It might make sense to check how they do it.
I'd also be interested in how elfshaker compares to those (and `bupstash`, which is written in Rust but doesn't have a FUSE mount yet) in terms of compression and speed.
Did you know of their existence when making elfshaker?
Edit: Question also posted in your Q&A: https://github.com/elfshaker/elfshaker/discussions/58#discus...
As an idea of how elfshaker performs, we see ~300ms time to create a snapshot for clang, and ~seconds-to-minute to create a binary pack containing thousands of revisions. Extraction takes less than a second. One difference of elfshaker compared with some other software I tested is that we do the compression and decompression in parallel, which can make a very big difference on today's many-core machines.