Re: Are 'guix gc' stats exaggerated?

[Felix Lechner]

Hi Efraim,

On Tue, May 28 2024, Efraim Flashner wrote:

> As your store grows larger the inherent deduplication from the
> guix-daemon approaches a 3:1 file deduplication ratio.

Thank you for your explanations and your data about btrfs!  Btrfs
compression is a well-understood feature, although even its developers
acknowledge that the benefit is hard to quantify.

It probably makes more sense to focus on the Guix daemon here.  I hope
you don't mind a few clarifying questions.

Why, please, does the benefit of de-duplication approach a fixed ratio
of 3:1?  Does the benefit not depend on the number of copies in the
store, which can vary by any number?  (It sounds like the answer may
have something to do with store size.)

Further, why is the removal of hardlinks counted as saving space even
when their inode reference count, which is widely available [1] is
greater than one?

Finally, barring a better solution should our output numbers be divided
by three to being them closer to the expected result for users?

Thanks!

Kind regards,
Felix

[1] https://en.wikipedia.org/wiki/Hard_link#Reference_counting