Johan Herland <johan@xxxxxxxxxxx> writes:
> On Wed, Jul 29, 2015 at 7:01 AM, Junio C Hamano <gitster@xxxxxxxxx> wrote:
>> Johan Herland <johan@xxxxxxxxxxx> writes:
>>
>>> I believe it is a bad compromise. It complicates the code, and it
>>> provides a concurrent notes merges that is unnecessarily tied to (and
>>> dependent on) worktrees. For example, if I wanted to perform N
>>> concurrent notes merges in a project that happens to have a huge
>>> worktree, I would now have to create N copies of the huge worktree...
>>
>> Who said worktree has to be populated? You should be able to have
>> an absolutely empty checkout just like "clone --no-checkout".
>
> IMHO that's an insane workaround that only serves to highlight the
> conceptual problems of binding notes merges (as they are implemented
> today) to worktrees.
Actually, the name "linked worktree" is probably a misnomer.
There is nothing fundamental in the mechanism or in the concept that
says that these multiple $GIT_DIR's must not be a bare one. The
main thing the separation between $GIT_DIR and $GIT_COMMON_DIR
affords you is that you can have some things shared across them
(e.g. refs/*, objects) while making others per $GIT_DIR (e.g. HEAD,
index, etc.).
With that in mind, it is not an insane workaround but a very natural
mechanism suited exactly for what you want to do: using a feature
(e.g. "notes merge") that currently can have at most one instance
running at a time because it stores its state inside $GIT_DIR, and
you want to have N concurrent one going. You keep that "state per
running instance" inside $GIT_DIR (i.e. not shared) and use the
"linked worktree" mechanism to have multiple $GIT_DIR, connected
to the same $GIT_COMMON_DIR.
> But, whatever. This is unrelated to David's current effort, and I
> don't want to hold that up, so please move along, nothing to see here.
I need this part from an earlier message answered to unblock David's
topic:
Now we are getting somewhere. So is there more that is needed
than separating NOTES_MERGE_REF per worktree to make this work
(remember, multiple notes-merge in a single worktree is a
non-goal, just like multiple merge in a single worktree is not
supported today and will not be)? Is there some other state
that is not captured by NOTES_MERGE_REF and friends that you
would end up recording a wrong merge result, if two worktrees
that have NOTES_MERGE_REF pointing at a different ref in
refs/notes/* try to do the notes-merge at the same time?
If we do not change anything (not even applying the [v3 2/6] patch
we are discussing), all these things prefixed with NOTES_ will
become per $GIT_DIR with linked worktrees.
NOTES_EDITMSG, NOTES_MERGE_REF, NOTES_MERGE_PARTIAL,
NOTES_MERGE_WORKTREE
The user could attempt to start different notes merges in her
multiple $GIT_DIRs. The question is to what degree we want to
support her.
Is it sufficient to have these per $GIT_DIR, when the user has two
$GIT_DIRs connected to the same repository and wants to do two
"notes merge" acting on different ref in refs/notes/*? Or are there
some other states in the shared part kept, which would be stomped on
by simultaneously running "notes merge" instances in different
$GIT_DIRs, that make this not to work? Any other problems in the
remainder of the current implementation of "notes merge"?
If there are reasons/limitations that make simultaneous "notes
merge" of different notes in different $GIT_DIRs impossible, then I
agree we shouldn't bother with [v3 2/6] patch. We should just
declare "do not do it, it does not (yet) work".
But if there isn't, [v3 2/6] is the absolute minimum thing we could
do to make "notes merge" usable by making sure that the user does
not attempt merging the same refs/notes/commits in two different
places.
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