feat(session-replay-browser): migrate sampling from Java hashCode to xxHash32#1629
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lewgordon-amplitude merged 4 commits intomainfrom Mar 26, 2026
Merged
feat(session-replay-browser): migrate sampling from Java hashCode to xxHash32#1629lewgordon-amplitude merged 4 commits intomainfrom
lewgordon-amplitude merged 4 commits intomainfrom
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Replace the Java-style 32-bit hashCode with xxHash32 for session ID sampling to improve uniformity at high bucket resolutions (1M+) and ensure cross-platform determinism (Web/iOS/Android). - Add pure JS xxHash32 implementation based on the official spec - Update isSessionInSample to use xxHash32(sessionId) % 1_000_000 - Add X-Sampling-Hash-Alg: xxhash32 header for server-side compat SR-1841 Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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bugbot run |
Session Replay Browser E2E Results
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![cursor[bot]](https://avatars.githubusercontent.com/in/1210556?s=60&v=4){kind=small}
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@Mercy811 I wasn't sure if I should move this to core. |
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Thanks @lewgordon-amplitude, we can start with SR and move it to core later |
Mercy811
approved these changes
Mar 25, 2026
Verify that the X-Sampling-Hash-Alg: xxhash32 header is sent on track API requests, and that sampling in/out decisions are correct for known session IDs with pre-computed xxHash32 ratios. Also expand playwright testMatch from capture.spec.ts to *.spec.ts so privacy.spec.ts (added in SR-2943) is included in the test run. SR-1841 Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Two issues in the header test: 1. waitForRequest matched the CORS OPTIONS preflight (no X-Sampling-Hash-Alg) before the POST — fixed by predicating on POST method 2. blur alone may not guarantee a flush — added explicit sessionReplay.flush() matching the pattern used in flushRecording() Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
jxiwang
approved these changes
Mar 25, 2026
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LGTM! Wonder why the lock diff is so big 🤔
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@jxiwang not sure. Let me check before merging. |
The lockfile was reformatted by a different pnpm environment in this worktree (multi-line → single-line resolution blocks, TypeScript peer dep re-resolution). No package changes were made, so restore to main. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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fixed! |
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Summary
Replace the Java-style 32-bit hashCode with xxHash32 for session ID sampling to improve uniformity at high bucket resolutions (1M+) and ensure cross-platform determinism (Web/iOS/Android).
Implements https://amplitude.atlassian.net/wiki/spaces/IG/pages/3375071237
SR-1841
Checklist
Note
Medium Risk
Changes the core session sampling decision algorithm, which can alter which sessions are recorded at a given
sampleRateand impact event volume/coverage. Adds a new request header that backend systems may rely on for compatibility.Overview
Updates Session Replay sampling to use a new deterministic
xxHash32-based hash (hash % 1_000_000) viaisSessionInSample, replacing the previous timestamp-based sampling helper.Track requests now include
X-Sampling-Hash-Alg: xxhash32for server-side compatibility, and new unit/integration/e2e coverage is added to validate sampling decisions, determinism, and the emitted header (Playwright config now runs all*.spec.ts).Written by Cursor Bugbot for commit e4e5136. This will update automatically on new commits. Configure here.