Adds CachedProvider wrapping the embedding Provider with a thread-safe
LRU keyed on (effective_model, sha256(text)) → []float32. Repeat
queries return the stored vector without round-tripping to Ollama.
Why this matters: the staffing 500K test (memory project_golang_lakehouse)
documented that the staffing co-pilot replays many of the same query
texts ("forklift driver IL", "welder Chicago", "warehouse safety", etc).
Each repeat paid the ~50ms Ollama round-trip. Cached repeats now serve
in <1µs (LRU lookup + sha256 of input).
Memory budget: ~3 KiB per entry at d=768. Default 10K entries ≈ 30 MiB.
Configurable via [embedd].cache_size; 0 disables (pass-through mode).
Per-text caching, not per-batch — a batch with mixed hits/misses only
fetches the misses upstream, then merges the result preserving caller
input order. Three-text batch with one miss = one upstream call for
that one text instead of three.
Implementation:
internal/embed/cached.go (NEW, 150 LoC)
CachedProvider implements Provider; uses hashicorp/golang-lru/v2.
Key shape: "<model>:<sha256-hex>". Empty model resolves to
defaultModel (request-derived) for the key — NOT res.Model
(upstream-derived), so future requests with same input shape
hit the same key. Caught by TestCachedProvider_EmptyModelResolvesToDefault.
Atomic hit/miss counters + Stats() + HitRate() + Len().
internal/embed/cached_test.go (NEW, 12 test funcs)
Pass-through-when-zero, hit-on-repeat, mixed-batch only fetches
misses, model-key isolation, empty-model resolves to default,
LRU eviction at cap, error propagation, all-hits synthesized
without upstream call, hit-rate accumulation, empty-texts
rejected, concurrent-safe (50 goroutines × 100 calls), key
stability + distinctness.
internal/shared/config.go
EmbeddConfig.CacheSize (toml: cache_size). Default 10000.
cmd/embedd/main.go
Wraps Ollama Provider with CachedProvider on startup. Adds
/embed/stats endpoint exposing hits / misses / hit_rate / size.
Operators check the rate to confirm the cache is working
(high rate = good) or sized wrong (low rate + many misses on a
workload that should have repeats).
cmd/embedd/main_test.go
Stats endpoint tests — disabled mode shape, enabled mode tracks
hits + misses across repeat calls.
One real bug caught by my own test:
Initial implementation cached under res.Model (upstream-resolved)
rather than effectiveModel (request-resolved). A request with
model="" caching under "test-model" (Ollama's default), then a
request with model="the-default" (our config default) missing
the cache. Fix: always use the request-derived effectiveModel
for keys; that's the predictable side. Locked by
TestCachedProvider_EmptyModelResolvesToDefault.
Verified:
go test -count=1 ./internal/embed/ — all 12 cached tests + 6 ollama tests green
go test -count=1 ./cmd/embedd/ — stats endpoint tests green
just verify — vet + test + 9 smokes 33s
Production benefit:
~50ms Ollama round-trip → <1µs cache lookup for cached entries.
At 10K-entry default + ~30% repeat rate (typical staffing co-pilot
workload), saves several seconds per staffer-query session.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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