From 38bdd0131d320b9ed92a2bfa3c86d00796c1c95f Mon Sep 17 00:00:00 2001
From: Naveen Naidu <naveennaidu479@gmail.com>
Date: Fri, 10 May 2024 11:53:49 +0530
Subject: [PATCH] Approach 8: Use mmap and bytes everywhere (Time: 78s)

In this appraoch we do two things:
1. Use mmap so that we can directly use bytes insted of depending on
   vectors
2. Replace all instances of Vec to bytes

We can see from the previous flamegraph that `to_vec` takes almost 14%
of the cycle in `read_line` function. The motivation to use mmap here
was to convert everything in bytes so that we can reduce the allocation
of memory on Heap for every line.

P.S: I hate the use of unsafe here, but I'm going with it for now and
plan to change it later once I make other stuff performant
---
 Cargo.toml                                    |   1 +
 .../flamegraph.svg                            | 491 ++++++++++++++++++
 src/main.rs                                   |  48 +-
 3 files changed, 515 insertions(+), 25 deletions(-)
 create mode 100644 flamegraphs/08-use-mmap-byte-everywhere/flamegraph.svg

diff --git a/Cargo.toml b/Cargo.toml
index 564c3af..c76e7ac 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -14,3 +14,4 @@ rust_decimal = "1.34"
 rust_decimal_macros = "1.34"
 fast-float = "0.2"
 rustc-hash = { version = "1.0"}
+memmap2 = {version = "0.9.4"}
diff --git a/flamegraphs/08-use-mmap-byte-everywhere/flamegraph.svg b/flamegraphs/08-use-mmap-byte-everywhere/flamegraph.svg
new file mode 100644
index 0000000..6fd1b9e
--- /dev/null
+++ b/flamegraphs/08-use-mmap-byte-everywhere/flamegraph.svg
@@ -0,0 +1,491 @@
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+#title { text-anchor:middle; font-size:17px; }
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+#search:hover, #search.show { opacity:1; }
+#subtitle { text-anchor:middle; font-color:rgb(160,160,160); }
+#unzoom { cursor:pointer; }
+#frames > *:hover { stroke:black; stroke-width:0.5; cursor:pointer; }
+.hide { display:none; }
+.parent { opacity:0.5; }
+</style><script type="text/ecmascript"><![CDATA[
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+        var fontwidth = 0.59;
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+        el[i].classList.remove("hide");
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+    for (var i = 0; i < el.length; i++) {
+        orig_load(el[i], "fill")
+    }
+    var params = get_params();
+    delete params.s;
+    history.replaceState(null, null, parse_params(params));
+}
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+    }
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+        if (func == null || rect == null)
+            continue;
+        // Save max width. Only works as we have a root frame
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+    var params = get_params();
+    params.s = term;
+    history.replaceState(null, null, parse_params(params));
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+    searchbtn.classList.add("show");
+    searchbtn.firstChild.nodeValue = "Reset Search";
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+    var lastx = -1;
+    var lastw = 0;
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+    var pct = 100 * count / maxwidth;
+    if (pct != 100) pct = pct.toFixed(1);
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+}
