Re: [Monotone-devel] resolving name conflicts; file suturing vs drop

[William Uther]

On 05/05/2008, at 7:49 PM, Stephen Leake wrote:
> > Have you considered what happens, if two developers both decide on
> > merging the files, but a different node-id is choosen? As node ids
> > are local only, I think you cannot prevent that easily (i.e. by
> > choosing the lower node id - those might be different - you'd have
> > to compare birth date of the files. And even then, it might be
> > possible they were born on exactly the same date...).
>
> Any time two developers try to resolve the conflict in parallel, there
> will probably be problems. The only solution is to revert one of those
> resolutions.

I think this is a deep issue.

I cannot see how you can suture without dropping one of the two
node-ids.  You start with two, you end up with one.  It doesn't
really matter what happens in the middle, at least one node-id
disappears.

At present, my understanding is that Monotone doesn't have an explicit
graveyard, it just uses the absence of a node-id as an indication
it has been dropped.  There is, currently, no place to mark 'why'
a node-id disappeared, or that it has changed to something else.

If there are further revisions added which use a missing node-id
then monotone will at least warn when they're merged, but that
is a safety net, not a solution.

As has been noted by others, when two people try this in parallel
and each choose a different side to die then DieDieDie merge will kick  
in
and cause both sides to die.  Ack.

All the solutions I can think of involve either a) getting rid of node- 
ids,
which is a very brave option and I haven't given it much thought, or b)
implementing a graveyard that would either i) remove DieDieDie issues,  
or
ii) allow a new type of node-id "removal by replacement".

> If we are truly "merging" via suturing, nothing is dropped, and
> everything is fine. If we are approximating suturing by dropping, then
> this is an issue.

Do you know a way to suture without dropping a node-id?  Or were you
thinking of implementing a graveyard?

Cheers,

Will          :-}