The Ubuntu Incident

Problem
In Rust, the stdlib’s HashMap is quite slow. It’s secure, resistant against DOS attacks, but slow. If I write a tool that I want to use myself, it doesn’t have to be cryptographically secure. I want it to be fast.

Solution
I tried several alternatives and fxhash proved to be the fastest. I compared the stdlib, hashbrown, ahash and fxhash, and fxhash proved to be the fastest.

Usage
In Cargo.toml:

[dependencies]
fxhash = "0.2"

In your code:

use fxhash::FxHashMap as HashMap;    // after these renames, it can be used
use fxhash::FxHashSet as HashSet;    // as a drop-in replacement

fn main() {
    let mut map: HashMap = HashMap::default();    // !!! it's called ::default(), not ::new()
    map.insert(1, "one");
    map.insert(2, "two");

    println!("{:?}", map);                  // {2: "two", 1: "one"}
    println!("{}", map.get(&1).unwrap());   // one
}

Credits
I asked on GitHub how to have a fast hashmap in Rust, and the author of hashbrown directed me to these crates. As Amanieu explained, FxHashMap and AHashMap are aliases of the stdlib’s hashmap with custom hashers.