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It's complicated. Probably what they were seeing was that mime-types was directly allocating a chunk of memory, let's say 8mb.

Now what could happen is if they app is on the edge of needing to increase it's own heap size, then the mime-types gem might push it over the edge.

For example. You have an app that needs 99mb to run. The Ruby VM allocates up to 100mb for it to run in. Now mime-types get's allocated and suddenly it needs 107mb to run. So Ruby has to increase the heap, it does this based off of a multiplier, for example 80% so it bumps the heap up to 180mb even though we really only need 107mb.

That might be what's happening and why they're seeing such a huge savings.

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source 'https://rubygems.org'


# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
gem 'rails',           github: "rails/rails"
gem 'arel',            github: "rails/arel"
gem "rack",            github: "rack/rack"
gem "sprockets",       github: "rails/sprockets"
gem "sprockets-rails", github: "rails/sprockets-rails"
gem 'coffee-rails',    github: "rails/coffee-rails"

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$ bundle exec foreman start
12:46:28 web.1  | started with pid 5807
12:46:28 web.1  | [5807] Puma starting in cluster mode...
12:46:28 web.1  | [5807] * Version 2.11.1 (ruby 2.2.2-p95), codename: Intrepid Squirrel
12:46:28 web.1  | [5807] * Min threads: 8, max threads: 32
12:46:28 web.1  | [5807] * Environment: development
12:46:28 web.1  | [5807] * Process workers: 4
12:46:28 web.1  | [5807] * Preloading application
12:46:28 web.1  | [5807] * Listening on tcp://0.0.0.0:9292
12:46:28 web.1  | [5807] ! WARNING: Detected 1 Thread(s) started in app boot:

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require 'net/http'
require 'json'


def rubygems_get(gem_name: "", endpoint: "")
  path = File.join("/api/v1/gems/", gem_name, endpoint).chomp("/") + ".json"
  JSON.parse(Net::HTTP.get("rubygems.org", path)) 
end

results = rubygems_get(gem_name: "mime-types", endpoint: "reverse_dependencies")

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Thread.new do 
  begin
    while true
      sleep
    end
  ensure
    puts "it's a TRAP"
  end
end
Process.kill("TERM", Process.pid)

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schneems

source 'https://rubygems.org'

# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
gem 'rails', '5.0.0.alpha', github: 'rails/rails'
gem 'arel', github: 'rails/arel'


# Use sqlite3 as the database for Active Record
gem 'sqlite3'
# Use SCSS for stylesheets

schneems

Why not set backlog on Heroku?

First read this: https://mikecoutermarsh.com/adjusting-pumas-backlog-for-heroku/

Now we're on the same page. Heroku will re-route bounced requests from your dynos but it assumes when this happens that your entire app is saturated. https://devcenter.heroku.com/articles/http-routing#dyno-connection-behavior. Each connection gets delayed by 5 seconds, so you're automatically being docked 5 seconds per request.

If you're setting your backlog to a low value (i.e. if you'll ever actually ever hit backlog) then you'll be in for pain. When you get a spike of requests from slashdot/reddit/whatever you're telling your dynos that you would rather they failed then returned slow responses. So this does mean that some requests will be served, but all the others will fail.

If your app ever hits your backlog (no matter what value it is) it is an indicator you don't have enough throughput and you need to scale out to more dynos. If you set this to an arbitrarilly low value, that point comes

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TIL attr_* methods are optomized.

class Whatever
  def foo
    @foo
  end

  attr_reader :bar
end

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Ruby on Rails is a popular web framework written in Ruby. This guide covers using Rails 4 on Heroku, running previous versions of Rails on Heroku see Getting Started with Rails 3.x on Heroku.

callout If you are already familiar with Heroku and Rails, reference the simplifed Rails 4 on Heroku guide instead. For general information on how to develop and architect apps for use on Heroku, see Architecting Applications for Heroku.

For this guide you will need: