uv Random errors on accessing cache with simultaneous installs on Windows

Quite often uv venv or uv pip install fails in our CI environment. There are multiple jobs creating virtual envs and/or installing requirements with uv pip install. Each is using a different venv but they all share user and thus the cache.

Example (synthetic reproduction):

host="jenkins@sf-win19-vm4"
python="C:/Python3.12/python.exe"

venv=$WORKSPACE/venv

ssh "$host" "uv venv --seed --python $python $venv"

Running this snippet as a Jenkins job from 9 hosts to the same Windows hosts sometimes works, but more often than not it fails on some of the hosts. Example:

11:09:38 + ssh jenkins@sf-win19-vm4 'uv venv --seed --python C:/Python3.12/python.exe /home/jenkins/workspace/gozdal/uv-repro-windows-cache-bug/node/sf-precision9/venv'
11:09:38 Using Python 3.12.2 interpreter at: C:\Python3.12\python.exe
11:09:38 Creating virtualenv at: /home/jenkins/workspace/gozdal/uv-repro-windows-cache-bug/node/sf-precision9/venv
11:09:42 uv::venv::seed
11:09:42 
11:09:42   × Failed to install seed packages
11:09:42   ├─▶ No solution found when resolving: pip
11:09:42   ├─▶ Failed to write to the client cache
11:09:42   ╰─▶ Failed to persist temporary file to
11:09:42       AppData\Local\uv\cache\simple-v6\pypi\pip.rkyv: Access is denied. (os
11:09:42       error 5)

11:09:38 + ssh jenkins@sf-win19-vm4 'uv venv --seed --python C:/Python3.12/python.exe /home/jenkins/workspace/gozdal/uv-repro-windows-cache-bug/node/sf-precision4/venv'
11:09:38 Using Python 3.12.2 interpreter at: C:\Python3.12\python.exe
11:09:38 Creating virtualenv at: /home/jenkins/workspace/gozdal/uv-repro-windows-cache-bug/node/sf-precision4/venv
11:09:42 uv::venv::seed
11:09:42 
11:09:42   × Failed to install seed packages
11:09:42   ├─▶ No solution found when resolving: pip
11:09:42   ├─▶ Failed to write to the client cache
11:09:42   ╰─▶ Failed to persist temporary file to
11:09:42       AppData\Local\uv\cache\simple-v6\pypi\pip.rkyv: Access is denied. (os
11:09:42       error 5)

11:09:38 + ssh jenkins@sf-win19-vm4 'uv venv --seed --python C:/Python3.12/python.exe /home/jenkins/workspace/gozdal/uv-repro-windows-cache-bug/node/sf-worker3/venv'
11:09:38   × Failed to persist temporary file to
11:09:38   │ AppData\Local\uv\cache\interpreter-v0\55968f1457792c80.msgpack: Access is
11:09:38   │ denied. (os error 5)

11:09:38 + ssh jenkins@sf-win19-vm4 'uv venv --seed --python C:/Python3.12/python.exe /home/jenkins/workspace/gozdal/uv-repro-windows-cache-bug/node/sf-worker2/venv'
11:09:38 Using Python 3.12.2 interpreter at: C:\Python3.12\python.exe
11:09:38 Creating virtualenv at: /home/jenkins/workspace/gozdal/uv-repro-windows-cache-bug/node/sf-worker2/venv
11:09:42 uv::venv::seed
11:09:42 
11:09:42   × Failed to install seed packages
11:09:42   ├─▶ No solution found when resolving: pip
11:09:42   ├─▶ Failed to write to the client cache
11:09:42   ╰─▶ Failed to persist temporary file to
11:09:42       AppData\Local\uv\cache\simple-v6\pypi\pip.rkyv: Access is denied. (os
11:09:42       error 5)

