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perf: monomorfic variables#801

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cesco69:monomorfic-variables
Jan 9, 2026
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perf: monomorfic variables#801
mcollina merged 3 commits intofastify:mainfrom
cesco69:monomorfic-variables

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@cesco69 cesco69 commented Oct 8, 2025 •
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Monomorphic: If a property always gets the same class shape.

It'a a good performance improvments on Array and Object, but not on primitive types

image

Raw benchmark

Checking out "remotes/origin/monomorfic-variables"
Execute "npm run bench"

> fast-json-stringify@6.1.1 bench
> node ./benchmark/bench.js

short string............................................. x 22,911,344 ops/sec ±4.53% (162 runs sampled)
unsafe short string...................................... x 73,650,931 ops/sec ±5.05% (144 runs sampled)
short string with double quote........................... x 9,470,207 ops/sec ±2.16% (150 runs sampled)
long string without double quotes........................ x 36,234 ops/sec ±1.78% (160 runs sampled)
unsafe long string without double quotes................. x 75,229,690 ops/sec ±4.33% (150 runs sampled)
long string.............................................. x 32,157 ops/sec ±2.33% (169 runs sampled)
unsafe long string....................................... x 66,281,516 ops/sec ±4.12% (156 runs sampled)
number................................................... x 75,618,262 ops/sec ±5.33% (140 runs sampled)
integer.................................................. x 57,630,179 ops/sec ±3.43% (140 runs sampled)
formatted date-time...................................... x 690,716 ops/sec ±2.03% (154 runs sampled)
formatted date........................................... x 630,836 ops/sec ±2.90% (152 runs sampled)
formatted time........................................... x 600,154 ops/sec ±2.42% (153 runs sampled)
short array of numbers................................... x 40,187 ops/sec ±1.25% (159 runs sampled)
short array of integers.................................. x 42,814 ops/sec ±2.64% (164 runs sampled)
short array of short strings............................. x 14,476 ops/sec ±4.01% (174 runs sampled)
short array of long strings.............................. x 13,235 ops/sec ±2.99% (161 runs sampled)
short array of objects with properties of different types x 5,675 ops/sec ±2.49% (158 runs sampled)
object with number property.............................. x 91,517,822 ops/sec ±6.67% (152 runs sampled)
object with integer property............................. x 84,343,207 ops/sec ±5.90% (178 runs sampled)
object with short string property........................ x 25,917,292 ops/sec ±1.44% (189 runs sampled)
object with long string property......................... x 47,750 ops/sec ±0.87% (192 runs sampled)
object with properties of different types................ x 1,638,590 ops/sec ±2.34% (183 runs sampled)
simple object............................................ x 9,364,675 ops/sec ±1.50% (185 runs sampled)
simple object with required fields....................... x 9,364,717 ops/sec ±1.52% (184 runs sampled)
object with const string property........................ x 119,169,683 ops/sec ±4.21% (171 runs sampled)
object with const number property........................ x 118,606,339 ops/sec ±4.47% (170 runs sampled)
object with const bool property.......................... x 111,100,119 ops/sec ±4.81% (166 runs sampled)
object with const object property........................ x 118,926,898 ops/sec ±4.21% (172 runs sampled)
object with const null property.......................... x 107,150,234 ops/sec ±5.15% (168 runs sampled)

Checking out "master"
Execute "npm run bench"

