Re: Are clone/checkout operations deterministic?

From: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Date: Jul 17, 2018, 09:48 UTC
Message-ID: <87bmb6chvm.fsf@evledraar.gmail.com>
In-Reply-To: <20180717091429.GA31043@sigkill.com>

On Tue, Jul 17 2018, J. Paul Reed wrote:

Show 15 quoted lines

> Hey Git Devs,
>
> I have a bit of an odd question: do git clone/checkout operations have a
> deterministic ordering?
>
> That is: are files guaranteed to be laid down onto disk in any specific
> (and deterministic) order as a clone and/or checkout operations occurs?
> (And if so, is it alphabetical order? Depth-first? Something else?)
>
> In case the answer is different (and I'd guess that it might be?), I'm
> mostly interested in the initial clone case... but it would be great to
> know if, indeed, the answer is different for just-checkouts too.
>
> I did some cursory googling, but nothing hopped out at me as an answer to
> this question.

In practice I think clone, checkout, reset etc. always work in the same order you see with `git ls-tree -r --name-only HEAD`, but as far as I know this has never been guaranteed or documented, and shouldn't be relied on.

E.g. there's probably cases where writing files in parallel is going to be faster than writing them sequentially. We don't have such a mode just because nobody's written a patch for it, but having that patch would break any assumptions of our current order.