added multithreaded version, no mmap optimization

Cargo.toml

@@ -3,8 +3,6 @@ name = "onebrc"
 version = "0.1.0"
 edition = "2021"
 
-# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
-
 [dependencies]
 fxhash = "0.2.1"
 rayon = "1.8.0"

README.md

@@ -2,5 +2,4 @@
 
 * Fastest single threaded runtime: 29.7s (4.5s to read the file into memory, 24s to process rows and ~150micros to generate the output)
 
-
-* Fastest multi threaded runtime on a machine with 12 cores: -
+* Fastest multi threaded runtime on a machine with 12 cores: read = 4.682276171s processed = 2.057576429s output_gen = 188.113µs

src/main.rs

@@ -1,10 +1,8 @@
 use fxhash::FxHashMap;
-use std::fs::File;
-use std::io::Read;
-use std::time::Instant;
+use rayon::prelude::*;
+use std::{fs::File, io::Read, time::Instant};
 
 fn main() {
-    let mut map = FxHashMap::default();
     let mut buf = Vec::new();
 
     let t1 = Instant::now();
@@ -18,10 +16,12 @@ fn main() {
 
     let t2 = Instant::now();
 
-    for line in buf.split(|&x| x == b'\n') {
+    let map: FxHashMap<&[u8], (i16, i32, i16, usize)> = buf
+        .par_split(|&x| x == b'\n')
+        .filter_map(|line| {
             let l = line.len();
             if l == 0 {
-            continue;
+                return None;
             }
 
             let loc = if line[l - 6] == b';' {
@@ -39,16 +39,36 @@ fn main() {
 
             let val = parse_float(val);
 
-        let (min, sum, max, counter) = map
+            Some((city, val))
+        })
+        .fold(FxHashMap::default, |mut a, (city, val)| {
+            let (min, sum, max, counter) = a
                 .entry(city)
-            .or_insert_with(|| (std::i16::MAX, 0, std::i16::MIN, 0));
+                .or_insert_with(|| (std::i16::MAX, 0, std::i16::MIN, 0usize));
 
             *min = val.min(*min);
             *max = val.max(*max);
             *counter += 1;
             *sum += val as i32;
+
+            a
+        })
+        .reduce_with(|mut m1, m2| {
+            for (k, (min1, sum1, max1, counter1)) in m2 {
+                let (min, sum, max, counter) = m1
+                    .entry(k)
+                    .or_insert_with(|| (std::i16::MAX, 0, std::i16::MIN, 0usize));
+
+                *min = min1.min(*min);
+                *max = max1.max(*max);
+                *counter += counter1;
+                *sum += sum1;
             }
 
+            m1
+        })
+        .unwrap();
+
     let t2_elapsed = t2.elapsed();
 
     let t3 = Instant::now();