> fast-json-stringify@6.1.1 bench
> node ./benchmark/bench.js

short string............................................. x 24,388,745 ops/sec ±2.12% (183 runs sampled)
unsafe short string...................................... x 84,244,363 ops/sec ±6.69% (148 runs sampled)
short string with double quote........................... x 9,644,133 ops/sec ±3.14% (155 runs sampled)
long string without double quotes........................ x 41,509 ops/sec ±4.43% (170 runs sampled)
unsafe long string without double quotes................. x 105,877,016 ops/sec ±5.25% (162 runs sampled)
long string.............................................. x 48,014 ops/sec ±1.04% (194 runs sampled)
unsafe long string....................................... x 117,193,911 ops/sec ±5.03% (169 runs sampled)
number................................................... x 106,082,837 ops/sec ±5.85% (159 runs sampled)
integer.................................................. x 100,649,516 ops/sec ±4.47% (172 runs sampled)
formatted date-time...................................... x 1,249,090 ops/sec ±1.22% (191 runs sampled)
formatted date........................................... x 669,947 ops/sec ±4.04% (152 runs sampled)
formatted time........................................... x 587,616 ops/sec ±0.73% (188 runs sampled)
short array of numbers................................... x 38,787 ops/sec ±1.61% (155 runs sampled)
short array of integers.................................. x 39,458 ops/sec ±2.21% (154 runs sampled)
short array of short strings............................. x 12,415 ops/sec ±2.22% (156 runs sampled)
short array of long strings.............................. x 12,322 ops/sec ±1.40% (155 runs sampled)
short array of objects with properties of different types x 5,810 ops/sec ±1.93% (154 runs sampled)
object with number property.............................. x 66,543,631 ops/sec ±5.88% (145 runs sampled)
object with integer property............................. x 58,760,516 ops/sec ±4.69% (142 runs sampled)
object with short string property........................ x 14,679,314 ops/sec ±2.50% (148 runs sampled)
object with long string property......................... x 39,914 ops/sec ±3.19% (183 runs sampled)
object with properties of different types................ x 1,576,563 ops/sec ±2.94% (162 runs sampled)
simple object............................................ x 8,133,777 ops/sec ±2.20% (180 runs sampled)
simple object with required fields....................... x 8,273,155 ops/sec ±2.32% (176 runs sampled)
object with const string property........................ x 109,001,760 ops/sec ±5.33% (164 runs sampled)
object with const number property........................ x 108,746,170 ops/sec ±5.35% (166 runs sampled)
object with const bool property.......................... x 103,566,758 ops/sec ±6.00% (159 runs sampled)
object with const object property........................ x 112,981,394 ops/sec ±4.63% (167 runs sampled)
object with const null property.......................... x 115,251,679 ops/sec ±4.77% (168 runs sampled)

short string..............................................-6.06%
unsafe short string......................................-12.57%
short string with double quote.............................-1.8%
long string without double quotes........................-12.71%
unsafe long string without double quotes.................-28.95%
long string..............................................-33.03%
unsafe long string.......................................-43.44%
number...................................................-28.72%
integer..................................................-42.74%
formatted date-time.......................................-44.7%
formatted date............................................-5.84%
formatted time............................................+2.13%
short array of numbers....................................+3.61%
short array of integers...................................+8.51%
short array of short strings..............................+16.6%
short array of long strings...............................+7.41%
short array of objects with properties of different types.-2.32%
object with number property..............................+37.53%
object with integer property.............................+43.54%
object with short string property........................+76.56%
object with long string property.........................+19.63%
object with properties of different types.................+3.93%
simple object............................................+15.13%
simple object with required fields.......................+13.19%
object with const string property.........................+9.33%
object with const number property.........................+9.07%
object with const bool property...........................+7.27%
object with const object property.........................+5.26%
object with const null property...........................-7.03%
Back to master 2b37f1d

cesco69 added 2 commits October 8, 2025 11:02
@cesco69
perf: monomorfic variables
003a4cf 
Signed-off-by: francesco <francesco.bagnoli.69@gmail.com>
@cesco69
fix: make const
d433cda 
Signed-off-by: francesco <francesco.bagnoli.69@gmail.com>
@cesco69 cesco69 marked this pull request as ready for review October 8, 2025 09:26
Uzlopak
Uzlopak reviewed Oct 8, 2025
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@cesco69
fix: avoid collision
ca9dbc7 
Signed-off-by: francesco <francesco.bagnoli.69@gmail.com>
@cesco69 cesco69 requested a review from Uzlopak October 8, 2025 15:49
mcollina
mcollina approved these changes Oct 8, 2025
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lgtm

@Uzlopak
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Uzlopak commented Oct 8, 2025

I have no opinion on this, but it feels strange, that primitives drop by nearly 50 %.

