If you insert point A and want to search for points that are within the radius r (i.e. less than the distance from any metric), you can make a really simple query:
select x1, x2, ..., xn
from points
where x1 between a1 - r and a1 + r
and x2 between a2 - r and a2 + r
...
and xn between an - r and an + r
... where A = (a1, a2, ..., an)to find an estimate. If you have an index for all fields x1, ... xn points, then this query does not require a full scan. Now this result may include points outside the neighborhood (i.e. Bits in the corners), but it is easy to win to find a suitable subset: now you can check the entries in this subquery, rather than checking every point in your table.
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