[RFC] Revision id aliases

[John Arbash Meinel]

Jelmer Vernooij wrote:
> Another feature that would come in handy for foreign Subversion branches
> is revision id aliasing. Are there any plans to support these in the
> near future or are they postponed until after 1.0 ?
> 
> Cheers,
> 
> Jelmer

What do you actually mean? That you have 2 revision_ids, but they refer
to the same information?

I think you are considering using aliases so you can push into
subversion, and then have bzr believe that it is the same revision that
I just committed. (Or more importantly, the same series of revisions).

And I think you want aliases, because Subversion doesn't let you denote
any sort of custom id, so you are stuck with their notation.

I can say that if you were treating SVN as just another branch, you
would actually be at the same place, where each merge generates a new
revision id. So it isn't like bzr can't cope with each commit to SVN
being a separate revision. As long as you make bzr think that they are
all merges.

There have been some discussion about file-id aliases (most specifically
when 2 people create the same file, it would be nice to merge their
histories together somehow. It is much more difficult if their set of
revisions are overlapped (ie both files existed in the same branch at
the same time)).

I don't know that much has been done for revision ids. It could be done
with a simple aliases table, but we would need to think out the
performance implications as well. eg. I want to pull from you, and you
have rev-ids 1,2,3,4, but I don't realize they are aliased to my
revision ids a,b,c,d so I don't need to pull anything. I assume aliases
can be updated after the revisions are created, so it isn't as simple as
just pulling new revisions and noting their aliases. (If a is newly
aliased to 1, then 1 is actually newly aliased to a as well).

As far as pre/post 1.0. It just depends if someone like you really wants
them, and comes up with a reasonable solution before we decide we are at
1.0. We are already at 0.8. With a major performance push coming up, I
wouldn't be surprised if we hit 1.0 fairly soon. (I don't really like to
say any absolutes, but probably this year, and it wouldn't surprise me
much if it was within 6 months or so).

John
=:->

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