Rebuild should be shorter because the lazy chunks have not changed

[doggy8088]

🐞 Bug report

Command (mark with an x)

- [ ] new
- [ ] build
- [x] serve
- [ ] test
- [ ] e2e
- [ ] generate
- [ ] add
- [ ] update
- [ ] lint
- [ ] xi18n
- [ ] run
- [ ] config
- [ ] help
- [ ] version
- [ ] doc

Is this a regression?

No.

Description

There are 3500 components/modules in this app. Everything lazy-loaded. When I run ng serve and edit any one file. The rebuild should be shorter because the lazy chunks have not changed.

🔬 Minimal Reproduction

git clone https://github.com/doggy8088/ng-cli-800-3500-components.git
cd ng-cli-800-3500-components
npm install
ng serve

Edit the src/app/features/page0001/page0001.component.ts file, it will wait more than 40 seconds to complete. It should be shorter.

🔥 Exception or Error

No error. It just slower than expected.

🌍 Your Environment

     _                      _                 ____ _     ___
    / \   _ __   __ _ _   _| | __ _ _ __     / ___| |   |_ _|
   / △ \ | '_ \ / _` | | | | |/ _` | '__|   | |   | |    | |
  / ___ \| | | | (_| | |_| | | (_| | |      | |___| |___ | |
 /_/   \_\_| |_|\__, |\__,_|_|\__,_|_|       \____|_____|___|
                |___/


Angular CLI: 8.0.6
Node: 10.16.0
OS: win32 x64
Angular: 8.0.3
... animations, common, compiler, compiler-cli, core, forms
... language-service, platform-browser, platform-browser-dynamic
... router

Package                            Version
------------------------------------------------------------
@angular-devkit/architect          0.800.6
@angular-devkit/build-angular      0.800.6
@angular-devkit/build-ng-packagr   0.800.6
@angular-devkit/build-optimizer    0.800.6
@angular-devkit/build-webpack      0.800.6
@angular-devkit/core               8.0.6
@angular-devkit/schematics         8.0.6
@angular/cli                       8.0.6
@ngtools/json-schema               1.1.0
@ngtools/webpack                   8.0.6
@schematics/angular                8.0.6
@schematics/update                 0.800.6
ng-packagr                         5.3.0
rxjs                               6.4.0
typescript                         3.4.5
webpack                            4.30.0

Anything else relevant?

N/A

[filipesilva]

Tried the repro, and could see ~40s rebuild time on my machine. Noticed that TS processing took very long, some processing that I wasn't expecting to happen with chunks did, and that there was some sort of hashing computation done for the lazy modules too.

Something else that I found interesting: rebuilding at still takes ~14s after removing AppRoutingModule import. Rebuilds get back to ~1s after I delete src/app/features and src/app/app-routing.module.ts. This points to TS compilation still building those TS files, likely because they are always included in tsconfig.app.json (which we want to change in #15030 and #15061).

@SanderElias also mentioned that he saw high CPU usage on this repo in between builds. He thought it was due to the file watchers.

[Dylan-Israel]

Having the same issue with similar dependencies.

[filipesilva]

Been looking into this and there are two parts to the problem:

• when you change just one file (like main.ts) all files are emitted by TS
• there's something about webpack processing sourcemaps for lazy modules even though they didn't change

Together these two things make the rebuild for a console.log(1); in main.ts be ~25s instead of ~1s.

The first problem was actually reported in #14775 and already addressed in #14778. I tested your repro with @angular-devkit/[email protected] and saw build times go down to 13s.

The second part I'm still trying to identify.

[filipesilva]

Opened an issue in Webpack: webpack/webpack#9460. I could reproduce that having many chunks slows down webpack compilations (without any CLI stuff) even when the lazy chunks don't change.

[filipesilva]

Updating to webpack 4.38 (#15170) should fix it, as the Webpack folks just added some very impressive (2x to 5x) rebuild perf improvements for this case.

[sokra]

Any real world metrics about the effect of the fix?

[filipesilva]

@sokra I compared dev rebuilds using @angular-devkit/[email protected] (which uses [email protected]) versus @angular-devkit/[email protected] (which uses [email protected], the version with your fixes) in a few projects:

• https://github.com/angular/angular/tree/master/aio, 12 lazy chunks, from ~365ms to ~300ms
• https://github.com/vmware/clarity, 39 lazy chunks, from ~1600ms to ~1250ms
• https://github.com/johannesjo/super-productivity, 0 lazy chunks, from ~1700ms to ~1700ms
• https://github.com/SAP/cloud-commerce-spartacus-storefront, 0 lazy chunks, from ~1650ms to ~1650ms

So no apparent improvement with 0 lazy chunks, and increasingly bigger improvement as more lazy chunks are present.

[filipesilva]

Closing as the fix has been merged and released.

[doggy8088]

@filipesilva I didn't see this issue on release notes. Which version been applied?

[filipesilva]

@doggy8088 the PR that updated our version of webpack was #15170, released first in https://github.com/angular/angular-cli/releases/tag/v8.2.0-rc.0. You should get it by updating to @angular-devkit/[email protected] or higher.

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