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diff rust/hg-core/src/discovery.rs @ 43844:5ac243a92e37

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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 ce6797ef6eab
children 2abffea40700
line wrap: on
line diff
--- a/rust/hg-core/src/discovery.rs	Mon Dec 02 14:44:26 2019 +0100
+++ b/rust/hg-core/src/discovery.rs	Mon Oct 14 13:57:30 2019 +0200
@@ -11,12 +11,11 @@
 //! `mercurial.setdiscovery`
 
 use super::{Graph, GraphError, Revision, NULL_REVISION};
-use crate::ancestors::MissingAncestors;
-use crate::dagops;
+use crate::{ancestors::MissingAncestors, dagops, FastHashMap};
 use rand::seq::SliceRandom;
 use rand::{thread_rng, RngCore, SeedableRng};
 use std::cmp::{max, min};
-use std::collections::{HashMap, HashSet, VecDeque};
+use std::collections::{HashSet, VecDeque};
 
 type Rng = rand_pcg::Pcg32;
 
@@ -25,7 +24,7 @@
     graph: G, // plays the role of self._repo
     common: MissingAncestors<G>,
     undecided: Option<HashSet<Revision>>,
-    children_cache: Option<HashMap<Revision, Vec<Revision>>>,
+    children_cache: Option<FastHashMap<Revision, Vec<Revision>>>,
     missing: HashSet<Revision>,
     rng: Rng,
     respect_size: bool,
@@ -61,7 +60,7 @@
 where
     I: Iterator<Item = Revision>,
 {
-    let mut distances: HashMap<Revision, u32> = HashMap::new();
+    let mut distances: FastHashMap<Revision, u32> = FastHashMap::default();
     let mut visit: VecDeque<Revision> = heads.into_iter().collect();
     let mut factor: u32 = 1;
     let mut seen: HashSet<Revision> = HashSet::new();
@@ -328,7 +327,8 @@
         }
         self.ensure_undecided()?;
 
-        let mut children: HashMap<Revision, Vec<Revision>> = HashMap::new();
+        let mut children: FastHashMap<Revision, Vec<Revision>> =
+            FastHashMap::default();
         for &rev in self.undecided.as_ref().unwrap() {
             for p in ParentsIterator::graph_parents(&self.graph, rev)? {
                 children.entry(p).or_insert_with(|| Vec::new()).push(rev);