@cesco69 cesco69 marked this pull request as draft October 9, 2025 07:08
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cesco69 commented Oct 9, 2025

I have no opinion on this, but it feels strange, that primitives drop by nearly 50 %.

Yep, this PR is not good. I want try to fix primitive type

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cesco69 commented Oct 9, 2025 •
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I’ve a bad news.

TLTR: the benchmark is not reliable

I was trying to understand why primitive types performed worse than objects in my PR, but I realized that on primitive types the code of the stringify method is the same (PR and Master),

eg, see this benchmark case https://github.com/fastify/fast-json-stringify/blob/main/benchmark/bench.js#L44

This schema

{
  "type": "string"
}

generate in both case (master and PR), this code:

module.exports = function anonymous(validator, serializer
) {

  const {
    asString,
    asNumber,
    asBoolean,
    asDateTime,
    asDate,
    asTime,
    asUnsafeString
  } = serializer

  const asInteger = serializer.asInteger.bind(serializer)


  const JSON_STR_BEGIN_OBJECT = '{'
  const JSON_STR_END_OBJECT = '}'
  const JSON_STR_BEGIN_ARRAY = '['
  const JSON_STR_END_ARRAY = ']'
  const JSON_STR_COMMA = ','
  const JSON_STR_COLONS = ':'
  const JSON_STR_QUOTE = '"'
  const JSON_STR_EMPTY_OBJECT = JSON_STR_BEGIN_OBJECT + JSON_STR_END_OBJECT
  const JSON_STR_EMPTY_ARRAY = JSON_STR_BEGIN_ARRAY + JSON_STR_END_ARRAY
  const JSON_STR_EMPTY_STRING = JSON_STR_QUOTE + JSON_STR_QUOTE
  const JSON_STR_NULL = 'null'

  function main(input) {
    let json = ''

    if (typeof input !== 'string') {
      if (input === null) {
        json += JSON_STR_EMPTY_STRING
      } else if (input instanceof Date) {
        json += JSON_STR_QUOTE + input.toISOString() + JSON_STR_QUOTE
      } else if (input instanceof RegExp) {
        json += asString(input.source)
      } else {
        json += asString(input.toString())
      }
    } else {
      json += asString(input)
    }

    return json
  }

  return main

}(validator, serializer)

The same code had to give the same results... so I decided to benchmark master vs master to see if I got the same results

image 

Checking out "master"
Execute "npm run bench"