1:09:38 + ssh jenkins@sf-win19-vm4 'uv venv --seed --python C:/Python3.12/python.exe /home/jenkins/workspace/gozdal/uv-repro-windows-cache-bug/node/sf-precision2/venv'
11:09:38 Using Python 3.12.2 interpreter at: C:\Python3.12\python.exe
11:09:38 Creating virtualenv at: /home/jenkins/workspace/gozdal/uv-repro-windows-cache-bug/node/sf-precision2/venv
11:09:42 uv::venv::seed
11:09:42 
11:09:42   × Failed to install seed packages
11:09:42   ├─▶ No solution found when resolving: pip
11:09:42   ├─▶ Failed to write to the client cache
11:09:42   ╰─▶ Failed to persist temporary file to
11:09:42       AppData\Local\uv\cache\simple-v6\pypi\pip.rkyv: Access is denied. (os
11:09:42       error 5)

uv 0.1.28 (0046a0d59 2024-04-02)

Apr 03 '24 15:04 gozdal

Example of an error in uv pip install:

[2024-04-03T12:12:32.983Z] Built 8 editables in 5.84s
[2024-04-03T12:12:41.046Z] Resolved 253 packages in 7.26s
[2024-04-03T12:12:41.046Z] error: Failed to download distributions
[2024-04-03T12:12:41.046Z]   Caused by: Failed to fetch wheel: python-swiftclient @ git+https://github.com/StarfishStorage/python-swiftclient.git@fbdac94cf75e2fb5d3cf20207d6883fc6bd280b4
[2024-04-03T12:12:41.046Z]   Caused by: Failed to write to the distribution cache
[2024-04-03T12:12:41.046Z]   Caused by: The process cannot access the file because another process has locked a portion of the file. (os error 33)

