Mercurial > public > mercurial-scm > hg-stable
diff rust/hg-core/src/lib.rs @ 43844:5ac243a92e37
rust-performance: introduce FastHashMap type alias for HashMap
Rust's default hashing is slow, because it is meant for preventing collision
attacks.
For all of the current Rust code, we don't care about those attacks, because
if an person with bad intentions has write access to your repo, you have other
issues.
I've chosen to use the TwoXHash crate because it was made by a reputable member
of the Rust community and has very good benchmarks.
For now it does not seem to improve performance by much for the current code,
but it's something else to not worry about when benchmarking code: in a
previous experiment with copytracing in Rust, it accounted for more than 10%
of the time of the entire script.
Differential Revision: https://phab.mercurial-scm.org/D7116
| author | Rapha?l Gom?s <rgomes@octobus.net> |
|---|---|
| date | Mon, 14 Oct 2019 13:57:30 +0200 |
| parents | 1fe2e574616e |
| children | 6a88ced33c40 |
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--- a/rust/hg-core/src/lib.rs Mon Dec 02 14:44:26 2019 +0100 +++ b/rust/hg-core/src/lib.rs Mon Oct 14 13:57:30 2019 +0200 @@ -24,6 +24,8 @@ pub use filepatterns::{ build_single_regex, read_pattern_file, PatternSyntax, PatternTuple, }; +use std::collections::HashMap; +use twox_hash::RandomXxHashBuilder64; /// Mercurial revision numbers /// @@ -53,6 +55,11 @@ pub type LineNumber = usize; +/// Rust's default hasher is too slow because it tries to prevent collision +/// attacks. We are not concerned about those: if an ill-minded person has +/// write access to your repository, you have other issues. +pub type FastHashMap<K, V> = HashMap<K, V, RandomXxHashBuilder64>; + #[derive(Clone, Debug, PartialEq)] pub enum GraphError { ParentOutOfRange(Revision),