Issue #19785 has been updated by peterzhu2118 (Peter Zhu). The `%d` part is the sizes returned from `GC.stat_heap`. On 64-bit systems, it's 40, 80, 160, 320, 640. On 32-bit systems it's 20, 40, 80, 160, 320. You use `RUBY_GC_HEAP_INIT_SIZE_40_SLOTS=4000000` to have 4M slots in the 40 byte size pool, for example. Yes, it is more difficult than setting one value, but users of this API should be aware of how the GC internals work if they want to use this. The idea of `RUBY_GC_HEAP_INIT_SIZE_%d_SLOTS` is to set initial sizes for Rails apps so the GC doesn't need to warm up. `RUBY_GC_HEAP_INIT_PAGES` will allocate pages to size pools based on the distribution of objects at boot, and I worry that it will be a different distribution than serving requests. ---------------------------------------- Feature #19785: Deprecate `RUBY_GC_HEAP_INIT_SLOTS` https://bugs.ruby-lang.org/issues/19785#change-104221 * Author: peterzhu2118 (Peter Zhu) * Status: Open * Priority: Normal ---------------------------------------- GitHub PR: https://github.com/ruby/ruby/pull/8147 The `RUBY_GC_HEAP_INIT_SLOTS` environment variable is replaced by `RUBY_GC_HEAP_INIT_SIZE_%d_SLOTS` (introduced in commit [3ab3455](https://github.com/ruby/ruby/commit/3ab34551450c7a3a3e1ae0b24bf6b7…), which allows for more fine-grained tuning of size pools. So it doesn't make sense to keep the environment variable `RUBY_GC_HEAP_INIT_SLOTS`. I'm proposing to deprecate `RUBY_GC_HEAP_INIT_SLOTS` and eventually remove it. -- https://bugs.ruby-lang.org/