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branchmap-v3: filter topo heads using node for performance reason...
branchmap-v3: filter topo heads using node for performance reason The branchmap currently contains heads as nodeid. If we build a set of revnum with the topological heads, we need to turn the nodeid in the branchmap to revnum to be able to check if they are topo-heads. That nodeid → revnum lookup is "expensive" and adds up to something noticeable if you do it hundreds of thousand of time. Instead we turn all the topo-heads revnums into nodes and build a set. So we can directly test membership of the nodeids stored in the branchmap. That is much faster. Ideally we would have revnum in the branchmap and could directly test revnum against a revnum set and that would be even faster. However that's an adventure for another time. Without this change, the branchmap format "v3" was significantly slower than the "v2" format. With this changes, some of that gap is recovered With rust + persistent nodemap, this overhead was smaller because the extra lookup did not had to to build the nodemap from scratch. In addition the mozilla-unified repository is able to use the "pure_top" mode of branchmap v3, so it was not really affected by this. Future changeset will work of the remaining of the performance gap. ### benchmark.name = hg.command.unbundle # bin-env-vars.hg.py-re2-module = default # benchmark.variants.issue6528 = disabled # benchmark.variants.resource-usage = default # benchmark.variants.reuse-external-delta-parent = yes # benchmark.variants.revs = any-1-extra-rev # benchmark.variants.source = unbundle # benchmark.variants.validate = default # benchmark.variants.verbosity = quiet ## data-env-vars.name = netbeans-2018-08-01-zstd-sparse-revlog # bin-env-vars.hg.flavor = default branch-v2: 0.233711 ~~~~~ branch-v3 before: 0.380994 (+63.02%, +0.15) branch-v3 after: 0.368769 (+57.79%, +0.14) # bin-env-vars.hg.flavor = rust branch-v2: 0.235230 ~~~~~ branch-v3 before: 0.385060 (+63.70%, +0.15) branch-v3 after: 0.372460 (+58.34%, +0.14) ## data-env-vars.name = netbeans-2018-08-01-ds2-pnm # bin-env-vars.hg.flavor = rust branch-v2: 0.255586 ~~~~~ branch-v3 before: 0.317524 (+24.23%, +0.06) branch-v3 after: 0.318907 (+24.78%, +0.06) ## data-env-vars.name = mozilla-central-2024-03-22-zstd-sparse-revlog # bin-env-vars.hg.flavor = default branch-v2: 0.339010 ~~~~~ branch-v3 before: 0.410007 (+20.94%, +0.07) branch-v3 after: 0.349752 (+3.17%, +0.01) # bin-env-vars.hg.flavor = rust branch-v2: 0.346525 ~~~~~ branch-v3 before: 0.410428 (+18.44%, +0.06) branch-v3 after: 0.354300 (+2.24%, +0.01) ## data-env-vars.name = mozilla-central-2024-03-22-ds2-pnm # bin-env-vars.hg.flavor = rust branch-v2: 0.380202 ~~~~~ branch-v3 before: 0.393871 (+3.60%, +0.01) branch-v3 after: 0.396293 (+4.23%, +0.02) ## data-env-vars.name = mozilla-unified-2024-03-22-zstd-sparse-revlog # bin-env-vars.hg.flavor = default branch-v2: 0.412165 ~~~~~ branch-v3 before: 0.438105 (+6.29%, +0.03) branch-v3 after: 0.424769 (+3.06%, +0.01) # bin-env-vars.hg.flavor = rust branch-v2: 0.412397 ~~~~~ branch-v3 before: 0.438405 (+6.31%, +0.03) branch-v3 after: 0.421796 (+2.28%, +0.01) ## data-env-vars.name = mozilla-unified-2024-03-22-ds2-pnm # bin-env-vars.hg.flavor = rust branch-v2: 0.429501 ~~~~~ branch-v3 before: 0.452692 (+5.40%, +0.02) branch-v3 after: 0.443849 (+3.34%, +0.01) ## data-env-vars.name = mozilla-try-2024-03-26-zstd-sparse-revlog # bin-env-vars.hg.flavor = default branch-v2: 3.403171 ~~~~~ branch-v3 before: 6.562345 (+92.83%, +3.16) branch-v3 after: 6.234055 (+83.18%, +2.83) # bin-env-vars.hg.flavor = rust branch-v2: 3.454876 ~~~~~ branch-v3 before: 6.160248 (+78.31%, +2.71) branch-v3 after: 6.307813 (+82.58%, +2.85) ## data-env-vars.name = mozilla-try-2024-03-26-ds2-pnm # bin-env-vars.hg.flavor = rust branch-v2: 3.465435 ~~~~~ branch-v3 before: 5.381648 (+55.30%, +1.92) branch-v3 after: 5.176076 (+49.36%, +1.71)

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rust.txt
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Mercurial can be augmented with Rust extensions for speeding up certain
operations.
Compatibility
=============
Though the Rust extensions are only tested by the project under Linux, users of
MacOS, FreeBSD and other UNIX-likes have been using the Rust extensions. Your
mileage may vary, but by all means do give us feedback or signal your interest
for better support.
No Rust extensions are available for Windows at this time.
Features
========
The following operations are sped up when using Rust:
- discovery of differences between repositories (pull/push)
- nodemap (see :hg:`help config.format.use-persistent-nodemap`)
- all commands using the dirstate (status, commit, diff, add, update, etc.)
- dirstate-v2 (see :hg:`help config.format.use-dirstate-v2`)
- iteration over ancestors in a graph
More features are in the works, and improvements on the above listed are still
in progress. For more experimental work see the "rhg" section.
Checking for Rust
=================
You may already have the Rust extensions depending on how you install
Mercurial::
$ hg debuginstall | grep -i rust
checking Rust extensions (installed)
checking module policy (rust+c-allow)
If those lines don't even exist, you're using an old version of `hg` which does
not have any Rust extensions yet.
Installing
==========
You will need `cargo` to be in your `$PATH`. See the "MSRV" section for which
version to use.
Using pip
---------
Users of `pip` can install the Rust extensions with the following command::
$ pip install mercurial --global-option --rust --no-use-pep517
`--no-use-pep517` is here to tell `pip` to preserve backwards compatibility with
the legacy `setup.py` system. Mercurial has not yet migrated its complex setup
to the new system, so we still need this to add compiled extensions.
This might take a couple of minutes because you're compiling everything.
See the "Checking for Rust" section to see if the install succeeded.
From your distribution
----------------------
Some distributions are shipping Mercurial with Rust extensions enabled and
pre-compiled (meaning you won't have to install `cargo`), or allow you to
specify an install flag. Check with your specific distribution for how to do
that, or ask their team to add support for hg+Rust!
From source
-----------
Please refer to the `rust/README.rst` file in the Mercurial repository for
instructions on how to install from source.
MSRV
====
The minimum supported Rust version is defined in `rust/clippy.toml`.
The project's policy is to keep it at or below the version from Debian testing,
to make the distributions' job easier.
rhg
===
There exists an experimental pure-Rust version of Mercurial called `rhg` with a
fallback mechanism for unsupported invocations. It allows for much faster
execution of certain commands while adding no discernable overhead for the rest.
The only way of trying it out is by building it from source. Please refer to
`rust/README.rst` in the Mercurial repository.
See `hg help config.rhg` for configuration options.
Contributing
============
If you would like to help the Rust endeavor, please refer to `rust/README.rst`
in the Mercurial repository.