Benchmark of various methods to retrieve a random record from a table using ActiveRecord and a Postgresql db behind.

postgresql_random_retrieve.rb

require 'benchmark'

# Disable logging if in development/test mode
ActiveRecord::Base.logger = nil

model_name = Icd
N = 100

Benchmark.bm(11) do |x|
  x.report('ruby rand') { N.times { model_name.offset(rand(model_name.count)).first } }
  x.report('psql RANDOM') { N.times { model_name.order('RANDOM()').first } }
end

For a fairly large table with 131883 rows, I got these timings:

                  user     system      total        real
ruby rand     0.320000   0.020000   0.340000 (  6.786860)
psql RANDOM   0.210000   0.010000   0.220000 ( 17.870080)

using Rails 4.2, Postgresql 9.4