Appendix

An immutable, append-only, thread safe, on-disk index mapping Copy keys to Copy values.

Writes use mutexes, but reads are lock-free.

Overwriting values is not possible, and any insert with pre-existing key will simply be ignored.

Example from test

```rust

[test]

fn multithreading() { let tempdir = TempDir::new("idx").unwrap(); let idx = Arc::new(Index::new(tempdir.path()).unwrap());

let n_threads = 16;
let mut handles = vec![];

for _ in 0..n_threads {
    let idx = idx.clone();
    handles.push(thread::spawn(move || {
        for i in 0..N {
            idx.insert(i, i).unwrap();
            }
        }))
}

for handle in handles {
    handle.join().unwrap();
}

for i in 0..N {
    assert_eq!(idx.get(&i).unwrap(), &i)
}

assert_eq!(idx.get(&N), None);

} ```