[Segment Cache] Skip prefetched segments on server

[acdlite]

Based on:

• [Segment Cache] Skip dynamic request if possible #73540

---

Currently if you navigate to a partially static route, the server will always start rendering at the first segment that's not present on the previous page. However, it should really start rendering at the first dynamic segment — if the client has already prefetched a segment, and it's fully static, there's no reason to render it again during the dynamic server render.

We can do this by sending a more specific Next-Router-State-Tree request header. Rather than send a tree that represents the previous route, we sent the tree of the target route, but with a refetch marker added to the first dynamic segment. (Without the refetch marker, the server would send back an empty response.) This is determined by diffing against both the previous route and the prefetch cache.

For now, this only works up to the first dynamic segment inside the new subtree; once the server starts rendering along a path, it renders everything else along that path. We could improve this in the future to also omit static segments that appear inside a dynamic layout, though this would likely require a change to the Next-Router-State-Tree protocol.

[ijjk]

Tests Passed

[ijjk]

Stats from current PR

Default Build (Increase detected ⚠️)

General Overall increase ⚠️

	vercel/next.js canary	acdlite/next.js segment-cache-skip-prefetched-segments	Change
buildDuration	18.3s	16.6s	N/A
buildDurationCached	15.8s	13.4s	N/A
nodeModulesSize	409 MB	410 MB	⚠️ +55.1 kB
nextStartRea..uration (ms)	489ms	480ms	N/A

Client Bundles (main, webpack)

	vercel/next.js canary	acdlite/next.js segment-cache-skip-prefetched-segments	Change
1187-HASH.js gzip	50.7 kB	50.7 kB	N/A
8276.HASH.js gzip	169 B	168 B	N/A
8377-HASH.js gzip	5.36 kB	5.36 kB	N/A
bccd1874-HASH.js gzip	53 kB	53 kB	N/A
framework-HASH.js gzip	57.5 kB	57.5 kB	N/A
main-app-HASH.js gzip	232 B	235 B	N/A
main-HASH.js gzip	34 kB	34 kB	N/A
webpack-HASH.js gzip	1.71 kB	1.71 kB	N/A
Overall change	0 B	0 B	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	acdlite/next.js segment-cache-skip-prefetched-segments	Change
polyfills-HASH.js gzip	39.4 kB	39.4 kB	✓
Overall change	39.4 kB	39.4 kB	✓

Client Pages

	vercel/next.js canary	acdlite/next.js segment-cache-skip-prefetched-segments	Change
_app-HASH.js gzip	193 B	193 B	✓
_error-HASH.js gzip	193 B	193 B	✓
amp-HASH.js gzip	512 B	510 B	N/A
css-HASH.js gzip	343 B	342 B	N/A
dynamic-HASH.js gzip	1.84 kB	1.84 kB	✓
edge-ssr-HASH.js gzip	265 B	265 B	✓
head-HASH.js gzip	363 B	362 B	N/A
hooks-HASH.js gzip	393 B	392 B	N/A
image-HASH.js gzip	4.49 kB	4.49 kB	N/A
index-HASH.js gzip	268 B	268 B	✓
link-HASH.js gzip	2.35 kB	2.34 kB	N/A
routerDirect..HASH.js gzip	328 B	328 B	✓
script-HASH.js gzip	397 B	397 B	✓
withRouter-HASH.js gzip	323 B	326 B	N/A
1afbb74e6ecf..834.css gzip	106 B	106 B	✓
Overall change	3.59 kB	3.59 kB	✓

Client Build Manifests

	vercel/next.js canary	acdlite/next.js segment-cache-skip-prefetched-segments	Change
_buildManifest.js gzip	747 B	746 B	N/A
Overall change	0 B	0 B	✓

Rendered Page Sizes

	vercel/next.js canary	acdlite/next.js segment-cache-skip-prefetched-segments	Change
index.html gzip	524 B	522 B	N/A
link.html gzip	539 B	537 B	N/A
withRouter.html gzip	520 B	519 B	N/A
Overall change	0 B	0 B	✓

Edge SSR bundle Size

	vercel/next.js canary	acdlite/next.js segment-cache-skip-prefetched-segments	Change
edge-ssr.js gzip	128 kB	128 kB	N/A
page.js gzip	203 kB	203 kB	N/A
Overall change	0 B	0 B	✓

Middleware size

	vercel/next.js canary	acdlite/next.js segment-cache-skip-prefetched-segments	Change
middleware-b..fest.js gzip	673 B	669 B	N/A
middleware-r..fest.js gzip	155 B	156 B	N/A
middleware.js gzip	31.1 kB	31.2 kB	N/A
edge-runtime..pack.js gzip	844 B	844 B	✓
Overall change	844 B	844 B	✓

Next Runtimes

	vercel/next.js canary	acdlite/next.js segment-cache-skip-prefetched-segments	Change
523-experime...dev.js gzip	322 B	322 B	✓
523.runtime.dev.js gzip	314 B	314 B	✓
app-page-exp...dev.js gzip	323 kB	323 kB	N/A
app-page-exp..prod.js gzip	127 kB	127 kB	✓
app-page-tur..prod.js gzip	140 kB	140 kB	✓
app-page-tur..prod.js gzip	135 kB	135 kB	✓
app-page.run...dev.js gzip	313 kB	313 kB	✓
app-page.run..prod.js gzip	123 kB	123 kB	✓
app-route-ex...dev.js gzip	37.3 kB	37.3 kB	✓
app-route-ex..prod.js gzip	25.4 kB	25.4 kB	✓
app-route-tu..prod.js gzip	25.4 kB	25.4 kB	✓
app-route-tu..prod.js gzip	25.2 kB	25.2 kB	✓
app-route.ru...dev.js gzip	38.9 kB	38.9 kB	✓
app-route.ru..prod.js gzip	25.2 kB	25.2 kB	✓
pages-api-tu..prod.js gzip	9.67 kB	9.67 kB	✓
pages-api.ru...dev.js gzip	11.6 kB	11.6 kB	✓
pages-api.ru..prod.js gzip	9.66 kB	9.66 kB	✓
pages-turbo...prod.js gzip	21.7 kB	21.7 kB	✓
pages.runtim...dev.js gzip	27.4 kB	27.4 kB	✓
pages.runtim..prod.js gzip	21.7 kB	21.7 kB	✓
server.runti..prod.js gzip	916 kB	916 kB	✓
Overall change	2.03 MB	2.03 MB	✓

build cache Overall increase ⚠️

	vercel/next.js canary	acdlite/next.js segment-cache-skip-prefetched-segments	Change
0.pack gzip	2.05 MB	2.05 MB	⚠️ +1.42 kB
index.pack gzip	72.8 kB	72 kB	N/A
Overall change	2.05 MB	2.05 MB	⚠️ +1.42 kB

Diff details

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Diff for main-HASH.js

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Commit: 2902677