Issue #19438 has been updated by byroot (Jean Boussier). Subject changed from Ruby 2.7 -> 3.2 Performance Regression to Ruby 2.7 -> 3.2 Performance Regression in CSV CSV being a gem, it's very likely that the regression isn't in ruby itself, but in the successive versions of the csv gem being bundled with Ruby: ``` ruby 3.2 => csv 3.2.6 ruby 3.1 => csv 3.2.2 ruby 3.0 => csv 3.1.9 ruby 2.7 => csv 3.1.2 ruby 2.6 => csv 3.0.9 ``` So if you wish to investigate this further, the best start would be to benchmark `csv 3.0.9` on Ruby 3.2, and `csv 3.2.6` on Ruby 2.7 or 2.6. I'm not very familiar with the `CSV` gem, but CSV as a format is losely defined, so I really wouldn't be surprised if over the years various fixes were added to handle corner cases and that it would impact performance. ---------------------------------------- Bug #19438: Ruby 2.7 -> 3.2 Performance Regression in CSV https://bugs.ruby-lang.org/issues/19438#change-101880 * Author: nick.schwaderer (Nicholas Schwaderer) * Status: Open * Priority: Normal * ruby -v: 3.2.0 * Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN ---------------------------------------- ## Introduction Recently I had been going through some of the old benchmarks in the [Ruby Great Implementation Shootout](https://programmingzen.com/the-great-ruby-shootout-july-2010/) from around 2010. As an experiment, one night I ran the benchmarks against Ruby 3.2.0, Ruby 3.2.0 --yjit, TruffleRuby, TruffleRuby +GraalVM, and Ruby 2.6.10. Most results were as expected. However there was a benchmark that Ruby 2.6.10 was _consistently_ outperforming all new Rubies on. ## Method After pairing with @eightbitraptor, we discovered that this old benchmark was remarkably similar to an existing benchmark in the `/benchmark` directory, [so_k_nucleotide.yml](https://github.com/ruby/ruby/blob/master/benchmark/so_k_nucleotide.yml). We decided to go with that benchmark. For brevity I have not included the full 150 lines of the benchmark here. I tested this benchmark out with 100 runs using `benchmark-driver` against Ruby 2.7,3.0,3.1,3.2. (I had discovered that 2.7 was even faster than 2.6.). It appears that about half of the regression occured from 2.7 -> 3.0; the other half from 3.0 -> 3.2. One other interesting finding is that each minor version does appear to regress from the last, even if a little. ## Code This is my benchmark running code and harnass. [The full code and data can be found here](https://gist.github.com/Schwad/16edf3d7cc5316af4baf23497f3c6a8f) ```ruby RUNS = 100 results = Hash.new { |h, k| h[k] = [] } RUNS.times do |i| puts i run = `benchmark-driver so_k_nucleotide.yml --chruby '2.7.5;3.0.5;3.1.3;3.2.0' -o simple` run.scan(/\d\.\d\.\d/).each_with_index do |version, index| results[version] << run.scan(/\d\.\d\d\d/)[index] end end require 'csv' columns = results.keys outdata = CSV.generate do |csv| csv << columns RUNS.times do |i| csv << columns.map { |c| results[c][i] } end end File.write("output.csv", outdata) ``` ## Data Ruby 2.7.5 was consistently ~18-20% faster than Ruby 3.2.0 in this Benchmark  ## Next Steps I am happy to help investigate or learn more about this regression if anyone has any ideas. -- https://bugs.ruby-lang.org/