Search
- Retrieval was hybrid in name only: the keyword filter was applied to the SQL
query, so results were the *intersection* of the two rankers. A question that
matched the meaning but not the literal string could never be returned. It is
now a union, fused with Reciprocal Rank Fusion (a text rank and a cosine
distance are not on comparable scales, so RRF uses only their orderings).
- Added a generated `search_vector` tsvector + GIN index, so the lexical half is
ranked full text rather than ILIKE substring matching.
- Chose Postgres + pgvector over OpenSearch/Elasticsearch: a search cluster
would add a second datastore to keep in sync and a JVM on this host, to
replace an index Postgres maintains inside the same transaction.
- Removed the keyword-only mode. It looks precise but silently drops the
question that asks the same thing in different words.
Embeddings — measured on 500 real questions, using each question's own
explanation as a paraphrase query (known answer, no hand labelling):
bge-small (local CPU, 384d) R@1 0.840 R@5 0.953 186ms/query
bge-m3 (LiteLLM proxy, 1024d) R@1 0.847 R@5 0.973 93ms/query
BGE-M3 wins on both quality and latency and needs no extra credential, since
llm.danvics.com already serves `openrouter-bge-m3`.
Three gaps this exposed, all fixed:
- Nothing recorded which model produced a stored vector, so changing models
silently mixed incomparable spaces. `embedding_model` / `embedded_at` now
stamp every vector, `GET /admin/embedding/health` reports current vs stale vs
missing, and regeneration defaults to stale-only.
- The generator read the model from env while the stamp read a Redis override,
so a vector could be labelled with a model that did not produce it. Both now
resolve through one function, with a regression test.
- Embedding at creation is best effort, and a failure left a question invisible
to semantic search forever. `retry_missing_embeddings` runs every 15 minutes
via Celery beat and backfills missing or stale rows.
- Query embeddings are cached in Redis per model, so typing is not a network
round-trip per keystroke.
`dimensions` is only sent to OpenAI's embedding-3 family; BGE-M3 rejects it.
Tests: 8 new backend tests (union not intersection, fusion ordering, per-ranker
failure degradation, provenance stamping, stale/missing accounting, generator
and stamp agreement). Full suites green: 95 backend, 127 frontend, build clean.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014yhHB8Pc7oQqyqn2Vo9DXA
