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Experiment to use hash4j algorithms for String#hash #9176

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@headius headius commented Jan 13, 2026

This experiment hooks up the hash4j library to String#hash. Any of the algorithms it provides can be used here by changing a line of code. This is proof-of-concept code used to compare the performance of the different algorithms.

Testing of the algorithms can use, among other things, the benchmark at https://bugs.ruby-lang.org/issues/21833 which compares different sizes of strings.

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Experiment to use hash4j algorithms for String#hash
0897ec4 
This experiment hooks up the hash4j library to String#hash. Any of
the algorithms it provides can be used here by changing a line of
code. This is proof-of-concept code used to compare the performance
of the different algorithms.

Testing of the algorithms can use, among other things, the
benchmark at https://bugs.ruby-lang.org/issues/21833 which compares
different sizes of strings.
@headius headius added this to the JRuby 10.1.0.0 milestone Jan 13, 2026
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headius commented Jan 13, 2026

An example comparison using rapidhash3 versus the Ruby 4.0.0 release.

Before (JRuby using perlhash):

Comparison:
                     tiny_strings
          jruby-head:    932733.1 i/s 
          ruby-4.0.0:    391861.1 i/s - 2.38x  slower

                    small_strings
          jruby-head:    795430.8 i/s 
          ruby-4.0.0:    395953.0 i/s - 2.01x  slower

                   medium_strings
          jruby-head:    502150.9 i/s 
          ruby-4.0.0:    383490.9 i/s - 1.31x  slower

                    large_strings
          ruby-4.0.0:    186680.3 i/s 
          jruby-head:     46827.9 i/s - 3.99x  slower

                     huge_strings
          ruby-4.0.0:       855.1 i/s 
          jruby-head:       130.0 i/s - 6.58x  slower

After (JRuby using rapidhash3):

Comparison:
                     tiny_strings
          jruby-head:    819299.3 i/s 
          ruby-4.0.0:    390872.0 i/s - 2.10x  slower

                    small_strings
          jruby-head:    832171.2 i/s 
          ruby-4.0.0:    393664.5 i/s - 2.11x  slower

                   medium_strings
          jruby-head:    742292.6 i/s 
          ruby-4.0.0:    384353.1 i/s - 1.93x  slower

                    large_strings
          jruby-head:    248515.2 i/s 
          ruby-4.0.0:    186317.3 i/s - 1.33x  slower

                     huge_strings
          ruby-4.0.0:       851.9 i/s 
          jruby-head:       759.3 i/s - 1.12x  slower

I do not have a good explanation for the performance drop on the larger strings, but it's substantially reduced by using rapidhash3.

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