From: merch-redmine@...
Date: 2021-06-16T14:52:29+00:00
Subject: [ruby-core:104309] [Ruby master Bug#16840] Decrease in Hash#[]= performance with object keys

Issue #16840 has been updated by jeremyevans0 (Jeremy Evans).

Status changed from Open to Closed

Apparently this case was optimized in Ruby 3.0.  Using the benchmark code provided:

```
$ for x in 25 26 27 30; do ruby$x -v; for y in 1 2 3; do ruby$x t/t51.rb; done; done
ruby 2.5.9p229 (2021-04-05 revision 67939) [x86_64-openbsd]
 10.040000   0.010000  10.050000 ( 10.045536)
  9.970000   0.010000   9.980000 (  9.995454)
 10.170000   0.000000  10.170000 ( 10.180147)
ruby 2.6.7p197 (2021-04-05 revision 67941) [x86_64-openbsd]
  9.340000   0.000000   9.340000 (  9.326443)
  9.420000   0.010000   9.430000 (  9.425656)
  9.300000   0.020000   9.320000 (  9.327280)
ruby 2.7.3p183 (2021-04-05 revision 6847ee089d) [x86_64-openbsd]
 10.790000   0.020000  10.810000 ( 10.809778)
 10.840000   0.020000  10.860000 ( 10.866930)
 10.820000   0.010000  10.830000 ( 10.852136)
ruby 3.0.1p64 (2021-04-05 revision 0fb782ee38) [x86_64-openbsd]
  4.780000   0.020000   4.800000 (  4.798934)
  4.760000   0.020000   4.780000 (  4.770590)
  4.720000   0.050000   4.770000 (  4.774958)
```

Possibly due to commit:5f6053824551aec947a1c53d08975595aca1e513, which changed from an else if chain to a switch, but I didn't confirm that.  Anyway, since it's now much faster than before, I think this can be closed.

----------------------------------------
Bug #16840: Decrease in Hash#[]= performance with object keys
https://bugs.ruby-lang.org/issues/16840#change-92531

* Author: ana06 (Ana Maria Martinez Gomez)
* Status: Closed
* Priority: Normal
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
----------------------------------------
I was playing around with Ruby hashing and I have discovered something strange/surprising.

The file ``test.rb`` looks like:

```ruby

require 'benchmark'
$N = 100000

class Ana 
end

objects = Array.new($N) { Ana.new() }
hash = {}
puts Benchmark.measure { 100.times { objects.each { |obj| hash[obj] = true } }}
```

I executed ``test.rb`` with different Ruby versions and it takes longer with newer versions. There is 1.5 seconds difference between Ruby 2.5 and master. Is that expected? And if so, why? Those are the execution results:

```
> rbenv shell 2.5.0
> ruby -v
ruby 2.5.0p0 (2017-12-25 revision 61468) [x86_64-linux]
> ruby test.rb
  2.236504   0.003546   2.240050 (  2.240256)
> ruby test.rb
  2.247041   0.003680   2.250721 (  2.250860)
> ruby test.rb
  2.276305   0.000351   2.276656 (  2.276829)
>�
> rbenv shell 2.6.2
> ruby -v
ruby 2.6.2p47 (2019-03-13 revision 67232) [x86_64-linux]
> ruby test.rb
  2.579052   0.004181   2.583233 (  2.583541)
> ruby test.rb
  2.580179   0.000000   2.580179 (  2.580362)
> ruby test.rb
  2.646516   0.000441   2.646957 (  2.647398)
>�
> rbenv shell 2.7.1
> ruby -v
ruby 2.7.1p83 (2020-03-31 revision a0c7c23c9c) [x86_64-linux]
> ruby test.rb
  2.915415   0.004209   2.919624 (  2.920206)
> ruby test.rb
  2.867767   0.007511   2.875278 (  2.875416)
> ruby test.rb
  2.877741   0.000410   2.878151 (  2.878431)
>�
> rbenv shell 2.8.0-dev
> ruby -v
ruby 2.8.0dev (2020-05-07T16:22:38Z master 7ded8fd29a) [x86_64-linux]
> ruby test.rb
  3.840961   0.007852   3.848813 (  3.849499)
> ruby test.rb
  3.748391   0.007833   3.756224 (  3.756520)
> ruby test.rb
  3.686487   0.001656   3.688143 (  3.688332)
```




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