AOT Dev builds in Angular v9+ are much slower than JIT

🐞 Bug report

Command (mark with an x)

• new
• build
• serve
• test
• e2e
• generate
• add
• update
• lint
• xi18n
• run
• config
• help
• version
• doc

Is this a regression?

Yes, not present in 8.2.

Description

Dev builds in Angular 9 are very slow. Builds of 8.2 took on average 30 seconds or so, and recompiles took 2-5 seconds. This same app in Angular 9, however, takes ~45-60 seconds to build initially, and recompiles take ~15-25 seconds even if nothing changes at all. Production builds are roughly 5-10 seconds faster in 9, so those are better at least. (Note that none of these times include ngcc, that’s taken care of before I attempt to build.) Additionally, the speed is slow regardless of whether Ivy is used or not.

The Angular 9 build always seems to freeze for a bit at a certain point. It frequently lists the same file, but it’s not always the same file that it seems to get stuck on. There’s nothing special about the file it usually lists, it’s actually quite small and has no advanced Angular or TypeScript features.

I found #34699 (and #33532 by extension), but those are unrelated. I’m using TS 3.8 and it happens regardless of the value of that option in tsconfig.json.

Is there a way I can audit what’s causing it to take so long? I tried ng build --watch --verbose, but it provides way more information than I can feasibly parse (and also doesn’t include timings from what I can tell).

🔬 Minimal Reproduction

This repo has a reproduction. Instructions are in the readme.

🔥 Exception or Error

N/A

🌍 Your Environment

Angular CLI: 9.1.3
Node: 13.12.0
OS: win32 x64

Angular: 9.1.3
... animations, cli, common, compiler, compiler-cli, core, forms
... language-service, platform-browser, platform-browser-dynamic
... router
Ivy Workspace: Yes

Package                            Version
------------------------------------------------------------
@angular-devkit/architect          0.901.3
@angular-devkit/build-angular      0.901.3
@angular-devkit/build-ng-packagr   0.901.3
@angular-devkit/build-optimizer    0.901.3
@angular-devkit/build-webpack      0.901.3
@angular-devkit/core               9.1.3
@angular-devkit/schematics         9.1.3
@ngtools/webpack                   9.1.3
@schematics/angular                9.1.3
@schematics/update                 0.901.3
ng-packagr                         9.0.3
rxjs                               6.5.4
typescript                         3.8.3
webpack                            4.42.0

Anything else relevant? N/A

[bhanna1693]

While the idea of AOT compilation is great, this issue is too much to ignore (if you ask me). Development times have skyrocketed for our team:

• ng serve (avg time)
  • w/o aot: 55s
  • w/ aot: 1m 45s
• ng build --prod (avg time)
  • w/o aot: 1m 26s
  • w/ aot: 3m 13s

This has to be a higher priority for the Angular team

[alan-agius4]

In version 9, AOT and JIT compilations time should be similar.

Unfortunately, since you cannot provide a reproduction not even privately. I don’t see how we can investigate this any further.