fix(tracing): Skip native frames and stall tracking for unsampled spans#5842
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fix(tracing): Skip native frames and stall tracking for unsampled spans#5842
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The NativeFrames and StallTracking integrations performed their full work (native bridge calls, 50ms polling loop) regardless of whether the span would be sampled, unlike the Profiling integration which already checks spanIsSampled() correctly. With tracesSampleRate: 0.2, this meant 80% of navigation spans triggered unnecessary fetchNativeFrames() bridge calls and stall tracking loop activations. On low-end devices these operations are significantly more expensive and contribute to the performance overhead reported in #5665. The fix adds a spanIsSampled() guard at the entry of fetchStartFramesForSpan in NativeFrames and _onSpanStart in StallTracking. Since end-frame fetching already bails when no start frames are found, the single guard in fetchStartFramesForSpan covers both start and end for NativeFrames. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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Semver Impact of This PR⚪ None (no version bump detected) 📋 Changelog PreviewThis is how your changes will appear in the changelog.
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lucas-zimerman
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Mar 19, 2026
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Sounds good to me, we can move with the changelog later.
This was referenced Mar 19, 2026
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📢 Type of change
📜 Description
Add a
spanIsSampled()guard toNativeFramesandStallTracking, consistent with howProfilingalready handles this.fetchStartFramesForSpan): returns early for unsampled spans, skipping allfetchNativeFrames()native bridge calls. SincefetchEndFramesForSpanalready bails when no start frames are found, a single guard covers both._onSpanStart): returns early for unsampled root spans, skipping the 50ms JS polling loop entirely.💡 Motivation and Context
Both integrations were doing their full work regardless of sampling decision. With
tracesSampleRate: 0.2, 80% of navigation spans were triggering unnecessary native bridge calls and stall tracking loop activations. On low-end devices (reported in #5665) these are measurably expensive.The
Profilingintegration already checksspanIsSampled()correctly — this brings the other two integrations in line.💚 How did you test it?
Added one new test per integration:
NativeFramesInstrumentation > unsampled spans > does not fetch native frames for unsampled spans— verifiesNATIVE.fetchNativeFramesis never called whentracesSampleRate: 0StallTracking > does not track stalls for unsampled spans— verifies no stall measurements are attached whentracesSampleRate: 0All 33 tests pass (31 existing + 2 new).
📝 Checklist
sendDefaultPIIis enabled🔮 Next steps
Part of a broader investigation into
reactNavigationIntegrationperformance on low-end devices (#5665).