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2.66%)</title><rect x="64.2857%" y="181" width="2.6561%" height="15" fill="rgb(207,117,47)" fg:x="22509" fg:w="930"/><text x="64.5357%" y="191.50">co..</text></g><g><title>core::hash::impls::&lt;impl core::hash::Hash for &amp;T&gt;::hash (930 samples, 2.66%)</title><rect x="64.2857%" y="165" width="2.6561%" height="15" fill="rgb(249,43,39)" fg:x="22509" fg:w="930"/><text x="64.5357%" y="175.50">co..</text></g><g><title>core::hash::impls::&lt;impl core::hash::Hash for [T]&gt;::hash (930 samples, 2.66%)</title><rect x="64.2857%" y="149" width="2.6561%" height="15" fill="rgb(209,38,44)" fg:x="22509" fg:w="930"/><text x="64.5357%" y="159.50">co..</text></g><g><title>core::hash::impls::&lt;impl core::hash::Hash for u8&gt;::hash_slice (845 samples, 2.41%)</title><rect x="64.5285%" y="133" width="2.4133%" height="15" fill="rgb(236,212,23)" fg:x="22594" fg:w="845"/><text x="64.7785%" y="143.50">co..</text></g><g><title>hashbrown::rustc_entry::&lt;impl hashbrown::map::HashMap&lt;K,V,S,A&gt;&gt;::rustc_entry (8 samples, 0.02%)</title><rect x="66.9189%" y="117" width="0.0228%" height="15" fill="rgb(242,79,21)" fg:x="23431" fg:w="8"/><text x="67.1689%" y="127.50"></text></g><g><title>&lt;hashbrown::raw::bitmask::BitMaskIter as core::iter::traits::iterator::Iterator&gt;::next (1,281 samples, 3.66%)</title><rect x="68.7125%" y="181" width="3.6585%" height="15" fill="rgb(211,96,35)" fg:x="24059" fg:w="1281"/><text x="68.9625%" y="191.50">&lt;has..</text></g><g><title>hashbrown::raw::bitmask::BitMask::lowest_set_bit (1,281 samples, 3.66%)</title><rect x="68.7125%" y="165" width="3.6585%" height="15" fill="rgb(253,215,40)" fg:x="24059" fg:w="1281"/><text x="68.9625%" y="175.50">hash..</text></g><g><title>core::num::nonzero::NonZero&lt;u16&gt;::new (1,034 samples, 2.95%)</title><rect x="69.4179%" y="149" width="2.9531%" height="15" fill="rgb(211,81,21)" fg:x="24306" fg:w="1034"/><text x="69.6679%" y="159.50">cor..</text></g><g><title>hashbrown::raw::RawTable&lt;T,A&gt;::bucket (479 samples, 1.37%)</title><rect x="72.3739%" y="165" width="1.3680%" height="15" fill="rgb(208,190,38)" fg:x="25341" fg:w="479"/><text x="72.6239%" y="175.50"></text></g><g><title>hashbrown::raw::Bucket&lt;T&gt;::from_base_index (479 samples, 1.37%)</title><rect x="72.3739%" y="149" width="1.3680%" height="15" fill="rgb(235,213,38)" fg:x="25341" fg:w="479"/><text x="72.6239%" y="159.50"></text></g><g><title>core::ptr::mut_ptr::&lt;impl *mut T&gt;::sub (479 samples, 1.37%)</title><rect x="72.3739%" y="133" width="1.3680%" height="15" fill="rgb(237,122,38)" fg:x="25341" fg:w="479"/><text x="72.6239%" y="143.50"></text></g><g><title>core::ptr::mut_ptr::&lt;impl *mut T&gt;::offset (479 samples, 1.37%)</title><rect x="72.3739%" y="117" width="1.3680%" height="15" fill="rgb(244,218,35)" fg:x="25341" fg:w="479"/><text x="72.6239%" y="127.50"></text></g><g><title>&lt;[A] as core::slice::cmp::SlicePartialEq&lt;B&gt;&gt;::equal (6,728 samples, 19.22%)</title><rect x="73.7419%" y="117" width="19.2152%" height="15" fill="rgb(240,68,47)" fg:x="25820" fg:w="6728"/><text x="73.9919%" y="127.50">&lt;[A] as core::slice::cmp::Slic..</text></g><g><title>[libc.so.6] (4,578 samples, 13.07%)</title><rect x="79.8823%" y="101" width="13.0748%" height="15" fill="rgb(210,16,53)" fg:x="27970" fg:w="4578"/><text x="80.1323%" y="111.50">[libc.so.6]</text></g><g><title>hashbrown::raw::RawTable&lt;T,A&gt;::find::_{{closure}} (7,224 samples, 20.63%)</title><rect x="72.3739%" y="181" width="20.6317%" height="15" fill="rgb(235,124,12)" fg:x="25341" fg:w="7224"/><text x="72.6239%" y="191.50">hashbrown::raw::RawTable&lt;T,A&gt;::f..</text></g><g><title>hashbrown::rustc_entry::_&lt;impl hashbrown::map::HashMap&lt;K,V,S,A&gt;&gt;::rustc_entry::_{{closure}} (6,745 samples, 19.26%)</title><rect x="73.7419%" y="165" width="19.2637%" height="15" fill="rgb(224,169,11)" fg:x="25820" fg:w="6745"/><text x="73.9919%" y="175.50">hashbrown::rustc_entry::_&lt;impl..