Ruby 2.6 Released: Just-In-Time Compilation Is Here

Summary

Ruby 2.6 introduces an initial Just-In-Time (JIT) compiler, making the feature available through the --jit option and on Heroku. The implementation follows Takashi Kokubun’s YARV-MJIT approach, retaining Ruby’s existing YARV instructions instead of replacing them with the proposed RTL intermediate representation; it starts a compiler process at startup and supports GCC, Clang, and Microsoft Visual C++. On Heroku, applications can select Ruby 2.6 in the Gemfile and enable JIT through a Procfile flag or RUBYOPT, although setting RUBYOPT with heroku config is not yet supported. The optcarrot benchmark showed a reported 1.8x speed increase over Ruby 2.5, while Rails and Sidekiq were slower because compilation costs and roughly 2MB per compiled method create overhead. JIT compaction reduces memory use near the 1,000-method cache limit, but the source says further work is needed before JIT becomes the default.

Takeaways

1. 1

   Ruby 2.6’s JIT uses the existing YARV instruction set rather than replacing it with the proposed RTL intermediate representation.

2. 2

   The optcarrot benchmark showed a reported 1.8x speed increase over Ruby 2.5 with --jit, while Rails and Sidekiq experienced decreased performance.

3. 3

   Each compiled method initially consumes about 2MB of memory; JIT compaction reduces method size near the 1,000-method cache limit but does not yet make Rails faster.