Re: Diff rename detection performance issues

From: D. Ben Knoble <ben.knoble@gmail.com>
Date: Feb 24, 2025, 17:50 UTC
Message-ID: <CALnO6CDpEfugTReF3j_3jefaDg2-YtMB-2XrKg07wD4cofHK7g@mail.gmail.com>
In-Reply-To: <CABPp-BHObCVqxWuBLgeiWghy5gM8-f_qjwYFdBL+=j1bwtPg_A@mail.gmail.com>

On Mon, Feb 24, 2025 at 11:31 AM Elijah Newren <newren@gmail.com> wrote:

>
> On Sun, Feb 23, 2025 at 2:30 AM Devste Devste <devstemail@gmail.com> wrote:

[snip]

Show 11 quoted lines

> > Funnily enough, when I have a merge commit that contains only that 1
> > excluded file, it's the same behavior.
> >
> > 1) if there's only a single file in a commit, why does --find-renames
> > cause a slowdown? There's nothing that could have been renamed in that
> > case (probably the same for --find-copies)
>
> I'm not sure what this has to do with the above; you seem to have
> switched tracks.  If you have a commit whose toplevel tree has exactly
> 1 file, and you're diffing it against some other commit with an
> unspecified number of files, [snip]

I'm only mentioning this in the vein of Elijah's requests for clarification: the wording "only a single file in a commit" is something I often see from newcomers who don't yet understand that a commit points to a tree of the entire repo, but the diff between a commit and it's parent might show only one modified file. (Sometimes I think we experts encourage this when we refer to that diff as the commit [1], [2].)

Now, Devste's posted commands indicate they may have more Git experience and didn't fall to this trap, so Elijah's interpretation of "a commit whose toplevel tree has exactly 1 file" is perfectly reasonable—but we'd probably all like to know a bit more to confirm. I originally read "if there's only a single file in the commit" (with my newcomer lenses on) as "if I only changed one file before commiting." This is also partly based on a (mis)read of "a merge commit that contains only that 1 excluded file" (perhaps OP meant "modified").

[1]: https://jvns.ca/blog/2023/11/01/confusing-git-terminology/#commit [2]: https://jvns.ca/blog/2024/01/05/do-we-think-of-git-commits-as-diffs--snapshots--or-histories/

-- 
D. Ben Knoble