Glossary

A working glossary of terms used across these docs.

adjacency — the derived, endpoint-first re-keying of graph edges into private __adj_out__/__adj_in__ namespaces so deletes cascade in O(edges-of-document) and neighbor reads are direct. Invisible: never listed, never dumped.

ANN (approximate nearest neighbor) — vector search served by an HNSW graph index instead of an exact scan. Candidates are approximate; scores are reranked exact. See Hit.approximate.

backfill — the process of building an index over an existing collection, committed page by page with a persisted cursor (Building{cursor} → Complete) so an interrupted creation resumes and queries never serve a partial index.

candidate superset — what an index window returns: a set guaranteed to contain every match (encoding ties may add extras); the builder re-checks each candidate against the exact predicate, so results are always exact.

CAS (compare-and-set) — an atomic conditional write: apply only if the stored value equals expected (or is absent). Uses semantic value equality.

change event — an Insert/Delete notification delivered synchronously post-commit to subscribers; the engine has no separate event log.

class order (ordering) — order_by’s fixed row classes: comparable values (numbers, then texts) → incomparable values (kind tag first, so NaN precedes the other incomparable kinds; then key) → rows missing the field; ties by key; descending reverses the within-class order — kind tag and value together — in both present classes, never the class order itself.

collection — a named namespace of documents, created lazily on first write; __-prefixed names are engine-reserved.

compound index — an index over an ordered field list serving prefix-equality plus at most one trailing range; carries the all_docs_indexed flag that gates prefix-only acceleration.

corvid — the engine. Corvid = crows/ravens: eat anything, highly intelligent, cache food across thousands of remembered locations.

cursor — an opaque byte token resuming a keyset page walk strictly after the last served key. Also the general term for the ABI’s _next-driven iterators.

derived index — an index maintained transactionally from the documents (the source of truth). Never stale at query time; re-creatable; corrupt state errors loudly.

dump — the logical, version-stamped export stream (CORVIDDUMPv1/v2) carrying documents plus definitions; the migration path across format breaks. load (and load_with_renames) replay it.

exact baseline — vector/text search without an index: brute-force streamed scoring. Correct at any scale (OOM-free); the default until you create an index.

fused score — the reciprocal-rank-fusion score of a row (Σ 1/(k + rank) across sources); 0.0 for pure filter/order queries.

golden fixtures — the 256-line fixture suite pinning ABI-observable behavior (NaN/±inf/−0.0, cursors, unique violations, geo boundaries, persistence); every binding replays it in CI.

HNSW — Hierarchical Navigable Small World: the graph index behind all corvid vector indexes, in-RAM or on-disk, optionally quantized/PQ.

keyset pagination — walking a collection by cursor instead of offset: each page returns rows plus the resume point; O(limit) per page regardless of depth.

MVCC — multi-version concurrency control: readers get point-in-time snapshots and never block (or get blocked by) the single writer.

MMR (maximal marginal relevance) — a rerank trading relevance for diversity; lambda ∈ [0,1] (1 = pure relevance, 0 = maximal diversity).

PQ (product quantization) — compressing vectors to m code bytes via a trained per-subspace codebook; the smallest footprint (e.g. 16× at 64d, m=16), scored via ADC (L2) or reconstruction.

predicate — a filter tree over dotted field paths; a true predicate runs before ranking (the top-k is computed among matches).

purge — the TTL deletion step (purge_expired(now)): expired records stay visible until you call it; the engine keeps no clock.

quantization — storing vectors lossily-compressed: Binary (1 bit/dim, ~32×, Hamming), Scalar (8-bit + header, ~4×), or PQ.

RRF (reciprocal rank fusion) — merging ranked lists by Σ 1/(k + rank); corvid’s default constant is 60.

scalar index — order-preserving keys making equality/range filters, counts, and order walks sub-linear.

schema — an optional per-collection declaration of field types/required/unique constraints, enforced on write.

semantic cache — a vector-keyed cache: nearest embedding within a threshold answers; distance units follow the metric.

snapshot — the MVCC point-in-time view behind every query, page, join, traverse, and dump; one query = one committed state.

tombstone — a delete marker inside an on-disk index; over-fetch scales with tombstone count, and compaction triggers when they exceed a third of the index.

true predicate — see predicate.

wave 4 — the audit-remediation wave that tightened name validation (interior __, NUL); pre-wave-4 dumps migrate via load_with_renames.