[NOTES 06/11] Repository maintenance long-term goals

[Taylor Blau <me@ttaylorr.com>]

Topic: Repository maintenance long-term goals
Leader: Taylor Blau

* Taylor's talk was limited towards the end. Could expand on that future work.
* Constant repacking into a single pack was historically the major problem.
* Doing that less (because of geometric repacking) helps, but it's still a
	potential issue when it does occur. Gets them 98% of the way.
* Future items were geometric reachability, ?, best effort gc
* Previously during geometric, used to accumulate loose objects too. 6 months
	ago they changed to an approach where the big cruft pack could be excluded
	from the midx.
* Challenge would be to do a full complete repack without rewriting all of the
	midx chain.
* Because bitmap is tied to object order in a pack, need something like
	tombstones to not break the bitmaps. Need the tombstone to know that we don't
	have the data.

* Unitary midx idea - Taylor designed the chained midx before he figured out the
	repacking strategy. MIDX and pack index duplicate the data. No reason to
	de-dup other than for space saving. Could even skip having idx, but plenty of
	old git versions can't read midx.
* brian - there may be other implementations, such as git lfs, that don't use
	midx and object id mappings in pack idx v3 aren't supported in midx either.

* Nothing preventing you from having two parallel repacks, one that's geometric
	and one that's trying to do an all-into-one.