[2024-04-03T12:12:33.275Z] error: Failed to build editables
[2024-04-03T12:12:33.275Z]   Caused by: Failed to build editable: file:///C:/jenkins/pr_integration_windows_multi_pipeline-PR-13659-2/part-1/remote/repo/starfish/agent
[2024-04-03T12:12:33.275Z]   Caused by: Build backend failed to determine extra requires with `build_editable()` with exit code: 1
[2024-04-03T12:12:33.275Z] --- stdout:
[2024-04-03T12:12:33.275Z] 
[2024-04-03T12:12:33.275Z] --- stderr:
[2024-04-03T12:12:33.275Z] Traceback (most recent call last):
[2024-04-03T12:12:33.275Z]   File "<string>", line 14, in <module>
[2024-04-03T12:12:33.275Z]   File "C:\Users\jenkins\AppData\Local\uv\cache\.tmp37BXNX\.venv\Lib\site-packages\setuptools\build_meta.py", line 448, in get_requires_for_build_editable
[2024-04-03T12:12:33.275Z]     return self.get_requires_for_build_wheel(config_settings)
[2024-04-03T12:12:33.275Z]            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[2024-04-03T12:12:33.275Z]   File "C:\Users\jenkins\AppData\Local\uv\cache\.tmp37BXNX\.venv\Lib\site-packages\setuptools\build_meta.py", line 325, in get_requires_for_build_wheel
[2024-04-03T12:12:33.275Z]     return self._get_build_requires(config_settings, requirements=['wheel'])
[2024-04-03T12:12:33.275Z]            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[2024-04-03T12:12:33.275Z]   File "C:\Users\jenkins\AppData\Local\uv\cache\.tmp37BXNX\.venv\Lib\site-packages\setuptools\build_meta.py", line 295, in _get_build_requires
[2024-04-03T12:12:33.275Z]     self.run_setup()
[2024-04-03T12:12:33.275Z]   File "C:\Users\jenkins\AppData\Local\uv\cache\.tmp37BXNX\.venv\Lib\site-packages\setuptools\build_meta.py", line 311, in run_setup
[2024-04-03T12:12:33.275Z]     exec(code, locals())
[2024-04-03T12:12:33.275Z]   File "<string>", line 1, in <module>
[2024-04-03T12:12:33.275Z]   File "C:\Users\jenkins\AppData\Local\uv\cache\.tmp37BXNX\.venv\Lib\site-packages\setuptools\__init__.py", line 104, in setup
[2024-04-03T12:12:33.275Z]     return distutils.core.setup(**attrs)
[2024-04-03T12:12:33.275Z]            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[2024-04-03T12:12:33.275Z]   File "C:\Users\jenkins\AppData\Local\uv\cache\.tmp37BXNX\.venv\Lib\site-packages\setuptools\_distutils\core.py", line 147, in setup
[2024-04-03T12:12:33.275Z]     _setup_distribution = dist = klass(attrs)
[2024-04-03T12:12:33.275Z]                                  ^^^^^^^^^^^^
[2024-04-03T12:12:33.275Z]   File "C:\Users\jenkins\AppData\Local\uv\cache\.tmp37BXNX\.venv\Lib\site-packages\setuptools\dist.py", line 307, in __init__
[2024-04-03T12:12:33.275Z]     _Distribution.__init__(self, dist_attrs)
[2024-04-03T12:12:33.275Z]   File "C:\Users\jenkins\AppData\Local\uv\cache\.tmp37BXNX\.venv\Lib\site-packages\setuptools\_distutils\dist.py", line 283, in __init__
[2024-04-03T12:12:33.275Z]     self.finalize_options()
[2024-04-03T12:12:33.275Z]   File "C:\Users\jenkins\AppData\Local\uv\cache\.tmp37BXNX\.venv\Lib\site-packages\setuptools\dist.py", line 657, in finalize_options
[2024-04-03T12:12:33.275Z]     for ep in sorted(loaded, key=by_order):
[2024-04-03T12:12:33.275Z]               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[2024-04-03T12:12:33.275Z]   File "C:\Users\jenkins\AppData\Local\uv\cache\.tmp37BXNX\.venv\Lib\site-packages\setuptools\dist.py", line 656, in <lambda>
[2024-04-03T12:12:33.275Z]     loaded = map(lambda e: e.load(), filtered)
[2024-04-03T12:12:33.275Z]                            ^^^^^^^^
[2024-04-03T12:12:33.275Z]   File "C:\Python\python.3.12.2\tools\Lib\importlib\metadata\__init__.py", line 205, in load
[2024-04-03T12:12:33.275Z]     module = import_module(match.group('module'))
[2024-04-03T12:12:33.275Z]              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[2024-04-03T12:12:33.275Z]   File "C:\Python\python.3.12.2\tools\Lib\importlib\__init__.py", line 90, in import_module
[2024-04-03T12:12:33.275Z]     return _bootstrap._gcd_import(name[level:], package, level)
[2024-04-03T12:12:33.275Z]            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[2024-04-03T12:12:33.275Z]   File "<frozen importlib._bootstrap>", line 1387, in _gcd_import
[2024-04-03T12:12:33.275Z]   File "<frozen importlib._bootstrap>", line 1360, in _find_and_load
[2024-04-03T12:12:33.275Z]   File "<frozen importlib._bootstrap>", line 1310, in _find_and_load_unlocked
[2024-04-03T12:12:33.275Z]   File "<frozen importlib._bootstrap>", line 488, in _call_with_frames_removed
[2024-04-03T12:12:33.275Z]   File "<frozen importlib._bootstrap>", line 1387, in _gcd_import
[2024-04-03T12:12:33.275Z]   File "<frozen importlib._bootstrap>", line 1360, in _find_and_load
[2024-04-03T12:12:33.275Z]   File "<frozen importlib._bootstrap>", line 1310, in _find_and_load_unlocked
[2024-04-03T12:12:33.276Z]   File "<frozen importlib._bootstrap>", line 488, in _call_with_frames_removed
[2024-04-03T12:12:33.276Z]   File "<frozen importlib._bootstrap>", line 1387, in _gcd_import
[2024-04-03T12:12:33.276Z]   File "<frozen importlib._bootstrap>", line 1360, in _find_and_load
[2024-04-03T12:12:33.276Z]   File "<frozen importlib._bootstrap>", line 1331, in _find_and_load_unlocked
[2024-04-03T12:12:33.276Z]   File "<frozen importlib._bootstrap>", line 935, in _load_unlocked
[2024-04-03T12:12:33.276Z]   File "<frozen importlib._bootstrap_external>", line 995, in exec_module
[2024-04-03T12:12:33.276Z]   File "<frozen importlib._bootstrap>", line 488, in _call_with_frames_removed
[2024-04-03T12:12:33.276Z]   File "C:\Users\jenkins\AppData\Local\uv\cache\.tmp37BXNX\.venv\Lib\site-packages\setuptools_scm\__init__.py", line 7, in <module>
[2024-04-03T12:12:33.276Z]     from ._config import Configuration
[2024-04-03T12:12:33.276Z]   File "C:\Users\jenkins\AppData\Local\uv\cache\.tmp37BXNX\.venv\Lib\site-packages\setuptools_scm\_config.py", line 15, in <module>
[2024-04-03T12:12:33.276Z]     from ._integration.pyproject_reading import (
[2024-04-03T12:12:33.276Z]   File "C:\Users\jenkins\AppData\Local\uv\cache\.tmp37BXNX\.venv\Lib\site-packages\setuptools_scm\_integration\pyproject_reading.py", line 8, in <module>
[2024-04-03T12:12:33.276Z]     from .setuptools import read_dist_name_from_setup_cfg
[2024-04-03T12:12:33.276Z]   File "<frozen importlib._bootstrap>", line 1360, in _find_and_load
[2024-04-03T12:12:33.276Z]   File "<frozen importlib._bootstrap>", line 1331, in _find_and_load_unlocked
[2024-04-03T12:12:33.276Z]   File "<frozen importlib._bootstrap>", line 935, in _load_unlocked
[2024-04-03T12:12:33.276Z]   File "<frozen importlib._bootstrap_external>", line 991, in exec_module
[2024-04-03T12:12:33.276Z]   File "<frozen importlib._bootstrap_external>", line 1128, in get_code
[2024-04-03T12:12:33.276Z]   File "<frozen importlib._bootstrap_external>", line 1186, in get_data
[2024-04-03T12:12:33.276Z] PermissionError: [Errno 13] Permission denied: 'C:\\Users\\jenkins\\AppData\\Local\\uv\\cache\\.tmp37BXNX\\.venv\\Lib\\site-packages\\setuptools_scm\\_integration\\setuptools.py'

