python-peps/pep-0347.txt

PEP: 347
Title: Migrating the Python CVS to Subversion
Version: $Revision $
Last-Modified: $Date$
Author: Martin v. L<>wis <martin@v.loewis.de>
Discussions-To: <python-dev@python.org>
Status: Draft
Type: Informational
Content-Type: text/x-rst
Created: 14-Jul-2004
Post-History: 14-Jul-2004


Abstract
========

The Python source code is currently managed in a CVS repository on
sourceforge.net.  This PEP proposes to move it to a subversion
repository on svn.python.org.


Rationale
=========

This change has two aspects: moving from CVS to subversion, and moving
from SourceForge to python.org.  For each, a rationale will be given.


Moving to Subversion
--------------------

CVS has a number of limitations that have been elimintation by
Subversion.  For the development of Python, the most notable
improvements are:

- the ability to rename files and directories, and to remove
  directories, while keeping the history of these files.

- support for change sets (sets of correlated changes to multiple
  files) through global revision numbers.

- support for offline diffs, which is useful when creating patches.


Moving to python.org
--------------------

SourceForge has kindly provided an important infrastructure for the
past years.  Unfortunately, the attention that SF received has also
caused repeated overload situations in the past, to which the SF
operators could not always respond in a timely manner.  In particular,
for CVS, they had to reduce the load on the primary CVS server by
introducing a second, read-only CVS server for anonymous access.  This
server is regularly synchronized, but lags behind the the read-write
CVS repository between synchronizations.  As a result, users without
commit access can see recent changes to the repository only after a
delay.

On python.org, it would be possible to make the repository accessible
for anonymous access.


Migration Procedure
===================

To move the Python CVS repository, the following steps need to be
executed.  The steps are elaborated upon in the following sections.

1. Assign passwords for all current committers for use on
   svn.python.org.  User names on SF and svn.python.org should be
   identical, unless some committer requests a different user name.

2. At the beginning of the migration, announce that the repository on
   SourceForge closed.

3. 24 hours after the last commit, download the CVS repository.

4. Convert the CVS repository into two Subversion repositories, one
   for Distutils and one for Python.

5. Publish the repositories with write access for committers, and
   read-only anonymous access.

6. Disable CVS access on SF.


Assign Passwords
----------------

Currently, access to Subversion on svn.python.org uses WebDAV over
https, using basic authentication.  For this to work, authorized users
need to provide a password.  This mechanism should be used, at least
initially, for the Python CVS as well, since various committers also
have a username/password pair for the www SVN repository already.

Alternatives to password-based access include:

- Subversion over SSH, using SSH key pairs. This would require
  committers to be given accounts on the machine, which currently is
  ruled out by the administration policy of svn.python.org.

- Subversion over WebDAV, using SSL client certificates. This would
  work, but would require to administrate a certificate authority.


Downloading the CVS Repository
------------------------------

The CVS repository can be downloaded from

    http://cvs.sourceforge.net/cvstarballs/python-cvsroot.tar.bz2

Since this tarball is generated only once a day, some time must pass
after the repository freeze before the tarball can be picked up.  It
should be verified that the last commit, as recorded on the
python-commits mailing list, is indeed included in the tarball.


Converting the CVS Repository
-----------------------------

The Python CVS repository contains two modules: distutils and python.
Keeping them together will produce quite long repository URLs, so it
is more convenient if the Python CVS and the Distutils CVS are
converted into two separate repositories.

Fsfs should be used as the repository format (requires Subversion
1.1).  Fsfs has the advantage of being more backup-friendly, as it
allows incremental repository backups, without requiring any dump
commands to be run.

The conversion should be done using the cvs2svn utility, available
e.g. in the cvs2svn Debian package.  The command for converting the
Python repository is ::

    cvs2svn -q --encoding=latin1 --force-branch=cnri-16-start \
      --force-branch=descr-branch --force-branch=release152p1-patches \
      --force-tag=r16b1 --fs-type=fsfs -s py.svn.new python/python

The command to convert the distutils repository is ::

    cvs2svn -q --encoding=latin1 --fs-type=fsfs -s dist.svn.new python/distutils

Sample results of this conversion are available at

    | http://www.dcl.hpi.uni-potsdam.de/python/
    | http://www.dcl.hpi.uni-potsdam.de/distutils/


Publish the Repositories
------------------------

The repositories should be published at https://svn.python.org/python
and https://svn.python.org/distutils.  Read-write access should be
granted through basic authentication to all current SF committers;
read-only anonymous access should also be granted.  As an option,
websvn (available e.g. from the Debian websvn package) could be
provided.

The current SF project admins should get write access to the password
file, in order to create or delete new users.


Disable CVS
-----------

It appears that CVS cannot be disabled entirely.  Only the user
interface can be removed from the project page; the repository itself
remains available.  If desired, write access to the python and
distutils modules can be disabled through a CVS commitinfo entry.


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