Re: [PATCH 0/7] speeding up cat-file by reordering object access

Jeff King [off-list ref] writes:

I think that makes sense. We already see duplicates from
for_each_packed_object() when they're in multiple packs, and callers
just need to be ready to deal with it (and depending on what you're
doing, you may actually _want_ the duplicates).

You of course would also see dups between loose and packed until
prune-packed is run.  

I also was thinking about the same thing after Derrick's response,
but unless you are very specialized caller, it does not allow you do
very much to learn that object X exists as a loose object locally,
also as a loose object in our alternate, and also in pack A, but not
in other packs.  You need a way to say "Read the contents of object
X from that place, not from any other place", "Remove that copy of
object X at that place, but not at any other place" etc. to make
effective use of that kind of information.

The codepath that implements runtime access has "I found a copy
here, but it is unusable, so let's go on to look for another usable
copy" fallback.  This is a tangent but it is something we should not
lose in the midx-enabled world.