[ruby-core:123187] [Ruby Bug#19288] Ractor JSON parsing significantly slower than linear parsing

8 Sep 2025

      Issue #19288 has been updated by maciej.mensfeld (Maciej Mensfeld).

I can confirm significant performance improvements with the new Ractor APIs. I will now proceed to benchmark this against real Karafka user payloads. If the performance gains match what we're seeing in these synthetic benchmarks, I'll move forward with implementing a Ractor-based deserialization backend for Karafka. Amazing work!

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Bug #19288: Ractor JSON parsing significantly slower than linear parsing
https://bugs.ruby-lang.org/issues/19288#change-114518

* Author: maciej.mensfeld (Maciej Mensfeld)
* Status: Closed
* 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.

---Files--------------------------------
json_parse_float.rb (727 Bytes)
json_parse_string.rb (1.22 KB)

-- 
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