Why Are Packages Installed Locally Instead of Linked Centrally?

Why Are Packages Installed Locally Instead of Linked Centrally?

Conda and other package managers typically install packages in isolated environments. Users may wonder why packages are not simply linked to a central location instead, given that conda caches downloaded packages.

Conda's Hardlink Mechanism

In fact, conda already employs this strategy. Conda packages are installed in hardlinked directories, which means that multiple directories appear to contain unique copies of packages, but actually share the same underlying data.

Space Savings

A common misconception is that each environment consumes a significant amount of space. However, due to the hardlinking mechanism, the actual disk usage is much lower than it appears. To demonstrate, we can use the du command to examine the uncorrected (per environment) and corrected (hardlinked) space usage:

# Uncorrected
$ for d in envs/*; do du -sh $d; done

# Corrected
$ du -sh envs/*

The output shows that a large portion of the space is being saved.

Shared Packages

The majority of hardlinks point to the pkgs directory, where shared packages are stored. This shared location reduces duplication and minimizes the size of individual environments. Including the pkgs directory in the analysis reveals that the environments themselves are relatively small:

$ du -sh pkgs envs/*

Conclusion

Conda's hardlinking mechanism effectively reduces the disk space consumed by packages and environments. While the isolated installation approach may appear inefficient at first glance, it offers significant space-saving benefits behind the scenes.

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