What is a key characteristic of HNSW vector indexes?

A key characteristic of HNSW (Hierarchical Navigable Small World) vector indexes is their hierarchical structure that incorporates multilayered connections. This design allows for efficient nearest neighbor searches by organizing data in a way that mimics small-world networks. In HNSW, multiple layers are utilized, with the top layers containing fewer nodes and serving as shortcuts through the graph, effectively reducing the search time because nodes can be quickly traversed across layers. As one moves down to lower layers, more nodes are examined, allowing for a trade-off between search speed and accuracy.

The other options do not accurately describe HNSW vector indexes. They are not strictly reliant on exact matches, as HNSW is designed for approximate nearest neighbor search, which allows for flexibility in retrieving similar, rather than identical, vectors. HNSW indexes can operate efficiently in memory rather than being strictly disk-based structures, although they can be implemented on disk if needed. Lastly, HNSW does not use hash-based clustering; instead, it employs a graph-based approach to facilitate neighbor searches. The multilayered design is what sets HNSW apart, making it particularly effective for handling high-dimensional datasets efficiently.