🐛 Prevent duplicate Next.js RUM views from discarded renders by BeltranBulbarellaDD · Pull Request #4940 · DataDog/browser-sdk

BeltranBulbarellaDD · 2026-08-12T10:01:17Z

Problem

DatadogAppRouter called startNextjsView() during React's render phase, guarded only by a useRef. React can discard and retry a render before it commits (e.g. Suspense, concurrent interruptions). Each retry got a fresh ref, so startNextjsView() fired again for renders that were later thrown away, creating several RUM views for one page.

There was also no reliable way to tell, once a render finally committed, whether a newer navigation had already started somewhere else in the meantime. The old guard compared pathnames, which breaks when a navigation returns to a pathname it had already visited.

Goal

Start a view as soon as navigation begins (so timing is accurate even for slow routes), but only ever create or rename a view from a render that actually commits — never from one that gets discarded or superseded.

Current behavior

Initial load: nextjsPlugin.onInit() starts one view immediately.
Navigation start: Next.js calls onRouterTransitionStart() before React renders the new route. This starts the view right away. Query/hash-only changes and duplicate callbacks for the same transition are filtered out.
Commit: DatadogAppRouter's useEffect calls setNextjsViewName() after React commits the route, normalizing the path (e.g. /user/42 -> /user/[id]). Each navigation bumps a generation counter; the effect only applies its rename if that generation is still the active one when it runs. If a newer navigation has started in the meantime, the commit is dropped instead of overwriting the view that's actually displayed now.

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datadog-datadog-prod-us1 · 2026-08-12T10:03:01Z

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❄️ 1 New flaky test detected

↳ plugin: nextjs › should start a slow navigation view before the route commits from plugins/nextjsPlugin.scenario.ts

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• Patch Coverage: 75.00%
• Overall Coverage: 77.18% (-0.00%)

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…utEffect

cit-pr-commenter-54b7da · 2026-08-27T10:00:11Z

Bundles Sizes Evolution

📦 Bundle Name	Base Size	Local Size	𝚫	𝚫%	Status
Rum Salesforce	N/A	185.56 KiB	N/A	N/A	N/A
Rum	185.54 KiB	185.54 KiB	0 B	0.00%	✅
Rum-salesforce Profiler	N/A	8.38 KiB	N/A	N/A	N/A
Rum Profiler	8.38 KiB	8.38 KiB	0 B	0.00%	✅
Rum-salesforce Recorder	N/A	30.57 KiB	N/A	N/A	N/A
Rum Recorder	30.57 KiB	30.57 KiB	0 B	0.00%	✅
Logs	59.00 KiB	59.00 KiB	0 B	0.00%	✅
Rum Slim	143.53 KiB	143.53 KiB	0 B	0.00%	✅
Worker	22.96 KiB	22.96 KiB	0 B	0.00%	✅
Rum Shopify	N/A	214.59 KiB	N/A	N/A	N/A
Rum-shopify Profiler	N/A	8.38 KiB	N/A	N/A	N/A
Rum-shopify Recorder	N/A	4.77 KiB	N/A	N/A	N/A

…ed pathname,

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chatgpt-codex-connector · 2026-09-08T09:32:34Z

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lierniel

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A layout-effect redirect that returns to an already-committed pathname (e.g. / -> /protected -> router.replace('/')) could let /protected's stale passive effect rename the restored view, because staleness was inferred from pathname equality, which can't tell a revisited pathname from a fresh one. Track a monotonic generation counter per router transition instead. DatadogAppRouter captures the active generation at render time, and setNextjsViewName compares it at commit time, dropping the commit if a newer transition has since started. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

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The generation counter used to reject stale commits was a global clock not scoped to any route, so a re-render of an old, still-mounted route while a different navigation was pending could pick up a freshly-bumped generation value alongside its own stale pathname, defeating the check. Compare the commit's pathname directly against activeAppRouterPathname instead — it catches the same stale-commit cases without needing any counter. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Next.js forwards the raw href from router.push()/replace() unresolved, which can be relative to the current page (e.g. '?sort=asc' or 'details') rather than root-relative. Resolving it against window.location.origin instead of the current URL produced the wrong path for these navigations. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

setNextjsViewName compared the committed pathname (from usePathname(), which strips basePath) against activeAppRouterPathname (set from window.location.pathname, which does not). On an app with a basePath configured, these never matched, so the initial route's normalized view name was never applied. Pass window.location.pathname as the commit identity instead, keeping usePathname() only for computing the normalized view name. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

