PostgreSQL also has built-in support for exact (as opposed to approximate) vector similarity search for some problems with the following constraints:

- you have smaller vectors (no more than 50D)

- Euclidean, taxicab, or Chebyshev distance is appropriate for your problem

Put a GiST index [0] on a cube column [1] and ORDER BY target_cube_value <-> cube_column.

[0] https://www.postgresql.org/docs/current/gist.html

[1] https://www.postgresql.org/docs/current/cube.html