connection_pool_example.rb

require 'rubygems'
require 'bundler/setup'

require 'mysql2'
require 'active_record'
require 'logger'


ActiveRecord::Base.logger = Logger.new(STDERR)
ActiveRecord::Base.establish_connection(:adapter => 'mysql2',
                                        :host => 'localhost',
                                        :database => 'test',
                                        :username => 'root',
                                        :pool => 1)

class Employee < ActiveRecord::Base
end

ts = []
10.times do
  ts << Thread.new do
    ActiveRecord::Base.connection_pool.with_connection do
      Employee.all
    end
  end
end

ts.each { |t| t.join }