Consolidated Engine Capability & Metric Matrix¶

This document provides a single consolidated matrix of target engines versus metrics, detailing exactness, evidence ceilings, and provenance per ADR-0013.

Metric Support Matrix by Engine¶

Metric / Feature	Synthetic	LanceDB	Qdrant	PostgreSQL / pgvector
Index Row / Vector Counts	`OK` (Exact)	`OK` (Exact)	`OK` (Exact / Telemetry)	`OK` (Proxy / Estimated)
Deletion Fraction (DFI)	`OK` (Exact)	`OK` (Exact)	`OK` (Exact / Telemetry)*	`OK` (Proxy, Table `n_dead_tup`)
Canary Recall (k-NN)	`OK` (Exact)	`OK` (Exact, `float16` upcast)	`OK` (Exact, `hnsw_ef`)	`OK` (Exact, `EXPLAIN` guarded)
IVF Partition CV	`OK` (Exact)	`OK` (Exact)	`UNAVAILABLE` (HNSW)	`UNAVAILABLE`
HNSW Graph Stats	`UNAVAILABLE`	`UNAVAILABLE` (IVF)	`UNAVAILABLE` (Telemetry gap)	`UNAVAILABLE` (SQL gap)
Filtered Search	`False`	`False`	`True`**	`False`
Custom Search Parameters	`OK` (`ef_search`, `nprobe`)	`OK` (`nprobes`)	`OK` (`hnsw_ef`)	`OK` (`hnsw.ef_search`, `ivfflat.probes`)

* Note on Qdrant DFI: Derived strictly from per-segment num_deleted_vectors telemetry. If segment telemetry is omitted by the server, DFI is reported as UNAVAILABLE rather than substituting points_count - indexed_vectors_count (which misreports unindexed vectors as deleted).

** Note on Filtered Search: Supported for Qdrant via Schema 1.1 per-tenant / grouped canary recall (canary_groups, P7-03). Other engines remain False.

Engine Detail Summaries & Guides¶

Synthetic Adapter: Memory-backed reference engine used in unit/property tests. Exposes exact partition and deletion parameters with zero network/file I/O.
LanceDB Guide: docs/engines/lancedb.md — Columnar PyArrow-based snapshot audits (--dataset-version N), exact fragment metadata, exact DFI, and IVF cell statistics.
Qdrant Guide: docs/engines/qdrant.md — HTTP/gRPC collection audits, segment telemetry deleted counts, exact canary recall, hnsw_ef parameter configuration.
Postgres / pgvector Guide: docs/engines/pgvector.md — Catalog introspection, n_dead_tup table-level DFI proxy (capped at MEDIUM evidence), EXPLAIN sequential-scan guard, read-only session isolation (default_transaction_read_only=on).
HNSW Graph Statistics Findings: docs/engines/graph-stats.md — Detailed investigation recording why HNSW internal topology statistics conclude as UNAVAILABLE for both Qdrant and pgvector under pinned versions.