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rust-discovery: using the children cache in add_missing
The DAG range computation often needs to get back to very old
revisions, and turns out to be disproportionately long, given
that the end goal is to remove the descendents of the given
missing revisons from the undecided set.
The fast iteration capabilities available in the Rust case make
it possible to avoid the DAG range entirely, at the cost of
precomputing the children cache, and to simply iterate on
children of the given missing revisions.
This is a case where staying on the same side of the interface
between the two languages has clear benefits.
On discoveries with initial undecided sets
small enough to bypass sampling entirely, the total cost of
computing the children cache and the subsequent iteration
becomes better than the Python + C counterpart, which relies on
reachableroots2.
For example, on a repo with more than one million revisions with
an initial undecided set of 11 elements, we get these figures:
Rust version with simple iteration
addcommons: 57.287us
first undecided computation: 184.278334ms
first children cache computation: 131.056us
addmissings iteration: 42.766us
first addinfo total: 185.24 ms
Python + C version
first addcommons: 0.29 ms
addcommons 0.21 ms
first undecided computation 191.35 ms
addmissings 45.75 ms
first addinfo total: 237.77 ms
On discoveries with large undecided sets, the initial price paid
makes the first addinfo slower than the Python + C version,
but that's more than compensated by the gain in sampling and
subsequent iterations.
Here's an extreme example with an undecided set of a million revisions:
Rust version:
first undecided computation: 293.842629ms
first children cache computation: 407.911297ms
addmissings iteration: 34.312869ms
first addinfo total: 776.02 ms
taking initial sample
query 2: sampling time: 1318.38 ms
query 2; still undecided: 1005013, sample size is: 200
addmissings: 143.062us
Python + C version:
first undecided computation 298.13 ms
addmissings 80.13 ms
first addinfo total: 399.62 ms
taking initial sample
query 2: sampling time: 3957.23 ms
query 2; still undecided: 1005013, sample size is: 200
addmissings 52.88 ms
Differential Revision: https://phab.mercurial-scm.org/D6428
author | Georges Racinet <georges.racinet@octobus.net> |
---|---|
date | Tue, 16 Apr 2019 01:16:39 +0200 |
parents | 964212780daf |
children | 8a3b045d9086 |
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=================== Mercurial Rust Code =================== This directory contains various Rust code for the Mercurial project. The top-level ``Cargo.toml`` file defines a workspace containing all primary Mercurial crates. Building ======== To build the Rust components:: $ cargo build If you prefer a non-debug / release configuration:: $ cargo build --release Features -------- The following Cargo features are available: localdev (default) Produce files that work with an in-source-tree build. In this mode, the build finds and uses a ``python2.7`` binary from ``PATH``. The ``hg`` binary assumes it runs from ``rust/target/<target>hg`` and it finds Mercurial files at ``dirname($0)/../../../``. Build Mechanism --------------- The produced ``hg`` binary is *bound* to a CPython installation. The binary links against and loads a CPython library that is discovered at build time (by a ``build.rs`` Cargo build script). The Python standard library defined by this CPython installation is also used. Finding the appropriate CPython installation to use is done by the ``python27-sys`` crate's ``build.rs``. Its search order is:: 1. ``PYTHON_SYS_EXECUTABLE`` environment variable. 2. ``python`` executable on ``PATH`` 3. ``python2`` executable on ``PATH`` 4. ``python2.7`` executable on ``PATH`` Additional verification of the found Python will be performed by our ``build.rs`` to ensure it meets Mercurial's requirements. Details about the build-time configured Python are built into the produced ``hg`` binary. This means that a built ``hg`` binary is only suitable for a specific, well-defined role. These roles are controlled by Cargo features (see above). Running ======= The ``hgcli`` crate produces an ``hg`` binary. You can run this binary via ``cargo run``:: $ cargo run --manifest-path hgcli/Cargo.toml Or directly:: $ target/debug/hg $ target/release/hg You can also run the test harness with this binary:: $ ./run-tests.py --with-hg ../rust/target/debug/hg .. note:: Integration with the test harness is still preliminary. Remember to ``cargo build`` after changes because the test harness doesn't yet automatically build Rust code.