Track `use cache` usage #75007

gaojude · 2025-01-16T22:08:00Z

We’re updating the SWC transform to track how the "use cache" directive is used during builds. Each use of "use cache" is counted based on the handler it’s linked to.

By default, "use cache" counts toward a feature called "useCache/default". If a custom handler is defined in the Next.js config (e.g., "custom"), then "use cache: custom" will count toward "useCache/custom".

The build process will collect these counts and combine them across all source files and workers. This data is reported under the NEXT_BUILD_FEATURE_USAGE event, allowing us to filter by "useCache/*" to see how often each cache handler is used.

*Only support webpack prod build for now.

Closes NDX-683

gaojude · 2025-01-16T22:08:26Z

Track use cache usage #75007 👈 (View in Graphite)
canary

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ijjk · 2025-01-17T22:52:00Z

Stats from current PR

Default Build (Increase detected ⚠️)

General Overall increase ⚠️

	vercel/next.js canary	vercel/next.js jude/use-cache-tracking-2	Change
buildDuration	19.5s	16.2s	N/A
buildDurationCached	15.2s	13s	N/A
nodeModulesSize	418 MB	418 MB	⚠️ +45 kB
nextStartRea..uration (ms)	420ms	423ms	N/A

Client Bundles (main, webpack)

	vercel/next.js canary	vercel/next.js jude/use-cache-tracking-2	Change
5306-HASH.js gzip	54 kB	54 kB	N/A
8276.HASH.js gzip	169 B	168 B	N/A
8377-HASH.js gzip	5.46 kB	5.46 kB	N/A
bccd1874-HASH.js gzip	52.9 kB	52.9 kB	✓
framework-HASH.js gzip	57.5 kB	57.5 kB	N/A
main-app-HASH.js gzip	240 B	242 B	N/A
main-HASH.js gzip	34.6 kB	34.6 kB	N/A
webpack-HASH.js gzip	1.71 kB	1.71 kB	N/A
Overall change	52.9 kB	52.9 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	vercel/next.js jude/use-cache-tracking-2	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	vercel/next.js jude/use-cache-tracking-2	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	4.59 kB	4.58 kB	N/A
index-HASH.js gzip	268 B	268 B	✓
link-HASH.js gzip	2.35 kB	2.35 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	vercel/next.js jude/use-cache-tracking-2	Change
_buildManifest.js gzip	748 B	747 B	N/A
Overall change	0 B	0 B	✓

Rendered Page Sizes

	vercel/next.js canary	vercel/next.js jude/use-cache-tracking-2	Change
index.html gzip	524 B	523 B	N/A
link.html gzip	540 B	538 B	N/A
withRouter.html gzip	520 B	520 B	✓
Overall change	520 B	520 B	✓

Edge SSR bundle Size

	vercel/next.js canary	vercel/next.js jude/use-cache-tracking-2	Change
edge-ssr.js gzip	129 kB	129 kB	N/A
page.js gzip	208 kB	208 kB	N/A
Overall change	0 B	0 B	✓

Middleware size

	vercel/next.js canary	vercel/next.js jude/use-cache-tracking-2	Change
middleware-b..fest.js gzip	670 B	665 B	N/A
middleware-r..fest.js gzip	155 B	156 B	N/A
middleware.js gzip	31.3 kB	31.3 kB	N/A
edge-runtime..pack.js gzip	844 B	844 B	✓
Overall change	844 B	844 B	✓

Next Runtimes

	vercel/next.js canary	vercel/next.js jude/use-cache-tracking-2	Change
274-experime...dev.js gzip	322 B	322 B	✓
274.runtime.dev.js gzip	314 B	314 B	✓
app-page-exp...dev.js gzip	375 kB	375 kB	✓
app-page-exp..prod.js gzip	130 kB	130 kB	✓
app-page-tur..prod.js gzip	143 kB	143 kB	✓
app-page-tur..prod.js gzip	139 kB	139 kB	✓
app-page.run...dev.js gzip	363 kB	363 kB	✓
app-page.run..prod.js gzip	126 kB	126 kB	✓
app-route-ex...dev.js gzip	37.6 kB	37.6 kB	✓
app-route-ex..prod.js gzip	25.6 kB	25.6 kB	✓
app-route-tu..prod.js gzip	25.6 kB	25.6 kB	✓
app-route-tu..prod.js gzip	25.4 kB	25.4 kB	✓
app-route.ru...dev.js gzip	39.2 kB	39.2 kB	✓
app-route.ru..prod.js gzip	25.4 kB	25.4 kB	✓
pages-api-tu..prod.js gzip	9.69 kB	9.69 kB	✓
pages-api.ru...dev.js gzip	11.6 kB	11.6 kB	✓
pages-api.ru..prod.js gzip	9.68 kB	9.68 kB	✓
pages-turbo...prod.js gzip	21.9 kB	21.9 kB	✓
pages.runtim...dev.js gzip	27.7 kB	27.7 kB	✓
pages.runtim..prod.js gzip	21.9 kB	21.9 kB	✓
server.runti..prod.js gzip	916 kB	916 kB	✓
Overall change	2.47 MB	2.47 MB	✓

build cache Overall increase ⚠️

	vercel/next.js canary	vercel/next.js jude/use-cache-tracking-2	Change
0.pack gzip	2.1 MB	2.11 MB	⚠️ +7.34 kB
index.pack gzip	75.6 kB	74.8 kB	N/A
Overall change	2.1 MB	2.11 MB	⚠️ +7.34 kB

