alt Hacker NewsLet's do a back of the envelope calculation. 150M u32 integers are 600MB. Modern SSD can do 14,000MB/s sequential read [1]. So reading 600MB takes about 600MB / 14,000MB/s = 43ms.
Memory like DDR4 can do 25GB/s [2]. It can go over 600MB in 600MB / 25,000MB/s = 24ms.
L1/L2 can do 1TB/s [3]. There're 32 CPU's, so it's roughly 32TB/s of L1/L2 bandwidth. 600MB can be processed by 32TB/s in 0.018ms. With 3ms budget, they can process the 600MB data 166 times.
The rank selection algorithms like QuickSelect and Floyd-Rivest have O(N) complexity. It's entirely possible to process 600MB in 70ms.
[1] https://www.tomshardware.com/features/ssd-benchmarks-hierarc...
[2] https://www.transcend-info.com/Support/FAQ-292
[3] https://www.intel.com/content/www/us/en/developer/articles/t...
They mentioned that they use 125 MiB/s SSD. However, one can notice that the column seems to contain only about 47500 unique values. Probably there are many reviews with zero or one votes. This column is probably stored compressed so it can be loaded much faster.