[2024-04-03T12:12:22.667Z] Installing sf-packaging requirements from C:\jenkins\pr_integration_windows_multi_pipeline-PR-13659-2\part-3\remote\repo\sf-packaging\requirements.txt
[2024-04-03T12:12:22.668Z] error: Failed to download and build: argparse-manpager @ git+https://github.com/StarfishStorage/argparse-manpager.git@e5b8176cbea4a48cdcad5390335a8a9464cd3537
[2024-04-03T12:12:22.668Z]   Caused by: Failed to write to the distribution cache
[2024-04-03T12:12:22.668Z]   Caused by: The process cannot access the file because another process has locked a portion of the file. (os error 33)
[2024-04-03T12:12:22.668Z] UpdatePackagingRequirements : uv pip install failed for C:\jenkins\pr_integrati
[2024-04-03T12:12:22.668Z] on_windows_multi_pipeline-PR-13659-2\part-3\remote\repo\sf-packaging\requiremen
[2024-04-03T12:12:22.668Z] ts.txt

Apr 03 '24 15:04 gozdal

The second issue is already fixed on main (#2800). The first issue I'm not really sure but your system seems to be rejecting moving files out of the temporary directory.

Apr 03 '24 15:04 charliermarsh

Thanks for such a quick reply! The thing is it's not deterministic - sometimes it works, sometimes it doesn't. Do you have any tips on how to debug?

Apr 03 '24 15:04 gozdal

"The process cannot access the file because another process has locked a portion of the file" sounds like another tool is reading the file while it's being moved. Maybe some sort of virus checker?

