Re: Consist timestamps within a checkout/clone

> 
> On Mon, Oct 31 2022, Mark Hills wrote:
> 
> > Our use case: we commit some compiled objects to the repo, where compiling 
> > is either slow or requires software which is not always available.
> >
> > Since upgrading Git 2.26.3 -> 2.32.4 (as part of Alpine Linux OS upgrade) 
> > we are noticing a change in build behaviour.
> >
> > Now, after a "git clone" we find the Makefile intermittently attempting 
> > (and failing) some builds that are not intended.
> >
> > Indeed, Make is acting reasonably as the source file is sometimes 
> > marginally newer than the destination (both checked out by Git), example 
> > below.
> >
> > I've never had to consider consistency timestamps within a Git checkout 
> > until now.
> >
> > It's entirely possible there's _never_ a guarantee of consistency here.
> >
> > But then something has certainly changed in practice, as this fault has 
> > gone from never happening to now every couple of days.
> >
> > Imaginging I can't be the first person to encounter this, I searched for 
> > existing threads or docs, but overwhemingly the results were question of 
> > Git tracking the timestamps (as part of the commit) which this is not; 
> > it's consistency within one checkout.
> >
> > $ git clone --depth 1 file:///path/to/repo.git
> >
> > $ stat winner.jpeg
> >   File: winner.jpeg
> >   Size: 258243          Blocks: 520        IO Block: 4096   regular file
> > Device: fd07h/64775d    Inode: 33696       Links: 1
> > Access: (0644/-rw-r--r--)  Uid: (  106/ luthier)   Gid: (  106/ luthier)
> > Access: 2022-10-31 16:05:17.756858496 +0000
> > Modify: 2022-10-31 16:05:17.756858496 +0000
> > Change: 2022-10-31 16:05:17.756858496 +0000
> >  Birth: -
> >
> > $ stat winner.svg
> >   File: winner.svg
> >   Size: 52685           Blocks: 112        IO Block: 4096   regular file
> > Device: fd07h/64775d    Inode: 33697       Links: 1
> > Access: (0644/-rw-r--r--)  Uid: (  106/ luthier)   Gid: (  106/ luthier)
> > Access: 2022-10-31 16:05:17.766859030 +0000
> > Modify: 2022-10-31 16:05:17.766859030 +0000
> > Change: 2022-10-31 16:05:17.766859030 +0000
> >  Birth: -
> >
> > Elsewhere in the repository, it's clear the timestamps are not consistent:
> >
> > $ stat Makefile
> >   File: Makefile
> >   Size: 8369            Blocks: 24         IO Block: 4096   regular file
> > Device: fd07h/64775d    Inode: 33655       Links: 1
> > Access: (0644/-rw-r--r--)  Uid: (  106/ luthier)   Gid: (  106/ luthier)
> > Access: 2022-10-31 16:05:51.628660212 +0000
> > Modify: 2022-10-31 16:05:17.746857963 +0000
> > Change: 2022-10-31 16:05:17.746857963 +0000
> >  Birth: -
> 
> I think you're almost certainly running into the parallel checkout,
> which is new in that revision range. Try tweaking checkout.workers and
> checkout.thresholdForParallelism (see "man git-config").

> I can't say without looking at the code/Makefile (and even then, I don't
> have time to dig here:), but if I had to bet I'd say that your
> dependencies have probably always been broken with these checked-in
> files, but they happend to work out if they were checked out in sorted
> order.
>
> And now with the parallel checkout they're not guaranteed to do that, as
> some workers will "race ahead" and finish in an unpredictable order.

> But that's all just a guess, perhaps it has nothing to do with parallel
> checkout, such dependency issues are sensitive to all sorts of other
> things, e.g. maybe git got slightly faster (or slower), so now files
> that were always on different seconds (or the same) aren't in the state
> they were in before...