Partial Fallback Prerendering #68958

wyattjoh · 2024-08-15T21:57:13Z

This work introduces the new concept of Partial Fallback Prerendering (PFPR).

Traditionally, when a dynamic page needed to be routed to that wasn't pregenerated, it required a render to generate even the first few bytes of the static page itself. This resulted in slow page loads for pages not frequently visited and a reduced Time to First Byte (TTFB) score on Core Web Vitals (CWV).

PFPR takes advantage of the new systems of Partial Prerendering (PPR) that allows the application to suspend at different points mid-render, and resume it later. We mark any unknown parameter access as dynamic access, and suspend the rendering up to the next suspense boundaries at those points. Under ideal conditions (correctly placed <Suspense /> boundaries or loading.jsx files) this generates a static shell that can be served to users as soon as the request hits Next.js, right out of the static cache. This minimizes the TTFB for all requests, dynamic or not for those pages that enable PPR. For example, the following page would create a usable shell:

// /app/users/[userID]/page.jsx
import { Suspense } from 'react'

function Profile({ params }) {
  const { userID } = params
  return <div>Hello {userID}!</div>
}

export default function ProfilePage({ params }) {
  return (
    <div>
      <h1>User Profile</h1>
      <Suspense fallback="Loading...">
        <Profile params={params} />
      </Suspense>
    </div>
  )
}

Due to the way that suspense works within React components, access of params within the root page component would cause the whole page to suspend. Thankfully, that's where the loading.jsx comes in handy. Adding a loading.jsx at a segment will automatically wrap the page.jsx with a suspense boundary, setting the contents of the root loading.jsx as the fallback component to use for it. This lets you maintain your existing style of accessing parameters at the root of the components while also taking advantage of PFPR.

To enable this feature, you first need to enable both PPR and PFPR:

module.exports = {
  experimental: {
    ppr: true,
    pprFallbacks: true,
  }
}

Once PFPR has stabilized with hosting providers, the experimental flag will go away and it will become the default with the PPR flag.

wyattjoh · 2024-08-15T21:57:28Z

Partial Fallback Prerendering #68958 : 2 dependent PRs (#69282 , #69378 ) 👈
fix: fix the safari and firefox test modes #69384
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ijjk · 2024-08-15T21:59:52Z

Tests Passed

ijjk · 2024-08-15T22:07:41Z

Stats from current PR

Default Build (Increase detected ⚠️)

General Overall increase ⚠️

	vercel/next.js canary	vercel/next.js feat/pfpr	Change
buildDuration	17.2s	15.5s	N/A
buildDurationCached	8.5s	7.2s	N/A
nodeModulesSize	355 MB	356 MB	⚠️ +624 kB
nextStartRea..uration (ms)	428ms	438ms	N/A

Client Bundles (main, webpack) Overall increase ⚠️

	vercel/next.js canary	vercel/next.js feat/pfpr	Change
2994-HASH.js gzip	37.8 kB	41.9 kB	⚠️ +4.09 kB
3095.HASH.js gzip	169 B	169 B	✓
9630-HASH.js gzip	5.25 kB	5.25 kB	N/A
a8273233-HASH.js gzip	51.9 kB	51.9 kB	N/A
framework-HASH.js gzip	56.7 kB	56.7 kB	N/A
main-app-HASH.js gzip	226 B	225 B	N/A
main-HASH.js gzip	32.5 kB	32.5 kB	N/A
webpack-HASH.js gzip	1.71 kB	1.71 kB	N/A
Overall change	37.9 kB	42 kB	⚠️ +4.09 kB

Legacy Client Bundles (polyfills)

	vercel/next.js canary	vercel/next.js feat/pfpr	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	vercel/next.js feat/pfpr	Change
_app-HASH.js gzip	194 B	193 B	N/A
_error-HASH.js gzip	192 B	192 B	✓
amp-HASH.js gzip	508 B	511 B	N/A
css-HASH.js gzip	344 B	342 B	N/A
dynamic-HASH.js gzip	1.84 kB	1.84 kB	N/A
edge-ssr-HASH.js gzip	265 B	266 B	N/A
head-HASH.js gzip	364 B	364 B	✓
hooks-HASH.js gzip	390 B	390 B	✓
image-HASH.js gzip	4.4 kB	4.4 kB	N/A
index-HASH.js gzip	267 B	268 B	N/A
link-HASH.js gzip	2.81 kB	2.81 kB	N/A
routerDirect..HASH.js gzip	328 B	328 B	✓
script-HASH.js gzip	397 B	396 B	N/A
withRouter-HASH.js gzip	323 B	324 B	N/A
1afbb74e6ecf..834.css gzip	106 B	106 B	✓
Overall change	1.38 kB	1.38 kB	✓

Client Build Manifests

	vercel/next.js canary	vercel/next.js feat/pfpr	Change
_buildManifest.js gzip	750 B	748 B	N/A
Overall change	0 B	0 B	✓

