Different versions of Rails have different default locations for the Action Cache. If your production server is using an older Rails Gem, then the action cache could be stored in memory.
Newer Rails versions use the RAILS_ROOT/tmp/cache directory by default.
I don't know when this changed.
You can configure to use the File system instead of using the default location in environment.rb:
ActionController::Base.fragment_cache_store = :file_store, "/path/to/cache/directory"