On Wed, Jul 18, 2018 at 7:45 PM Jeff King <peff@xxxxxxxx> wrote: > > 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. Both good points. Callback it is then. -- Duy
