Re: [PATCH v2] Document pack v4 format

> On Thu, Sep 5, 2013 at 11:52 PM, Duy Nguyen <pclouds@gmail.com> wrote:
> > On Thu, Sep 5, 2013 at 12:39 PM, Nicolas Pitre <nico@fluxnic.net> wrote:
> >> Now the pack index v3 probably needs to be improved a little, again to
> >> accommodate completion of thin packs.  Given that the main SHA1 table is
> >> now in the main pack file, it should be possible to still carry a small
> >> SHA1 table in the index file that corresponds to the appended objects
> >> only. This means that a SHA1 search will have to first use the main SHA1
> >> table in the pack file as it is done now, and if not found then use the
> >> SHA1 table in the index file if it exists.  And of course
> >> nth_packed_object_sha1() will have to be adjusted accordingly.
> >
> > What if the sender prepares the sha-1 table to contain missing objects
> > in advance? The sender should know what base objects are missing. Then
> > we only need to append objects at the receiving end and verify that
> > all new objects are also present in the sha-1 table.
> 
> One minor detail to sort out: the size of sha-1 table. Previously it's
> the number of objects in the pack. Now it's not true because the table
> may have more entries. So how should we record the table size? We
> could use null sha-1 as the end of table marker. Or we could make
> pack-objects to write nr_objects as the number of entries _after_ pack
> completion, not the true number of objects in thin pack. I like the
> latter (no more rehashing the entire pack after completion) but then
> we need a cue to know that we have reached the end of the pack..