[ruby-core:120932] [Ruby master Bug#19288] Ractor JSON parsing significantly slower than linear parsing

10 Feb 2025

      Issue #19288 has been updated by Eregon (Benoit Daloze).

tenderlovemaking (Aaron Patterson) wrote in #note-17:
...
We could also add an fstring table to each Ractor [...] but at least we would be limited to the number of Ractors
The number of Ractors can be high though since M-N threads.
Also one might rely that the result of `String#-@` is always the same object for equivalent strings, even across Ractors.
Concretely this means a string that is interned in one Ractor won't be interned in another Ractor, that seems surprising.

(FWIW TruffleRuby solves this using a ConcurrentHashMap with weak values)

----------------------------------------
Bug #19288: Ractor JSON parsing significantly slower than linear parsing
https://bugs.ruby-lang.org/issues/19288#change-111823

* Author: maciej.mensfeld (Maciej Mensfeld)
* Status: Open
* ruby -v: ruby 3.2.0 (2022-12-25 revision a528908271) [x86_64-linux]
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN
----------------------------------------
a simple benchmark:

```ruby
require 'json'
require 'benchmark'

CONCURRENT = 5
RACTORS = true
ELEMENTS = 100_000

data = CONCURRENT.times.map do
  ELEMENTS.times.map do
    {
      rand => rand,
      rand => rand,
      rand => rand,
      rand => rand
    }.to_json
  end
end

ractors = CONCURRENT.times.map do
  Ractor.new do
    Ractor.receive.each { JSON.parse(_1) }
  end
end

result = Benchmark.measure do
  if RACTORS
    CONCURRENT.times do |i|
      ractors[i].send(data[i], move: false)
    end

    ractors.each(&:take)
  else
    # Linear without any threads
    data.each do |piece|
      piece.each { JSON.parse(_1) }
    end
  end
end

puts result
```

Gives following results on my 8 core machine:

```shell
# without ractors:
  2.731748   0.003993   2.735741 (  2.736349)

# with ractors
12.580452   5.089802  17.670254 (  5.209755)
```
I would expect Ractors not to be two times slower on the CPU intense work.

-- 
https://bugs.ruby-lang.org/