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DuckDB vss vs Alopex DB
The HNSW index provided by the DuckDB vss extension, and how it handles persistence. Also explains how it differs from Alopex DB.
Updated: Oct 11, 2026
What the vss extension is
vss is an extension that adds a vector search index to DuckDB. You load it with INSTALL vss; LOAD vss;.
How it works
You can create an HNSW index on an ARRAY column and choose the distance.
Index persistence is experimental; by default indexes can only be created on tables in in-memory databases.
Main features
- An HNSW index (on
ARRAYcolumns). - A choice of distance (
metric). - You can check whether the index is used with
EXPLAIN.
Limits
Persisting the index in an on-disk database is experimental. Isolation, storage, and distribution follow DuckDB itself.
How it differs from Alopex DB
Both let you create an HNSW index on a column of a SQL table.
In Alopex DB, the vector type and HNSW index are in the core and work right after installation. The index you build is saved in the database file. Choose the distance from cosine, L2, and inner product.
Alopex DB keeps vectors and SQL data together under transactions. Give it a try with the quickstart.