TL;DRWe focused to improve Rails application performance in Ruby 2.7 JIT, but the last year's assumption was wrong and Ruby 2.7 JIT didn't meet the goal. We'll change the approach for it in Ruby 3.0. Ruby 2.7 is released!Merry Christmas! The new Ruby is out. As I've sometimes promised to make performance improvements in Ruby 2.7 JIT, let me explain how it went. See also The method JIT compiler for