On my M1 Macbook, on APFS:
* Reads/views are 10-12µs when clone files can be reused.
* List operations: 22µs.
* File cloning is 60µs, tending toward 75µs for larger files.
* Empty reads (and the sqlite read transaction): 360ns.
* Empty writes (but a forced immediate write transaction): 3µs.