From: "jemmai (Jemma Issroff) via ruby-core" <ruby-core@...>
Date: 2023-01-25T20:01:47+00:00
Subject: [ruby-core:112040] [Ruby master Bug#19334] Defining many instance variables and accessing them is slow in Ruby 3.2.0

Issue #19334 has been updated by jemmai (Jemma Issroff).


We merged [this PR](https://github.com/ruby/ruby/pull/7183) as a temporary fix. After 50 IV transitions, it falls back to the obj_too_complex shape, which uses a hash lookup. If we want, we could backport this change. I am unsure whether it's worth it because I don't know how likely this case is to occur in production code.

We could also increase the choice of max IVs from 50 to some other number.

New performance numbers with this change are:

```
$ time ruby -v test.rb 
ruby 3.3.0dev (2023-01-25T16:50:33Z limit-num-shapes 29c90b22bb) [arm64-darwin22]
:start
ruby -v test.rb  0.13s user 0.03s system 96% cpu 0.159 total
```

```
$ time ruby -v test.rb
ruby 3.1.3p185 (2022-11-24 revision 1a6b16756e) [arm64-darwin22]
:start
ruby -v test.rb  0.13s user 0.03s system 97% cpu 0.165 total
```

We are planning a more permanent fix as well. Our thinking is that after every 50 IV shapes, we could insert a "hash_iv_index_shape," which will have a pointer to an `rb_id_table` which stores iv_name -> index mapping for the previous 50 shapes, and a pointer to the previous "hash_iv_index_shape". This will significantly speed up the case above as well.

----------------------------------------
Bug #19334: Defining many instance variables and accessing them is slow in Ruby 3.2.0
https://bugs.ruby-lang.org/issues/19334#change-101473

* Author: mame (Yusuke Endoh)
* Status: Open
* Priority: Normal
* Assignee: tenderlovemaking (Aaron Patterson)
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN
----------------------------------------
```
class C
  eval("def initialize; #{ (0..100000).map { "@x#{ _1 } = 0; " }.join } end")
  attr_reader :x50000
end
p :start
C.new.x50000
```

This script takes less than one second in Ruby 3.1.3, and does more than ten second in Ruby 3.2.0.

```
$ time ruby -v test.rb
ruby 3.1.3p185 (2022-11-24 revision 1a6b16756e) [x86_64-linux]
:start

real    0m0.210s
user    0m0.167s
sys     0m0.044s
```

```
$ time ruby -v test.rb
ruby 3.2.0 (2022-12-25 revision a528908271) [x86_64-linux]
:start

real    0m11.026s
user    0m10.950s
sys     0m0.040s
```

This problem is not critical, but is there any room for improvement?



-- 
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