Commit 1f550350 authored by Arseniy Alekseyev's avatar Arseniy Alekseyev
Browse files

rhg: stop manifest traversal when no more files are needed

Stopping the traversal early can skip a significant part
of the manifest traversal, to avoid some of its cost.

The worst-case benchmarks are favorable, as well.
Running [hg cat] on the last file in the manifest of
a large repo, I'm seeing a ~4ms improvement (150ms -> 146ms),
so this time is now almost indistinguishable from the
baseline ("brute force") implementation.

Running [hg cat] on ~220 files together with the last file
of the repo is further improved by ~5ms or so.

I suspect the raw performance improvements are caused by splitting
the manifest search and the file data access into separate phases,
instead of interleaving them.

Differential Revision:
parent 6b5773f89183
Pipeline #27780 failed with stages
in 120 minutes and 7 seconds
......@@ -9,10 +9,12 @@ use crate::repo::Repo;
use crate::revlog::revlog::RevlogError;
use crate::revlog::Node;
use crate::utils::hg_path::HgPath;
use crate::utils::hg_path::HgPathBuf;
use itertools::EitherOrBoth::{Both, Left, Right};
use itertools::Itertools;
use itertools::put_back;
use itertools::PutBack;
use std::cmp::Ordering;
pub struct CatOutput {
/// Whether any file in the manifest matched the paths given as CLI
......@@ -26,6 +28,49 @@ pub struct CatOutput {
pub node: Node,
// Find an item in an iterator over a sorted collection.
fn find_item<'a, 'b, 'c, D, I: Iterator<Item = (&'a HgPath, D)>>(
i: &mut PutBack<I>,
needle: &'b HgPath,
) -> Option<I::Item> {
loop {
match {
None => return None,
Some(val) => match needle.as_bytes().cmp(val.0.as_bytes()) {
Ordering::Less => {
return None;
Ordering::Greater => continue,
Ordering::Equal => return Some(val),
fn find_files_in_manifest<
I: Iterator<Item = (&'a HgPath, D)>,
J: Iterator<Item = &'b HgPath>,
manifest: I,
files: J,
) -> (Vec<(&'a HgPath, D)>, Vec<&'b HgPath>) {
let mut manifest = put_back(manifest);
let mut res = vec![];
let mut missing = vec![];
for file in files {
match find_item(&mut manifest, file) {
None => missing.push(file),
Some(item) => res.push(item),
return (res, missing);
/// Output the given revision of files
/// * `root`: Repository root
......@@ -42,34 +87,26 @@ pub fn cat<'a>(
.expect("should succeed when repo.manifest did");
let mut bytes = vec![];
let mut bytes: Vec<u8> = vec![];
let mut found_any = false;
let mut missing = vec![];
let (found, missing) = find_files_in_manifest(
files.iter().map(|f| f.as_ref()),
for entry in manifest
.merge_join_by(files.iter(), |(manifest_file, _), file| {
match entry {
Left(_) => (),
Right(path) => missing.push(path),
Both((manifest_file, node_bytes), _) => {
found_any = true;
let file_log = repo.filelog(manifest_file)?;
let file_node = Node::from_hex_for_repo(node_bytes)?;
let entry = file_log.data_for_node(file_node)?;
for (manifest_file, node_bytes) in found {
found_any = true;
let file_log = repo.filelog(manifest_file)?;
let file_node = Node::from_hex_for_repo(node_bytes)?;
let missing: Vec<HgPathBuf> = missing
.map(|file| (*(file.as_ref())).to_owned())
.map(|file| (*file).to_owned())
Ok(CatOutput {
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