Improve performance of mergeLocaleMessage (#1099)

[cslee]

No description provided.

[codecov-io]

Codecov Report

Merging #1101 (8a8c774) into v8.x (4b34aa9) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             v8.x    #1101   +/-   ##
=======================================
  Coverage   96.49%   96.49%           
=======================================
  Files          10       10           
  Lines         913      913           
=======================================
  Hits          881      881           
  Misses         32       32           

Impacted Files	Coverage Δ
src/index.js	97.83% <100.00%> (ø)

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[exoego]

Thanks for PR 👍

Could you tell me how this change will improve performance when _vm.messages[locale] is undefined or empty object ?
This change introduce Object.keys, which seems to add extra execution time.

I also assume _vm.messages[locale] is likely to have several messages for many cases, so this change will degrade performance for many cases.

[cslee]

Hi exoego,

vue-i18n/src/index.js

Line 769 in 4b34aa9

this._vm.$set(this._vm.messages, locale, merge({}, this._vm.messages[locale] || {}, message))

With reference to the current logic, the merge call becomes either merge({}, this._vm.messages[locale], message) or merge({}, {}, message) when _vm.messages[locale] is defined or undefined respectively. The merge function loops the messages twice in both cases.

With this change, the messages will only be looped once.

Below simple test gives me the result as follows. The time difference will be greater when there are more messages.

const i18n = new VueI18n({
  locale: 'en',
  messages: {
    ja: { hello: 'world' }
  }
})

const start = process.hrtime()
for (let i = 0; i < 1000000; i++) {
  i18n.mergeLocaleMessage('en', { foo: 'bar' })
}
const end = process.hrtime(start)
console.log(end)

const start2 = process.hrtime()
for (let i = 0; i < 1000000; i++) {
  i18n.mergeLocaleMessage('ja', { foo: 'bar' })
}
const end2 = process.hrtime(start2)
console.log(end2)

// Before the change
// [ 2, 627509043 ]
// [ 3, 271436487 ]

// After the change
// [ 0, 600614057 ]
// [ 0, 417202963 ]

[exoego]

Thanks for explanation and quick benchmark.

The time difference will be greater when there are more messages.

Yes, this is exactly the case I am afraid in the previous comment: _vm.messages[locale] is likely to have several messages for many cases, so this change will degrade performance for many cases.

Could you tell more detail of your use case #1099, where mergeLocaleMessage is invoked over undefined or empty message ?

[cslee]

Thanks for your review.

The time difference will be greater when there are more messages.

Sorry for my vague statement, I meant the time difference (before and after the change) will be greater. So the improvement of this pull request will be greater when there are more messages to merge which should be the usual cases.

If I replace { foo: 'bar' } in above benchmark with an object of 10 keys. The result becomes:

// Before the change
// [ 10, 646949552 ]
// [ 11, 363784417 ]

// After the change
// [ 0, 882620796 ]
// [ 0, 689321051 ]

Could you tell more detail of your use case #1099, where mergeLocaleMessage is invoked over undefined or empty message ?

I just tried to improve the performance without logic change. The use case was introduced in #752 by another person and was released in version 8.15.3.

[kazupon]

@cslee
Thank you for your reporting!
I actually tried to check about performance.

The more locale messages, the more noticeable the performance degradation becomes.
This is a problem.
You can solve the performance degradation with PR.
Thanks! :)

[canjianx]

This change can let watch failed with Vue2.

[kazupon]

@cslee
Thank you for your reporting!
I actually tried to check about performance.

The more locale messages, the more noticeable the performance degradation becomes.
This is a problem.
You can solve the performance degradation with PR.
Thanks! :)