On Wed, Jun 1, 2016 at 3:37 PM, Duy Nguyen <pclo...@gmail.com> wrote: > On Tue, May 31, 2016 at 8:18 PM, Christian Couder > <christian.cou...@gmail.com> wrote: >>>> I wonder if this mechanism could also be used or extended to clone and >>>> fetch an alternate object database. >>>> >>>> In [1], [2] and [3], and this was also discussed during the >>>> Contributor Summit last month, Peff says that he started working on >>>> alternate object database support a long time ago, and that the hard >>>> part is a protocol extension to tell remotes that you can access some >>>> objects in a different way. >>>> >>>> If a Git client would download a "$name.bndl" v3 bundle file that >>>> would have a "data: $URL/alt-odb-$name.odb" extended header, the Git >>>> client would just need to download "$URL/alt-odb-$name.odb" and use >>>> the alternate object database support on this file. >>> >>> What does this file contain exactly? A list of SHA-1 that can be >>> retrieved from this remote/alternate odb? >> >> It would depend on the external odb. Git could support different >> external odb that have different trade-offs. >> >>> I wonder if we could just >>> git-replace for this marking. The replaced content could contain the >>> uri pointing to the alt odb. >> >> Yeah, interesting! >> That's indeed another possibility that might not need the transfer of >> any external odb. >> >> But in this case it might be cleaner to just have a separate ref hierarchy >> like: >> >> refs/external-odbs/my-ext-odb/<sha1> >> >> instead of using the replace one. >> >> Or maybe: >> >> refs/replace/external-odbs/my-ext-odb/<sha1> >> >> if we really want to use the replace hierarchy. > > Yep. replace hierarchy crossed my mind. But then I thought about > performance degradation when there are more than one pack (we have to > search through them all for every SHA-1) and discarded it because we > would need to do the same linear search here. I guess we will most > likely have one or two name spaces so it probably won't matter.
Yeah. >>> We could optionally contact alt odb to >>> retrieve real content, or just show the replaced/fake data when alt >>> odb is out of reach. >> >> Yeah, I wonder if that really needs the replace mechanism. > > Replace mechanism provides good hook point. But it really depends how > invasive this remote odb is. If a fake content is enough to avoid > breakages up high, git-replace is enough. If you really need to pass > remote odb info up so higher levels can do something more fancy, then > it's insufficient. > >> By the way this makes me wonder if we could implement resumable clone >> using some kind of replace ref. >> >> The client while cloning nearly as usual would download one or more >> special replace refs that would points to objects with links to >> download bundles using standard protocols. >> Just after the clone, the client would read these objects and download >> the bundles from these objects. >> And then it would clone from these bundles. > > I thought we have settled on resumable clone, just waiting for an > implementation :) Doing it your way, you would need to download these > special objects too (in a pack?) and come back download some more > bundles. It would be more efficient to show the bundle uri early and > go download the bundle on the side while you go on to get the > addition/smaller pack that contains the rest. Yeah, something like the bundle v3 mechanism is probably more efficient. Thanks, Christian. -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
