loop_example.rb

timed_loop_batch(0.25, 1000, 100) do |batch_size|
  changed = GiantMetric.connection.update_sql("DELETE FROM giant_metrics WHERE created_at <= #{1.month.ago} LIMIT #{batch_size}")
  break if changed < batch_size
end 

timed_batch_loop.rb

def timed_batch_loop(target_secs, start_size, step, min_size=1, max_size=nil)
  current = start_size

  loop do
    start_time = Time.now
    yield current

    if Time.now - start_time > target_secs
      current = [min_size, current - step].max
    else
      if max_size
        current = [max_size, current + step].min
      else
        current += step
      end
    end
  end
end