A gem for your rails project that suggests indices for you to add in your database. It looks for unindexed foreign keys, and what columns actually get queried.
http://www.youtube.com/watch?v=FTt5mVdGVXQ
Add this line to your application's Gemfile:
gem 'suggest-db-indices'
And then execute:
$ bundle
bundle exec rake suggest_db_indices
Also see: http://www.youtube.com/watch?v=FTt5mVdGVXQ
0.1.0 (July 8, 2012) - Added the rake task.
0.0.3 (July 4, 2012) - Added justification for each index added, made log file handling more robust