Rendered Page Sizes

	vercel/next.js canary	vercel/next.js feat/pfpr	Change
index.html gzip	522 B	522 B	✓
link.html gzip	538 B	536 B	N/A
withRouter.html gzip	519 B	517 B	N/A
Overall change	522 B	522 B	✓

Edge SSR bundle Size Overall increase ⚠️

	vercel/next.js canary	vercel/next.js feat/pfpr	Change
edge-ssr.js gzip	127 kB	128 kB	⚠️ +345 B
page.js gzip	173 kB	176 kB	⚠️ +2.62 kB
Overall change	301 kB	304 kB	⚠️ +2.97 kB

Middleware size

	vercel/next.js canary	vercel/next.js feat/pfpr	Change
middleware-b..fest.js gzip	669 B	673 B	N/A
middleware-r..fest.js gzip	156 B	156 B	✓
middleware.js gzip	29.9 kB	29.9 kB	N/A
edge-runtime..pack.js gzip	844 B	844 B	✓
Overall change	1 kB	1 kB	✓

Next Runtimes Overall increase ⚠️

	vercel/next.js canary	vercel/next.js feat/pfpr	Change
928-experime...dev.js gzip	322 B	322 B	✓
928.runtime.dev.js gzip	314 B	314 B	✓
app-page-exp...dev.js gzip	312 kB	313 kB	⚠️ +1.17 kB
app-page-exp..prod.js gzip	123 kB	123 kB	⚠️ +675 B
app-page-tur..prod.js gzip	136 kB	137 kB	⚠️ +683 B
app-page-tur..prod.js gzip	131 kB	132 kB	⚠️ +700 B
app-page.run...dev.js gzip	301 kB	302 kB	⚠️ +1.16 kB
app-page.run..prod.js gzip	118 kB	119 kB	⚠️ +694 B
app-route-ex...dev.js gzip	30.8 kB	30.8 kB	N/A
app-route-ex..prod.js gzip	20.8 kB	20.8 kB	N/A
app-route-tu..prod.js gzip	20.8 kB	20.8 kB	N/A
app-route-tu..prod.js gzip	20.6 kB	20.7 kB	N/A
app-route.ru...dev.js gzip	32.4 kB	32.5 kB	N/A
app-route.ru..prod.js gzip	20.6 kB	20.7 kB	N/A
pages-api-tu..prod.js gzip	9.62 kB	9.62 kB	✓
pages-api.ru...dev.js gzip	11.5 kB	11.5 kB	✓
pages-api.ru..prod.js gzip	9.61 kB	9.61 kB	✓
pages-turbo...prod.js gzip	20.8 kB	20.8 kB	✓
pages.runtim...dev.js gzip	26.4 kB	26.4 kB	✓
pages.runtim..prod.js gzip	20.8 kB	20.8 kB	✓
server.runti..prod.js gzip	56.8 kB	57.6 kB	⚠️ +856 B
Overall change	1.28 MB	1.28 MB	⚠️ +5.93 kB

build cache Overall increase ⚠️

	vercel/next.js canary	vercel/next.js feat/pfpr	Change
0.pack gzip	1.49 MB	1.56 MB	⚠️ +67.3 kB
index.pack gzip	127 kB	129 kB	⚠️ +2.49 kB
Overall change	1.62 MB	1.69 MB	⚠️ +69.8 kB

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+      const _imageconfigcontextsharedruntime = __webpack_require__(9427);
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       // This is replaced by webpack define plugin
       const configEnv = {
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@@ -1030,12 +1030,12 @@
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Commit: d6bb4e9

gnoff · 2024-08-20T18:54:53Z

packages/next/src/client/components/navigation-untracked.ts

+function hasUnknownRouteParams() {
+  if (typeof window === 'undefined') {
+    // AsyncLocalStorage should not be included in the client bundle.
+    const { staticGenerationAsyncStorage } =
+      require('./static-generation-async-storage.external') as typeof import('./static-generation-async-storage.external')
+
+    const staticGenerationStore = staticGenerationAsyncStorage.getStore()
+    if (!staticGenerationStore) return false
+
+    const { unknownRouteParams } = staticGenerationStore
+    return isUnknownRouteParams(unknownRouteParams)
+  }
+
+  return false
+}


maybe put this all in an RSC scope and pass something to a client Context that way you don't need the window check. during prerender it would indicate there are unknown route params and during resume/dynamic render it would not.

