feat: use Rspack persistent cache by default (#81399)
Rspack now enables persistent caching by default.
## Performance Comparison
### Pages Router
I benchmarked performance using this repo:
https://github.com/SyMind/chakra-ui-docs/tree/next-rspack to test the
Next.js pages router.
I tested the performance with the following steps:
1. Execute `pnpm run dev`
2. Wait for the server to be ready (indicated by the 'Ready' message)
3. Run curl on the root endpoint (/)
Each build was run 5 times, and the shortest time to reach "Compiled
successfully" was recorded.
Test environment: Apple M1 Pro CPU
| Tool | Build without cache | Build with cache | Dev without cache |
Dev with cache |
|-------------|---------------------|------------------|---------------------------------|----------------|
| Rspack | 3.8s | 2.6s | 1.7s | 3ms |
| Webpack | 14.0s | 4.0s | 7.8s | 3.2s |
### App Router
I benchmarked performance using this repo:
https://github.com/SyMind/shadcn-ui/tree/next-rspack to test the Next.js
app router.
I tested the performance with the following steps:
1. Execute `pnpm run dev` or `pnpm run build`
2. Wait for the server to be ready (indicated by the 'Ready' message)
3. Run curl on the root endpoint (/)
Each build was run 5 times, and the shortest time to reach "Compiled
successfully" was recorded.
Test environment: Apple M1 Pro CPU
| Bundler | Build (No Cache) | Build (Cache) | Dev (No Cache) | Dev
(Cache) |
|------------|----------------------|-------------------|--------------------|-----------------|
| Rspack | 12.3s | 5.9s | 7.1s | 1941ms |
| Webpack | 27.0s | 13.0s | 11s | 9.6s |
## About Rspack Persistent Cache Strategy
> packages/next/src/server/dev/hot-reloader-rspack.ts
Rspack's persistent caching differs from Webpack in how it manages
module graphs. While Webpack incrementally updates modules, Rspack
operates on complete module graph snapshots for cache restoration.
Problem:
- Next.js dev server starts with no page modules in the initial entry
points
- When Rspack restores from persistent cache, it finds no modules and
purges the entire module graph
- Later page requests find no cached module information, preventing
cache reuse
Solution:
- Track successfully built page entries after each compilation
- Restore these entries on dev server restart to maintain module graph
continuity
- This ensures previously compiled pages can leverage persistent cache
for faster builds
## Note
I have updated the test case configuration in
`test/integration/telemetry/next.config.use-cache` to disable persistent
cache.
This is because, whether using webpack or Rspack, when persistent
caching is enabled, modules are no longer recompiled by loaders, which
prevents the Telemetry plugin from collecting information.
Please note that this issue also exists with webpack. You can reproduce
it locally by running `pnpm run test
test/integration/telemetry/test/config.test.js` twice.
