On Mon, Mar 06, 2017 at 03:40:30PM -0800, Jonathan Nieder wrote:

David Lang wrote:

quoted

quoted

Translation table
~~~~~~~~~~~~~~~~~
A fast bidirectional mapping between sha1-names and sha256-names of
all local objects in the repository is kept on disk. The exact format
of that mapping is to be determined.

All operations that make new objects (e.g., "git commit") add the new
objects to the translation table.

This seems like a rather nontrival thing to design. It will need to
hold millions of mappings, and be quickly searchable from either
direction (sha1->new and new->sha1) while still be fairly fast to
insert new records into.

I am currently thinking of using LevelDB, since it has the advantages of
being simple, already existing, and having already been ported to Java
(allowing JGit can read and write the same format).

If that doesn't work, we'd try some other key-value store like Samba's
tdb or Kyoto Cabinet.

FWIW, I'm using notes-like data to store mercurial->git mappings in
git-cinnabar, (ab)using the commit type in tree items. It's fast enough.

Mike