Re: Missing Refs after Garbage Collection

From: Dmitry Potapov <dpotapov@gmail.com>
Date: Dec 22, 2012, 22:26 UTC
Message-ID: <CAHkcotjJ8nyPVEbDFcGVYqirY4HBNBPN-PNCMriLyeU8iBEKXg@mail.gmail.com>
In-Reply-To: <C0A16EC8-D05A-41D0-BF2A-34BF3B1B839E@codeaurora.org>

Hi,

On Sat, Dec 22, 2012 at 5:41 AM, Earl Gresh <egresh@codeaurora.org> wrote:

>
> Is anyone familiar with git gc deleting valid references? I'm running
> git version 1.7.8. Have there been any patches in later git releases
> that might address this issue ( if it is a git problem )?

I have not seen any relevant changes in git. I have looked at the code, and what git-gc is running "git pack-refs --all --prune", which is very careful in packing and fsyncing the new file with all packed references before deleting anything. Only those references that were packed can be deleted. Also, it does not matter whether a reference is valid or not, or whether it is stored in refs/changes or in some other place, like refs/heads. So if references were really lost as you described, I think other people would notice that by now.

The only plausible explanation that comes to my mind now is that file creation using O_EXCL is not atomic on your system, then the lock did not work and one process could overwrite packed references created by another.

Dmitry