[iampims]

At a certain scale, exact computations (p50 for instance) become impractical. I’ve had great luck switching to approximate calculations with guaranteed error bounds.

An approachable paper on the topic is "Effective Computation of Biased Quantiles over Data Streams" http://dimacs.rutgers.edu/%7Egraham/pubs/papers/bquant-icde....

[hipadev23]

The quantile() method in clickhouse is also approximate although it uses a more simplistic reservoir sampling model than GK, but quantileGK() is also available. quantileExact() exists but indeed becomes impractical as you point out.