Re: Multiple pushurls, different 'objects\info\packs'

[Mikhail Strelnikov <mikhail.strelnikov@gmail.com>]

Thanks Brian,

> delta compression is multithreaded

That is great news that this is expected behavior and I'm not dealing
with some sort of obscure data corruption. :)
Now see there is `git config --global pack.threads 1` (I'm doing
everything locally, so this might work for me)

> reason for wanting bit-for-bit identical

My plan was to have 3 pushurls and shoot one of them if it is not
bit-for-bit identical to the other two. But you are right, all I need
is `git fsck`.

On Wed, Apr 22, 2020 at 6:15 AM brian m. carlson
<sandals@crustytoothpaste.net> wrote:
>
> On 2020-04-21 at 18:07:42, Mikhail Strelnikov wrote:
> > Hi,
> >
> > I have a repo with two pushurls configured like this:
> >
> >
> > C:\folder\1>git init --bare
> > Initialized empty Git repository in C:/folder/1/
> >
> > C:\folder\2>git init --bare
> > Initialized empty Git repository in C:/folder/2/
> >
> > C:\folder\w>git init
> > Initialized empty Git repository in C:/folder/w/.git/
> >
> > C:\folder\w>git add work.txt
> >
> > C:\folder\w>git commit -m "Initial commit"
> > [master (root-commit) 1b314f3] Initial commit
> > 1 file changed, 1 insertion(+)
> > create mode 100644 work.txt
> >
> > C:\folder\w>git remote add origin C:\folder\1
> >
> > C:\folder\w>git remote set-url origin --push --add C:\folder\1
> >
> > C:\folder\w>git remote set-url origin --push --add C:\folder\2
> >
> > C:\folder\w>git push --set-upstream origin master
> >
> >
> > I would expect those two folders (C:\folder\1 and C:\folder\2) to
> > contain exactly the same bytes. And they did for quite some time. But
> > now there is a difference in 'objects\info\packs' (and some of
> > objects\pack\pack-*.idx/pack are also different).
> >
> > (all the commits are the same in both and all my data is also the same
> > and 'fast-export --all' yields the same result)
> >
> > I'd like to know what might have caused this nondeterminism and if
> > there is something to do to prevent that.
>
> You can get nondeterminism because the push to each repository happens
> independently and delta compression is multithreaded.  You can therefore
> compute different packs on push and get different packs in the result.
>
> You could try to avoid it by disabling threading for pushes, but that
> has to be done on each client that pushes to them.  In general, this is
> not worth worrying about as long as the data is intact (that is, it
> passes git fsck) and the refs are identical.  It is also not especially
> easy to avoid, since determinism of pack files is not considered a goal
> of Git.
>
> Maybe if you tell us a little more about your reason for wanting
> bit-for-bit identical replicas we can provide some assistance in helping
> you achieve your goals.
> --
> brian m. carlson: Houston, Texas, US
> OpenPGP: https://keybase.io/bk2204