some questions

some questions

[Thomas Pasch]

Hello,

I try to migrate our old cvs repo to git.
However, I still have to following questions
that I found difficult to answer with
the documentation.

- Is there a way to convert a indexVersion 1
  repo to indexVersion 2? (And vice versa?)

- Is there a way to find out if a repository
  is indexVersion 1 or indexVersion 2 (from
  the pack/index files)?

- http for git seems to be read-only/fetch.
  Would it be (theoretically) possible to
  support write/push (with WebDAV or so)?

- I do not fully understand the implication
  of 'git repack -a' (or 'git repack -A -d').
  Is this bad for remote repos that are used
  with http? (as '-a' is 'Especially useful when
  packing a repository that is used for private
  development and there is no need to worry about
  people fetching via dumb protocols from it').

- What would be the implication to mount the
  git repo with nts (or another remote fs).
  Is it save to use such a mounted repo from
  more than one computer?

Kind regards,

Thomas

-- 

Re: some questions

[Matthieu Moy]

Thomas Pasch <thomas.pasch@jentro.com> writes:

> Hello,
>
> I try to migrate our old cvs repo to git.
> However, I still have to following questions
> that I found difficult to answer with
> the documentation.
>
> - Is there a way to convert a indexVersion 1
>   repo to indexVersion 2? (And vice versa?)

The index itself is just a little file in .git/index. There might be a
better solution, but just

  rm .git/index
  git reset

seems to do it (of course, don't do while you have staged changes in
the index !).

> - http for git seems to be read-only/fetch.
>   Would it be (theoretically) possible to
>   support write/push (with WebDAV or so)?

http://www.kernel.org/pub/software/scm/git/docs/howto/setup-git-server-over-http.txt

(BTW, that's the first result in
http://www.google.com/search?q=git+webdav ;-) )

-- 
Matthieu

Re: some questions

[Jakub Narebski]

Thomas Pasch <thomas.pasch@jentro.com> writes:

> I try to migrate our old cvs repo to git.
> However, I still have to following questions
> that I found difficult to answer with
> the documentation.
> 
> - Is there a way to convert a indexVersion 1
>   repo to indexVersion 2? (And vice versa?)

I think the only solution is to simply remove index,
ensure configuration (pack.indexVersion), and recreate
it using git-index-pack(1).
 
> - Is there a way to find out if a repository
>   is indexVersion 1 or indexVersion 2 (from
>   the pack/index files)?

There is some magic number used to distinguish between
pack index version 1 and version 2.

See Documentation/technical/pack-format.txt for details.

> - http for git seems to be read-only/fetch.
>   Would it be (theoretically) possible to
>   support write/push (with WebDAV or so)?

It *is* supported (via https).

There was even attempt to create 'smart' http
push via web server module or CGI script, but
IIRC it hit feature freeze and discussion petered
out, so only parts of it are in 'pu'.

Search for "Add Git-aware CGI for Git-aware smart
HTTP transport", "More on git over HTTP POST"

  http://thread.gmane.org/gmane.comp.version-control.git/91104
 
> - I do not fully understand the implication
>   of 'git repack -a' (or 'git repack -A -d').
>   Is this bad for remote repos that are used
>   with http? (as '-a' is 'Especially useful when
>   packing a repository that is used for private
>   development and there is no need to worry about
>   people fetching via dumb protocols from it').

Dumb protocols currently _always_ download whole packfiles,
so if you want to serve dumb protocols you might want to
offer (also?) smaller packfiles.  You can, for example,
use .keep files and 'git repack -a' wouldn't matter.

You can try to search archives for "generational packing"
or something like that...

> - What would be the implication to mount the
>   git repo with nts (or another remote fs).
>   Is it save to use such a mounted repo from
>   more than one computer?

Should work without problems, _unless_ you mean that
you want to use multiple working directories with single
repository.  Then there are a couple of thing that you
have to be beware of (but you can instead use alternates
mechanism).

