[ruby-core:115153] [Ruby master Bug#19969] Regression of memory usage with Ruby 3.1
From:
"Eregon (Benoit Daloze) via ruby-core" <ruby-core@...>
Date:
2023-10-24 15:05:34 UTC
List:
ruby-core #115153
Issue #19969 has been updated by Eregon (Benoit Daloze).
So apparently some applications were relying on `Set#dup`/`Hash#dup` to do like C++ [shrink_to_fit](https://en.cppreference.com/w/cpp/container/vector/shrink_to_fit).
Ruby does not have such a method and it feels quite low-level, so it seems better to resize the internal data structure when removing elements/entries and going below some threshold.
----------------------------------------
Bug #19969: Regression of memory usage with Ruby 3.1
https://bugs.ruby-lang.org/issues/19969#change-105060
* Author: hsbt (Hiroshi SHIBATA)
* Status: Open
* Priority: Normal
* Backport: 3.0: DONTNEED, 3.1: REQUIRED, 3.2: REQUIRED
----------------------------------------
Our company that is ANDPAD, Inc. encountered to increase memory usage after upgrading Ruby 3.2 from 3.0 on our Rails application. This increase size is about 20%.
My colleague found this [root cause](https://bugs.ruby-lang.org/issues/16996) and reproduction code:
```
$ 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 #{$$}`.to_i'
ruby 3.0.6p216 (2023-06-29 revision bdfe1958a8) +JIT [arm64-darwin22]
248096
$ ruby -v -rset -e 's1 = Set.new(10000.times); s2 = Set.new(9999.times); Array.new(10000) { s1 - s2 - [0] }; puts `ps -o rss= -p #{$$}`.to_i'
ruby 3.2.2 (2023-07-05 revision 2f603bc4d7) +YJIT [arm64-darwin22]
2949280
```
Should we revert #16996 for Ruby 3.1 or later? I'm not sure this increased memory usage is reasonable with performance improvement.
--
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