Re: newbie questions about git design and features (some wrt hg)

On 02.02.2004, Matt Mackall wrote:

On Fri, Feb 02, 2007 at 10:55:48AM +0100, Jakub Narebski wrote:

quoted

How Mercurial solves problem of multiple _persistent_ branches? Does it
add pointers to commits somewhere deeper in changelog / revlog?

Each changeset may have a branch marker.

By changeset you mean commit-revlog (changelog)? 

Where those branch markers are stored? Are those markers moving pointers,
meaning that if you make a commit while on branch, branch marker for
current branch will move?

Static markers cannot identify branch in the presence of branch points:

                   ---a<---b ........ side branch
                  /
  1<---2<---3<---4<---5<---6<---7 ... main branch
            ^
            :   
             ''''' tag

Here's branches in use with an import of mutt's CVS history:

$ hg branches
mutt-0-94                      208:b2cc0abd8fe0
HEAD                           207:a505693b54c1
mutt-0-93                      134:d59345944030
muttintl                       1:29510de8b3fc

What is the first number? I understand that second is shortened (is it
stored shortened, I wonder) hash identifier of a commit...

$ hg co HEAD
176 files updated, 0 files merged, 8 files removed, 0 files unresolved

Git (at least for now) writes nothing on checkout; it is planned that
it would write changes status-like; perhaps summary would be enough...
or is it only working area status that is to be written...

$ hg branch
HEAD
$ hg branch devel
$ hg branch
devel
$ hg branch devel

quoted

BTW does Mercurial have tags?

Yes. Both local and revision-controlled.

Revision-controlled (in-tree) tags are inane idea. Tags are non-moving
(and sometimes annotated) pointers to given point in history. They should
not depend on which branch you are, or what version you have checked out.

Otherwise the following would not work:
 $ git reset --hard v1.0.0
 $ git reset --hard v1.4.4.4
(it could be "git checkout" instead of "git reset --hard" in 'master'
version of git, with "detached HEAD" / "anonymous branch" feature).

quoted

Nice to know. You compress only file deltas, or also file revision
metadata? Do you compress manifests (trees) and commits (or at least
commit messages) too?

All three use the same underlying storage format, so yes.

But do you compress metadata (like base of a delta for file deltas,
authorship of a commit and reference to manifest-log entry)? Do manifest
is delta-encoded?

-- 
Jakub Narebski
Poland