René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Potentially serious regression in garbage collector performance in Python 3.14","articleBody":"# Bug report\n\n### Bug description:\n\nThe following code, consisting of a bunch of `dict` lookups and writes, runs in\n\n* _\u003c 1 second_ on Python 3.13\n* _\u003e 2 seconds_ on Python 3.14\n \n```python\nn = 1000\nd = {}\nfor i in range(n):\n    d[(i, i)] = d[(i, 0)] = d[(0, i)] = 0\nfor i in range(1, n):\n    for j in range(1, n):\n        d[(i, j)] = i + j + d[(i - 1, j)] + d[(i, j - 1)] + d[(i - 1, j - 1)]\nprint(d[(n - 1, n - 1)])\n```\n\nTests are run on a Dell Precision 5490, running Ubuntu:\n\n```\nLinux precision 6.14.0-33-generic #33-Ubuntu SMP PREEMPT_DYNAMIC Wed Sep 17 23:22:02 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux\n\nUbuntu 25.04 (Plucky)\n```\n\nThe cpython is from [python-build-standalone](https://github.com/astral-sh/python-build-standalone)\n\n* `cpython-3.14.0+20251010-x86_64-unknown-linux-gnu-install_only.tar.gz`\n* `cpython-3.13.8+20251010-x86_64-unknown-linux-gnu-install_only.tar.gz`\n\n\n## Log\n\n```\n[~/regression-testing]$ hyperfine --warmup=10 \"cp313/python/bin/python3.13 dicttest.py\" \"cp314/python/bin/python3.14 dicttest.py\"\nBenchmark 1: cp313/python/bin/python3.13 dicttest.py\n  Time (mean ± σ):     880.8 ms ± 119.7 ms    [User: 730.1 ms, System: 150.1 ms]\n  Range (min … max):   713.3 ms … 1066.2 ms    10 runs\n \nBenchmark 2: cp314/python/bin/python3.14 dicttest.py\n  Time (mean ± σ):      2.235 s ±  0.035 s    [User: 2.066 s, System: 0.168 s]\n  Range (min … max):    2.168 s …  2.295 s    10 runs\n \nSummary\n  cp313/python/bin/python3.13 dicttest.py ran\n    2.54 ± 0.35 times faster than cp314/python/bin/python3.14 dicttest.py\n```\n\nIt seems to scale very poorly too.  With the same code, but `n = 2000` (instead of `n = 1000`), leads to 3.3 sec (Python 3.13) vs 20 seconds (Python 3.14)!  I.e., Python 3.13 being 5 times faster.\n\n```\n[~/regression-testing]$ hyperfine --warmup=10 \"cp313/python/bin/python3.13 dicttest.py\" \"cp314/python/bin/python3.14 dicttest.py\"\nBenchmark 1: cp313/python/bin/python3.13 dicttest.py\n  Time (mean ± σ):      3.458 s ±  0.048 s    [User: 2.889 s, System: 0.568 s]\n  Range (min … max):    3.375 s …  3.521 s    10 runs\n \nBenchmark 2: cp314/python/bin/python3.14 dicttest.py\n  Time (mean ± σ):     20.084 s ±  0.230 s    [User: 19.503 s, System: 0.577 s]\n  Range (min … max):   19.749 s … 20.345 s    10 runs\n \nSummary\n  cp313/python/bin/python3.13 dicttest.py ran\n    5.81 ± 0.10 times faster than cp314/python/bin/python3.14 dicttest.py\n```\n\n\u003cimg width=\"1920\" height=\"1054\" alt=\"Time comparison plot of Python 3.13 vs Python 3.14\" src=\"https://github.com/user-attachments/assets/b06f1b4c-3ac5-4ec2-9a0a-0f6fe226c67a\" /\u003e\n\nPlotting time (in seconds) of the script run with `n = 0 ... 2000`.\n\n### CPython versions tested on:\n\n3.14\n\n### Operating systems tested on:\n\nLinux\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-140204\n* gh-140262\n* gh-140304\n* gh-140362\n* gh-140363\n* gh-140423\n* gh-140447\n* gh-140575\n* gh-140701\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/pgdr","@type":"Person","name":"pgdr"},"datePublished":"2025-10-11T10:11:47.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":31},"url":"https://github.com/139951/cpython/issues/139951"}