ActiveSupport HashWithIndifferentAccess vs Java HashMap performance

bench.rb

#!/usr/bin/env jruby

require "rubygems"
require "active_support/hash_with_indifferent_access"
require "java"
require "benchmark"

SYMBOLS = []
STRINGS = []
GET_REPEAT = 100

puts "Preparing keys..."

1_000_000.times do |i|
  i_s = i.to_s
  STRINGS << i_s
  SYMBOLS << i_s.to_sym
end

def bench(reporter, name, h)
  reporter.report("#{name} set Symbol") do    
    SYMBOLS.each_with_index do |e,i|
      h[e] = i
    end
  end
  
  reporter.report("#{name} get String") do
    GET_REPEAT.times do
      STRINGS.each do |e|
        h[e]
      end
    end
  end
  
  reporter.report("#{name} get Symbol") do
    GET_REPEAT.times do
      SYMBOLS.each do |e|
        h[e]
      end
    end
  end
  
end

Benchmark::bmbm do |x|
  bench x, "HWIA", HashWithIndifferentAccess.new
  bench x, "HashMap", java.util.HashMap.new
end

results.txt

Preparing keys...
Rehearsal ------------------------------------------------------
HWIA set Symbol      4.480000   0.090000   4.570000 (  3.423000)
HWIA get String     70.870000   0.420000  71.290000 ( 67.325000)
HWIA get Symbol    165.900000   0.530000 166.430000 (166.823000)
HashMap set Symbol   0.890000   0.050000   0.940000 (  0.709000)
HashMap get String  53.500000   0.280000  53.780000 ( 52.815000)
HashMap get Symbol  24.830000   0.100000  24.930000 ( 24.955000)
------------------------------------------- total: 321.940000sec

                         user     system      total        real
HWIA set Symbol      1.490000   0.030000   1.520000 (  1.347000)
HWIA get String     58.700000   0.190000  58.890000 ( 59.274000)
HWIA get Symbol    157.110000   0.460000 157.570000 (158.355000)
HashMap set Symbol   0.250000   0.000000   0.250000 (  0.257000)
HashMap get String  54.910000   0.230000  55.140000 ( 54.216000)
HashMap get Symbol  26.190000   0.090000  26.280000 ( 26.082000)

NOTE: I tried setting both Symbols and Strings initially as well. There was no significant different difference with HWIA after rehearsal with a large enough set. HashMap generally had a 30%-50% advantage with Symbols.

Neither made any difference to the get performance (as you would expect).

To summarize, getting a String from a HashMap was consistently slightly faster than HWIA. Insertion to a HashMap is several times faster (consistently). Getting a Symbol from a HashMap is also several times faster.

Keep in mind this is all through Ruby. If you have a mixed-language project, where the Java side accessing a shared HashMap wouldn't be generating wrapping JRuby::RubyObject wrappers, and performing coercion for every K/V I'd expect the difference to be much greater.