Zanie Blue
f7e9a33d48
In https://github.com/astral-sh/uv/issues/18026, we received a report that resolution took >90m and the root cause appears to be that repeated conflicts with a single extra causes an exponential explosion. I used Codex to find an optimization to avoid this. > When processing N pairwise conflict sets that share a common extra (e.g., {pinned, a}, {pinned, b}, {pinned, c}, ...), the resolver creates forks by iterating over each conflict set and splitting every existing fork into N+1 sub-forks. Without the optimization, this is multiplicative — each conflict set multiplies the fork count, producing O(2^N) forks even though most are redundant. > > The key observation is: if a prior conflict set already excluded an extra from a fork, then a later conflict set involving that same extra is already satisfied in that fork — there's nothing left to separate. For example, after processing {pinned, a}, one fork has pinned excluded. When we then process {pinned, b}, that fork already can't have pinned active, so the constraint "at most one of pinned or b" is trivially true. We call this fork dominated by the earlier split — no further forking is needed. > > The one subtlety: even if a conflict set is satisfied in a fork, we might still need to fork if the remaining non-excluded item appears in another conflict set that's still live (i.e., has two or more non-excluded items). That's the refined check — we only skip forking when the item is truly dominated across all conflict sets, not just the current one. I then did some rough benchmarking ``` ┌────┬────────┬───────┬─────────┐ │ N │ Before │ After │ Speedup │ ├────┼────────┼───────┼─────────┤ │ 5 │ 29ms │ 27ms │ ~1× │ ├────┼────────┼───────┼─────────┤ │ 8 │ 58ms │ 27ms │ 2× │ ├────┼────────┼───────┼─────────┤ │ 10 │ 185ms │ 26ms │ 7× │ ├────┼────────┼───────┼─────────┤ │ 15 │ 20.0s │ 46ms │ 435× │ ├────┼────────┼───────┼─────────┤ │ 20 │ >60s │ 28ms │ >2,000× │ └────┴────────┴───────┴─────────┘ ```
Crates
uv-bench
Functionality for benchmarking uv.
uv-cache-key
Generic functionality for caching paths, URLs, and other resources across platforms.
uv-distribution-filename
Parse built distribution (wheel) and source distribution (sdist) filenames to extract structured metadata.
uv-distribution-types
Abstractions for representing built distributions (wheels) and source distributions (sdists), and the sources from which they can be downloaded.
uv-install-wheel-rs
Install built distributions (wheels) into a virtual environment.
uv-once-map
A waitmap-like concurrent hash map for executing tasks
exactly once.
uv-pep440-rs
Utilities for interacting with Python version numbers and specifiers.
uv-pep508-rs
Utilities for parsing and evaluating dependency specifiers, previously known as PEP 508.
uv-platform-tags
Functionality for parsing and inferring Python platform tags as per PEP 425.
uv-cli
Command-line interface for the uv package manager.
uv-build-frontend
A PEP 517-compatible build frontend for uv.
uv-cache
Functionality for caching Python packages and associated metadata.
uv-client
Client for interacting with PyPI-compatible HTTP APIs.
uv-dev
Development utilities for uv.
uv-dispatch
A centralized struct for resolving and building source distributions in isolated environments.
Implements the traits defined in uv-types.
uv-distribution
Client for interacting with built distributions (wheels) and source distributions (sdists). Capable of fetching metadata, distribution contents, etc.
uv-extract
Utilities for extracting files from archives.
uv-fs
Utilities for interacting with the filesystem.
uv-git
Functionality for interacting with Git repositories.
uv-installer
Functionality for installing Python packages into a virtual environment.
uv-python
Functionality for detecting and leveraging the current Python interpreter.
uv-normalize
Normalize package and extra names as per Python specifications.
uv-requirements
Utilities for reading package requirements from pyproject.toml and requirements.txt files.
uv-resolver
Functionality for resolving Python packages and their dependencies.
uv-shell
Utilities for detecting and manipulating shell environments.
uv-types
Shared traits for uv, to avoid circular dependencies.
uv-pypi-types
General-purpose type definitions for types used in PyPI-compatible APIs.
uv-virtualenv
A venv replacement to create virtual environments in Rust.
uv-warnings
User-facing warnings for uv.
uv-workspace
Workspace abstractions for uv.
uv-requirements-txt
Functionality for parsing requirements.txt files.