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BeltranBulbarellaDD · 2026-10-06T10:18:01Z

Closing this one in favour of #5111

test nextjs rendering issue

7039343

BeltranBulbarellaDD changed the title ~~test nextjs rendering issue~~ 🐛 Prevent duplicate Next.js RUM views from discarded renders Aug 17, 2026

BeltranBulbarellaDD marked this pull request as ready for review August 19, 2026 15:16

BeltranBulbarellaDD requested a review from a team as a code owner August 19, 2026 15:16

lierniel reviewed Aug 19, 2026

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Comment thread packages/browser-rum-nextjs/src/domain/nextJSRouter/useStartNextjsView.ts Outdated

sbarrio requested a review from bdibon August 20, 2026 07:06

BeltranBulbarellaDD marked this pull request as draft August 27, 2026 09:49

BeltranBulbarellaDD removed the request for review from bdibon August 27, 2026 09:49

Use onroutertransitionstart to start views and setViewName on useLayo…

e58b69d

…utEffect

BeltranBulbarellaDD added 4 commits August 27, 2026 12:38

App Router transition filtering now compares against the last committ…

568025e

…ed pathname,

Add redirect extra coverage

ed230b1

Merge branch 'main' into beltran.bulbarella/next_js_render_issue

9a29a1d

Remove useLayoutEffect

31857be

BeltranBulbarellaDD marked this pull request as ready for review August 28, 2026 14:11

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Comment thread packages/browser-rum-nextjs/src/domain/nextJSRouter/datadogAppRouter.tsx Outdated

Comment thread packages/browser-rum-nextjs/src/domain/nextjsPlugin.ts Outdated

sbarrio requested a review from bdibon September 1, 2026 07:04

Use event.id for dedupe, useEffect for setting the view name.

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Comment thread packages/browser-rum-nextjs/src/domain/nextjsPlugin.ts Outdated

BeltranBulbarellaDD added 2 commits September 8, 2026 11:52

Restore the committed view when navigation returns to it

ae84385

remove unnecesary test app code

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Comment thread packages/browser-rum-nextjs/src/domain/nextjsPlugin.ts

Comment thread packages/browser-rum-nextjs/src/domain/nextjsPlugin.ts Outdated

Preserve a newer pending pathname during commit effects

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Comment thread packages/browser-rum-nextjs/src/domain/nextjsPlugin.ts Outdated

BeltranBulbarellaDD requested review from lierniel and removed request for bdibon September 24, 2026 13:32

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Merge branch 'main' into beltran.bulbarella/next_js_render_issue

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BeltranBulbarellaDD force-pushed the beltran.bulbarella/next_js_render_issue branch from d19f03a to ce58867 Compare September 24, 2026 13:42

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Comment thread packages/browser-rum-nextjs/src/domain/nextjsPlugin.ts Outdated

Reapply normalized name when restoring a committed route

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Comment thread packages/browser-rum-nextjs/src/domain/nextjsPlugin.ts Outdated

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Comment thread packages/browser-rum-nextjs/src/domain/nextjsPlugin.ts Outdated

Comment thread packages/browser-rum-nextjs/src/domain/nextjsPlugin.ts

Comment thread packages/browser-rum-nextjs/src/domain/nextjsPlugin.ts Outdated

BeltranBulbarellaDD and others added 3 commits September 24, 2026 18:37

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Comment thread packages/browser-rum-nextjs/src/domain/nextjsPlugin.ts

sbarrio requested a review from bdibon September 25, 2026 07:08

BeltranBulbarellaDD marked this pull request as draft September 29, 2026 12:25

BeltranBulbarellaDD removed the request for review from bdibon September 29, 2026 12:25

sahil505 mentioned this pull request Oct 1, 2026

🐛 Router components create duplicate RUM views: render-phase startView() guarded only by useRef #4931

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