RE: [PATCH] repack: respect gc.pid lock

> -----Original Message-----
> From: Jeff King [mailto:peff@peff.net]
> Sent: Tuesday, April 18, 2017 1:20 PM
> To: David Turner <David.Turner@twosigma.com>
> Cc: git@vger.kernel.org; christian.couder@gmail.com; mfick@codeaurora.org;
> jacob.keller@gmail.com
> Subject: Re: [PATCH] repack: respect gc.pid lock
> 
> On Tue, Apr 18, 2017 at 05:16:52PM +0000, David Turner wrote:
> 
> > > -----Original Message-----
> > > From: Jeff King [mailto:peff@peff.net]
> > > Sent: Monday, April 17, 2017 11:42 PM
> > > To: David Turner <David.Turner@twosigma.com>
> > > Cc: git@vger.kernel.org; christian.couder@gmail.com;
> > > mfick@codeaurora.org; jacob.keller@gmail.com
> > > Subject: Re: [PATCH] repack: respect gc.pid lock
> > >
> > > On Mon, Apr 17, 2017 at 11:29:18PM +0000, David Turner wrote:
> > >
> > > > We saw this failure in the logs multiple  times (with three
> > > > different shas, while a gc was running):
> > > > April 12, 2017 06:45 -> ERROR -> 'git -c repack.writeBitmaps=true
> > > > repack -A -d
> > > --pack-kept-objects' in [repo] failed:
> > > > fatal: packfile ./objects/pack/pack-[sha].pack cannot be accessed
> > > > Possibly some other repack was also running at the time as well.
> > > >
> > > > My colleague also saw it while manually doing gc (again while
> > > > repacks were likely to be running):
> > >
> > > This is sort of a side question, but...why are you running other
> > > repacks alongside git-gc? It seems like you ought to be doing one or the
> other.
> >
> > But actually, it would be kind of nice if git would help protect us from doing
> this?
> 
> A lock can catch the racy cases where both run at the same time. But I think that
> even:
> 
>   git -c repack.writeBitmaps=true repack -Ad
>   [...wait...]
>   git gc
> 
> is questionable, because that gc will erase your bitmaps. How does git-gc know
> that it's doing a bad thing by repacking without bitmaps, and that you didn't
> simply change your configuration or want to get rid of them?