jschmotzer / karmaville

Part 1: Denormalization

Welcome to KarmaVille! Things would be great if things weren't so slow.

We have a pre-built Rails application with two models: User and KarmaPoint. After seeding the database with data, you'll have 100,000 rows in the users table and 1,500,000 rows in the karma_points table. The index page is sl-o-o-ow and it's your job to speed it up without using any fancy technologies like memcache, redis, or Rails' fragment caching.

Setting Up the Application

Clone this repository, checkout a feature branch, then get the application running as follows:

$ bundle install
$ rake db:setup

The rake db:setup command could take a few minutes. Once it's done run rails server and visit http://localhost:3000.

We use a gem called activerecord-import to mass import data into the database. Here is an issue to be aware of: this issue It should take a few seconds to load. If you look at the last line of your server logs, you'll see it telling you how much time was spent rendering the views versus how much time was executing ActiveRecord methods. Where's the bottleneck?

Make it fast!

Your goal is to get the index page server response time to under 200ms. Yes, that's milliseconds. You're permitted to do the following:

1. Add new fields to the users and karma_points tables
2. Add new indexes to the users and karma_points tables
3. Add new class or instance methods to the User or KarmaPoint models

The test suite should remain green. If you add any new public methods make sure you add appropriate corresponding tests.

You should write a custom rake tasks to handle populating new database tables.

You should not change the controller or view code.

Submit your solution as a pull request.

Part 2: Pagination

Let's add pagination to our application so we can page through all 100,000 users quickly.

Pagination is a common feature so it's worth knowing how it works.

Multiple Pages

Before you build the UI, make it so you can visit a URL like http://localhost:3000?page=3 and have it do the correct thing. You're free to change the number of users displayed per page. Read the ActiveRecord documentation on limit and offset, which will be necessary to get pagination behavior.

TDD User.page

Add a method User.page that works as follows:

User.by_karma.page(3) # returns the 3rd page of users, sorted by karma

Write tests for this method and implement it. If the input is nil it should return the first page of users.

TDD Pagination Links

Because we're already using Twitter Bootstrap, add pagination links to the bottom of the index page using Bootstrap's pagination component. Make sure the user experience is correct. This means:

1. It should display the correct number of pages
2. The correct page should be marked as active
3. If a user is on the first or last page, the previous or next links should be disabled (respectively)

TDD this feature using capybara.

Submit your solution as a pull request.