In Oracle Database 23ai, vector indexes (e.g., HNSW, IVF) are built with a specific distance metric
(e.g., cosine, Euclidean) that defines how similarity is computed. If a query specifies a different
metric (e.g., querying with Euclidean on a cosine-based index), the index cannot be used effectively,
and the query fails (A) with an error, as the mismatch invalidates the index’s structure. An exact
match search (B) doesn’t occur automatically; Oracle requires explicit control. The index doesn’t
update itself (C), and warnings (D) are not the default behavior—errors are raised instead. Oracle’s
documentation mandates metric consistency for index usage.
Reference:Oracle Database 23ai AI Vector Search Guide, Section on Vector Index Metrics.
