On Fri, Aug 17, 2018 at 03:57:18PM -0700, Stefan Beller wrote: > On Fri, Aug 17, 2018 at 2:06 PM Jeff King <peff@xxxxxxxx> wrote: > > > > When we serve a fetch, we pass the "wants" and "haves" from > > the fetch negotiation to pack-objects. That tells us not > > only which objects we need to send, but we also use the > > boundary commits as "preferred bases": their trees and blobs > > are candidates for delta bases, both for reusing on-disk > > deltas and for finding new ones. > > > > However, this misses some opportunities. Modulo some special > > cases like shallow or partial clones, we know that every > > object reachable from the "haves" could be a preferred base. > > We don't use them all for two reasons: > > s/all/at all/ ? No, I meant "we don't use all of them". As in the Pokemon "gotta catch 'em all" slogan. ;) Probably writing out "all of them" is better. > > The first is that check_object() needs access to the > > relevant information (the thin flag and bitmap result). We > > can do this by pushing these into program-lifetime globals. > > I discussed internally if extending the fetch protocol to include > submodule packs would be a good idea, as then you can get all > the superproject+submodule updates via one connection. This > gives some benefits, such as a more consistent view from the > superproject as well as already knowing the have/wants for > the submodule. > > With this background story, moving things into globals > makes me sad, but I guess we can flip this decision once > we actually move towards "submodule packs in the > main connection". I don't think it significantly changes the existing code, which is already relying on a ton of globals (most notably to_pack). The first step in doing multiple packs in the same process is going to be to shove all of that into a "struct pack_objects_context" or similar, and these can just follow the rest. > > > > The second is that the rest of the code assumes that any > > reused delta will point to another "struct object_entry" as > > its base. But by definition, we don't have such an entry! > > I got lost here by the definition (which def?). > > The delta that we look up from the bitmap, doesn't may > not be in the pack, but it could be based off of an object > the client already has in its object store and for that > there is no struct object_entry in memory. > > Is that correct? Right, we are interested in objects that we _couldn't_ find a struct for. I agree this could be more clear. -Peff
