On Fri, Oct 11, 2024 at 03:54:51AM -0400, Jeff King wrote:
> [1] I wish we had good names to distinguish the various cases, because
> the term "reuse" is kind of overloaded. The "slower" regular
> object-sending path may still reuse verbatim bytes found in an
> on-disk path. But this "blit out matching parts of a pack without
> otherwise considering the objects" feature happens outside of that.
> We called it "pack reuse" back in 2013, but that was not a good name
> even then. I don't have a good suggestion, though.
Actually, confusing things more, there are really _three_ layers of
reuse:
1. At the beginning of a pack, we can blit out the bytes for objects
starting from the beginning of the pack that are being sent (we
know any delta will be satisfied since its base comes before it).
2. After that, we process objects one by one, but do so very cheaply
by just deciding if we can blit them out one by one, fixing up
delta base offsets to account for gaps.
3. Otherwise, we generate an object_entry struct in packing_data for
them, try to find new deltas, and so on. We may then reuse the
on-disk bytes after deciding they're suitable.
We call all of these "reuse", and certainly both (1) and (2) are "pack
reuse", but I think that term is sufficiently vague that it could apply
to (3) as well.
-Peff
