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× │ └────┴────────┴───────┴─────────┘ ```
uv-resolver
This crate is an internal component of uv. The Rust API exposed here is unstable and will have frequent breaking changes.
This version (0.0.24) is a component of uv 0.10.4. The source can be found here.
See uv's crate versioning policy for details on versioning.