Preheat¶ ↑

IN DEVELOPMENT DISCLAMER: This gem is still under development and hasn’t been put through intensive real-world testing yet. Any comments/concerns/recommendations would be greatly appreciated.

Keep your Rails.cache up to date without:

• code bloat in your Rails.cache.fetch invocations

• tedious dependency setup in a cron task to mimic what your controller does, just so you can call your model/library methods which have the Rails.cache.fetch invocations

Anything executed in a Preheat.it block will change all fetch calls into a fetch calls with :force => true. (:force => true will force a cache-miss and a subsequent cache-write)

Example¶ ↑

This will “preheat” all your Rails.cache.fetch calls on your homepage. It is as simple as that!

Preheat.it do
  app.get("/")
end

Note: If you have not seen “app.get” used before, the “app” object is not related to my preheat gem. It ships with rails: more detail here. I use app.get because ActiveSupport’s fetch method is being modified only in the ruby process which is using Preheat, so something like mechanize/wget/curl would call the page through your frontend webserver and would not be effected by Preheat.it, while app.get will directly call your controller in that same ruby process.

A more detailed example¶ ↑

Let’s say we have a list of product pages where we want the cached to be updated every hour.

#app/models/product.rb
def slow_method
  Rails.cache.fetch("product-slow-method-#{self.id}") do
    sleep 15
    Time.now
  end
end

#lib/tasks/preheat.rake
namespace :preheat do
  desc "Preheat product caches"
  task (:products => :environment) do
    Preheat.it do
      Product.all.each do |product|
        app.get(app.products_path(product)) #or you could just call product.slow_method directly, whatever makes more sense
      end
    end
  end
end

#crontab -e
0 * * * * /path/to/rake preheat:products RAILS_ENV=production 2>&1 >> #{Rails.root}/log/preheat.log &

Installation¶ ↑

1. gem install preheat

2. Add the gem to environment.rb or your Gemfile

Thanks¶ ↑

John Hume for helping me cleanup part of my code. Brian Guthrie for getting me all learned up on gem dependencies and the like.