to_json in Rails project is not the same as JSON.generate or to_json in non-Rails project. See benchmarks Rails to_json + Oj.mimic_JSON vs No Rails to_json + Oj.mimic_JSON (below).
Comparing Rails to_json with other JSON implementations:
bundle exec ruby compatibility_test.rb
Comparing Rails to_json with other JSON implementations
+---------------------------------+--------------+---------+------------------+------------+-----------------+
| class | JSON to_json | Oj.dump | Oj::Rails.encode | Oj to_json | msgpack "rails" |
+---------------------------------+--------------+---------+------------------+------------+-----------------+
| Regexp | 👌 | 👌 | 👌 | 👌 | 👌 |
| FalseClass | 👌 | 👌 | 👌 | 👌 | 👌 |
| NilClass | 👌 | 👌 | 👌 | 👌 | 👌 |
| Object | ❌ | 👌 | 👌 | 👌 | 👌 |
| TrueClass | 👌 | 👌 | 👌 | 👌 | 👌 |
| String | 👌 | 👌 | 👌 | 👌 | 👌 |
| StringChinese | 👌 | 👌 | 👌 | 👌 | 👌 |
| StringSpecial | ❌ | 👌 | 👌 | 👌 | 👌 |
| StringSpecial2 | 👌 | 👌 | 👌 | 👌 | 👌 |
| StringSpecial3 | 👌 | 👌 | 👌 | 👌 | 👌 |
| Numeric | 👌 | 👌 | 👌 | 👌 | 👌 |
| Symbol | 👌 | 👌 | 👌 | 👌 | 👌 |
| Time | ❌ | 👌 | 👌 | 👌 | 👌 |
| Array | 👌 | 👌 | 👌 | 👌 | 👌 |
| Hash | 👌 | 👌 | 👌 | 👌 | 👌 |
| HashNotEmpty | 👌 | 👌 | 👌 | 👌 | 👌 |
| Date | 👌 | 👌 | 👌 | 👌 | 👌 |
| DateTime | ❌ | 👌 | 👌 | 👌 | 👌 |
| Enumerable | ❌ | 👌 | 👌 | 👌 | 👌 |
| BigDecimal | ❌ | 👌 | 👌 | 👌 | 👌 |
| BigDecimalInfinity | ❌ | 👌 | 👌 | 👌 | 👌 |
| Struct | ❌ | 👌 | 👌 | 👌 | 👌 |
| Float | 👌 | 👌 | 👌 | 👌 | 👌 |
| FloatInfinity | 💀 | 👌 | 👌 | 👌 | ❌ |
| Range | 👌 | 👌 | 👌 | 👌 | 👌 |
| Complex | 👌 | 👌 | 👌 | 👌 | 👌 |
| Exception | ❌ | 👌 | 👌 | 👌 | 👌 |
| OpenStruct | ❌ | 👌 | 👌 | 👌 | 👌 |
| Rational | 👌 | 👌 | 👌 | 👌 | 👌 |
| Process::Status | ❌ | 👌 | 👌 | 👌 | 👌 |
| ActiveSupport::TimeWithZone | ❌ | 👌 | 👌 | 👌 | 👌 |
| ActiveModel::Errors | ❌ | 👌 | 👌 | 👌 | 👌 |
| ActiveSupport::Duration | ❌ | 👌 | 👌 | 👌 | 👌 |
| ActiveSupport::Multibyte::Chars | ❌ | 👌 | 👌 | 👌 | 👌 |
| ActiveRecord::Relation | ❌ | 👌 | 👌 | 👌 | 👌 |
| ActiveRecord | ❌ | 👌 | 👌 | 👌 | 👌 |
+---------------------------------+--------------+---------+------------------+------------+-----------------+
Note: msgpack is not JSON, so comparing results of serialization + deserialization e.g.
ActiveSupport::JSON.decode(obj.to_json) vs MessagePack.unpack(obj.to_msgpack)See comparison across Ruby/Rails version in test_report.txt. Report was generated with command: wwtd &> test_report.txt.
Tests based on as_json implementations.
See also:
Calculating -------------------------------------
to_json: 340.131M memsize ( 168.000 retained)
6.660M objects ( 2.000 retained)
50.000 strings ( 0.000 retained)
Oj.dump o 55.880M memsize ( 0.000 retained)
990.000k objects ( 0.000 retained)
38.000 strings ( 0.000 retained)
Oj.dump c 55.880M memsize ( 0.000 retained)
990.000k objects ( 0.000 retained)
38.000 strings ( 0.000 retained)
Oj.dump c, aj 55.880M memsize ( 0.000 retained)
990.000k objects ( 0.000 retained)
38.000 strings ( 0.000 retained)
Comparison:
Oj.dump c, aj: 55880000 allocated
Oj.dump o: 55880000 allocated - same
Oj.dump c: 55880000 allocated - same
to_json:: 340130720 allocated - 6.09x more
---------------------------------------------
user system total real
to_json: 2.810000 0.170000 2.980000 ( 3.048407)
Oj.dump o 0.630000 0.020000 0.650000 ( 0.666360)
Oj.dump c 0.440000 0.010000 0.450000 ( 0.459752)
Oj.dump c, aj 0.530000 0.020000 0.550000 ( 0.554771)
bundle exec ruby benchmark1.rb
Calculating -------------------------------------
to_json: 18.730M memsize ( 0.000 retained)
270.000k objects ( 0.000 retained)
3.000 strings ( 0.000 retained)
JSON: 2.970M memsize ( 0.000 retained)
20.000k objects ( 0.000 retained)
1.000 strings ( 0.000 retained)
Oj: 2.970M memsize ( 0.000 retained)
20.000k objects ( 0.000 retained)
1.000 strings ( 0.000 retained)
Comparison:
Oj:: 2970000 allocated
JSON:: 2970000 allocated - same
to_json:: 18730000 allocated - 6.31x more <---- PAY ATTENTION
---------------------------------------------
user system total real
to_json: 0.080000 0.000000 0.080000 ( 0.079702)
JSON: 0.010000 0.000000 0.010000 ( 0.012702)
Oj: 0.020000 0.000000 0.020000 ( 0.015271)
bundle exec ruby benchmark1.rb
Calculating -------------------------------------
to_json: 2.970M memsize ( 0.000 retained)
20.000k objects ( 0.000 retained)
1.000 strings ( 0.000 retained)
JSON: 2.970M memsize ( 0.000 retained)
20.000k objects ( 0.000 retained)
1.000 strings ( 0.000 retained)
Oj: 2.970M memsize ( 0.000 retained)
20.000k objects ( 0.000 retained)
1.000 strings ( 0.000 retained)
Comparison:
to_json:: 2970000 allocated
JSON:: 2970000 allocated - same
Oj:: 2970000 allocated - same
---------------------------------------------
user system total real
to_json: 0.020000 0.000000 0.020000 ( 0.014124)
JSON: 0.020000 0.010000 0.030000 ( 0.024667)
Oj: 0.020000 0.000000 0.020000 ( 0.028081)