1.9.2_out.txt

 $ ruby split_vs_regex.rb
                user     system      total        real
split       9.080000   0.020000   9.100000 (  9.081937)
regex       9.810000   0.010000   9.820000 (  9.810586)

jruby_out.txt

 $ ruby split_vs_regex.rb
                user     system      total        real
split       3.776000   0.000000   3.776000 (  3.731000)
regex       3.729000   0.000000   3.729000 (  3.729000)

split_vs_regex.rb

require 'date'
require 'time'
require 'benchmark'


def parse_by_split(str)
  day, time = str.split(':', 2)

  day, month, year = day.split('/')
  month = Date::ABBR_MONTHNAMES.index(month)

  hour, minute, second = time.split(':')

  Time.utc(year.to_i, month.to_i, day.to_i, hour.to_i, minute.to_i, second.to_f)
end

REGEX = /(\d+)\/(\w+)\/(\d+):(\d+):(\d+):(\d+) (-?\d+)/
def parse_by_regex(str)
  match = REGEX.match(str)
  month = Date::ABBR_MONTHNAMES.index(match[2])
  Time.utc(match[3].to_i, month, match[1].to_i, match[4].to_i, match[5].to_i, match[6].to_i)
end

STRING = "01/Aug/2011:13:26:51 -0700"

N = 1_000_000
Benchmark.bm(10) do |bm|
  bm.report("split") do
    N.times { parse_by_split(STRING) }
  end

  bm.report("regex") do
    N.times { parse_by_regex(STRING) }
  end
end