I tried to use the snippet from this https://dba.stackexchange.com/posts/163915/revisions answer, where I saw your comment about this image. I tried to create 5000 entries with 512 dimensional vector, but I am getting the following error ERROR: failed to add item to index page in "mytable" SQL state: XX000 Have you tested it with such vectors with such dimensions?

Here's the query

CREATE TABLE mytable
AS
  SELECT i, cube(array_agg(random()::float)) AS c
  FROM generate_series(1,5000) AS i
  CROSS JOIN LATERAL generate_series(1,512)
    AS x
  GROUP BY i;

CREATE INDEX ON mytable USING gist ( c );
ANALYZE mytable;