Vector: DDL accepts ternary/opq quantization — search paths reject the codecs they advertise

[EnRaiha]

Version / build tested against

origin/main @ e235fe5 (2026-09-29)

Deployment mode

Origin — single node (local)

Engine(s) involved

Vector

Summary

CREATE VECTOR INDEX ... quantization='ternary' | 'opq' is accepted by the DDL parser and implied by docs, but no query path serves these codecs: the rerank gating returns RerankError::BadInput, and the ANN path warns 'no match' then proceeds with the actual codec. Advertised capability is unreachable.

Steps to reproduce

CREATE a vector index with quantization = 'ternary' (accepted), then run any search using it — rerank gating errors BadInput; ANN path substitutes silently. (static verification at the pin; runtime repro pending)

Expected behavior

Either the codecs are served end-to-end, or DDL/docs reject them explicitly until implemented.

Actual behavior

Parser/docs advertise; gating rejects (BadInput); ANN warns and substitutes.

What actually happened? (severity facts)

• Acknowledged/committed data was lost, corrupted, or silently wrong
• The server crashed, hung, or failed to start
• A security or isolation boundary was crossed
• Core functionality is broken with no acceptable workaround
• A workaround exists (use supported quantizations)

Proposed severity

SEV-3 — Medium: advertised feature unusable; workaround exists.

Reproducibility

Always — every attempt

Last known-good version / commit (if a regression)

(unknown / not a regression)

Environment & logs

Linux x86_64; Verified by static code reading at the pin above; runtime reproduction pending.
Code references:

• (see prior-art line below)

Before submitting

• I searched existing issues and this is not a duplicate. (#25 closed via PR [#27](fix(pgwire): wire quantization params through CREATE/ALTER VECTOR INDEX DDL #27); did not cover ternary/opq)
• Reproduced on a released tag or current main build (pending) — code path verified at e235fe55c.
• This is not a security vulnerability.

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Additional evidence (origin/main @ e235fe55c)

• What: parse_quantization accepts "ternary"/"opq" (vector_primary.rs:430-431, listed in VALID_QUANTIZATIONS:21-23); docs/vectors.md and nodedb-codec/README.md list them as tiers. map_collection_quant returns RerankError::BadInput for both (gating.rs:141,147) and quantization_matches maps them to false (vector_search_ann.rs:75).
• Where: nodedb-sql/src/ddl_ast/parse/vector_primary.rs:426-431; nodedb-vector/src/rerank/gating.rs:141,147; nodedb/src/data/executor/handlers/vector_search_ann.rs:75; docs/vectors.md:18,20,77,141,145; nodedb-codec/README.md:5.
• Evidence: quotes above.
• Impact: a user creates a collection/index with quantization='ternary' (accepted at DDL), then a search with the same hint fails with BadInput, or (via the SQL ANN hint path) silently proceeds with a different codec after a warning. The advertised capability is unreachable.
• Fix (claim direction): remove ternary/opq from the parser grammar and docs until HNSW integration exists, or wire the codecs through end to end.
• Prior-art: #25 (closed by PR [#27](fix(pgwire): wire quantization params through CREATE/ALTER VECTOR INDEX DDL #27)) made PQ reachable from SQL; it did not cover ternary/opq, which remain parser-accepted but unroutable. No open issue covers it.
  Why: users can declare quantization='ternary'|'opq' in DDL and read docs implying support, but no query path serves the codec (rerank gating returns BadInput; the ANN hint merely warns and proceeds with the actual codec).
  Steps to test: create an index with quantization = 'ternary', run any search -> rerank path errors BadInput (gating.rs); ANN path warns and substitutes. Either back the codecs or reject them at DDL.