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On 2011-04-21 13:58, Nico Kadel-Garcia wrote:
> On Thu, Apr 21, 2011 at 5:15 AM, Ian Wild <ian.wild_at_wandisco.com> wrote:
>> That sounds like a good translation to me. The maths gets complicated to put
>> it mildly, but I know Dr Yeturu's work is in some part at least based on
>> Paxos ( http://en.wikipedia.org/wiki/Paxos_algorithm ). AIUI we've got the
>> only implementation of this model that can guarantee the consistency and
>> ordering of transactions; important when you need your repositories to
>> remain identical on every site!
> *NOTHING* can guarantee this.. This is key to the difficulty of the
> "merge" process for multiple branches against a common trunk.
I believe you misunderstand how the repositories are kept in sync.
> Maintaining two sets of changes on distinct repositories that wind up
> altering the same set of text, or code, in divergent ways cannot be
> guaranteed to be resolved "correctly" by a mechanical process, because
> the process would have to "understand" the discrepancies and resolve
> them. It can be as simple as a copyright notice, whose changes
> represent social information outside the scope of the source control
> system, or code changes in a subroutine in one branch and the handling
> of the error codes generated by that subroutine in a distinct branch.
> It may do a much better *job* of this than other tools. That would be
> cool, tricky merges have always been an issue. But mere ordering and
> consistency is not sufficient, overlapping merges require attention.
While your observation regarding merging is correct, it does not apply
to the replication technique that WANdisco use in their product.
The network nodes handling the repositories are distributed, but not
isolated. The nodes actively agree on how to apply a proposed change to
their repository replicas, effectively avoiding the merge problem.
WANdisco provide a well-written White Paper explaining this.
Michael Diers, elego Software Solutions GmbH, http://www.elego.de
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Received on 2011-04-24 13:21:24 CEST