when recursive into a directory of 6.2GB with 767 files in it, I thought the insane fast one will:

1. compute a summary for each file by the csum of each block included in the file;
2. Do a sort / uniq of these files

Since csum is already computed, this shouldn't take more than a minute in a modern computer. Instead, the process has been running 30 minutes now and the result already showing 2020 non-matching results.