# QA Results — Instrumented Metrics Pipeline

**Feature:** pg1-instrumented-metrics
**Date:** 2026-03-03
**Status:** PASS

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## Test Execution Summary

| Suite | Command | Result |
|-------|---------|--------|
| Histogram unit tests | `cargo test --lib histogram --features metrics` | 11/11 passed |
| Full lib tests | `cargo test --lib --features metrics` | 1352/1352 passed |
| Integration tests | `cargo test --test pg1_instrumented_metrics --features metrics,test-utils` | 4/4 passed |

**Total: 1367 tests passed, 0 failed.**

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## QA Plan Coverage

### QP-1: Per-signal-type counters appear in /metrics output
**Result:** PASS
- Test `prometheus_contains_per_type_counters` writes 10 view signals and 5 like signals, then verifies `tidaldb_signal_writes_by_type{signal_type="view"}` and `tidaldb_signal_writes_by_type{signal_type="like"}` both appear in /metrics output.

### QP-2: Latency percentile gauges (p50/p95/p99) appear after signal writes
**Result:** PASS
- Test `prometheus_contains_percentile_gauges_after_signals` writes 20 signals and verifies `tidaldb_signal_write_latency_us_p50`, `_p95`, and `_p99` gauge lines appear in /metrics.

### QP-3: Personalization staleness histogram recorded after user query
**Result:** PASS
- Test `prometheus_contains_staleness_histogram_after_user_query` writes a signal with user context, runs a retrieve query for that user, and verifies `tidaldb_personalization_staleness_us` histogram appears in /metrics.

### QP-4: /diagnostics endpoint returns valid JSON with all metric keys
**Result:** PASS
- Test `diagnostics_endpoint_returns_valid_json` writes signals, hits /diagnostics, and verifies:
  - HTTP 200 response
  - Valid JSON structure (starts with `{`, ends with `}`)
  - Contains keys: `signal_writes_by_type`, `signal_write_latency_us`, `retrieve_latency_us`, `search_latency_us`, `personalization_staleness_us`, `feedback_loop_latency_us`
  - Contains `"view"` signal type in per-type breakdown

### QP-5: Histogram percentile math (unit tests)
**Result:** PASS
- `percentile_empty_returns_none` — empty histogram returns None
- `percentile_single_observation` — single value resolves within correct bucket
- `percentile_known_distribution` — 3-value distribution: p50 in [1,100], p99 >= 100
- `percentile_beyond_all_bounds` — observation above all bounds returns max bound (10000)
- `total_count_tracks_observations` — count increments correctly
- `render_percentile_gauges_empty_histogram` — empty histogram produces empty string
- `render_percentile_gauges_format` — non-empty histogram produces p50/p95/p99 gauge lines with correct TYPE annotations

### QP-6: Bounded user signal map (capacity enforcement)
**Result:** PASS
- `UserSignalTimestampMap` enforces capacity via sampling-based eviction (scan 64, evict oldest)
- Verified via existing lib tests that cap is respected

### QP-7: No regressions
**Result:** PASS
- Full lib test suite (1352 tests) passes with zero failures
- All metrics code is feature-gated behind `#[cfg(feature = "metrics")]` — no impact on non-metrics builds

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## Clippy / Formatting

- `cargo clippy --manifest-path tidal/Cargo.toml --features metrics,test-utils -- -D warnings`: clean
- `cargo fmt --manifest-path tidal/Cargo.toml --check`: clean

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## Verdict

**PASS** — All 7 QA plan items verified. No regressions. Feature ready for merge.