Re: CAREFUL! No more delta object support!

LT> But the savings get increasingly bigger the more history we have. That's LT> also why the packed git archive is about 1/14th of the size of the fully LT> unpacked disk usage of the git project,...

GIT archive may be an odd-ball because the project itself is so small, but a fair comparison should include the disk usage of 256 fan-out directories. Counting them, empty .git/objects/ with the 1.4MB packed archive and 90KB index file ends up being somewhere around 2.4MB on my machine, compared with 17MB for the traditional one.

Still a good space reduction.  Good job!

I am now dreaming if we someday would enhance the mechanism with append-only updates to the *.pack files with complete rewrite of the *.idx files, and get rid of files under .git/objects totally.

This would make things reasonably friendly to rsync. The kernel pack has around 60M pack with 1.1M index, so everyday use would involve incremental updates to the pack [*1*] and full download of the index file.

[Footnote]

*1* Presumably many objects are deltified against older objects which is suboptimal. Most likely the newer objects are accessed far more often and they are what we would want to keep in full not as delta. So even with this scheme we would want to have weekly repacking. Interestingly enough, pack-objects gets the objects via usual read_sha1_file() interface so it can produce a new pack from an existing pack.