[ruby-core:112000] [Ruby master Bug#19288] Ractor JSON parsing significantly slower than linear parsing

24 Jan 2023

      Issue #19288 has been updated by luke-gru (Luke Gruber).

```ruby
RACTORS = ARGV.first == "ractor"
r = rand
J = { rand => rand }.to_json
Ractor.make_shareable(J)
if RACTORS
  rs = []
  10.times.each do
    rs << Ractor.new(r) do |num|
      data = receive()
      i = 0
      while i < 10_000
        JSON.parse(data)
        i+=1
      end
    end
  end
  rs.each do |r|
    r.send(J)
  end
  rs.each(&:take)
else
  1_000_000.times do
    JSON.parse(J)
  end
end
```

$ time ./ruby json_test.rb
real	0m5.622s
user	0m5.396s

$ time ./ruby json_test.rb ractor
real	0m0.890s
user	0m0.798s

This is with debug build of ruby too, so should be faster, but this shows that the issue is with the large data being sent with Ractor#send. Chunk the data into smaller pieces (more calls send and receive in a loop) and it will be faster.

----------------------------------------
Bug #19288: Ractor JSON parsing significantly slower than linear parsing
https://bugs.ruby-lang.org/issues/19288#change-101434

* Author: maciej.mensfeld (Maciej Mensfeld)
* Status: Open
* Priority: Normal
* 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/