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>
> On Wed, Jul 18, 2018 at 07:31:40PM +0200, Duy Nguyen wrote:
>
> > > Sort of an aside to the patch under discussion, but I think it may make
> > > sense for prune_shallow() to take a callback function for determining
> > > whether a commit is reachable.
> > >
> > > I have an old patch that teaches git-prune to lazily do the reachability
> > > check, since in many cases "git repack" will have just packed all of the
> > > loose objects. But it just occurred to me that this patch is totally
> > > broken with respect to prune_shallow(), because it would not set the
> > > SEEN flag (I've literally been running with it for years, which goes to
> > > show how often I use the shallow feature).
> > >
> > > And if we were to have repack do a prune_shallow(), it may want to use a
> > > different method than traversing and marking each object SEEN.
> >
> > All of this sounds good. The only thing I'd like to do a bit
> > differently is to pass the reachable commits in prune_shallow() as a
> > commit-slab instead of taking a callback function. I'll refactor this
> > code, move prune_shallow() to a separate command prune-shallow and do
> > the locking thing.
>
> I think using a slab is much nicer than the current global-struct flags.
> But it's not as flexible as a callback, for two reasons:
>
> - in the lazy case, the caller might not even have loaded the slab
> yet. On the other hand, it might be sufficient to just be broad
> there, and just always pre-populate the slab when
> is_repository_shallow(), before we even call into prune_shallow().
> If we have _any_ entries in the shallow file, we'd need to compute
> reachability.
>
> - it precludes any optimizations that compute partial reachability.
> Asking "is XYZ reachable" is a much easier question to answer than
> "show me the full reachability graph." At the least, it lets you
> stop the graph traversal early. And with generation numbers, it can
> even avoid traversing down unproductive segments of the graph.
Duy Nguyen <pclouds@gmail.com>