Guard against pathologically connected dependency graphs #13424
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Since the DFS of the dependency graph is brute force it is exponential in the number of children. If a graph is pathological in nature (i.e. many cross-dependencies) then this will not complete in "reasonable" time. To address this we limit the number of visits to any node in the graph, thus capping the complexity to be linear in nature.
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Again, thanks for contributing, as before, please bear in mind it might take some time for a maintainer to review this as we are all volunteers. But once I do get a chance I was going to test a few real world scenarios from simple to massive. If you need any assistance passing the pre-commit or CI let me know. |
Minor formatting fix. Added changelog entry.
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Sure thing. I fixed the pre-merge checks, very simple. And in your own time. I am not blocked on this or anything so you can handle it as and when you deem fit. I have a day-job too, and also maintain some OSS, so I know the score. And, since I don't know if folks say this enough: Thanks for being a pip maintainer! |
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When determining the install order for dependencies the code does a DFS of the dependency graph, if it finds dependency cycle.
However, should the graph be pathologically connected, then this walk can take a log time, being exponential in nature. To mitigate this we limit the number of times any particular node may be visited during the walk. This should have little or no impact for well behaved graphs, while still yielding a fair approximation of a good installation order for densely connected graphs.
This is a less invasive version of #13416.