⚗️feat: collect INP sub-parts RUM-14310 by HugoGarrido · Pull Request #4158 · DataDog/browser-sdk

HugoGarrido · 2026-02-10T14:42:45Z

Motivation

Similar to LCP subparts, this PR goal is to collect INP subparts.

This feature is gated behind the inp_subparts experimental feature flag and is based on Chrome's implementation.

Subpart	Meaning
Input Delay	Time from user input to processing start
Processing Time	Event handler execution time
Presentation Delay	Rendering time happening after processing

You can review commit by commit

TODO rum-events-format PR

Changes

Add the flag 42c483f
Update relevant types 6fc488f
Add logic to group entries by interactionId to compute the parts with correct values 190734d
Compute and report the subparts breakdown f03e852
Empty the Map storing the groups in the stop() callback
Add tests

Test instructions

Checklist

Tested locally
Tested on staging
Added unit tests for this change.
Added e2e/integration tests for this change.
Updated documentation and/or relevant AGENTS.md file

cit-pr-commenter-54b7da · 2026-02-10T14:44:35Z

Bundles Sizes Evolution

📦 Bundle Name	Base Size	Local Size	𝚫	𝚫%	Status
Rum	168.98 KiB	170.26 KiB	+1.28 KiB	+0.76%	✅
Rum Profiler	4.31 KiB	4.31 KiB	0 B	0.00%	✅
Rum Recorder	24.54 KiB	24.54 KiB	0 B	0.00%	✅
Logs	56.27 KiB	56.30 KiB	+30 B	+0.05%	✅
Flagging	944 B	944 B	0 B	0.00%	✅
Rum Slim	125.82 KiB	127.05 KiB	+1.23 KiB	+0.98%	✅
Worker	23.63 KiB	23.63 KiB	0 B	0.00%	✅

🚀 CPU Performance

Action Name	Base CPU Time (ms)	Local CPU Time (ms)	𝚫%
RUM - add global context	0.0051	0.0043	-15.69%
RUM - add action	0.0186	0.0187	+0.54%
RUM - add error	0.016	0.0173	+8.12%
RUM - add timing	0.0033	0.003	-9.09%
RUM - start view	0.0169	0.0216	+27.81%
RUM - start/stop session replay recording	0.0009	0.0011	+22.22%
Logs - log message	0.0205	0.0191	-6.83%

🧠 Memory Performance

Action Name	Base Memory Consumption	Local Memory Consumption	𝚫
RUM - add global context	27.78 KiB	27.71 KiB	-63 B
RUM - add action	52.25 KiB	50.56 KiB	-1.69 KiB
RUM - add timing	26.63 KiB	26.88 KiB	+248 B
RUM - add error	56.50 KiB	55.31 KiB	-1.19 KiB
RUM - start/stop session replay recording	25.49 KiB	25.27 KiB	-232 B
RUM - start view	452.97 KiB	457.48 KiB	+4.52 KiB
Logs - log message	46.33 KiB	46.67 KiB	+341 B

🔗 RealWorld

datadog-datadog-prod-us1 · 2026-02-10T14:45:02Z

✅ Tests

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

_{This comment will be updated automatically if new data arrives.

🔗 Commit SHA: 5189c30 | Docs | Datadog PR Page | Was this helpful? Give us feedback!}

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packages/rum-core/src/domain/view/viewMetrics/trackInteractionToNextPaint.ts

HugoGarrido · 2026-02-10T17:10:49Z

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packages/rum-core/src/domain/view/viewMetrics/trackInteractionToNextPaint.ts

HugoGarrido · 2026-02-11T10:38:54Z

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chatgpt-codex-connector · 2026-02-11T10:45:13Z

packages/rum-core/src/domain/view/viewMetrics/trackInteractionToNextPaint.ts

+      if (isExperimentalFeatureEnabled(ExperimentalFeature.INP_SUBPARTS)) {
+        interactionToNextPaintSubParts = computeInpSubParts(newInteraction, sanitizeInpValue(interactionToNextPaint))


Update INP subparts only when selected interaction changes

interactionToNextPaintSubParts is recomputed on every newInteraction even when newInteraction.duration is unchanged, while time and targetSelector are intentionally not updated in that case. If p98 switches to a different interaction with the same duration (for example when interaction count crosses a 50-interaction bucket and tied durations exist), the payload can mix sub_parts from one interaction with timestamp/target_selector from another, which corrupts attribution data.

