I don't have a good enough grasp HLL to summarize accurately, so for convenience here is the original paper[0] and hopefully HN comes through with a more diges

I don't have a good enough grasp HLL to summarize accurately, so for convenience here is the original paper[0] and hopefully HN comes through with a more digestible explanation. The blog post uses Citus' Postgres extension[1] which uses an augmented various of the original algorithm to reduce the size of the data structure so that it is fixed-size [0] HLL paper: http://algo.inria.fr/flajolet/Publications/FlFuGaMe07.pdf http://algo.inria.fr/flajolet/Publications/FlFuGaMe07.pdf [1] postgresql-hll: https://github.com/citusdata/postgresql-hll https://github.com/citusdata/postgresql-hll