Bug #22210: Check if issue #19969 is still reproducible / re-opened in 4.0.x

• Status: Open
• Assignee: -
• Target version: -
• Backport: 3.3: DONTNEED, 3.4: DONTNEED, 4.0: REQUIRED

[saka_omo (Yuki Takei)]

Hi team,

I am writing to ask if Bug #19969 might still be reproducible in the current version of Ruby.
Could you please check if the issue is still present or if a regression has occurred?

I ran the reproduction script from #19969 across several Ruby versions on macOS (arm64-darwin), and while Ruby 3.2.4 fixed the high memory consumption (dropping to 29 MiB), Ruby 4.0.5 spikes back up to 2215 MiB.

ruby -v -rset -e 's1 = Set.new(10000.times); s2 = Set.new(9999.times); Array.new(10000) { s1 - s2 - [0] }; puts "#{`ps -o rss= -p #{$$}`.to_i / 1024} MiB"'

Results across versions:

ruby 3.0.3p157 (2021-11-24 revision 3fb7d2cadc) [arm64-darwin22]
183 MiB

ruby 3.2.2 (2023-03-30 revision e51014f9c0) [arm64-darwin22]
2364 MiB

ruby 3.2.4 (2024-04-23 revision af471c0e01) [arm64-darwin22]
29 MiB

ruby 4.0.5 (2026-05-20 revision 64336ffd0e) +PRISM [arm64-darwin24]
2215 MiB

[jeremyevans0 (Jeremy Evans)]

• Backport changed from 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN to 3.3: DONTNEED, 3.4: DONTNEED, 4.0: REQUIRED

Thank you for the report. I looked into this and the related functions for st_table are implemented for set_table (set_rebuild_table_with, set_rebuild_move_table, set_rebuild_cleanup, rb_set_compact_table). For the Set class, set_compact_after_delete is implemented, and the following functions call it:

• delete
• delete?
• delete_if
• reject!
• clear

Methods that remove elements from a set but did not call set_compact_after_delete:

• ^
• -
• difference
• subtract
• keep_if
• select!
• filter!

I've submitted a pull request to fix these issues: https://github.com/ruby/ruby/pull/18058