Re: Sparse Checkout Trouble (2.5.0)

From: Derrick Stolee <stolee@gmail.com>
Date: Jan 28, 2020, 20:47 UTC
Message-ID: <e4bb20e9-ad90-3e9b-7ed2-c7793cb8cb22@gmail.com>
In-Reply-To: <CABPp-BHRAA71LmfYb61N+qAgwhtii7TSEVJksiAGnnO-4bk2dQ@mail.gmail.com>

On 1/28/2020 12:21 AM, Elijah Newren wrote:

Show 19 quoted lines

> On Sun, Jan 26, 2020 at 6:09 AM Derrick Stolee <stolee@gmail.com> wrote:
>>
>> On 1/25/2020 3:59 PM, Elijah Newren wrote:
>>> On Fri, Jan 24, 2020 at 7:41 AM Derrick Stolee <stolee@gmail.com> wrote:
>>>> I'm CC'ing Elijah because he also made changes to dir.c, and
>>>> perhaps he has some idea of what's going on.
>>>
>>> If you think it might be related to the dir.c changes, I can take a
>>> look.  I don't have any immediate ideas off the top of my head.
>>
>> The only thing I can think of is that these paths are already
>> marked as sparse, but something is requiring us to test if the
>> path can be created with the filesystem. I'll try to debug
>> more into exactly where that is. It's telling that this happens
>> both in cone mode and without.
> 
> Yeah, I'll take a look.  The exponentially slow 'status --ignored'
> report is forcing me to look at dir.c again anyway, though it's also
> delaying me from getting a chance to look at this particular report.

I made some progress, at least, in root-causing the issue. The problem bisects down to 4dc42c6c1 (mingw: refuse paths containing reserved names, 2019-12-21) [1]. CC'ing Dscho.

That commit updates is_valid_win32_path() to fail on these paths. We were _already_ calling this method even for paths outside the sparse cone, but the method didn't fail for these examples.

This means the fix is probably even more complicated: we need to not call this method when traversing paths that have the skip-worktree bit enabled. This may lead to some tiny performance gains when hydrating a very small fraction of a very large index.

Thanks, -Stolee

[1] http://github.com/git/git/commit/4dc42c6c1867a52e22f1f04a1a247b5a7538b8af