ActiveRecord pool stats for Rails < 5.1

ar_pool_stats.rb

unless ActiveRecord::ConnectionAdapters::ConnectionPool.method_defined?(:stat) # will be in Rails 5.1
  class ActiveRecord::ConnectionAdapters::ConnectionPool
    def stat
      synchronize do
        {
          size: size,
          connections: @connections.size,
          busy: @connections.count { |c| c.in_use? && c.owner.alive? },
          dead: @connections.count { |c| c.in_use? && !c.owner.alive? },
          idle: @connections.count { |c| !c.in_use? },
          waiting: num_waiting_in_queue,
          checkout_timeout: checkout_timeout
        }
      end
    end
  end
end