Re: Git push race condition?

[Nasser Grainawi <nasser@codeaurora.org>]

On Mar 24, 2014, at 4:54 PM, Jeff King <peff@peff.net> wrote:

> On Mon, Mar 24, 2014 at 03:18:14PM -0400, Scott Sandler wrote:
> 
>> I've noticed that a few times in the past several weeks, we've had
>> events where pushes have been lost when two people pushed at just
>> about the same time. The scenario is that two users both have commits
>> based on commit A, call them B and B'. The user with commit B pushes
>> at about the same time as the user who pushes B'. Both pushes are
>> determined to be fast-forwards and both succeed, but B' overwrites B
>> and B is no longer on origin/master. The server does have B in its
>> .git directory but the commit isn't on any branch.
> 
> What version of git are you running on the server? Is it possible that
> there is a simultaneous process running `git pack-refs` (e.g., a `git
> gc` run by a cron job or similar)?

`git gc --auto` could be getting triggered as well, so if you suspect
that you could set gc.auto=0 on the server side.

> 
> There were some race conditions fixed last year wherein git could see
> stale values of refs, but I do not think they could impact writing to a
> ref like this.  When we take the lock on the ref, we always go straight
> to the filesystem, so the value we see is up-to-date.
> 
> -Peff
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