omnigraph/docs/user/indexes.md

Indexes

L1 — Lance index types OmniGraph exposes

Index	Use	Notes
BTREE scalar	range / equality on any scalar	created on @key, @index(...), and on key columns by ensure_indices()
Inverted (FTS)	search, fuzzy, match_text, bm25	created on text columns referenced by FTS queries
Vector	nearest() k-NN	Lance picks IVF_PQ vs HNSW family by configuration; OmniGraph stores as FixedSizeList(Float32, dim)

L2 — OmniGraph orchestration

• ensure_indices() / ensure_indices_on(branch) — idempotent build of BTREE + inverted indexes for the current head; safe to re-run.
• Indexes are built on the branch head (not on a snapshot), so reads always see the current index state.
• Lazy branch forking for indexes: a branch that hasn't mutated a sub-table doesn't need its own index — the main lineage's index is reused until the first write triggers a copy-on-write fork.
• Vector index parameters (metric, nlist, nprobe, etc.) are not exposed in the schema; they default at the Lance layer and are picked up automatically when an index is asked for on a Vector column.

L2 — Graph topology index (graph_index/mod.rs)

This is OmniGraph-specific (not Lance):

• TypeIndex: dense u32 ↔ String id mapping per node type.
• CsrIndex: Compressed Sparse Row representation of edges per edge type — offsets[i]..offsets[i+1] slices into targets.
• GraphIndex { type_indices, csr (out), csc (in) } — built on demand from a snapshot's edge tables.
• Cached in RuntimeCache::graph_indices (LRU, max 8 entries, keyed by snapshot id + edge table versions).
• Built only when an Expand or AntiJoin IR op is present in the lowered query, so pure scans skip it.