Alex B and Claude Opus 5.5
38ed9d6ce6
perf(store): count path hops without decoding the JSON ( #2187 )
...
## Problem
`pathLen` is how `pickBestObservation` chooses each transmission's best
(longest-path) observation, so it runs for every observation on every
load and ingest, and again from the resolved-path index. It decoded the
path JSON into a `[]interface{}` only to take its length.
## Change
- `countStringArray` counts the usual array of plain hex strings in
place, with no allocation (helpers `skipJSONSpace` and
`skipPlainJSONString`).
- Anything else falls back to the decoder exactly as before: escapes,
non-string elements, `null`, or malformed input. So the result is always
what decoding gives, including 0 for invalid JSON.
## Perf justification (AGENTS.md rule 0)
- **Complexity.** O(len(path_json)), a single pass with no allocation.
The old version was also linear but went through reflection and
allocated per element.
- **Scale.** It runs once per observation on every load and ingest (400k
observations in a busy regional network's 7-day window), plus each time
the best observation is re-picked.
Throwaway benchmark (not committed), current master vs this branch:
| `path_json` | master | this PR |
|---|---|---|
| `[]` | 215 ns, 32 B, 2 allocs | 4 ns, 0 allocs |
| 6 hops, 1-byte | 1825 ns, 488 B, 18 allocs | 27 ns, 0 allocs |
| 10 hops, 3-byte | 2815 ns, 936 B, 27 allocs | 72 ns, 0 allocs |
On a copy of that 7-day window:
| | master | this PR |
|---|---|---|
| allocated over startup (the whole server) | 5.41 GB | 5.10 GB |
| server CPU over the run | 175.6 s | 169.2 s |
`pathLen` accounted for about 275 MB of the startup allocations.
## Tests
- `TestPathLenDoesNotAllocate`: zero allocations for typical paths. Red
commit first (2–11 allocations), then green.
- `TestPathLenMatchesDecoding` compares the result with `json.Unmarshal`
into `[]interface{}` on 27 edge cases and 20,000 random inputs built
from JSON punctuation, escapes, `null`, objects and numbers.
- `cd cmd/server && go test ./...` passes.
- SonarQube: quality gate passed, no issues on added lines.
Backend only: no UI, API shape or config change.
🤖 Generated with [Claude Code](https://claude.com/claude-code )
https://claude.ai/code/session_01KaR4xu8gVykQBkH8yG8m6H
---------
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com >
2026-10-12 12:45:41 +02:00
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