> fast-json-stringify@6.1.1 bench
> node ./benchmark/bench.js

short string............................................. x 25,906,545 ops/sec ±2.29% (183 runs sampled)
unsafe short string...................................... x 117,503,246 ops/sec ±5.48% (165 runs sampled)
short string with double quote........................... x 16,994,413 ops/sec ±1.85% (187 runs sampled)
long string without double quotes........................ x 58,221 ops/sec ±1.35% (193 runs sampled)
unsafe long string without double quotes................. x 123,399,562 ops/sec ±5.09% (166 runs sampled)
long string.............................................. x 45,787 ops/sec ±2.68% (190 runs sampled)
unsafe long string....................................... x 107,531,043 ops/sec ±5.14% (161 runs sampled)
number................................................... x 115,566,825 ops/sec ±5.00% (163 runs sampled)
integer.................................................. x 99,205,667 ops/sec ±4.17% (170 runs sampled)
formatted date-time...................................... x 1,026,106 ops/sec ±3.43% (179 runs sampled)
formatted date........................................... x 967,191 ops/sec ±3.49% (184 runs sampled)
formatted time........................................... x 1,117,047 ops/sec ±1.31% (193 runs sampled)
short array of numbers................................... x 71,463 ops/sec ±1.94% (186 runs sampled)
short array of integers.................................. x 63,587 ops/sec ±2.36% (183 runs sampled)
short array of short strings............................. x 21,564 ops/sec ±2.08% (188 runs sampled)
short array of long strings.............................. x 20,146 ops/sec ±3.08% (176 runs sampled)
short array of objects with properties of different types x 10,665 ops/sec ±1.43% (186 runs sampled)
object with number property.............................. x 117,962,939 ops/sec ±5.60% (168 runs sampled)
object with integer property............................. x 108,928,099 ops/sec ±3.71% (175 runs sampled)
object with short string property........................ x 27,080,635 ops/sec ±1.51% (188 runs sampled)
object with long string property......................... x 49,784 ops/sec ±1.14% (192 runs sampled)
object with properties of different types................ x 1,719,671 ops/sec ±3.24% (183 runs sampled)
simple object............................................ x 10,356,645 ops/sec ±0.91% (188 runs sampled)
simple object with required fields....................... x 10,100,139 ops/sec ±1.65% (187 runs sampled)
object with const string property........................ x 124,866,455 ops/sec ±4.99% (172 runs sampled)
object with number property.............................. x 117,962,939 ops/sec ±5.60% (168 runs sampled)
object with integer property............................. x 108,928,099 ops/sec ±3.71% (175 runs sampled)
object with short string property........................ x 27,080,635 ops/sec ±1.51% (188 runs sampled)
object with long string property......................... x 49,784 ops/sec ±1.14% (192 runs sampled)
object with properties of different types................ x 1,719,671 ops/sec ±3.24% (183 runs sampled)
simple object............................................ x 10,356,645 ops/sec ±0.91% (188 runs sampled)
simple object with required fields....................... x 10,100,139 ops/sec ±1.65% (187 runs sampled)
object with const string property........................ x 124,866,455 ops/sec ±4.99% (172 runs sampled)
object with const number property........................ x 123,480,168 ops/sec ±4.87% (172 runs sampled)
object with integer property............................. x 108,928,099 ops/sec ±3.71% (175 runs sampled)
object with short string property........................ x 27,080,635 ops/sec ±1.51% (188 runs sampled)
object with long string property......................... x 49,784 ops/sec ±1.14% (192 runs sampled)
object with properties of different types................ x 1,719,671 ops/sec ±3.24% (183 runs sampled)
simple object............................................ x 10,356,645 ops/sec ±0.91% (188 runs sampled)
simple object with required fields....................... x 10,100,139 ops/sec ±1.65% (187 runs sampled)
object with const string property........................ x 124,866,455 ops/sec ±4.99% (172 runs sampled)
object with const number property........................ x 123,480,168 ops/sec ±4.87% (172 runs sampled)
object with long string property......................... x 49,784 ops/sec ±1.14% (192 runs sampled)
object with properties of different types................ x 1,719,671 ops/sec ±3.24% (183 runs sampled)
simple object............................................ x 10,356,645 ops/sec ±0.91% (188 runs sampled)
simple object with required fields....................... x 10,100,139 ops/sec ±1.65% (187 runs sampled)
object with const string property........................ x 124,866,455 ops/sec ±4.99% (172 runs sampled)
object with const number property........................ x 123,480,168 ops/sec ±4.87% (172 runs sampled)
simple object............................................ x 10,356,645 ops/sec ±0.91% (188 runs sampled)
simple object with required fields....................... x 10,100,139 ops/sec ±1.65% (187 runs sampled)
object with const string property........................ x 124,866,455 ops/sec ±4.99% (172 runs sampled)
object with const number property........................ x 123,480,168 ops/sec ±4.87% (172 runs sampled)
object with const string property........................ x 124,866,455 ops/sec ±4.99% (172 runs sampled)
object with const number property........................ x 123,480,168 ops/sec ±4.87% (172 runs sampled)
object with const number property........................ x 123,480,168 ops/sec ±4.87% (172 runs sampled)
object with const bool property.......................... x 110,656,949 ops/sec ±5.57% (170 runs sampled)
object with const object property........................ x 121,682,299 ops/sec ±4.89% (166 runs sampled)
object with const null property.......................... x 115,386,130 ops/sec ±4.61% (167 runs sampled)

Checking out "master"
Execute "npm run bench"

