`git stash --include-untracked` touches .pack files

`git stash --include-untracked` touches .pack files

[johnkw]

`git stash --include-untracked` causes the timestamp to be touched for 
some .pack files.  It's not always all .pack files, although I don't see 
a pattern regarding how some survive the operation with the timestamp 
intact.  For a given repo it seems consistent though on the .pack files 
impacted by the issue.

This breaks backup systems such as rsync, causing pointless churn.

The issue occurs with or without ".keep" files for the ".pack" files in 
question.

`git stash` without `--include-untracked` does not have this issue.

The issue occurs with no untracked files actually even in the repo for 
`--include-untracked` to take action on.

Re: `git stash --include-untracked` touches .pack files

[Patrick Steinhardt]

On Wed, Aug 06, 2025 at 09:27:05PM -0500, johnkw wrote:
> `git stash --include-untracked` causes the timestamp to be touched for some
> .pack files.  It's not always all .pack files, although I don't see a
> pattern regarding how some survive the operation with the timestamp intact. 
> For a given repo it seems consistent though on the .pack files impacted by
> the issue.
> 
> This breaks backup systems such as rsync, causing pointless churn.
> 
> The issue occurs with or without ".keep" files for the ".pack" files in
> question.
> 
> `git stash` without `--include-untracked` does not have this issue.
> 
> The issue occurs with no untracked files actually even in the repo for
> `--include-untracked` to take action on.

What you probably see here is Git freshening its objects: when Git is
asked to write objects into the object database that it already knows
about it will freshen the access time of each such object. If the object
is stored in a packfile, then the whole packfile is getting freshened.

This is overall an expected outcome, and Git relies on those freshened
access times to do garbage collection. So this isn't something that we
can change. One _could_ have a look at `save_untracked_files()` and
teach it to skip writing objects in case there is nothing to be done.
But honestly, I doubt that this would really solve the underlying issue
for you, as any other command that writes objects might also cause Git
to freshen the packfile.

Patrick