Still need to make sure there are not mismatches between prerender and resume but that's also true in the current setup so you presumably are already handling that

packages/next/src/client/components/navigation-untracked.ts

gnoff · 2024-08-20T18:59:03Z

packages/next/src/client/components/navigation.ts

@@ -63,6 +69,26 @@ export function useSearchParams(): ReadonlyURLSearchParams {
  return readonlySearchParams
 }

+function trackParamsAccessed(expression: string) {
+  if (typeof window === 'undefined') {


we're just begging for import map support for this kind of thing. Ideally we have an implementation for the browser and a separate one for SSR. This one can't as easily be pulled out of the client scope because it actually has to call a function which reads from the async local storage

packages/next/src/client/components/navigation.ts

packages/next/src/client/components/params.ts

packages/next/src/server/app-render/app-render.tsx

This replaces the custom behaviour of `getFallback` in the server with the existing ResponseCache. This sets us up for #68958 which has fallbacks that should be revalidatable.

ztanner · 2024-08-27T20:38:39Z

packages/next/src/build/index.ts

            const page = appNormalizedPaths.get(originalAppPath) || ''
            const appConfig = appDefaultConfigs.get(originalAppPath) || {}
-            let hasDynamicData =
+
+            let hasRevalidateZero =


nit: I found the original name a bit clearer since we use a revalidation of 0 synonymously with dynamic access. The significance of this check becomes lost and it creates a bit of confusion with later comments (ie, right below, "if the page was marked as being static but it contains dynamic data..."

In a PPR world though, we don't actually use the revalidate: 0 to indicate if a page has dynamic data or not, we simply postpone. Renaming this here adds additional clarity so lower in the code it's clearer what we're comparing directly.

packages/next/src/build/index.ts

packages/next/src/server/app-render/postponed-state.test.ts

…anifest, improved serialization speed

…d comments, remove server code from client bundles

…arsing, updated serialization format

ijjk added created-by: Next.js team PRs by the Next.js team. tests type: next labels Aug 15, 2024

This was referenced Aug 15, 2024

refactor: incremental cache cleanup #68602

Merged

refactor: update fallbacks to use response cache #68603

Merged

refactor: fallback updates #68631

Merged

wyattjoh force-pushed the refactor/fallback-incremental-cache branch from 6ed3d1f to 5aae257 Compare August 16, 2024 15:25

wyattjoh force-pushed the feat/pfpr branch 7 times, most recently from f12d23d to 6268654 Compare August 19, 2024 23:22

wyattjoh force-pushed the refactor/fallback-incremental-cache branch from 8504f98 to 5c9de13 Compare August 19, 2024 23:25

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wyattjoh force-pushed the feat/pfpr branch from 2585be0 to 8f617d5 Compare August 20, 2024 18:06

wyattjoh force-pushed the refactor/fallback-incremental-cache branch from 0b566b7 to e44ee41 Compare August 20, 2024 18:49

wyattjoh force-pushed the feat/pfpr branch from 8f617d5 to 12f5133 Compare August 20, 2024 18:52

gnoff reviewed Aug 20, 2024

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wyattjoh changed the base branch from refactor/fallback-incremental-cache to graphite-base/68958 August 20, 2024 20:33

wyattjoh force-pushed the feat/pfpr branch from 12f5133 to 7c556e3 Compare August 20, 2024 20:35

wyattjoh force-pushed the graphite-base/68958 branch from e44ee41 to cc484b9 Compare August 20, 2024 20:35

wyattjoh force-pushed the feat/pfpr branch from d843d22 to 0c807f4 Compare August 27, 2024 20:32

ztanner reviewed Aug 27, 2024

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wyattjoh force-pushed the feat/pfpr branch 3 times, most recently from 8bcc38e to 01b0828 Compare August 27, 2024 22:28

wyattjoh changed the base branch from canary to fix/safari-firefox-test-modes August 27, 2024 22:28

wyattjoh mentioned this pull request Aug 27, 2024

fix: fix the safari and firefox test modes #69384

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gnoff approved these changes Aug 27, 2024

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Base automatically changed from fix/safari-firefox-test-modes to canary August 27, 2024 22:35

wyattjoh force-pushed the feat/pfpr branch 3 times, most recently from 7a13005 to d6bb4e9 Compare August 27, 2024 22:37

wyattjoh added 14 commits August 27, 2024 17:36

feat: added support for Partial Fallback Prerendering

4ac7656

refactor: modify postponed state instead of serverside patching

0604a2c

feat: support partial dynamic path parameters

4377696

fix: trap metadata access

a36cf98

feat: added new experimental.pprFallbacks option for enabling PFPR

86011b7

refactor: change the key for pfpr

90e5a8e

refactor: break fallback handling into separate branches

da03262

fix: test updates

32cf758

fix: increase test module size limit

85ac7fa

fix: remove component importing:

60b84b8

refactor: cleanup impl, simplified logic, added fields to prerender m…

63a7cd9

…anifest, improved serialization speed

review: updated prop assignments, removed unneeded type assertions an…

1e7e090

…d comments, remove server code from client bundles

test: add tests for HTML and data postponed state serialization and p…

99b2136

…arsing, updated serialization format

fix: don't use params from props as it's uninitialized

eca0344

wyattjoh force-pushed the feat/pfpr branch from d6bb4e9 to eca0344 Compare August 27, 2024 23:36

ztanner approved these changes Aug 28, 2024

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wyattjoh merged commit f4c1a40 into canary Aug 28, 2024
103 of 109 checks passed

wyattjoh deleted the feat/pfpr branch August 28, 2024 05:31

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Partial Fallback Prerendering #68958

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Partial Fallback Prerendering #68958

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