> fast-json-stringify@6.1.1 bench
> node ./benchmark/bench.js

short string............................................. x 25,309,923 ops/sec ±2.39% (180 runs sampled)
unsafe short string...................................... x 95,582,481 ops/sec ±6.63% (157 runs sampled)
short string with double quote........................... x 16,337,301 ops/sec ±2.08% (182 runs sampled)
long string without double quotes........................ x 52,829 ops/sec ±2.25% (182 runs sampled)
unsafe long string without double quotes................. x 113,528,713 ops/sec ±4.57% (166 runs sampled)
long string.............................................. x 46,067 ops/sec ±1.92% (183 runs sampled)
unsafe long string....................................... x 107,277,481 ops/sec ±6.01% (152 runs sampled)
number................................................... x 107,642,408 ops/sec ±5.38% (159 runs sampled)
integer.................................................. x 93,384,162 ops/sec ±4.77% (164 runs sampled)
formatted date-time...................................... x 1,125,076 ops/sec ±2.66% (182 runs sampled)
formatted date........................................... x 901,179 ops/sec ±2.94% (176 runs sampled)
formatted time........................................... x 903,817 ops/sec ±3.39% (182 runs sampled)
short array of numbers................................... x 59,918 ops/sec ±3.20% (175 runs sampled)
short array of integers.................................. x 54,251 ops/sec ±3.20% (168 runs sampled)
short array of short strings............................. x 17,364 ops/sec ±3.48% (173 runs sampled)
short array of long strings.............................. x 17,580 ops/sec ±3.18% (174 runs sampled)
short array of objects with properties of different types x 8,326 ops/sec ±4.31% (173 runs sampled)
object with number property.............................. x 92,969,503 ops/sec ±5.93% (155 runs sampled)
object with integer property............................. x 91,242,327 ops/sec ±4.87% (166 runs sampled)
object with short string property........................ x 22,060,252 ops/sec ±3.22% (170 runs sampled)
object with long string property......................... x 38,606 ops/sec ±3.67% (172 runs sampled)
object with properties of different types................ x 1,671,650 ops/sec ±2.98% (172 runs sampled)
simple object............................................ x 8,164,079 ops/sec ±3.10% (183 runs sampled)
simple object with required fields....................... x 7,888,268 ops/sec ±4.11% (161 runs sampled)
object with const string property........................ x 106,484,075 ops/sec ±5.97% (166 runs sampled)
object with const number property........................ x 114,081,367 ops/sec ±5.23% (162 runs sampled)
object with const bool property.......................... x 105,516,771 ops/sec ±5.75% (156 runs sampled)
object with const object property........................ x 101,331,208 ops/sec ±4.76% (161 runs sampled)
object with const null property.......................... x 103,993,101 ops/sec ±4.73% (159 runs sampled)

short string..............................................+2.36%
unsafe short string......................................+22.93%
short string with double quote............................+4.02%
long string without double quotes........................+10.21%
unsafe long string without double quotes..................+8.69%
long string...............................................-0.61%
unsafe long string........................................+0.24%
number....................................................+7.36%
integer...................................................+6.23%
formatted date-time........................................-8.8%
formatted date............................................+7.33%
formatted time...........................................+23.59%
short array of numbers...................................+19.27%
short array of integers..................................+17.21%
short array of short strings.............................+24.19%
short array of long strings...............................+14.6%
short array of objects with properties of different types+28.09%
object with number property..............................+26.88%
object with integer property.............................+19.38%
object with short string property........................+22.76%
object with long string property.........................+28.95%
object with properties of different types.................+2.87%
simple object............................................+26.86%
simple object with required fields.......................+28.04%
object with const string property........................+17.26%
object with const number property.........................+8.24%
object with const bool property...........................+4.87%
object with const object property........................+20.08%
object with const null property..........................+10.96%
Back to master 2b37f1d

instead, even if I compared the same branch, I got the result that the second run was better than the first one!
I have the impression that the garbage collector give an advantage to the second branch to be executed,

We need a more reliable benchmark to accept PR on performance like this one (see #803).

This was referenced Oct 9, 2025
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@cesco69 cesco69 marked this pull request as ready for review January 9, 2026 15:10
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cesco69 commented Jan 9, 2026

NB: Before accepting, we need a more precise benchmark. see #803

@mcollina mcollina merged commit 78b6368 into fastify:main Jan 9, 2026
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