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Explicitly configure uv to use hard links #2044

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Merged
edmorley merged 1 commit into from
Mar 3, 2026
Merged

Explicitly configure uv to use hard links #2044

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1 change: 1 addition & 0 deletions CHANGELOG.md
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Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,7 @@
## [Unreleased]

- Updated pip from 25.3 to 26.0.1. ([#2032](https://github.com/heroku/heroku-buildpack-python/pull/2032))
- Explicitly configured uv to use hard links to maintain the behaviour of previous versions. ([#2044](https://github.com/heroku/heroku-buildpack-python/pull/2044))

## [v336] - 2026-03-02

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4 changes: 4 additions & 0 deletions lib/uv.sh
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Expand Up @@ -88,13 +88,17 @@ function uv::install_uv() {
# Prevent uv from downloading/using its own Python installation.
export UV_NO_MANAGED_PYTHON="1"
export UV_PYTHON_DOWNLOADS="never"
# Force uv to use hardlinks rather than the new default of reflinks, since the latter are
# significantly slower on Kodon: https://github.com/astral-sh/uv/issues/18259
export UV_LINK_MODE="hardlink"

# Set the same env vars in the environment used by later buildpacks.
cat >>"${export_file}" <<-EOF
export PATH="${uv_dir}:\${PATH}"
export UV_PROJECT_ENVIRONMENT="${python_home}"
export UV_NO_MANAGED_PYTHON="1"
export UV_PYTHON_DOWNLOADS="never"
export UV_LINK_MODE="hardlink"
EOF

# As a performance optimisation, uv attempts to use hardlinks instead of copying files from its
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2 changes: 2 additions & 0 deletions spec/hatchet/ci_spec.rb
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Expand Up @@ -319,6 +319,7 @@
PATH=/tmp/cache\\w+/.heroku/python-uv:/app/.heroku/python/bin:/usr/local/bin:/usr/bin:/bin:/app/.sprettur/bin/
PKG_CONFIG_PATH=/app/.heroku/python/lib/pkg-config
PYTHONUNBUFFERED=1
UV_LINK_MODE=hardlink
UV_NO_MANAGED_PYTHON=1
UV_PROJECT_ENVIRONMENT=/app/.heroku/python
UV_PYTHON_DOWNLOADS=never
Expand All @@ -331,6 +332,7 @@
PYTHONHOME=/app/.heroku/python
PYTHONPATH=/app
PYTHONUNBUFFERED=true
UV_LINK_MODE=hardlink
UV_NO_MANAGED_PYTHON=1
UV_PROJECT_ENVIRONMENT=/app/.heroku/python
UV_PYTHON_DOWNLOADS=never
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2 changes: 2 additions & 0 deletions spec/hatchet/uv_spec.rb
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Expand Up @@ -33,6 +33,7 @@
remote: PKG_CONFIG_PATH=/app/.heroku/python/lib/pkg-config
remote: PYTHONUNBUFFERED=1
remote: UV_CACHE_DIR=/tmp/uv-cache
remote: UV_LINK_MODE=hardlink
remote: UV_NO_MANAGED_PYTHON=1
remote: UV_PROJECT_ENVIRONMENT=/app/.heroku/python
remote: UV_PYTHON_DOWNLOADS=never
Expand All @@ -46,6 +47,7 @@
remote: PYTHONPATH=/app
remote: PYTHONUNBUFFERED=true
remote: UV_CACHE_DIR=/tmp/uv-cache
remote: UV_LINK_MODE=hardlink
remote: UV_NO_MANAGED_PYTHON=1
remote: UV_PROJECT_ENVIRONMENT=/app/.heroku/python
remote: UV_PYTHON_DOWNLOADS=never
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