sequel_pg overwrites the inner loop of the Sequel postgres adapter row fetching code with a C version. The C version is significantly faster (2-6x) than the pure ruby version that Sequel uses by default. sequel_pg also offers optimized versions of some dataset methods, as well as adds support for using PostgreSQL streaming.
Gemfile gem 'sequel_pg', '~> 1.6.9'
install gem install sequel_pg -v 1.6.9