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cache: Short TTL negative cache for 404/410 depot objects #50

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eva merged 1 commit from cache/negative-ttl-404 into main 2026-09-08 16:49:07 +00:00
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Ghost commented 2026-09-08 16:42:27 +00:00
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Why

A 404/410 depot chunk was re-fetched on every miss, hammering Steam for definitive gone objects while looking like normal cache misses.

What changed

  • Store short-TTL negative markers for upstream 404/410 in the same VFS cache under the same depot-path key (SC2C optional 4th expires-unix field; positives stay 3-field).
  • Within TTL, serve the cached 404/410 without re-hitting upstream; expired negatives are deleted and treated as miss.
  • Do not retry 404/410 with backoff; do not cache 5xx as negative.
  • New /metrics counter negative_cache_hits (also still counts as cache_hits).
  • Config: cache.negative_ttl (Go duration, default 5m; 0/0s disables storing).
  • Brief README docs for TTL/behavior near existing metrics/cache notes.

How tested

  • go test -count=1 ./steamcache/ ./config/ on jumpbox (pass)
  • TestNegativeCache404: first 404 hits upstream once; second within TTL does not; negative_cache_hits present
  • Also 410, TTL expiry refetch, SC2C 4th-field roundtrip, metrics emission

Risks / rollback

  • Negative entries occupy the same cache capacity as positives (short TTL + small bodies mitigate).
  • Clients now receive real 404/410 for gone objects instead of a generic 500 on the first miss (intentional).
  • Rollback: revert this PR / unset or set cache.negative_ttl: 0s.

Fixes #40

Waterfall

Produced by xAI grok (waterfall step 1: grok -p --effort medium).

## Why A 404/410 depot chunk was re-fetched on every miss, hammering Steam for definitive gone objects while looking like normal cache misses. ## What changed - Store short-TTL negative markers for upstream **404/410** in the **same** VFS cache under the same depot-path key (SC2C optional 4th `expires-unix` field; positives stay 3-field). - Within TTL, serve the cached 404/410 without re-hitting upstream; expired negatives are deleted and treated as miss. - Do **not** retry 404/410 with backoff; do **not** cache 5xx as negative. - New `/metrics` counter `negative_cache_hits` (also still counts as `cache_hits`). - Config: `cache.negative_ttl` (Go duration, default `5m`; `0`/`0s` disables storing). - Brief README docs for TTL/behavior near existing metrics/cache notes. ## How tested - `go test -count=1 ./steamcache/ ./config/` on jumpbox (pass) - `TestNegativeCache404`: first 404 hits upstream once; second within TTL does not; `negative_cache_hits` present - Also 410, TTL expiry refetch, SC2C 4th-field roundtrip, metrics emission ## Risks / rollback - Negative entries occupy the same cache capacity as positives (short TTL + small bodies mitigate). - Clients now receive real 404/410 for gone objects instead of a generic 500 on the first miss (intentional). - Rollback: revert this PR / unset or set `cache.negative_ttl: 0s`. Fixes #40 ## Waterfall Produced by **xAI grok** (waterfall step 1: `grok -p --effort medium`).
cache: Short TTL negative cache for 404/410 depot objects
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036ea1ea7f 
Stop re-fetching gone depot objects on every miss: store 404/410 in the
existing VFS cache under the same key with a short TTL (default 5m).
Ghost requested review from eva 2026-09-08 16:42:38 +00:00
eva merged commit a0e929c525 into main 2026-09-08 16:49:07 +00:00
eva deleted branch cache/negative-ttl-404 2026-09-08 16:49:07 +00:00
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