Here is the pull request...

Enable Puma's nakayoshi_fork feature #11121

benhalpern posted on Oct 27, 2020

What type of PR is this? (check all applicable)

• [ ] Refactor
• [ ] Feature
• [ ] Bug Fix
• [x] Optimization
• [ ] Documentation Update

Description

Here are a few posts about GC.compact in Rails....

• https://dev.to/palkan_tula/cables-profiling-returns-gc-compact-jemalloc-33c9
• https://engineering.appfolio.com/appfolio-engineering/2019/3/22/ruby-27-and-the-compacting-garbage-collector
• https://www.infoworld.com/article/3404481/ruby-27-improves-garbage-collection-pattern-matching.html

My thoughts here are that if tests pass, this is something we could deploy and observe. There may be more ways we could use this in specific cases.

View on GitHub

Puma's current experimental nakayoshi_fork configuration essentially does this...

4.times { GC.start }
GC.compact # if available

GC.compact is a newer Ruby operation, and you can read a lot more about it in some of the linked resources in the PR.

The outcome in our app was... maybe 2% memory reduction in 24 hours of observation. It's hard to tell if this is actually 2% or just random variance.

2% is not much to write home about, but it's also not nothing. So for one line of code, it's probably worth it, however there are definitely bigger gains to be had elsewhere