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astral-sh / uv

An extremely fast Python package and project manager, written in Rust.
https://docs.astral.sh/uv
Apache License 2.0
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Is uv supposed to use hard links when installing dependencies in virtualenvs? #3886

Closed pawamoy closed 5 months ago

pawamoy commented 5 months ago

The README says:

Disk-space efficient, with a global cache for dependency deduplication.

I always interpreted this as uv using hard links (or other more efficient platform-specific techniques) to avoid wasting space when installing the same dependencies in many different virtualenvs.

But in practice, it looks like the same module, yaml_env_tag.py, installed in many venvs, for the same Python version (3.11), has a different inode number in each venv:

% ls -i */.venv/lib/*/site-packages/yaml_env_tag.py                       
27449386 ansito/.venv/lib/python3.11/site-packages/yaml_env_tag.py
27954769 catalog/.venv/lib/python3.11/site-packages/yaml_env_tag.py
28483068 copier-uv/.venv/lib/python3.11/site-packages/yaml_env_tag.py
32066757 duty/.venv/lib/python3.11/site-packages/yaml_env_tag.py
27450383 fastui/.venv/lib/python3.11/site-packages/yaml_env_tag.py
27463092 fulfill/.venv/lib/python3.11/site-packages/yaml_env_tag.py
30738026 git-changelog/.venv/lib/python3.11/site-packages/yaml_env_tag.py
27609526 griffe2md/.venv/lib/python3.11/site-packages/yaml_env_tag.py
28209604 griffe-inherited-docstrings/.venv/lib/python3.11/site-packages/yaml_env_tag.py
27588071 griffe/.venv/lib/python3.11/site-packages/yaml_env_tag.py
33464782 handler-template/.venv/lib/python3.11/site-packages/yaml_env_tag.py
27529488 markdown-exec/.venv/lib/python3.11/site-packages/yaml_env_tag.py
30676935 mkdocs-autorefs/.venv/lib/python3.11/site-packages/yaml_env_tag.py
27932068 mkdocs-gallery/.venv/lib/python3.11/site-packages/yaml_env_tag.py
28015846 mkdocs-manpage/.venv/lib/python3.11/site-packages/yaml_env_tag.py
27566322 mkdocs-pygments/.venv/lib/python3.11/site-packages/yaml_env_tag.py
34976719 mkdocs-spellcheck/.venv/lib/python3.11/site-packages/yaml_env_tag.py
27672260 mkdocstrings-python/.venv/lib/python3.11/site-packages/yaml_env_tag.py
34634104 mkdocstrings-shell/.venv/lib/python3.11/site-packages/yaml_env_tag.py
30750852 mkdocstrings/.venv/lib/python3.11/site-packages/yaml_env_tag.py
28156683 mono/.venv/lib/python3.11/site-packages/yaml_env_tag.py
28203268 qtile/.venv/lib/python3.11/site-packages/yaml_env_tag.py
28722205 textual/.venv/lib/python3.11/site-packages/yaml_env_tag.py

Same for any file really:

% ls -i */.venv/lib/*/site-packages/griffe/__init__.py
28470384 ansito/.venv/lib/python3.11/site-packages/griffe/__init__.py
27929408 catalog/.venv/lib/python3.11/site-packages/griffe/__init__.py
32619592 duty/.venv/lib/python3.11/site-packages/griffe/__init__.py
30556482 fastapi/.venv/lib/python3.12/site-packages/griffe/__init__.py
28382439 fastui/.venv/lib/python3.11/site-packages/griffe/__init__.py
28274305 fulfill/.venv/lib/python3.11/site-packages/griffe/__init__.py
30922324 git-changelog/.venv/lib/python3.11/site-packages/griffe/__init__.py
30436256 griffe2md/.venv/lib/python3.11/site-packages/griffe/__init__.py
28209421 griffe-inherited-docstrings/.venv/lib/python3.11/site-packages/griffe/__init__.py
27962824 markdown-exec/.venv/lib/python3.11/site-packages/griffe/__init__.py
30695448 mkdocs-autorefs/.venv/lib/python3.11/site-packages/griffe/__init__.py
28720467 mkdocs-gallery/.venv/lib/python3.11/site-packages/griffe/__init__.py
29250701 mkdocs-manpage/.venv/lib/python3.11/site-packages/griffe/__init__.py
33986747 mkdocs-pygments/.venv/lib/python3.11/site-packages/griffe/__init__.py
34981811 mkdocs-spellcheck/.venv/lib/python3.11/site-packages/griffe/__init__.py
27666376 mkdocstrings-python/.venv/lib/python3.11/site-packages/griffe/__init__.py
34639730 mkdocstrings-shell/.venv/lib/python3.11/site-packages/griffe/__init__.py
30723121 mkdocstrings/.venv/lib/python3.11/site-packages/griffe/__init__.py
28185249 qtile/.venv/lib/python3.11/site-packages/griffe/__init__.py
32963180 textual/.venv/lib/python3.11/site-packages/griffe/__init__.py

So I wonder: is caching enabled by default, and supported on my platform? I'm on ArchLinux.

Coming from PDM, which supports different methods for this (recursive symlinking, hardlinks, etc.), I was happy to see that uv supported it too. Byt maybe I misunderstood?

charliermarsh commented 5 months ago

Yes, we recursively hardlink by default on Linux. On macOS, we recursively reflink.

Is your cache on the same filesystem as your environment?

pawamoy commented 5 months ago

Thanks for the astral-fast answer. Ah, that might be the issue :thinking: (facepalm) No, uv's cache is on a different disk and partition than my projects. Closing! :slightly_smiling_face: Is there a recommendation here? Should I just move the cache? Or can I have two (or more) cache locations (one per partition or something)?

charliermarsh commented 5 months ago

No prob! Thanks for asking, it made me double-check that we're doing it right. I tested on macOS with --link-mode=hardlink and it does seem like the inodes line up:

❯ ls -i venv1/lib/python3.12/site-packages/flask/app.py venv2/lib/python3.12/site-packages/flask/app.py
268196813 venv1/lib/python3.12/site-packages/flask/app.py 268196813 venv2/lib/python3.12/site-packages/flask/app.py

(They don't line up on macOS by default since we default to reflinks.)

charliermarsh commented 5 months ago

Hmm, I'd probably recommend setting UV_CACHE_DIR to something in the same disk / partition as your projects.

pawamoy commented 5 months ago

I'll do just that. Thanks a lot!

charliermarsh commented 5 months ago

Thank you! Always appreciate your questions.

pawamoy commented 5 months ago

(Just free'd 81GB :flushed:)