SubGit is a server-side tool that helps to accomplish Svn to Git migration or Svn/Git synchronization task. This talk describes SubGit pros and cons and compares SubGit with its client-side Git-Svn alternative.

1. Subversion Day
Using Subversion and Git Together
June 14th 2012, Berlin

2. About Us
●
TMate Software
●
We create VCS tools since year 2003
●
Products at pre-release stage
●
SubGit (RC, self-hosting for 6 months)
●
HG4J (Beta)
●
Our mature products:
●
SvnKit (1.7.4, 30% of the ASF requests)
●
SqlJet (1.1.2)

3. Subversion and Git
●
Subversion:
●
Mature, well known and widely used
●
Centralized
●
Manager-friendly
●
Git:
●
Fast growing VCS
●
Distributed
●
Geek-friendly

4. Subversion and Git
server
●
Single repository at ●
Many repositories
shared centralized server
●
Forks
●
All branches and forks are
in the same repository ●
Delayed commits

5. Subversion and Git
How is it possible to use both?!

6. Two Approaches
Git-Svn
or SubGit

7. Git-Svn Approach
overview
server server

8. Git-Svn Approach
client-side, partisan deployment
server
User 1 User 2

9. Git-Svn Approach
double translation, resulting in data loss
server
2. pull: 1. push:
Svn to Git Git to Svn
User 1 User 2

10. Git-Svn Approach
custom non-Git workflow
Git-Svn commands:
server ● fetch
● dcommit
● rebase
● branch
...
User 1

11. Git-Svn Approach
custom non-Git workflow
Standard Git push:
- local commit
- remote commit
local state git pull, git push,
merge commit created new commits pushed

12. Git-Svn Approach
custom non-Git workflow
Git-Svn dcommit:
local state git svn dcommit, git svn dcommit, git svn dcommit,
requires rebase first (commit) (fetchback, sign)

13. Git-Svn Approach
summary
●
Client side
●
Each user needs to translate at least part of
the repository
●
Non-standard workflow
●
Part of standard Git package, but...
●
…git-svn is 5000 lines script of perl code

14. SubGit
overview
subgit
server

15. SubGit
approach details
●
Installed into repository
●
Uses hooks
●
Translation is performed in the background
to minimize overhead

16. SubGit
default installation
Server
Subversion svn pre-commit hook
SubGit
translation
daemon
git pre-receive hook
git post-receive hook
Git

17. SubGit
Apache configuration example
<Location /svn>
# http://repos.host.com/svn/project
DAV Svn
SVNParentPath /var/svn/repos
Require valid-user
AuthType Basic
AuthUserFile /var/svn/repos/passwords
</Location>
<Location /git>
# http://repos.host.com/git/project
ScriptAlias /git/ …
…
Require valid-user
AuthType Basic
AuthUserFile /var/svn/repos/passwords
</Location>

18. SubGit
asynchronous translation
svn subgit git
data transfer
translation scheduled
pre-commit
revision installed
revision added to
post-commit SubGit translation queue
git commit created

19. SubGit
asynchronous translation
git subgit svn
data transfer
translation scheduled
pre-receive
references updated
post-receive commit(s) added to
SubGit translation queue
svn revision created

20. SubGit
asynchronous translation
git subgit svn

21. SubGit
summary
●
Server side
●
One-time centralized deployment
●
Reuse of existing infrastructure
●
Pure Git/Subversion experience
●
Safe and smooth migration
●
Commercial quality tool

22. SubGit
safe migration
subgit

23. SubGit
smooth migration
VCS transparency
“Clean cut” Git adoption t
migration
VCS transparency
SubGit smooth t
migration

24. Subversion<=>Git Translation
●
Branches and Tags ●
References
●
Deltas ●
Trees
●
Special properties ●
Special files
●
Merge tracking info ●
Commit parents

25. Branches and Tags
overview
master 1.1.x 1.0.x
/trunk
/branches
/branches/1.0.x
/branches/1.1.x
/tags
/tags/1.0.0
1.0.0
--- r10
M /branches/1.0.x/file.txt

26. Branches and Tags
mapping
trunk = trunk:refs/heads/master
branches = branches/*:refs/heads/*
tags = tags/*:refs/tags/*
shelves = shelves/*:refs/shelves/*

27. Branches and Tags
master
Which history line is a trunk?
And which is a branch?
Heuristics help!

28. Branches and Tags
shelves
master
Unnamed Git branch
/shelves/author[_date]
--- r20
M /shelves/alex/file.txt

29. Branches and Tags
attic references
master branch master master
attic/
branch

30. Braches and Tags
●
From Subversion to Git
●
Single Subversion revision might be
translated to multiple Git commits
●
From Git to Subversion
●
Heuristics help to detect target
branch in complex cases
●
/shelves directory is used to store
anonymous branches

31. Deltas and Trees
●
Subversion revision is a delta:
--- r20
A /trunk/file.txt
M /trunk/dir/file.txt
A /trunk/dir/copy.txt
from /trunk/file.txt@r10
D /trunk/dir/old_file.txt
●
Delta tracks copies
●
Git commit is always a full file tree

32. Deltas and Trees
●
From Subversion to Git
●
Relevant part of the delta is applied
to the parent commit tree
●
From Git to Subversion
●
Renames and copies are detected at
translation time
●
Branches and tags creation uses
copy operation

33. Special Properties
●
properties: ●
files:
●
svn:ignore ●
.gitignore
●
svn:eol-style ●
.gitattributes
●
svn:mime-type
file.txt .gitattributes
svn:eol-style=native * text=auto !eol

34. Special Properties
●
From Subversion to Git
●
svn:ignore; svn:mime-type and
svn:eol-style are translated
●
From Git to Subversion
●
.gitignore and relevant values set
in .gitattributes are translated

35. Merge Tracking
Git merge commits:
In Git merges are tracked by:
●
Natural history
●
Merge commits parents
●
Merge unit is commit

36. Merge Tracking
●
Subversion tracks merges by
●
Natural history
●
Revisions ranges (including cherry-picks)
●
Merge unit is file or a directory
/trunk@r100
svn:mergeinfo=/branches/1.0.x:1-100,105
/trunk/file.txt@r100
svn:mergeinfo=/branches/1.0.x/file.txt:102

37. Merge Tracking
●
From Subversion to Git
●
Branch-level merges are translated
to merge commits
●
From Git to Subversion
●
Merge commits are represented with
svn:mergeinfo

38. Not Yet Translated
(in SubGit 1.0)
●
Empty directories
●
Arbitrary properties
●
Revision properties
●
Externals references

39. It Works!
$ svnadmin create repos
....
$ subgit install repos
$ git clone repos git-clone
....
$ svn co svn://host/repos wc
....

40. SubGit Target Audience
●
Managers who listen to their Geeks
●
Hosting providers
●
Safe and smooth migration
●
Java 1.5 or newer is needed
●
Linux, OS X, Windows Server 2003

41. On SubGit Availabilty
●
SubGit 1.0 release: June 2012
●
SubGit is free for Open Source
and Start-Up Projects
●
Closed-source projects will have to register
SubGit (purchase a registration key)
●
Dedicated technical support for SubGit

42. Thank you!
●
SubGit on Web: http://subgit.com/
●
SubGit on Twitter: @subgit
●
Page on Google+ (SubGit)
●
Blog: http://blog.subgit.com/
●
Using Gerrit with Subversion
●
Thank you! :)