From: Josef Wolf <jw@raven.inka.de>
To: Git Mailing List <git@vger.kernel.org>
Subject: Re: Why is "Sparse checkout leaves no entry on working directory" a fatal error?
Date: Wed, 9 Oct 2019 11:37:19 +0200 [thread overview]
Message-ID: <20191009093719.GC30443@raven.inka.de> (raw)
In-Reply-To: <CABPp-BE8YmVTS=4UWy5jvxBwr3EOcqzbnpWf2Wc78Kv6YScKgQ@mail.gmail.com>
Thanks for your comprehensive answer, Elijah!
On Di, Okt 08, 2019 at 09:14:27 -0700, Elijah Newren wrote:
> On Mon, Oct 7, 2019 at 11:52 PM Josef Wolf <jw@raven.inka.de> wrote:
> >
> > I am trying to add a file to an arbitrary branch without touching the current
> > worktree with as little overhead as possible.
>
> I can see the logical progression that a sparse worktree would be less
> overhead than a full worktree, and that a bare worktree would be even
> better. But you're still dealing with unnecessary overhead; you don't
> need a worktree at all to achieve what you want.
Well, the "as little overhead as possible" must be seen from the context. This
is a repository with roundabout 10GB and more than 6200 files. Shared-clones
with sparse-worktree is a BIG BIG BIG improvement here, which reduces
operations from "minutes" to "withhin a second".
> Traditionally, if you wanted to modify another branch without touching
> the worktree at all, you would use a combination of hash-object,
> mktree, commit-tree, and update-ref. That would be a better solution
> to your problem than trying to approximate it with a sparse checkout.
> However, that's at least four invocations of git, and you said as
> little overhead as possible, so I'd recommend you use fast-import.
I have taken a look into the commands you are recommending, and indeed, they
seem to be better suited. Especially fast-import looks very
promising. Unfortunately, those commands require intimate knowledge about git
internals. I'll take a closer look into this!
> It is very easy to mess up the sparse specifications. We can't check
> for all errors, but a pretty obvious one is when people specify
> restrictions that match no path.
But why erroring out only on completely empty tree? Why not requiring that
_every_ line in .git/info/sparse-checkout should match at least one file?
Would make no sense, right?
> We can at least give an error in that case.
Why must this be a fatal error? Wouldn't a warning suffice?
> 2) When they've learned about sparse checkouts and just want to test
> what things are like in extreme situations.
[ ... ]
> For case 2, people learn that an empty working tree is a too extreme
> situation that we'll throw an error at and so they adjust and make
> sure to match at least one path.
When I am trying to learn how a new feature works, I tend to double-check the
results. If I expect contens but end up with an empty WT, I'd go and double
check the specifications I've given anyway.
I can easily understand that a warning might be desirable. But erroring out
and failing to honor the "-b" flag is a bit too drastic, IMHO.
> > Strange enough, I have some repositories at this machine where the
> > .git/info/sparse-checkout file contains only non-existing files and git
> > happily executes this "git checkout -b XXX remotes/origin/XXX" command leaving
> > the working tree totally empty all the time.
>
> I can't reproduce:
>
> $ git config core.sparseCheckout true
> $ echo 'non-existent' > .git/info/sparse-checkout
> $ git checkout -b next origin/next
> error: Sparse checkout leaves no entry on working directory
>
> Can you provide any more details about how you get into this state?
Unfortunately not.
Honestly, I have tried to reproduce for several days, since I tried
to find a way how to work around that fatal error. Unfortunately, I could not
find how to reproduce it. The only thing I can say is: threre are several
clones on my disk which happily switch branches with an empty WT and without
any complaints.
> > Someone understands this inconsistent behaviour?
>
> No, but I wouldn't be surprised if there are bugs and edge cases. I
> think I ran into one or two when testing things out, didn't take good
> enough notes, and had trouble reproducing later. The sparse checkout
> stuff has been under-tested and not well documented, something Stolee
> is trying to fix right now.
Yes, I've seen the work on the ML. But I am only a user of git and have a very
hard time to understand what is going on there.
--
Josef Wolf
jw@raven.inka.de
prev parent reply other threads:[~2019-10-09 9:40 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-08 6:45 Why is "Sparse checkout leaves no entry on working directory" a fatal error? Josef Wolf
2019-10-08 16:14 ` Elijah Newren
2019-10-09 9:37 ` Josef Wolf [this message]
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