Question

I’m trying to do a simple benchmark to know how many octets are read from the cache in each page of my Rails site. I’m talking about the data retrieve from Rails.cache.

I would like to display something like 123Ko/145Ko at the bottom of my pages.

Does a gem exist to perform this task or perhaps is there something included in the ruby standard library?

Answer 1

One option is to subclass the store you’re using and extend the protected read_entry method declared in ActiveSupport::Cache::Store, which FileStore and the other caches themselves subclass.

FileStoreWithReadTracking < ActiveSupport::Cache::FileStore
  def start_page
    @octets_read = 0
  end

  def octets_read
    @octets_read
  end

  protected

    def read_entry(key, options)
      entry = super(key, options)
      @octets_read += entry.size if entry
      entry
    end
end

When starting a page, you can call start_page to zero out the octet count. Since read_entry is a low-level method used every time the cache tries to perform a read, you can intercept any data read and get its size before returning it. You might have to convert size to octets.

To set this as your custom cache store, add config.cache_store = FileStoreWithReadTracking.new('/path/to/file/store') to your environment. I think you can subclass all the stores this way.