</text></g><g><title>core::cmp::impls::&lt;impl core::cmp::PartialEq&lt;&amp;B&gt; for &amp;A&gt;::eq (6,745 samples, 19.26%)</title><rect x="73.7419%" y="149" width="19.2637%" height="15" fill="rgb(250,166,2)" fg:x="25820" fg:w="6745"/><text x="73.9919%" y="159.50">core::cmp::impls::&lt;impl core::..</text></g><g><title>core::slice::cmp::&lt;impl core::cmp::PartialEq&lt;[B]&gt; for [A]&gt;::eq (6,745 samples, 19.26%)</title><rect x="73.7419%" y="133" width="19.2637%" height="15" fill="rgb(242,216,29)" fg:x="25820" fg:w="6745"/><text x="73.9919%" y="143.50">core::slice::cmp::&lt;impl core::..</text></g><g><title>hashbrown::rustc_entry::&lt;impl hashbrown::map::HashMap&lt;K,V,S,A&gt;&gt;::rustc_entry (17 samples, 0.05%)</title><rect x="92.9571%" y="117" width="0.0486%" height="15" fill="rgb(230,116,27)" fg:x="32548" fg:w="17"/><text x="93.2071%" y="127.50"></text></g><g><title>hashbrown::raw::h2 (513 samples, 1.47%)</title><rect x="93.0085%" y="181" width="1.4651%" height="15" fill="rgb(228,99,48)" fg:x="32566" fg:w="513"/><text x="93.2585%" y="191.50"></text></g><g><title>core::intrinsics::copy_nonoverlapping (10 samples, 0.03%)</title><rect x="94.4736%" y="149" width="0.0286%" height="15" fill="rgb(253,11,6)" fg:x="33079" fg:w="10"/><text x="94.7236%" y="159.50"></text></g><g><title>hashbrown::raw::sse2::Group::load (94 samples, 0.27%)</title><rect x="94.4736%" y="181" width="0.2685%" height="15" fill="rgb(247,143,39)" fg:x="33079" fg:w="94"/><text x="94.7236%" y="191.50"></text></g><g><title>core::core_arch::x86::sse2::_mm_loadu_si128 (94 samples, 0.27%)</title><rect x="94.4736%" y="165" width="0.2685%" height="15" fill="rgb(236,97,10)" fg:x="33079" fg:w="94"/><text x="94.7236%" y="175.50"></text></g><g><title>hashbrown::rustc_entry::&lt;impl hashbrown::map::HashMap&lt;K,V,S,A&gt;&gt;::rustc_entry (84 samples, 0.24%)</title><rect x="94.5022%" y="149" width="0.2399%" height="15" fill="rgb(233,208,19)" fg:x="33089" fg:w="84"/><text x="94.7522%" y="159.50"></text></g><g><title>hashbrown::raw::sse2::Group::match_byte (1,320 samples, 3.77%)</title><rect x="94.7421%" y="181" width="3.7699%" height="15" fill="rgb(216,164,2)" fg:x="33173" fg:w="1320"/><text x="94.9921%" y="191.50">hash..</text></g><g><title>core::core_arch::x86::sse2::_mm_movemask_epi8 (1,320 samples, 3.77%)</title><rect x="94.7421%" y="165" width="3.7699%" height="15" fill="rgb(220,129,5)" fg:x="33173" fg:w="1320"/><text x="94.9921%" y="175.50">core..</text></g><g><title>hashbrown::raw::sse2::Group::match_empty (308 samples, 0.88%)</title><rect x="98.5120%" y="181" width="0.8796%" height="15" fill="rgb(242,17,10)" fg:x="34493" fg:w="308"/><text x="98.7620%" y="191.50"></text></g><g><title>hashbrown::raw::sse2::Group::match_byte (308 samples, 0.88%)</title><rect x="98.5120%" y="165" width="0.8796%" height="15" fill="rgb(242,107,0)" fg:x="34493" fg:w="308"/><text x="98.7620%" y="175.50"></text></g><g><title>core::core_arch::x86::sse2::_mm_movemask_epi8 (308 samples, 0.88%)</title><rect x="98.5120%" y="149" width="0.8796%" height="15" fill="rgb(251,28,31)" fg:x="34493" fg:w="308"/><text x="98.7620%" y="159.50"></text></g><g><title>hashbrown::raw::RawTableInner::find_inner (11,167 samples, 31.89%)</title><rect x="67.5615%" y="197" width="31.8930%" height="15" fill="rgb(233,223,10)" fg:x="23656" fg:w="11167"/><text x="67.8115%" y="207.50">hashbrown::raw::RawTableInner::find_inner</text></g><g><title>hashbrown::rustc_entry::&lt;impl hashbrown::map::HashMap&lt;K,V,S,A&gt;&gt;::rustc_entry (22 samples, 0.06%)</title><rect x="99.3917%" y="181" width="0.0628%" height="15" fill="rgb(215,21,27)" fg:x="34801" fg:w="22"/><text x="99.6417%" y="191.50"></text></g><g><title>hashbrown::rustc_entry::&lt;impl hashbrown::map::HashMap&lt;K,V,S,A&gt;&gt;::rustc_entry (13,254 samples, 37.85%)</title><rect x="61.6125%" y="229" width="37.8534%" height="15" fill="rgb(232,23,21)" fg:x="21573" fg:w="13254"/><text x="61.8625%" y="239.50">hashbrown::rustc_entry::&lt;impl hashbrown::map::HashMap&lt;K,V,S,A&gt;..