speedup sequel datetime parse

gistfile1.txt

~/tmp/ruby-sequel$ ruby test_sequel_times.rb
            user     system      total        real
base    6.870000   0.200000   7.070000 (  7.534538)
~/tmp/ruby-sequel$ ruby test_sequel_times.rb home_run
            user     system      total        real
home_run  5.350000   0.160000   5.510000 (  5.856684)
~/tmp/ruby-sequel$ ruby test_sequel_times.rb fix
            user     system      total        real
fix     2.490000   0.150000   2.640000 (  2.807951)

sequel_time_parse.rb

class Time
  class << self
    def relaxed_rfc3339(date)
      if /\A\s*
          (-?\d+)-(\d\d)-(\d\d)
          [T ]
          (\d\d):(\d\d):(\d\d)
          (?:\.(\d+))?
          (Z|[+-]\d\d(?::?\d\d)?)?
          \s*\z/ix =~ date
        year = $1.to_i
        mon = $2.to_i
        day = $3.to_i
        hour = $4.to_i
        min = $5.to_i
        sec = $6.to_i
        usec = $7 ? "#{$7}000000"[0,6].to_i : 0
        if $8
          zone = $8
          if zone == 'Z'
            offset = 0
          elsif zone =~ /^([+-])(\d\d):?(\d\d)?$/
            offset = ($1 == '+' ? 1 : -1) * ($2.to_i * 3600 + ($3 || 0).to_i * 60)
          end
          year, mon, day, hour, min, sec =
            apply_offset(year, mon, day, hour, min, sec, offset)
          t = self.utc(year, mon, day, hour, min, sec, usec)
          t.localtime unless zone =~ /Z|-00:?(00)?/
          t
        else
          self.local(year, mon, day, hour, min, sec, usec)
        end
      end
    end
  end
end

module Sequel
  def self.string_to_datetime(string)
    begin
      if datetime_class == DateTime
        DateTime.parse(string, convert_two_digit_years)
      elsif datetime_class.respond_to?(:relaxed_rfc3339)
        datetime_class.relaxed_rfc3339(string) || datetime_class.parse(string)
      else
        datetime_class.parse(string)
      end
    rescue => e
      raise convert_exception_class(e, InvalidValue)
    end
  end
end

test_sequel_times.rb

require 'home_run' if ARGV[0] == 'home_run'
require 'rubygems'
require 'sequel'
require 'benchmark'
require './sequel_time_parse' if ARGV[0] == 'fix'


include Benchmark

Sequel.single_threaded = true
DB = Sequel.sqlite

DB.create_table :items do
  primary_key :id
  String :login
  String :name
  DateTime :created_at
  DateTime :updated_at
end

items = DB[:items]
for i in 1..100
  items.insert(:login => "login#{i}", :name => "name#{i}",
               :created_at => Time.now - i,
               :updated_at => Time.now + i 
               )
end
  

class Item < Sequel::Model
end

bm(6) do |x|
  x.report(ARGV[0] || 'base') do 100.times { Item.all } end
end