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Life & fun · March 25, 2026

DuckDB community extension for prefiltered HNSW using ACORN-1

Hey folks! As someone doing hybrid search daily and wishing I could have a pgvector-like experience but with actual prefiltered approximate nearest neighbours, I decided to just take a punt on implementing ACORN on a fork of the DuckDB VSS extension. I had to make some changes to (vendored) usearch that I'm thinking of submitting upstream. But this does the business. Approximate nearest neighbours with WHERE prefiltering. Edit: Just to clarify, this has been accepted into the community extensions repo. So you can use it like: ``` INSTALL hnsw_acorn FROM community; LOAD hnsw_acorn; ```

DuckDB community extension for prefiltered HNSW using ACORN-1 launched on March 25, 2026 with 90 votes, #526 of 23,380 launches that month and more than 95% of that year's launches.

Visit github.com ↗Alternativestop 2% of March 2026

In plain words

HNSW_ACORN is a DuckDB community extension that enables approximate nearest neighbor searches with WHERE clause prefiltering. Built as an enhancement to DuckDB's Vector Search Support extension, it implements the ACORN algorithm to combine hybrid search capabilities similar to pgvector but with efficient prefiltered approximate nearest neighbor queries. The extension is installable from DuckDB's community extensions repository and integrates modifications to the underlying usearch library.

written from the facts on this page · September 2026

From the sources

ACORN-1 pre-filtered HNSW search for DuckDB. Contribute to cigrainger/duckdb-hnsw-acorn development by creating an account on GitHub.

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