</text></g><g><title>hashbrown::raw::RawTable&lt;T,A&gt;::find (11,388 samples, 32.52%)</title><rect x="66.9418%" y="213" width="32.5241%" height="15" fill="rgb(244,5,23)" fg:x="23439" fg:w="11388"/><text x="67.1918%" y="223.50">hashbrown::raw::RawTable&lt;T,A&gt;::find</text></g><g><title>hashbrown::rustc_entry::&lt;impl hashbrown::map::HashMap&lt;K,V,S,A&gt;&gt;::rustc_entry (4 samples, 0.01%)</title><rect x="99.4545%" y="197" width="0.0114%" height="15" fill="rgb(226,81,46)" fg:x="34823" fg:w="4"/><text x="99.7045%" y="207.50"></text></g><g><title>all (35,014 samples, 100%)</title><rect x="0.0000%" y="437" width="100.0000%" height="15" fill="rgb(247,70,30)" fg:x="0" fg:w="35014"/><text x="0.2500%" y="447.50"></text></g><g><title>rust-1brc (35,014 samples, 100.00%)</title><rect x="0.0000%" y="421" width="100.0000%" height="15" fill="rgb(212,68,19)" 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height="15" fill="rgb(247,173,49)" fg:x="8" fg:w="35006"/><text x="0.2728%" y="351.50">std::rt::lang_start_internal</text></g><g><title>std::rt::lang_start::_{{closure}} (35,006 samples, 99.98%)</title><rect x="0.0228%" y="325" width="99.9772%" height="15" fill="rgb(224,114,35)" fg:x="8" fg:w="35006"/><text x="0.2728%" y="335.50">std::rt::lang_start::_{{closure}}</text></g><g><title>std::sys_common::backtrace::__rust_begin_short_backtrace (35,006 samples, 99.98%)</title><rect x="0.0228%" y="309" width="99.9772%" height="15" fill="rgb(245,159,27)" fg:x="8" fg:w="35006"/><text x="0.2728%" y="319.50">std::sys_common::backtrace::__rust_begin_short_backtrace</text></g><g><title>core::ops::function::FnOnce::call_once (35,006 samples, 99.98%)</title><rect x="0.0228%" y="293" width="99.9772%" height="15" fill="rgb(245,172,44)" fg:x="8" fg:w="35006"/><text x="0.2728%" y="303.50">core::ops::function::FnOnce::call_once</text></g><g><title>rust_1brc::main (35,006 samples, 99.98%)</title><rect x="0.0228%" y="277" width="99.9772%" height="15" fill="rgb(236,23,11)" fg:x="8" fg:w="35006"/><text x="0.2728%" y="287.50">rust_1brc::main</text></g><g><title>rust_1brc::calculate_station_values (35,006 samples, 99.98%)</title><rect x="0.0228%" y="261" width="99.9772%" height="15" fill="rgb(205,117,38)" fg:x="8" fg:w="35006"/><text x="0.2728%" y="271.50">rust_1brc::calculate_station_values</text></g><g><title>std::collections::hash::map::HashMap&lt;K,V,S&gt;::entry (13,606 samples, 38.86%)</title><rect x="61.1413%" y="245" width="38.8587%" height="15" fill="rgb(237,72,25)" fg:x="21408" fg:w="13606"/><text x="61.3913%" y="255.50">std::collections::hash::map::HashMap&lt;K,V,S&gt;::entry</text></g><g><title>std::collections::hash::map::map_entry (187 samples, 0.53%)</title><rect x="99.4659%" y="229" width="0.5341%" height="15" fill="rgb(244,70,9)" fg:x="34827" fg:w="187"/><text x="99.7159%" y="239.50"></text></g></svg></svg>
\ No newline at end of file
diff --git a/src/main.rs b/src/main.rs
index f209289..51cfa99 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,11 +1,10 @@
 use clap::Parser;
 use std::collections::BTreeMap;
-use std::fs::File;
-use std::io::BufRead;
-use std::io::BufReader;
+// use std::str::from_utf8;
 use std::time::Instant;
 use fast_float;
 use rustc_hash::FxHashMap;
+use memmap2::Mmap;
 
