YSlow and Rails performance: Getting UJS and AssetPackager to play nice

Robby Russell — Fri, 27 Jul 2007 13:40:00 -0500

Yesterday, I started to dig deeper into YSlow and decided to pick an application that we recently launched for a client. The performance grade that I saw at first was an F, which wasn’t surprising to me because we knew that there was going to be some fine tuning in the near future.

There is a lot of JavaScript in this application and we have several files to break up stuff to make it more maintainable. However, in production, we really don’t need to send the client (browser) 19 different JS files. We’ve been using mod_deflate to compress these files, but it doesn’t solve the problem of having several connections opening to download all the necessary JavaScript. The same is true for our CSS files.

At RailsConf, DHH announced that an upcoming version of Rails would bundle all the stylesheet and javascript files into one file and compress it. We’re running on 1.2.x for this application and decided to look at the AssetPackager plugin as a good solution to this problem.

I installed the plugin via piston and ran the following task, which is provided by AssetPackager.

rake asset:packager:create_yml

This went ahead and created config/assets_packager.yml. I then went ahead and updated our capistrano configuration to call the rake task after updating the code on the server when deploying.


desc "all of our other tasks/commands to run after updating the code" 
task :after_update_code do
  #
  # all of our other tasks/commands
  #
  run "cd #{release_path} && rake RAILS_ENV=production asset:packager:build_all" 
end

The first thing that I noticed was that the yml file that gets generated will not make any assumption as to what order the javascript libraries should be loaded. So, immediately, line 1 of our compressed javascript file was causing an error as the code was trying to reference a library that hadn’t been defined yet (showed up later in the file). So, when you do this, you’ll need to organize the yml file to load things in order that they are needed. This was also a good opportunity for us to say, “oh, we’re not using that one anymore. Let’s remove it.”


--- 
javascripts: 
- base: 
  - prototype  
  - effects
  - scriptaculous
  - controls
  - dragdrop
  - application
  - slider
  - pngfix
  - nav
  - lowpro
  - lightbox
  - folder
  - builder

Great, so we re-dployed and everything at first glance seemed fine… or so we thought!

We used the unobtrusive javascript plugin for this project and it seems that we couldn’t just compress every single file. Each page has a behaviors javascript file and since everything was being compressed into one file (and cached), RJS calls quickly broke throughout the site. OH NO!

So, I opted to merge all of the other javascript files and use the standard way of including unobtrusive javascript in the application layout.


<%= javascript_include_merged :base %>
<%= javascript_include_tag :unobtrusive %>

We also removed lowpro from the list of javascript files to compress since the ujs plugin is currently including this when we call <%= javascript_include_tag :unobtrusive %>. I plan to look into modifying this so we it’ll only include the page-specific behaviors and not load the lowpro javascript file (so we can compress that as well).

Once this was re-deployed, we saw that the RJS issues were resolved and everything felt to be loading quicker. But, let’s look at YSlow again for step 1 in improving the performance of the application.

side note: the following grading was also after making some other adjustments that were suggested by YSlow, which I’ll discuss in another blog post soon.

So, where we once had a grade F, we now have an D… which is due to the client having us add several (four) external javascript files for mint, google analytics, etc. We’re only loading 3 javascript files for the application, when we were originally loading many more.

Obviously, there is some more tuning to be done, but we went from a grading of 43 to 74 in about three hours of time spent reading the YSlow documentation, adding asset_packager, and making various tweaks to our web servers (as suggested by YSlow).

Until next time…

Every Second Counts with a Piston in your Trunk

Robby on Rails: Tag yslow

YSlow and Rails performance: Getting UJS and AssetPackager to play nice