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cache: Serve Range GET from disk when present
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Steam clients lean on Range requests. Hit/miss looked fine while downloads
still felt cold when a Range miss returned the full upstream body as 200.

Add range_cache / range_upstream metrics. HIT path already sliced 206 from
the cached full object; count range_cache there. On MISS, keep stripping
Range for the upstream fetch (full object still cached) but serve the
client's requested slice as 206 and count range_upstream.

Tests in steamcache/range_test.go cover Range HIT (local, no upstream),
Range MISS (206 + full object cached), and /metrics emission.
This commit is contained in:
moss
2026-09-07 16:32:36 +00:00
parent c43bfba568
commit ac2d36f1ad
5 changed files with 456 additions and 7 deletions
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README.md
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@@ -81,11 +81,14 @@ curl -s -i http://localhost/lancache-heartbeat
| Field | Meaning |
| --- | --- |
| `cache_hits` / `cache_misses` / `hit_rate` | Whether later requests were served from cache |
| `range_cache` / `range_upstream` | Range GETs served as 206 from a cached object vs after a full upstream fetch |
| `memory_cache_hits` / `disk_cache_hits` | Which tier served the hits |
| `total_requests` / `errors` | Volume and failures |
A first pass through new content is mostly misses (`hit_rate` near 0). Repeat the same content and `cache_hits` / `hit_rate` should rise.
Steam clients lean on Range requests. When an object is already cached, a Range GET is served locally as 206 from that full object (`range_cache`). On a Range miss the cache still fetches and stores the full upstream body, then returns the requested byte range as 206 (`range_upstream`).
To confirm the process is up (HTTP 204 and `X-LanCache-Processed-By: SteamCache2`):
```bash
@@ -179,7 +182,7 @@ The recommended validation config is at [docs/examples/validate-config.yaml](doc
Running a realistic SteamPrefill benchmark workload through a built steamcache2 exercises the complete public surface that matters for production use:
- Steam User-Agent detection and depot/manifest/chunk URL patterns
- Full MISS → cache write → HIT (and HIT-COALESCED) paths
- Range request handling from cached full responses
- Range request handling from cached full responses (local 206 on HIT via `range_cache`; MISS fetches the full object then serves the requested slice as 206 via `range_upstream`)
- Request coalescing under concurrent load
- Memory tier + disk tier interaction (including async disk attach)
- Garbage collection and eviction under pressure