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chatgpt-codex-connector · 2026-02-11T10:45:13Z

packages/rum-core/src/domain/view/viewMetrics/trackInteractionToNextPaint.ts

+    }
+
+    // Create new group
+    groupsByInteractionId.set(entry.interactionId, {


Cap grouped interaction map per view

With inp_subparts enabled, every interaction ID is stored in groupsByInteractionId and never evicted until stop(), so long-lived views grow this map linearly with user interactions. That introduces unbounded per-view memory growth (despite the existing MAX_INTERACTION_ENTRIES guard for INP tracking) and can degrade pages with many interactions; groups that can no longer affect the p98 candidate should be pruned.

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HugoGarrido · 2026-02-12T15:13:05Z

/to-staging

gh-worker-devflow-routing-ef8351 · 2026-02-12T15:13:09Z

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2026-02-12 15:13:09 UTC ℹ️ Start processing command /to-staging

2026-02-12 15:13:18 UTC ℹ️ Branch Integration: starting soon, merge expected in approximately 14m (p90)

Commit 5189c309de will soon be integrated into staging-07.

2026-02-12 15:27:19 UTC ℹ️ Branch Integration: this commit was successfully integrated

Commit 5189c309de has been merged into staging-07 in merge commit 106178662f.

Check out the triggered DDCI request.

If you need to revert this integration, you can use the following command: /code revert-integration -b staging-07

…aging-07 Integrated commit sha: 5189c30 Co-authored-by: HugoGarrido <9059402+HugoGarrido@users.noreply.github.com> Co-authored-by: hugo.garridoysaez <hugo.garridoysaez@datadoghq.com>

HugoGarrido added 7 commits February 10, 2026 14:36

⚗ feat: add new flag for the feature

42c483f

⚗ feat: update types for inp supbarts

6fc488f

⚗ feat: add map to group entries for subpart computation

190734d

⚗ feat: compute inp subparts

f03e852

⚡️ fix: clear map on stop callback

5bb7635

⚗ feat: report inp subparts to view collection

f65b697

✅ feat: add inp subparts specific tests

41283a4

HugoGarrido changed the title ~~Hugo.garridoysaez/feat/support inp subparts~~ ⚗️feat: collect INP sub-parts RUM-14310 Feb 10, 2026

HugoGarrido added 2 commits February 10, 2026 15:55

✅ fix tests in domain/view

8bdf5db

🎨 fix: format code

1fbf5a1

HugoGarrido marked this pull request as ready for review February 10, 2026 16:50

HugoGarrido requested a review from a team as a code owner February 10, 2026 16:50

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packages/rum-core/src/domain/view/viewMetrics/trackInteractionToNextPaint.ts Outdated Show resolved Hide resolved

packages/rum-core/src/domain/view/viewMetrics/trackInteractionToNextPaint.ts Outdated Show resolved Hide resolved

HugoGarrido added 2 commits February 10, 2026 18:09

👌 fix: gate groupEntriesByRenderTime behind the feature flag

106e82d

👌 fix: always use safe inp value for subparts

ecc7e42

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packages/rum-core/src/domain/view/viewMetrics/trackInteractionToNextPaint.ts Outdated Show resolved Hide resolved

packages/rum-core/src/domain/view/viewMetrics/trackInteractionToNextPaint.ts Outdated Show resolved Hide resolved

HugoGarrido added 3 commits February 11, 2026 11:16

👌 fix: only rely on group that should exists to compute subparts

4f1ce8b

👌 fix: stop storing entries in group since not used

2c2ad12

👌 fix: prevents 0 value being falsy in checks for interactionId

5189c30

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HugoGarrido mentioned this pull request Feb 11, 2026

feat: update view schema to support INP subparts RUM-14475 DataDog/rum-events-format#348

Merged

gh-worker-dd-devflow-36fce6 bot added the staging-07 label Feb 12, 2026

		if (isExperimentalFeatureEnabled(ExperimentalFeature.INP_SUBPARTS)) {
		interactionToNextPaintSubParts = computeInpSubParts(newInteraction, sanitizeInpValue(interactionToNextPaint))

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