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Linus Torvalds wrote:

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>

> On Mon, 16 Oct 2006, Aaron Bentley wrote:

>> Bazaar's namespace is "simple" because all branches can be named by a

>> URL, and all revisions can be named by a URL + a number.

> I pretty much _guarantee_ that a "number" is not a valid way to uniquely

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> name a revision in a distributed environment, though. I bet the "number"

> really only names a revision in one _single_ repository, right?

Right.  That's why I said all revisions can be named by a URL + a

number, because it's the combination of the URL + a number that is

unique.  (In bzr, each branch has a URL.)
> In contrast, in git, a revision is a revision is a revision. 
I agree that a revision is a revision, but I don't think that's a

property unique to git. :-)
> If you give

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> the SHA1 name, it's well-defined even between different repositories, and

> you can tell somebody that "revision XYZ is when the problem started", and

> they'll know _exactly_ which revision it is, even if they don't have your

> particular repository.

When two people have copies of the same revision, it's usually because

they are each pulling from a common branch, and so the revision in that

branch can be named.  Bazaar does use unique ids internally, but it's

extremely rare that the user needs to use them.
> Now _that_ is true simplicity. It does automatically mean that the names

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> are a bit longer, but in this case, "longer" really _does_ mean "simpler".

>

> If you want a short, human-readable name, you _tag_ it. It takes all of a

> hundredth of a second to to or so.

But tags have local meaning only, unless someone has access to your

repository, right?
>>> About "checkouts", i.e. working directories with repository elsewhere:

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>>> you can use GIT_DIR environmental variable or "git --git-dir" option,

>>> or symlinks, and if Nguyen Thai Ngoc D proposal to have .gitdir/.git

>>> "symref"-like file to point to repository passes, we can use that.

>> It sounds like the .gitdir/.git proposal would give Git "checkouts", by

>> our meaning of the term.

>

> Well, in the git world, it's really just one shared repository that has

> separate branch-namespaces, and separate working trees (aka "checkouts").

> So yes, it probably matches what bazaar would call a checkout.

The key thing about a checkout is that it's stored in a different

location from its repository.  This provides a few benefits:
- - you can publish a repository without publishing its working tree,

  possibly using standard mirroring tools like rsync.
- - you can have working trees on local systems while having the

  repository on a remote system.  This makes it easy to work on one

  logical branch from multiple locations, without getting out of sync.
- - you can use a checkout to maintain a local mirror of a read-only

  branch (I do this with http://bazaar-vcs.com/bzr/bzr.dev).
> Almost nobody seems to actually use it that way in git - it's mostly more

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> efficient to just have five different branches in the same working tree,

> and switch between them. When you switch between branches in git, git only

> rewrites the part of your working tree that actually changed, so switching

> is extremely efficient even with a large repo.

You can operate that way in bzr too, but I find it nicer to have one

checkout for each active branch, plus a checkout of bzr.dev.  Our switch

command also rewrites only the changed part of the working tree.
Aaron

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