前幾天 Ruby 推出了 2.4.0 (Ruby 2.4.0 Released)，其中特別被拿出來提的：「Introduce hash table improvement (by Vladimir Makarov)」。
討論串很長而且歷時很久，但可以看出來方向是提高 CPU cache 效率：
Modern processors have several levels of cache. Usually,the CPU reads one or a few lines of the cache from memory (or another level of cache). So CPU is much faster at reading data stored close to each other. The current implementation of Ruby hash tables does not fit well to modern processor cache organization, which requires better data locality for faster program speed.
中間還有拿 Redmine 當作測試項目... XD