Re: Commit graph chains with no corresponding files?

From: Bryan Turner <bturner@atlassian.com>
Date: Feb 25, 2021, 04:54 UTC
Message-ID: <CAGyf7-G_OdS_0o7j64HA79n9Qv13SxciQSG+gfY7Qj8kNRQS5Q@mail.gmail.com>
In-Reply-To: <92b218ca-f2b4-db9d-9f9c-1d071ea4fa97@gmail.com>

On Mon, Jun 29, 2020 at 6:51 PM Derrick Stolee <stolee@gmail.com> wrote:

Show 10 quoted lines

>
> On 6/29/2020 6:07 PM, Jonathan Tan wrote:
> > At $DAYJOB, a few people have reported "warning: unable to find all
> > commit-graph files" warnings. Their commit-graph-chain files have a few
> > lines, but they only have one commit graph file with very few commits. I
> > suspected something happening during fetch, because (as far as I know) a
> > fetch may cause an incremental commit graph to be written, but I ran a
> > fetch on a large repository myself and didn't run into this problem.
> >
> > Has anyone ran into this problem before, and know how to reproduce?

I don't have any specific reproduction steps, but we've just run into our first case of this on Git 2.29. I ended up kicking off a full `git commit-graph write` to fix it. That displayed the same warning, but commands run after it no longer do. Prior to writing the new graph, I had this: $ ls commit-graph-chain graph-88f5fe6e0c659e3742e556982263813d528ead81.graph

Afterward, the `objects/info/commits-graphs` directory still exists but is empty, and there is now an `objects/commit-graph` that didn't exist before. `git commit-graph verify` seems happy with the state of things.

Show 11 quoted lines

>
> The incremental commit-graph code deletes any commit-graph files
> that do not appear in the chain. I believe this is done by comparing
> the contents of the ".git/objects/info/commit-graphs/" directory to
> the contents of the chain file.
>
> These appear to be case-sensitive, full-path comparisons.
>
> It is _possible_ that something like a case switch or a symlink
> could be causing a problem here. That's where I would look on
> the affected systems.

Are commit graphs potentially problematic in repositories that are borrowing objects from other repositories via alternates? Have there been important changes to commit graphs since 2.29?

Show 10 quoted lines

>
> Likely the full-path comparison in expire_commit_graphs() should
> be dropped in favor of local filename comparisons. A case-
> sensitive match is less likely to be important here since Git
> is writing the paths itself and should get the proper case back
> from the directory listing.
>
> Thanks,
> -Stolee
>

-b