faro-embedded-search 0.1.0

Incremental hybrid retrieval (lexical + vector, RRF-fused) with identical semantics on server Postgres and on-device SQLite

faro-embedded-search

Incremental hybrid retrieval with identical semantics on the server and on-device.

faro-embedded-search is a small, dependency-light library for searching a continuously growing collection of heterogeneous objects — notes, contacts, emails, tasks, tools, anything — without ever rebuilding an index. It is built for the pattern modern assistant apps need:

Index server-side, retrieve on-device. Embeddings are computed once, centrally. Each user's slice of the index is replicated into a local SQLite shard, and the device answers queries locally — fast, offline, and private — with exactly the same ranking the server would produce.

Built and dogfooded by Faro; also the embedded retrieval engine of Scope.

Why another retrieval library?

Most RAG tooling assumes a batch world: ingest a corpus, build a tree/graph/index, query it. Real applications have object-level CRUD — a contact edited, a task created, an email deleted — and small/on-device context windows that punish irrelevant results. faro-embedded-search makes two opinionated choices:

1. Incremental-first. One upsert per object write. Postgres (pgvector HNSW + tsvector GIN) and SQLite (FTS5 + vector blobs) both take per-row inserts natively, so there is no "rebuild" anywhere in the design. Hierarchical enrichment (summary and cluster nodes) lives in the same flat pool as extra rows — never on the write path.
2. Rank-based fusion. Lexical and semantic retrievers run in parallel and are fused with Reciprocal Rank Fusion (RRF, K=60). Because RRF consumes ranks, not raw scores, the incomparable scoring scales of ts_rank_cd (Postgres) and bm25() (SQLite FTS5) don't matter: the same corpus and query rank identically on both backends. That is what makes "same engine, server and device" honest rather than aspirational.

Quick start

from faro_embedded_search import IndexDoc, SearchIndex, OpenAICompatibleEmbedder
from faro_embedded_search.backends.sqlite import SQLiteBackend

index = SearchIndex(
    SQLiteBackend("search.db"),
    OpenAICompatibleEmbedder("https://api.openai.com/v1", api_key, "text-embedding-3-small"),
)

await index.upsert(IndexDoc(
    object_type="note", object_id="n1",
    title="Quantum entanglement notes",
    body="spooky action at a distance",
    partition="user-42",                      # isolation + shard key
))

results = await index.search("entanglement", partition="user-42", k=5)
# SearchResult(object_id='n1', match_type='hybrid', score=..., ...)

Deleting and updating are first-class — deletes are tombstones so they propagate through shard sync:

await index.delete("note", "n1")

Server-side: Postgres

from faro_embedded_search.backends.postgres import PostgresBackend  # pip install faro-embedded-search[postgres]

backend = PostgresBackend("postgresql+asyncpg://...", table="faro_embedded_search_index", dim=1536)
await backend.create_schema()     # idempotent; or transcribe the DDL into your migrations
index = SearchIndex(backend, embedder)

On-device: replicate a shard, query locally

from faro_embedded_search import export_shard, replicate

# Full export of one user's partition into a SQLite file:
shard = await export_shard(server_backend, "user-42.db", partition="user-42")

# Later, incremental delta sync (inserts, updates, AND deletes):
cursor = await replicate(server_backend, shard, partition="user-42", cursor=cursor)

The shard is a plain SQLite file whose schema is the interchange format — any runtime that can read SQLite (a future Swift/Kotlin reader, for instance) can retrieve against it. Embeddings travel with the shard; the device never needs to re-embed the corpus. Query embedding on-device can use a local model, a cached vector, or one tiny server round-trip for the query alone.

Tiering without batch trees

RAPTOR-style hierarchies buy small-context windows a lot — but a recursive tree can't be rebuilt on every insert. faro-embedded-search keeps the index flat and gets the benefit through node kinds:

• leaf — the object itself (default).
• summary — an optional one-line abstract of an object, indexed alongside it. O(1) per object, generated on your write path or a background pass.
• cluster — optional theme summaries produced by a periodic background sweep over existing embeddings.

All kinds live in the same pool and are retrieved by the same top-k ("collapsed" retrieval); by default multiple hits on one object collapse into its best row, with matched_node_kinds telling you which handles matched:

await index.upsert_many([
    IndexDoc(object_type="note", object_id="n9", title="Meeting notes", body=transcript),
    IndexDoc(object_type="note", object_id="n9", node_kind="summary",
             title="Summary: hiring sync", body="decided to open two roles"),
])

Heterogeneous objects

Per-type behavior lives in code, not schema, via a tiny registry:

from faro_embedded_search import register, docs_for

@register("contact")
def index_contact(c) -> IndexDoc:
    return IndexDoc(object_type="contact", object_id=str(c.id),
                    title=c.name, body=f"{c.role} at {c.company}",
                    payload={"avatar": c.avatar_url})

await index.upsert_many(docs_for("contact", some_contact))

payload is carried into results (and shards), so result lists render without joining back to your application database.

Design notes

• Embedding failure is non-fatal. A row written without a vector still serves lexical queries and gains semantic retrieval after a backfill — availability over completeness.
• Exact semantic scan on SQLite. Per-user shards are small (tens of thousands of rows); an exact cosine scan (numpy-accelerated when present) costs no index maintenance and returns exact results. ANN acceleration (e.g. sqlite-vec) can be added without changing the file format.
• Diversity, not padding. An optional per-group cap (diversity_key) drops near-duplicate siblings instead of deferring them.
• No framework. Plain SQL on both backends, zero required dependencies in the core.

Installation

pip install faro-embedded-search                # core (SQLite backend, stdlib only)
pip install faro-embedded-search[postgres]      # + Postgres/pgvector backend
pip install faro-embedded-search[http]          # + OpenAI-compatible embedder
pip install faro-embedded-search[numpy]         # + fast cosine on SQLite

License

MIT