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Created July 13, 2012 19:15
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Speedup Rails Asset Pipeline precompile process

Speedup Rails Asset Pipeline precompile process

This post is based on my blog post:

Here are my three tips for speedup asset pipeline precompile process:

  1. Capistrano deployment speedup
  2. Use @import carefully.
  3. don’t require .scss & .coffee for no reason

1. Capistrano deployment speedup

(1) use capistrano built-in task 'deploy/assets' to deploy.

Capistrano has its own built-in task 'deploy/assets'. It will automatically do task for you.

The difference between your own handcraft task is it only load assets group to precompile assets, not whole environment.

cd /home/apps/APP_NAME/releases/20120708184757 && bundle exec rake RAILS_ENV=production RAILS_GROUPS=assets assets:precompile

(2) skip precompile process when assess aren't changed.


  • app/assets
  • lib/assets
  • vendor/assets
  • Gemfile.lock
  • confir/routes.rb

are changed, it will recompile assets. Otherwise, it will skip the pecompile process, save a lot of time.

2. Use @import carefully.

(1) avoid using @import "compass"; directly.

It will both work when you

@import "compass"; or @import "compass/typography/links/link-colors"; in SCSS.

But @import "compass/typography/links/link-colors"; is 9 times faster than @import "compass"; when you compile assets.

That is because when @import "compass";, it compile whole compass assets. not only just link-colors part.

(2) avoid using partials

In SCSS, we like to use partial to organize our assets.

But only if you need to share variables, or there are necessary dependencies, otherwise

//= require "reset"
//= require "base"
//= require "product"

is faster than

@import "reset";
@import "base";
@import "product";

3. don’t require .scss & .coffee for no reason

(1) avoid using require_tree

When we use Rails generator to generate controllers. Rails will also generate assets likes this

  • product.css.scss

and mount assets in application.js using this techniques:

//= require_tree

But the empty assets (output nothing) which only contain this lines:

# Place all the behaviors and hooks related to the matching controller here.
# All this logic will automatically be available in application.js.
# You can use CoffeeScript in this file:

It will cost you about 250ms to compile each of them. If you have 10 empty assets, it will be 2.5 seconds .

Remove them from your project, or mount them individually in application.js like this:

//= require prodcuts
//= require users
//= require albums

(2) Don't use css.scss or if unnecessary.

  • Compiled jquery-ui-1.8.16.custom.css (0ms) (pid 19108)
  • Compiled (0ms) (pid 19108)
  • Compiled jquery.js (5ms) (pid 19108)
  • Compiled jquery_ujs.js (0ms) (pid 19108)
  • Compiled custom.css (14ms) (pid 19108)

custom.css is custom.css.scss

Compile pure CSS and pure JS is fast ( cost almost 0 ms). But compile .scss and .coffee still cost some time.


  1. replace deploy.rb assets task.
  2. check logs/product.log
  • find slow assets
  • remove @import "compass"; use alternative solution.
  • use require instead @import; ( use @import when it is really necessary )
  • remove require_tree, mount assets individually
  • remove empty .scss and .coffeescript
  • use .css when assets are pure CSS.
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