 #[derive(Parser, Debug)]
 #[command(
@@ -26,26 +25,24 @@ struct StationValues {
     count: u32,
 }
 
-fn read_line(data: &Vec<u8>) -> (Vec<u8>, f32) {
+fn read_line(data: &[u8]) -> (&[u8], f32) {
     let mut parts = data.rsplit(|&c| c == b';');
     let value_str = parts.next().expect("Failed to parse value string");
     let value = fast_float::parse(value_str).expect("Failed to parse value");
     let station_name = parts.next().expect("Failed to parse station name");
-    (station_name.to_vec(), value)
+    (station_name, value)
 }
 
 // Calculate the station values
-fn calculate_station_values(reader: &mut BufReader<File>) -> FxHashMap<Vec<u8>, StationValues> {
-    let mut result: FxHashMap<Vec<u8>, StationValues> = FxHashMap::default();
-    let mut buf = Vec::new();
-
-    while let Ok(bytes_read) = reader.read_until(b'\n', &mut buf) {
-        if bytes_read == 0 {
-            break;
+fn calculate_station_values(data:&[u8]) -> FxHashMap<&[u8], StationValues> {
+    let mut result: FxHashMap<&[u8], StationValues> = FxHashMap::default();
+    let lines = data.split(|&c| c == b'\n');
+    for line in lines {
+        if line.is_empty() {
+            continue;
         }
-        // remove new line character
-        buf.truncate(bytes_read - 1);
-        let (station_name, value) = read_line(&buf);
+
+        let (station_name, value) = read_line(line);
         result
             .entry(station_name)
             .and_modify(|e| {
@@ -64,9 +61,6 @@ fn calculate_station_values(reader: &mut BufReader<File>) -> FxHashMap<Vec<u8>,
                 mean: value,
                 count: 1,
             });
-        
-        buf.clear();
-
     }
 
     // Calculate the mean for all entries and round off to 1 decimal place
@@ -83,7 +77,7 @@ fn round_off(value: f32) -> f32 {
     (value * 10.0).round() / 10.0
 }
 
-fn write_result_stdout(result: FxHashMap<Vec<u8>, StationValues>) -> () {
+fn write_result_stdout(result: FxHashMap<&[u8], StationValues>) -> () {
     let mut ordered_result = BTreeMap::new();
     for (station_name, station_values) in result {
         ordered_result.insert(station_name, station_values);
@@ -110,9 +104,10 @@ fn main() {
     let args = Args::parse();
 
     let file = std::fs::File::open(&args.file).expect("Failed to open file");
-    let mut reader = BufReader::new(file);
+    let mmap = unsafe { Mmap::map(&file).expect("Failed to map file") };
+    let data = &*mmap;
 
-    let result = calculate_station_values(&mut reader);
+    let result = calculate_station_values(data);
     write_result_stdout(result);
     let duration = start.elapsed();
     println!("\nTime taken is: {:?}", duration);
@@ -122,7 +117,9 @@ fn main() {
 #[cfg(test)]
 mod tests {
     use crate::{calculate_station_values, StationValues};
-    use std::{collections::HashMap, fs, io::BufReader, path::PathBuf};
+    use std::{collections::HashMap, fs, path::PathBuf};
+    use memmap2::Mmap;
+
     #[test]
     fn test_measurement_data() {
         let test_dir = PathBuf::from(env!("CARGO_MANIFEST_DIR")).join("tests");
@@ -138,13 +135,14 @@ mod tests {
             let test_output = read_test_output_file(output_file_name);
 
             let file = std::fs::File::open(test_file_name.clone()).expect("Failed to open file");
-            let mut reader = BufReader::new(file);
-            let mut result = calculate_station_values(&mut reader);
+            let mmap = unsafe { Mmap::map(&file).expect("Failed to map file") };
+            let data = &*mmap;
+            let mut result = calculate_station_values(data);
             let mut test_output_map_copy = test_output.clone();
 
             // compare two hashmaps
             for (station_name, station_values) in test_output.into_iter() {
-                let result_station_values = result.remove(&station_name.as_bytes().to_vec()).expect(
+                let result_station_values = result.remove(station_name.as_bytes()).expect(
                     ("Station not found: ".to_string() + &station_name + " in result hashmap")
                         .as_str(),
                 );