Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

Webpack 5 triggers a slow V8 concat path resulting in significant performance degradation in some scenarios #14580

Closed
eoin opened this issue Oct 27, 2021 · 4 comments · Fixed by #14653
Closed

Webpack 5 triggers a slow V8 concat path resulting in significant performance degradation in some scenarios #14580

eoin opened this issue Oct 27, 2021 · 4 comments · Fixed by #14653
Labels
enhancement webpack-5

Comments

@eoin
Copy link

eoin commented Oct 27, 2021

Early in Webpack 5 development the arrayToSetDeprecation helper was added to support migrating some objects from Array to Set. In order to maintain Array-like behaviour in concat the helper sets Symbol.isConcatSpreadable. On V8, setting Symbol.isConcatSpreadable anywhere puts all subsequent invocations of concat within an Isolate on a slow path.

There are cases where this can result in significant performance degradation. In this repro case, builds go from 1s with Webpack 4 to 16s with Webpack 5. We came across this when debugging this Linaria issue, where our production build slowed from ~10s to 2m+. I wonder if this could be the cause of some issues in #12102.
@sokra
Copy link
Member

sokra commented Oct 27, 2021

Oh interesting...

I wanted to add an option to opt out of deprecations anyway. Something like experiments.webpack4Compat: false. And they will be removed in webpack 6. So another reason to release that sooner than later...

@sokra sokra mentioned this issue Nov 5, 2021
Merged
@alan-agius4 alan-agius4 mentioned this issue Nov 9, 2021
Merged
dgp1130 pushed a commit to angular/angular-cli that referenced this issue Nov 17, 2021
@alan-agius4 @dgp1130
perf(@angular-devkit/build-angular): disable webpack backwards compat…
789ddfa 
…ible APIs

See https://github.com/webpack/webpack/releases/tag/v5.62.0 and webpack/webpack#14580 for more context.
@eoin
Copy link
Author

eoin commented Nov 18, 2021 •
edited

For anyone who might be interested we did a writeup of how we tracked down this issue.

@zloirock
Copy link

zloirock commented Nov 20, 2021 •
edited

@eoin deprecated versions of core-js (version < 3.3) cause the same problems, now about 20-25% (a little obsolete results of naive detection) of TOP 10000 websites use those deprecated core-js versions. It's @@isConcatSpreadable and (mainly) @@species feature detection, even without polyfilling. Workarounds of those V8 whims were added 2+ years ago, but who read deprecation notes?

image

@lior-frezi
Copy link

@eoin deprecated versions of core-js (version < 3.3) cause the same problems, now about 20-25% (a little obsolete results of naive detection) of TOP 10000 websites use those deprecated core-js versions. It's @@isConcatSpreadable and (mainly) @@species feature detection, even without polyfilling. Workarounds of those V8 whims were added 2+ years ago, but who read deprecation notes?

image

So helpful. Our website had a lot of [].concat([...]) on loading from initiating some old validations. replacing old core-js speed up the runtime by a LOT.

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
Assignees
No one assigned
Labels
enhancement webpack-5
Projects
None yet
Milestone
No milestone
Development

Successfully merging a pull request may close this issue.

allow to disable some deprecations webpack/webpack
5 participants
@eoin @sokra @zloirock @webpack-bot @lior-frezi