As you may know, one area of Ruby performance optimization that particularly interests me is memory usage. Given that most Ruby deployments rely on fork, improving Copy-on-Write performance is generally where you get the biggest bang for your buck, but that only helps with the somewhat static part of an application heap.

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RUBYLAND

A deep dive into Ruby Hash memory usage across versions, tracing the evolution from Ruby 2.3 to 4.1. Covers the history of ar_table (array table), Variable Width Allocation, and the lower-byte hashcode optimization. The author explains current work to shrink st_table by 8 bytes via struct packing (moving entries_start into a 1-byte field), enabling mutable hashes to fit in 64B GC slots. Also covers frozen hash optimization already merged, and an in-progress patch for dynamic ar_table sizes that could bring small hash memory usage much closer to theoretical minimums. Includes practical advice: prefer Struct or plain Ruby objects over Hash when structure is known.

Shrinking Ruby Hashes