Fastup builds an index from $LOAD_PATH and patches require to use
that index to significantly speed up booting up large Rails apps with
many dependencies.
When require 'code' is called, Ruby searches each element of
$LOAD_PATH, attempting to load code.rb from each directory in
$LOAD_PATH. Watching the output of strace while starting a Ruby
program reveals a large number of failed attempts to open non-existent
files, until the correct path is found. The index built by fastup
allows skipping many of these failed attempts.
The speedup is most noticeable in applications with many
dependencies. With few dependencies, the overhead of fastup will
cause a small slowdown. Test the speedup first, to see if fastup is
worth it or not for any particular application.
fastup/autoapply should be required after bundler/setup and before
Bundler.require, or more generally, after $LOAD_PATH has been
populated with all dependencies and before most of them have been
require'd.
For example in config/boot.rb of a Rails app:
require 'rubygems'
# Set up gems listed in the Gemfile.
ENV['BUNDLE_GEMFILE'] ||= File.expand_path('../../Gemfile', __FILE__)
require 'bundler/setup' if File.exists?(ENV['BUNDLE_GEMFILE'])
require 'fastup/autoapply'This has not been used in production.