Re: [PATCH] repack: allow simultaneous packing and pruning

[Linus Torvalds <torvalds@osdl.org>]

On Tue, 10 Oct 2006, Sam Vilain wrote:
>
> If using git-repack -a, unreferenced objects are kept behind in the
> pack.  This might be the best default, but there are no good ways
> to clean up the packfiles if a lot of rebasing is happening, or
> branches have been deleted.

Don't do this.

I understand why you want to do it, but the fact is, it's dangerous.

Right now, "git repack" is actually safe to run even on a repository which 
is being modified! And that's actually important, if you have something 
like a shared repo that gets re-packed every once in a while from a 
cron-job!

So the refs might be up-dated as it runs, and if that happens, your 
pruning doesn't really do the right thing - it might consider a new loose 
object to be unreachable, because it didn't check whether the refs have 
changed since it read them so that it might actually _be_ reachable after 
all.

So please don't do this. 

It's important for operations to always think about "what happens if 
somebody does a 'commit' or pushes into the tree at the same time?".

For example, the "git prune-packed" that gets run afterwards is _not_ 
racy, because it will only prune objects that already exist in the pack.

		Linus