-- 
Jakub Narebski
Poland
ShadeHawk on #git

Re: some questions

[Shawn O. Pearce]

Matthieu Moy <Matthieu.Moy@imag.fr> wrote:
> Thomas Pasch <thomas.pasch@jentro.com> writes:
> >
> > I try to migrate our old cvs repo to git.
> > However, I still have to following questions
> > that I found difficult to answer with
> > the documentation.
> >
> > - Is there a way to convert a indexVersion 1
> >   repo to indexVersion 2? (And vice versa?)
> 
> The index itself is just a little file in .git/index. There might be a
> better solution, but just
> 
>   rm .git/index
>   git reset
> 
> seems to do it (of course, don't do while you have staged changes in
> the index !).

True, that would reset the dircache (aka .git/index).  But we only
have effectively 1 version of the dircache.  Sure there was an older
version, way back before it got a version header and the ability to
get extension sections added.  I don't think there are many clients
using that format anymore.  That format predates the 1.4 series,
and we really encourage people to be on 1.5 or later.

The original poster asked about indexVersion 1 and indexVersion 2,
which means he is probably talking about pack.indexVersion and thus
a .idx file alongside a pack, not the dircache file that tracks
the working tree state.
 
-- 
Shawn.

Re: some questions

[Shawn O. Pearce]

Jakub Narebski <jnareb@gmail.com> wrote:
> Thomas Pasch <thomas.pasch@jentro.com> writes:
> 
> > I try to migrate our old cvs repo to git.
> > However, I still have to following questions
> > that I found difficult to answer with
> > the documentation.
> > 
> > - Is there a way to convert a indexVersion 1
> >   repo to indexVersion 2? (And vice versa?)
> 
> I think the only solution is to simply remove index,
> ensure configuration (pack.indexVersion), and recreate
> it using git-index-pack(1).

Just change pack.indexVersion in .git/config to have the version
you want and run `git gc` to repack the repository.  If you created
this repository by cloning another you may need to first delete
any .keep files:

	rm -f .git/objects/pack/*.keep
  
> > - Is there a way to find out if a repository
> >   is indexVersion 1 or indexVersion 2 (from
> >   the pack/index files)?
> 
> There is some magic number used to distinguish between
> pack index version 1 and version 2.
> 
> See Documentation/technical/pack-format.txt for details.

  for i in .git/objects/pack/pack-*.idx; do
  dd if=$i bs=12 count=1 | od -c
  done

A line like:

0000000   �   t   O   c  \0  \0  \0 002  \0  \0  \0 002

indicates index version 2, as it has the magic byte sequence in
front of '\xFFt0c'.  Most version 1 indexes will have 2 zeros
in the first two bytes:

0000000  \0  \0  \0  \0  \0  \0  \0 001  \0  \0  \0 003

> > - http for git seems to be read-only/fetch.
> >   Would it be (theoretically) possible to
> >   support write/push (with WebDAV or so)?
> 
> It *is* supported (via https).
> 
> There was even attempt to create 'smart' http
> push via web server module or CGI script, but
> IIRC it hit feature freeze and discussion petered
> out, so only parts of it are in 'pu'.
> 
> Search for "Add Git-aware CGI for Git-aware smart
> HTTP transport", "More on git over HTTP POST"
> 
>   http://thread.gmane.org/gmane.comp.version-control.git/91104

I'm picking this up again and working on it more.  Its not dead.
  
> > - What would be the implication to mount the
> >   git repo with nts (or another remote fs).
> >   Is it save to use such a mounted repo from
> >   more than one computer?

I've found that accessing a Git pack file over a network file
system like NFS or SMB is kinda slow.  The issue is we do many
reads scattered throughout the file.  Its hard for the client
to batch up reads and hide the network latency.

You may get better performance by building Git without mmap
support:

	make NO_MMAP=1

but that is going to hurt access to local files.

-- 
Shawn.