Mercurial > hg
view rust/hgcli/README.md @ 49491:c6a1beba27e9
bisect: avoid copying ancestor list for non-merge commits
During a bisection, hg needs to compute a list of all ancestors for every
candidate commit. This is accomplished via a bottom-up traversal of the set of
candidates, during which each revision's ancestor list is populated using the
ancestor list of its parent(s). Previously, this involved copying the entire
list, which could be very long in if the bisection range was large.
To help improve this, we can observe that each candidate commit is visited
exactly once, at which point its ancestor list is copied into its children's
lists and then dropped. In the case of non-merge commits, a commit's ancestor
list consists exactly of its parent's list plus itself. This means that we can
trivially reuse the parent's existing list for one of its non-merge children,
which avoids copying entirely if that commit is the parent's only child. This
makes bisections over linear ranges of commits much faster.
During some informal testing in the large publicly-available `mozilla-central`
repository, this noticeably sped up bisections over large ranges of history:
Setup:
$ cd mozilla-central
$ hg bisect --reset
$ hg bisect --good 0
$ hg log -r tip -T '{rev}\n'
628417
Test:
$ time hg bisect --bad tip --noupdate
Before:
real 3m35.927s
user 3m35.553s
sys 0m0.319s
After:
real 1m41.142s
user 1m40.810s
sys 0m0.285s
author | Arun Kulshreshtha <akulshreshtha@janestreet.com> |
---|---|
date | Tue, 30 Aug 2022 15:29:55 -0400 |
parents | 16c3fe46929a |
children | 45ba8416afc4 |
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# Oxidized Mercurial This project provides a Rust implementation of the Mercurial (`hg`) version control tool. Under the hood, the project uses [PyOxidizer](https://github.com/indygreg/PyOxidizer) to embed a Python interpreter in a binary built with Rust. At run-time, the Rust `fn main()` is called and Rust code handles initial process startup. An in-process Python interpreter is started (if needed) to provide additional functionality. # Building First, acquire and build a copy of PyOxidizer; you probably want to do this in some directory outside of your clone of Mercurial: $ git clone https://github.com/indygreg/PyOxidizer.git $ cd PyOxidizer $ cargo build --release Then build this Rust project using the built `pyoxidizer` executable: $ /path/to/pyoxidizer/target/release/pyoxidizer build --release If all goes according to plan, there should be an assembled application under `build/<arch>/release/app/` with an `hg` executable: $ build/x86_64-unknown-linux-gnu/release/app/hg version Mercurial Distributed SCM (version 5.3.1+433-f99cd77d53dc+20200331) (see https://mercurial-scm.org for more information) Copyright (C) 2005-2020 Olivia Mackall and others This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. # Running Tests To run tests with a built `hg` executable, you can use the `--with-hg` argument to `run-tests.py`. But there's a wrinkle: many tests run custom Python scripts that need to `import` modules provided by Mercurial. Since these modules are embedded in the produced `hg` executable, a regular Python interpreter can't access them! To work around this, set `PYTHONPATH` to the Mercurial source directory. e.g.: $ cd /path/to/hg/src/tests $ PYTHONPATH=`pwd`/.. python3.9 run-tests.py \ --with-hg `pwd`/../rust/hgcli/build/x86_64-unknown-linux-gnu/release/app/hg