Apr 16 '24 11:04 pfmoore

There is no AV software on those machines.

Apr 16 '24 11:04 gozdal

The ERROR_ACCESS_DENIED 'Failed to persist temporary file' errors are straightforward to reproduce -- try deleting %LOCALAPPDATA%\uv\cache and then running, say, five uv venv --seed <my-venv-dir> commands in parallel, where <my-venv-dir> is unique across all the invocations.

Looking at a Process Monitor trace with uv 0.1.39, it looks that these concurrent uv.exe processes are racing to write to wheel.rykv/pip.rykv/setuptools.rykv in %LOCALAPPDATA%\uv\cache\simple-v7\pypi. Specifically, the uv processes are writing to a temporary file that is then renamed to wheel.rykv/pip.rykv/setuptools.rykv. However, these rename operations fail with ERROR_ACCESS_DENIED if any process (i.e. another of the concurrent uv processes) has an open handle to the file being replaced.

(Replacing an open file can actually be done on recent Windows 10, but is a bit tricky. I believe all opens need to have used the FILE_SHARE_DELETE share flag, and the rename operation needs to be done with an API such as SetFileInformationByHandle with SetFileRenameInfoEx and the FILE_RENAME_FLAG_POSIX_SEMANTICS flag. SetFileRenameInfoEx is only available for Windows 10 1607 and newer.)

Process Monitor screenshot showing the failed rename op:

Apr 27 '24 15:04 nickhutchinson

Thanks, that's really helpful. Not sure how to resolve that then, other than to make Windows 10 1607 our minimum-supported version and implement POSIX semantics there.

Apr 27 '24 15:04 charliermarsh

Thanks, that's really helpful. Not sure how to resolve that then, other than to make Windows 10 1607 our minimum-supported version and implement POSIX semantics there.

If you've got a hard requirement on having POSIX-style file renames for uv, then yeah, I guess so. Otherwise, perhaps you could use some form of file-level locking to avoid having multiple uv processes race to write to the same path in the cache.

Apr 30 '24 19:04 nickhutchinson

Would love to see this remedied - uv speeds up our CI by a huge amount but this issue has forced us to revert. Glad the root cause seems to be understood!

Aug 28 '24 08:08 george-palmsens

I had a similar problem with uv , GitLab and a Windows build server. Parallel builds caused conflicts with the uv cache. The cache was stored for each build in the same directory of the user: Failed to retrieve temporary file while trying to persist to C:\Users\GitLabUser\AppData\Local\uv\cache\simple-v14\pypi\docutils.rkyv

What solved the issue was to set a specific cache directory for each build: --cache-dir .cache

With this solution each parallel build uses its own cache.

Dec 24 '24 10:12 codeLemur

I had a similar problem with uv , GitLab and a Windows build server. Parallel builds caused conflicts with the uv cache. The cache was stored for each build in the same directory of the user: Failed to retrieve temporary file while trying to persist to C:\Users\GitLabUser\AppData\Local\uv\cache\simple-v14\pypi\docutils.rkyv

What solved the issue was to set a specific cache directory for each build: --cache-dir .cache

With this solution each parallel build uses its own cache.

Thanks! Recently hit this while using uvx with Claude's MCP mcp-server-sqlite

If anyone is in the same boat as me, this is the config

{
  "mcpServers": {
    "sqlite": {
      "command": "uvx",
      "args": [
        "--cache-dir",
        ".cache",
        "mcp-server-sqlite",
        "--db-path",
        "/path/to/sqlite.db"
      ]
    }
  }
}

Jan 19 '25 09:01 dinhphieu

Just wanted to let people know that I hit the issue of Caused by: Failed to persist temporary file to ... as well during a build using cmake and uv. I read about AV being the issue and some caching things, but I had another solution that worked for me.

In my case, it seems to have hit the Maximum Path Length Limitation, because after I moved the repository to a short-named folder in the root of the drive (e.g. C:\Code), I was able to run the build successfully.

Perhaps this helps others as well.

May 23 '25 08:05 skaasjager