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Re: [Koha-devel] Re: distributed VCS, some thoughts.


From: Jerry Van Baren
Subject: Re: [Koha-devel] Re: distributed VCS, some thoughts.
Date: Fri, 16 Mar 2007 14:39:49 -0400
User-agent: Thunderbird 1.5.0.10 (Windows/20070221)

Yes on the concepts, no on the level of effort.  :-)

I'm not very familiar with koha's current VCS structure and methods since I'm not actively developing koha code (I installed koha at the private school that I donate my time too ;-) and only monitor the list for developments).

It sounds like there are several developers with write access to the master repo. This could be carried forward, but isn't the way git is being used elsewhere. Git is being used mostly as single-user per repo with the repos being available via http: or git: (preferably the latter). Hierarchy with single developers is an excellent way of providing scaling and preventing inadvertent interference.

Git background and tutorials:
<http://git.or.cz/>
<http://www.kernel.org/pub/software/scm/git/docs/tutorial.html>
<http://www.kernel.org/pub/software/scm/git/docs/everyday.html>

The following is the concept, likely not 100% correct since I didn't actually execute the commands. It is also just one way of doing it (for example, pull is a fetch+merge - doing a fetch, inspect the potential changes, and then merge them has its benefits).

address@hidden would have his repo and create New Code[tm]. He would either do this development in a new branch in his repo or would create a new branch for Chris:
  git checkout -b for_chris
  git pull . <commitID>
(where <commitID> is his previously committed changes in his master branch) and email Chris "hey, pull for_chris".

address@hidden would pull it into his repo by creating a temporary testing branch "from_kyle" and pulling the changes:
  git checkout -b from_kyle
  git pull git://kyle.com for_chris
Chris tests the updates and likes them.  He merges it into his mainline:
  git checkout master
  git pull . from_kyle
and emails Josh "hey, pull "from_kyle".

address@hidden does the equivalent, but, since he trusts Chris, doesn't bother creating a temporary branch for testing:
  git pull git://chris.com from_kyle

Some time later Chris and Kyle update their copies from koha.org:
  git pull
at which time the changes that came from Chris will be fast forwarded and they can delete their respective branches
Kyle:
  git branch -d for_chris
Chris:
  git branch -d from_kyle

It really doesn't take much time because, by the time the changes bubble to the top, the trust and testing has been performed and the change just needs to be pulled. Since the pulls are just the changes, they are very quick.

Linus is doing this at the top level for linux with a handful of lieutenants (I don't know the current count, probably under 10). The number of active developers and changed lines of code is or should be way higher than what koha has. Linus isn't doing it full time, he still has time to rewrite portions of gnome.
  <http://www.linux.com/article.pl?sid=07/02/16/1937237>
;-) The git methodology scales well because it was designed from the ground up to be robust, efficient, and scalable.

gvb


Kyle Hall wrote:
I've been chatting with kados, and he suggested I get some feedback from Jerry.

It seems that if we switched to git we would need someone full-time just managing commits from the way I read Jerry Van Baren's post. It seems like the koha community, though dedicated, just isn't big enough to absorb the cost of losing development time to managing source code control. I doubt there are many programmers out there that would prefer to be managing the code they've written rather than writing more code ; )

What leads me to these conclusions is the whole hierarchy of 'pull' rather than push. It means that at each level of development, say me->chris->josh, everyone except the first person (me ) has to actively pull changes from the level below them. Please correct me if I am mistaken.

Kyle

On 3/16/07, *Jerry Van Baren* <address@hidden <mailto:address@hidden>> wrote:

    Paul POULAIN wrote:
     > thinking of it, I was wondering wether a distributed VCS should be
     > considered as a "Release Manager" oriented VCS.
     >
     > I explain : unless i'm mistaken, it means :
     > - kados is the RM
     > - paul & chris are working on some feature
     > - paul "commit" the feature to kados repository, who will accept
    it (or
     > how is he warned that I made something ?)
     > - chris update his copy from kados one.
     >
     > iiuc, a D-VCS is in fact a RM-VCS to my mind. Thus the question :
    do we
     > have a RM that can afford that task/responsability ?
     > Once again, I may be mistaken, but i'm a little bit less
    enthusiasm if
     > i'm right...

    This is where a D-VCS *really* shines (at least git, probably the others
    as well).  The advantages of D-VCS is that you have not only branches
    but also replicated repositories to work with.  The following is how
    things work with linux and git.  It may apply to other D-VCS, but I
    don't know.

    You have a development master repository.  For linux, it is Linus
    Torvald's on kernel.org <http://kernel.org>.  For Koha, this likely
    would be the 3.x
    development one.  Only Paul Poulain (or whoever is the development
    master) does commits into this repo.  Paul and Chris would have their
    own feeder repos and _ask_ Paul to pull changes, they would not
    (normally) push changes into the RM repo.

    The RM (Kados) also has a master repository.  Bugfixes and also any
    backporting of new features get pulled into the repository by Kados.
    Pulls is the norm, pushes are generally not done.

    You then have feeder repositories that the master maintainer (Paul for
    the development repo, Kados for the release repo) pulls improvements
    from after they've been vetted.  This would be Paul & Chris & everybody
    else in a hierarchy.

    All the koha developers then have their local working repository, which
    is a clone of the master + "value added".  In the local repository, they
    pull changes from the master RM repo to keep up to date, as well as
    doing their local work.  If another feeder repo has a change they
    want/need, they can pull that change directly from the feeder repo
    (including "cherry-picking" changes).  Since git keeps track of changes
    by their hash name, when the master RM repo picks up a feeder's change,
    the local repos that already have that change just say "been there, done
    that, fast forward" and life is good.  Otherwise a merge is done and
    life is still good (except for a collision, but that is unavoidable and
    is no different than what happens with CVS/SVN).

    Local changes are source controlled in the local repo - something I've
    never succeeded in doing well with CVS/SVN, but is transparently
    trivial
    with git.  When a local change is considered ready for inclusion, by
    convention a branch is created in the local repo with a distinctive name
    and the appropriate upstream repo owner is notified (traditionally by
    posting a patch on the developers' email list so everybody can review
    the change).  The upstream repo owner then pulls the change into the
    upstream repo, ultimately ending up in the master RM repo (or the "new
    HEAD" repo) and spreading back out over the world from there.

    Poor ASCII-art diagram:

                 backport
    Development --------> Release
        ^   ^               ^  ^
        |    \      _______/  /
        |     \    /    _____/ bugfixes
    feeder1 feeder2   /
       ^  ^  ^ ^  ^   /
      /   |/   |   \ /
    dev1 |   dev3 dev4
         dev2

    (I tried to make a line from "dev2" into both feeder1 and feeder2 - the
    tree need not be a strict hierarchy.  Dev2 can generate a change that
    gets pulled into both feeder1 and feeder2 and subsequently into
    Development with no confusion - if feeder2 gets pulled into Development
    first, the duplicate in feeder1 will be identified and "fast
    forwarded.")

    HTH,
    gvb


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--
IT Tech
Crawford County Federated Library System
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