cache source code.

def dev_cache
  if File.exist? 'tmp/caching-dev.txt'
    File.delete 'tmp/caching-dev.txt'
    puts 'Development mode is no longer being cached.'
    FileUtils.touch 'tmp/caching-dev.txt'
    puts 'Development mode is now being cached.'

  FileUtils.touch 'tmp/restart.txt'

What is the advantage

The advantage is that we do not need to restart the server manually if we want to turn caching “on” or “off”. It is internally taken care by the dev_cache method that is executed when rails dev:cache is executed. You can see in the source code that tmp/restart.txt is being touched.

Please note that this feature is not supported by unicorn, thin and webrick. My guess is that DHH wants this feature because his team uses pow and pow restarts when tmp/restart.txt is touched. He also created an issue for spring to watch tmp/restart.txt long time back.

Disabling development cache

Execute the same command that was used to enable caching. If caching was previously enabled then it will be turned “off” now.

$ rails dev:cache
Development mode is no longer being cached.