This session was led by Ævar Arnfjörð Bjarmason (on behalf of Han-Wen
Nienhuys, the driving force behind the reftable patches, who did not
attend the Summit). Supporting cast: Jonathan "jrnieder" Nieder, Johannes
"Dscho" Schindelin, Philip Oakley, Jeff "Peff" King, and Junio Hamano.
Notes:
1. Ævar: helping Han-Wen with reviewing
2. Was split into multiple patch series
3. Han-Wen implemented the reftable library, has been kicking on the mailing
list for over a year
4. Before reftable, need to merge some preliminaries
5. Odd cases:
1. slightly different semantics of reflog
2. Probably more things that haven’t cropped up yet
3. Some tests are still broken, question is still: are the tests wrong, or
the code
6. Plan is to get reftable library and underlying fixes in place, and then do
the process of actual reftable-as-ref-backend afterward
1. Jrnieder: sounds like you’re alluding to a mailing list thread. Do you
have a link?
2. Ævar: there are multiple, as the initial patch series has been split
multiple times
3. “Reftable plan”:
https://lore.kernel.org/git/87h7jqz7k5.fsf@xxxxxxxxxxxxxxxxxxx/
4. Also alluded to in Han-Wen’s later rerolls
7. What is reftable?
1. It’s a custom way to store refs
2. Instead of writing individual files per ref, it’s a single file (or
multiple files when updating the refs)
8. Dscho: three issues that were outstanding when I reviewed it
1. That said, I clashed with Han-Wen
2. 1. licensing / contribution model
2. Ævar: through the Software Freedom Conservancy we have good access
to legal advice. I got advice there about how to document this well,
will be getting us into an end state that will hopefully satisfy
everybody
3. To be clear, we already have some code in-tree that is under
different licenses. xdiff is LGPL code used by libgit2, there’s
contrib/ + compat/ code under various licenses
4. For legal purposes want to make sure this is clear and unambiguous
to everyone
5. jrnieder: about contribution model, there is on-list discussion
about this, taking patches in the normal way to this directory in
git@xxxxxxxxxxxxxxx is where I thought that ended up
6. Ævar: yes, git.git as source-of-truth. Not like gitk where there’s a
separate upstream repo
3. 2. coding style consistency, + not using git core data structures
enough
3. Ævar: still substantially true. Integrating into git.git means any
stylistic or structural changes to fit well into git are fair game.
Carlo has been helping with that
4. 3. I forgot the third :)
9. Philip Oakley: debugging when things go wrong
1. When reftable arrives, will people be unable to look behind the scenes
at what’s going on when issues happen?
2. Especially for people who don’t understand refs as well
3. Jonathan: format =
www.kernel.org/pub/software/scm/git/docs/technical/reftable.html
[http://www.kernel.org/pub/software/scm/git/docs/technical/reftable.html]
4. Ævar: That’s a fair summary. It’s as though we didn’t have packfiles
and only had loose files and then switched to using packfiles. Can’t
just “cat” any more. Switching to a binary format
5. That said, you get advantages out of that. Situations where people end
up needing to examine the low-level details are
6. Not a fully fair comparison, but we have this problem already with
packed-refs, having to look in two places
7. Philip: An inspection tool to export as a directory tree might be
handy, as an inspection tool
8. Peff: We have pretty good inspection tools that look at the whole ref
database
9. Reftable has a set of files that go together. May want debugging tool
to dump the content of a binary reftable file. But we can
incrementally add those
10. As we discover bugs, I expect to have to build tooling
11. Dscho: We also have a .git/index file and don’t have tooling to
interact with it other than the standard Git tools
12. Ævar: To be clear, once these patches land it would still be optional,
would not be the default ref backend
13. Even if it’s 100% bug free, we still have concern for users in the
wild that make it not so easy to just flip the switch
14. Not going to be the default backend any time soon
15. jrnieder: makes sense to wait for a while to make it the default, even
once it is robust, since we have to pay attention to what Git versions
+ implementations are out there in the wild
16. Ævar: When you run “git init”, it currently still creates a branches/
directory. Dscho tried to get rid of it before
17. jrnieder: I think that previous attempt was getting rid of read
capability, too
18. Dscho: don’t remember the details, has been a couple years
19. Junio: I do not think it is a bad idea to drop branches from template.
10. jrnieder: Question about how to handle this kind of large contribution
11. At some point does it make sense to take it, mark as experimental, and
improve in place?
12. Hoping the previous discussion will help me think about that
13. Ævar: I agree about importing the bulk of the code as-is and iterating
from there
14. At that point it’s still not accessible to users but we get portability,
testing, etc
15. Dscho: Agreed, that makes sense to me
