parser_json: use JSON as fallback parser instead of Yajl for performance

[Watson1978]

Which issue(s) this PR fixes:
Fixes #

What this PR does / why we need it:
Recently, Ruby's json has incredible performance improvements.
It might be faster than oj gem.
So, I think json is a suitable as fallback.

This is similar with #4759

Here is easily benchmark. (I used same log file in #4759)

• Before

  • It spent 90.50963662 sec to handle 10 GB file

• After

  • It spent 74.624230077 sec to handle 10 GB file

• config

<source>
  @type tail
  path "#{File.expand_path '~/tmp/access*.log'}"
  pos_file "#{File.expand_path '~/tmp/fluentd/access.log.pos'}"
  tag log
  read_from_head true
  <parse>
    @type json
  </parse>
</source>

<match **>
  @type file
  path "#{File.expand_path '~/tmp/fluentd/log'}"
</match>

FYI)

• https://byroot.github.io/ruby/json/2024/12/15/optimizing-ruby-json-part-1.html
• https://byroot.github.io/ruby/json/2024/12/18/optimizing-ruby-json-part-2.html
• https://byroot.github.io/ruby/json/2024/12/27/optimizing-ruby-json-part-3.html
• https://byroot.github.io/ruby/json/2024/12/29/optimizing-ruby-json-part-4.html
• https://byroot.github.io/ruby/json/2025/01/04/optimizing-ruby-json-part-5.html
• https://byroot.github.io/ruby/json/2025/01/12/optimizing-ruby-json-part-6.html
• https://byroot.github.io/ruby/json/2025/01/14/optimizing-ruby-json-part-7.html

Docs Changes:
fluent/fluentd-docs-gitbook#560

Release Note:

[kenhys]

we are happy if we could observe micro benchmark result.

[Watson1978]

Micro benchmark

benchmark code

require 'bundler/inline'
gemfile do
  source 'https://rubygems.org'
  gem 'benchmark-ips'
  gem 'oj'
  gem 'json'
  gem 'yajl-ruby', require: 'yajl'
end

Benchmark.ips do |x|
  json = '{"a":"Alpha","b":true,"c":12345,"d":[true,[false,[-123456789,null],3.9676,["Something else.",false],null]],"e":{"zero":null,"one":1,"two":2,"three":[3],"four":[0,1,2,3,4]},"f":null,"h":{"a":{"b":{"c":{"d":{"e":{"f":{"g":null}}}}}}},"i":[[[[[[[null]]]]]]]}'

  x.report('Oj.load') { Oj.load(json) }
  x.report('JSON.load') { JSON.load(json) }
  x.report('Yajl.load') { Yajl.load(json) }

  x.compare!
end

result

ruby 3.4.1 (2024-12-25 revision 48d4efcb85) +PRISM [x86_64-linux]
Warming up --------------------------------------
             Oj.load    31.383k i/100ms
           JSON.load    35.513k i/100ms
           Yajl.load    13.839k i/100ms
Calculating -------------------------------------
             Oj.load    319.187k (± 1.5%) i/s    (3.13 μs/i) -      1.601M in   5.015522s
           JSON.load    364.950k (± 0.5%) i/s    (2.74 μs/i) -      1.847M in   5.060214s
           Yajl.load    137.015k (± 2.5%) i/s    (7.30 μs/i) -    691.950k in   5.053679s

Comparison:
           JSON.load:   364950.5 i/s
             Oj.load:   319187.1 i/s - 1.14x  slower
           Yajl.load:   137015.2 i/s - 2.66x  slower

[kenhys]

By the way, which json gem version did you tested with?
Do we need to use specific version of json gem?

[Watson1978]

By the way, which json gem version did you tested with? Do we need to use specific version of json gem?

I tested with json v2.9.1 (latest version), it is default version in Ruby 3.4.1
https://github.com/ruby/ruby/blob/master/doc/NEWS/NEWS-3.4.0.md

If we will use Ruby 3.4 or later in the next fluent-package LTS, hmmm, I think we don't need to specify the version...

[byroot]

You probably want JSON.method(:parse): https://bugs.ruby-lang.org/issues/19528

It's also very marginally faster.

[Watson1978]

Thanks.