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> One interesting question is which of these two types we should use
> for the size of objects Git uses.
>
> Most of the "interesting" operations done by Git require that the
> thing is in core as a whole before we can do anything (e.g. compare
> two such things to produce delta, have one in core and apply patch),
> so it is tempting that we deal with size_t, but at the lowest level
> to serve as a SCM, i.e. recording the state of a file at each
> version, we actually should be able to exceed the in-core
> limit---both "git add" of a huge file whose contents would not fit
> in-core and "git checkout" of a huge blob whose inflated contents
> would not fit in-core should (in theory, modulo bugs) be able to
> exercise the streaming interface to handle such case without holding
> everything in-core at once. So from that point of view, even size_t
> may not be the "correct" type to use.
A few additions to the above observations.
- We have varint that encodes how far the location from a delta
representation of an object to its base object in the packfile.
Both encoding and decoding sides in the current code use off_t to
represent this offset, so we can already reference an object that
is far in the same packfile as a base.
- I think it is OK in practice to limit the size of individual
objects to size_t (i.e. on 32-bit arch, you cannot interact with
a repository with an object whose size exceeds 4GB). Using off_t
would allow occasional ultra-huge objects that can only be added
and checked in via the streaming API on such a platform, but I
suspect that it may become too much of a hassle to maintain.
It may help reducing the maintenance if we introduced obj_size_t
that is defined to be size_t for now, so that we can later swap
it to ofs_t or some larger type when we know we do need to
support objects whose size cannot be expressed in size_t, but I
do not offhand know what the pros-and-cons with such an approach
would look like.
Thanks.
Junio C Hamano <gitster@pobox.com>