Approximate counters are much much older than HyperLogLog. Here’s something from 1978: https://www.inf.ed.ac.uk/teaching/courses/exc/reading/morris.... Of course this solves a different problem because HyperLogLog is an, uh, interesting way to count followers (why would you need to do a count-distinct query? You can’t follow someone multiple times). In any case, the Flajolet Martin sketch dates back to 1985 and solves the same problem as HyperLogLog: https://en.wikipedia.org/wiki/Flajolet%E2%80%93Martin_algori...