Improve local build speed with parallel build threads

Note

This feature was introduced in Engine 4.1.8 and 5.0.4 releases that brings additional compiler options using a new arc.config.json configuration file. See arc.config.json documentation to learn more about other compiler options.

Arc XP Client developers can now toggle parallelization for faster webpack builds using a arc.config.json file added to the bundle source. This option will speed up the local development builds.

Demo

Play

How to enable

To opt-into this capability, add the following to your arc.config.json in the root of your bundle folder:

{
  "compiler": {
    "parallel": true,
    "devtool": "eval"
  }
}

• The parallel property toggles the behavior of webpack running in a single node process with an Array of configs versus spawning a pool of Node processes to run the webpack configurations in parallel. If not present, the default value is false, which is the existing behavior.
• The devtool property enables users to override the default setting of eval-source-map to eval for faster build times at the cost of source maps. If source maps are not important to your web development workflow, setting the devtool option to eval is the recommended choice for development builds with maximum performance. If not present, the default value is the existing behavior.

Benchmarks

We benchmarked this change across a few realistic bundles (using a mix of simple and complex codebases). Here are two examples in total build time numbers (in milliseconds):

Bundle 1 (requires more memory, such as increased JS Heap size limits):

	Baseline	With Parallelization Enabled	with devtool=eval	parallelization + devtool=eval
Run 1	52102	49252	36698	34423
Run 2	50410	47588	31578	34648
Run 3	51095	48276	32004	35895
Average	51202	48372	33426	34988
Change from Baseline		- 6%	- 35%	- 32%

All benchmarks are in total milliseconds to complete the build.

Bundle2 (complex dependency tree):

	Baseline	With Parallelization Enabled	with devtool=eval	parallelization + devtool=eval
Run 1	86023	73734	59291	54119
Run 2	85590	72031	60437	54900
Run 3	86274	75822	60877	54997
Average	85962	73862	60201	54672
Change from Baseline		- 15%	- 30%	- 37%

Note

All benchmarks are in total milliseconds to complete the build.

Even though we see consistent around 30% decrease in total build time, it’s hard to quote a general number, because the compilation performance is highly correlated to the dependencies used and the code structure (number of output types, blocks, and the dependency tree for the webpack entrypoints).