Diff details

Diff for main-HASH.js

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Commit: a17d90e

packages/next/src/build/index.ts

ijjk · 2025-01-20T20:47:47Z

Tests Passed

ijjk · 2025-01-21T22:56:41Z

packages/next/src/build/webpack/plugins/telemetry-plugin/use-cache-tracker-utils.ts

+    for (const key in tracker2) {
+      if (Object.prototype.hasOwnProperty.call(tracker2, key)) {
+        const typedKey = key as UseCacheTrackerKey
+        if (mergedTracker[typedKey] !== undefined) {


If a component/file that uses use cache is imported in both a nodejs page and a edge page will it be counted twice one from each compilation?

use cache requires dynamicIO, but I saw the error that "runtime" is not compatible with nextConfig.experimental.dynamicIO. so I assume we don't support edge runtime for use cache components anymore. Hence, it should not run into this double-counting issue.

To reassure this is the case, #75007 (comment)

gaojude · 2025-01-22T15:15:42Z

packages/next/src/build/webpack-config.ts

@@ -1937,6 +1939,11 @@ export default async function getBaseWebpackConfig(
            ].filter<[Feature, boolean]>(Boolean as any)
          )
        ),
+      !dev &&
+        isNodeServer &&


@ijjk to avoid double counting in general, I added this check here to skip tracking edge stuff.

…usage with `Rc<RefCell<FxHashMap<_, _>>>` (#75534) This is a follow-up to #75007 `DashMap` is needed for situations where you have many threads (or tokio tasks) modifying the same data at the same time. It introduces a lot of memory and CPU overhead to create individually lockable `RwLock` shards. This type of data structure implements `Sync`, indicating that it can be shared between threads. `Rc` is not `Sync` (`Arc` is `Sync`), so wrapping `DashMap` in `Rc` doesn't make a lot of sense: You're paying a pretty high overhead for the ability to share data between threads, and wrapping it in something that does not support sharing data between threads. This visitor code is entirely single-threaded, so just use `Rc<RefCell<FxHashMap>>` instead. `RefCell` is a very cheap single-threaded version of a `Mutex`. `FxHashMap` is just a `HashMap` with the faster `FxHash` algorithm used.

ijjk added created-by: Next.js team PRs by the Next.js team. Turbopack Related to Turbopack with Next.js. type: next labels Jan 16, 2025

gaojude changed the title ~~track use cacheu usage~~ track use cache usage Jan 16, 2025

gaojude force-pushed the jude/use-cache-tracking-2 branch from c8ddb3f to f278e64 Compare January 17, 2025 22:37

gaojude changed the title ~~track use cache usage~~ Track use cache usage Jan 17, 2025

gaojude force-pushed the jude/use-cache-tracking-2 branch from f278e64 to bec67bb Compare January 17, 2025 22:40

ijjk added the tests label Jan 17, 2025

gaojude marked this pull request as ready for review January 17, 2025 22:46

gaojude requested a review from ijjk January 17, 2025 22:56

gaojude force-pushed the jude/use-cache-tracking-2 branch from bec67bb to 6b903da Compare January 17, 2025 22:57

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ijjk reviewed Jan 18, 2025

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gaojude force-pushed the jude/use-cache-tracking-2 branch from 7e8234c to 9ca84f6 Compare January 20, 2025 20:29

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gaojude added 2 commits January 22, 2025 09:52

track use cache uasge

ef3731b

track cache handlers

afd436b

gaojude requested a review from ijjk January 22, 2025 15:12

DashMap doesn't need RefCell

a17d90e

gaojude force-pushed the jude/use-cache-tracking-2 branch from be11323 to a17d90e Compare January 22, 2025 15:14

gaojude commented Jan 22, 2025

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gaojude merged commit 07d2820 into canary Jan 22, 2025
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gaojude deleted the jude/use-cache-tracking-2 branch January 22, 2025 16:41

bgw mentioned this pull request Jan 31, 2025

perf(next-custom-transforms): Replace non-Sync Rc<DashMap<_, _>> usage with Rc<RefCell<FxHashMap<_, _>>> #75534

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