[MERGE] Support fetching a restricted set of revisions

[Robert Collins]

On Sat, 2007-07-14 at 12:20 -0400, Aaron Bentley wrote:
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> Jelmer Vernooij wrote:
> > The attached bundle adds a parameter to InterRepository.fetch() to
> > retrieve a limited set of revisions from the source repository and adds
> > an implementation for retrieving a limited set to KnitRepository1. This
> > is a step towards shallow branches.
> 
> Wouldn't it be more efficient (e.g. with the smart server) to specify
> the history horizon revision, rather than the particular revisions to fetch?

Only by one round trip. e.g.

revs = source_repository.select_breadth_first_revisions(branch_tip, 10)
 -> RemoteSet(opaque data from the server - probably a hundred bytes or
less)
target.fetch(..., limit_revisions=revs)

should work just fine: if revs gets iterated locally, we make a call and
realise its value, if it doesn't (because its streaming from the server)
then we never send the entire list over the wire. And allowing a set or
iterable of revisions is more flexible - so if the cost is one round
trip; I think thats ok.

-Rob
-- 
GPG key available at: <http://www.robertcollins.net/keys.txt>.
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