Re: [Monotone-devel] Re: 3-way merge considered harmful

[Nathaniel Smith]

On Tue, May 03, 2005 at 01:26:49PM -0700, K. Richard Pixley wrote:
> Each "directory" is a file containing records, each record contains a 
> filename + inode number.
> 
> The inode table points to file extents, protections, a link count, and 
> perhaps back pointers, etc.  Atomic operations include "link" and 
> "unlink" and possibly "rename".

Sure, this is the basic representation you want to use for merging.

> If you collapse all of the directories into an archive resembling a 
> normalized "ls -iR", then I believe that you can indeed translate 
> textual changes into file system operations.  You'll need to be careful 
> about the ordering so you make the new links before removing the old 
> ones, but that should be straightforward.  Even the archive isn't 
> strictly necessary.  Since we're talking about a system with atomic 
> commits of changesets, top-down, bottom-up, doesn't really matter.  You 
> do stand the possibility of committing a partial tree with no path to 
> the root.  However, since this partial tree can't be accessed in any of 
> the normal ways, short of commiting a change set which reconnects it to 
> the root of an existing branch, I submit that it can't possibly create 
> any conflicts you aren't already solving.

Sure, you can write down a textual representation of this information.
manifests and change_set's more or less are such a representation.

The problem isn't that it's impossible, it's that it doesn't actually
help solve any of the problems we need to solve, as far as I can tell.

> Clearcase does something comparable.  I can even commit manual surgery 
> on a directory by manually linking an arbitrary inode into it with an 
> arbitrary name.
> 
> I'm surprised that monotone isn't doing this already.  Of course, you'd 
> need to find some identifier to stand in for the inode number...

See "tid" in change_set.cc :-).

-- Nathaniel

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