[SingleStore vector-indexing docs]: if INTERNAL_VECTOR_SEARCH is not in the ColumnStoreFilter line of EXPLAIN, the vector index is not being used. Two classic causes: the query uses USE INDEX () which disables ANN indexes, and ORDER BY in the wrong direction, DOT_PRODUCT needs DESC, EUCLIDEAN_DISTANCE needs ASC. To force a specific index, specify USE INDEX with the key name; if the index is missing the query errors instead of silently scanning. Place the USE INDEX clause right after ORDER BY.

Context: A vector query runs slowly as if the vector index does not exist. Check EXPLAIN to see whether the index is used at all.