Re: [Monotone-devel] resolving name conflicts; implementation

[Stephen Leake]

Thomas Moschny <address@hidden> writes:

> Stephen Leake wrote:
>> differences; roster_deltas can use node ids instead of file names, for
>> example.
>
> Yes. Node ids are also strictly local and never travel across the net.
>
> Of course there are more differences, like the fact the changeset
> for one revision shows differences against all parents, 

Not quite; if there are two parents (in a merge), there are two
changesets; they are stored in the 'edges' component of revision.hh
revision_t.

The result of applying the two changesets to the two parents is often
not quite identical; they get "fixed up" by roster.cc unify_rosters.
Which I think I have now sorted out for suture ancestors, but I'm not
entirely sure.

> whereas the roster delta for a revision contains the differences
> against exactly one child. 

Right, because it's actually a "reverse delta". Changesets are used to
go from parent to child; roster deltas go from child to parent. 

Hmm. That means there are actually two roster deltas for a merge; I'm
not clear how that is managed. Ah; database.cc
database_imple::get_roster_delta takes two roster ids; 'ident' and
'base'. Then theres a "roster_reconstruction_graph" which specifies
the adjacent roster ids.

Since roster deltas store node ids and other "local data", there is no
need for a "fix up" step for merges. In other words, roster deltas are
exact, while changesets are not.

Roster deltas appear to be mainly a form of data compression, just as
file deltas are. To retrieve an old revision, you get the latest, and
apply successive deltas to it.

Which will be a problem when I implement split; then there will be n
children with one parent. That will be interesting! But we need split
to be able to undo a suture.

> Also, changesets do know nothing about markings.

Right.

-- 
-- Stephe