Sled high memory use example with many small objects

Cargo.lock

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Cargo.toml

[package]
name = "sled_oom"
version = "0.1.0"
authors = ["Alex Roper <alex@aroper.net>"]
edition = "2018"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
sled = "0"
rayon = "1"

main.rs

use std::io::Write;
use std::path::PathBuf;

// Not needed to repro -- just makes the generation go faster.
use rayon::prelude::*;

const SIZE: u64 = 400;

fn cmd_gen(tree: &sled::Tree) {
    let path = b"/home/user/big/stuff/potato/long/thingimie/words".to_vec();
    let jb = path.len();

    let top: Vec<_> = (0..SIZE).collect();
    top
        .par_iter().map(|j| {
            let mut path = path.clone();
            let mut buf = [0; 24];
            write!(&mut path, "/foo{}", j).unwrap();
            let kb = path.len();
            for k in 0..SIZE {
                write!(&mut path, "/bar{}", k).unwrap();
                let lb = path.len();
                for l in 0..SIZE {
                    write!(&mut path, "/baz{}", l).unwrap();
                    buf[0..8].copy_from_slice(&j.to_le_bytes());
                    buf[8..16].copy_from_slice(&k.to_le_bytes());
                    buf[16..24].copy_from_slice(&l.to_le_bytes());
                    tree.insert(&path, &buf).unwrap();
                    path.truncate(lb);
                }
                path.truncate(kb);
            }
            path.truncate(jb);
        })
        .for_each(drop);
    tree.flush().unwrap();
}

fn cmd_oom(tree: &sled::Tree) {
    tree.clear().unwrap();
    tree.flush().unwrap();
}

fn main() {
    let args: Vec<_> = std::env::args().collect();
    if args.len() < 3 || (args[2] != "gen" && args[2] != "oom") {
        eprintln!("Usage: {} <db_path> <gen|oom>", &args[0]);
        return;
    }

    let db = sled::Config::new()
        .cache_capacity((4 * 1024 * 1024) as u64)
        .path(&args[1])
        .open()
        .unwrap();
    let tree = db.open_tree(b"path_to_id").unwrap();

    if args[2] == "gen" {
        cmd_gen(&tree);
    } else {
        cmd_oom(&tree)
    }
}