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Re: [Gnu-arch-users] arch lkml

From: Tom Lord
Subject: Re: [Gnu-arch-users] arch lkml
Date: Thu, 25 Sep 2003 13:04:19 -0700 (PDT)

    > From: Andrea Arcangeli <address@hidden>

    > On Thu, Sep 25, 2003 at 11:15:33AM -0600, Eric W. Biederman wrote:

    >> poorly and is not distributed.  SVN is not distributed.  ARCH is
    >> barely distributed and architecturally it makes distributed merging
    >> hard.  [..]

I think (Eric) that you'll find that many of us believe pretty much
the opposite of what you say about arch.    That raises the
interesting question:  what the heck do you mean?

(If we're missing something fundamental, let's hear about it  --- if
you've misunderstood something, perhaps we can clear that up.)

    > actually it seems I can use it for my tree too, after I modify it
    > to be able to tag into a plain source tree forked with hardlinks
    > (something I certainly couldn't do with b*tkeeper), and a way to change
    > the patchsets internally (and a way to extract all the patches ordered
    > with meaningful names for marcelo and other trees not based on
    > arch).

I don't quite follow you (Andrea) there.   Perhaps you could explain further.

    > This my proposal to change arch to be able to hook into a random tree in
    > the filesystem (instead of a base-0 tarball), could radically change the
    > way of doing distributed development, in term of resource savings (I bet
    > that would be an order of magnitude better than bk too, I mean, I've
    > lots of tarballs open anyways here, since various trees starts on top of
    > official tar.gz packages, not bkcvs, I so I could save gigabytes of
    > space and dcache efficiency with that feature, even across the non arch
    > usages that are the most common to me at the moment). The hardlinks will
    > make an huge difference and it'll be natural the way arch is designed to
    > take the best advance of them as soon as we can hook into an unpacked
    > tar.gz.

Again, I don't _quite_ follow you however, perhaps this is relevent:

You can use `mkpatch/dopatch' (the arch changeset tools) more or less
independently of using arch.    `dopatch', in particular, "does the
right thing" when patching a tree that is the clone of some other tree
created using hardlinks.

    > arch looks infact more an 'archive for patches' than anything
    > else. 

Archive, cataloging system, and _set_of_tools_for_manipulating_ in
various useful ways, yes.

    > But in terms of automated "merging" design between two separate
    > distributed trees ala b*tkeeper, the problem after you run into rejects
    > is just unsolvable better than 'arch' already does, as far as I can
    > tell. I don't see how b*tkeeper can do better just because I can't
    > imagine anything better possible to do during merging (I can't use bk
    > myself so I can't know if it does it differently). And not even
    > b*tkeeper can know that the merging went right like an human can do,
    > there's no way it can understand the sematics of the code during merging
    > (actually defined as star-merging as from the arch specifications). If
    > one product does better than the other given the same development
    > simulation, it could be simply that its heuristics are less strict (i.e.
    > simular to diff -u0 vs diff -u vs diff -u10)

I really don't know much about bk's merge operators -- but it is
highly likely that (syntactic trivialities and GUIs aside) they come
out to be a subset of what you can do with arch.   Andrea is right
with his suggestion (my paraphrase) that we've nailed that space.

(The syntactic triviality: conflict mark-ups that look like unified
diffs, is in the patch-queue.   GUIs: I think we have all the
arch-side bits lined up and now its mostly a matter of someone making
the interface to any of the existing graphical merge tools fit
smoothly into use.)

    > Then there are quite tons of issues with the on disk format, I feel the
    > gzip slows down things, I didn't try to remove it, but that's my
    > feeling. Those are small patches, and small files, a tar is sure a good
    > idea, but gzip I think should be optional. 

They reduce network traffic in a natural way.   In purely local
set-ups, we have not seen any evidence that they impact performance in
any way worth worrying about.

    > About the inventories I would simply go forcing the extended mode, that
    > force the equivalent of cvs add on every file archived, this is much
    > prefereable IMHO because in a big thing like the kernel there's lots of
    > garbage with all sort of names, and so the commit operation could never
    > get right which files to checkin and which not. It's much easier to
    > consider only the files explicitly added to the repository with an
    > 'arch' command during the commit/update/reply etc...

Do you mean `explicit' mode?   I think it can be configured to do
pretty much what you want.

    > About other misc comments I don't see:

    > 1) the difference between update/reply/merge-star


    > 2) why there isn't an automated make-log + vi + commit command
    > 3) why the +/= in front of the names

    > About the {arch} directory, using the { is a great idea to reduce
    > dramatically the namespace pollution. I've never seen a { in a directory
    > before ;)

    > I also had a problem with cvs2arch, it worked fine for a repository (not
    > the kernel, a small one) but not for another. It happened on a directory
    > that didn't exist in the original cvs import, then it was created over
    > time. At the time the directory is created in cvs, cvs2arch fails and
    > says the directory doesn't exist in the arch data directory.

I wonder if the new gateway mechanisms BM is working on provide an
alternative worth considering.


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