Using Subversion and Git Together

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.

Transcript

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. server Subversion and Git • Single repository at shared centralized server • All branches and forks are in the same repository • Many repositories • Forks • 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 User 1 User 2 1. push: Git to Svn 2. pull: Svn to Git
10. Git-Svn Approach custom non-Git workflow server User 1 Git-Svn commands: • fetch • dcommit • rebase • branch ...
11. Git-Svn Approach custom non-Git workflow - local commit - remote commit Standard Git push: local state git pull, merge commit created git push, new commits pushed
12. Git-Svn Approach custom non-Git workflow Git-Svn dcommit: local state git svn dcommit, requires rebase first git svn dcommit, (commit) git svn dcommit, (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 server subgit
15. SubGit approach details • Installed into repository • Uses hooks • Translation is performed in the background to minimize overhead
16. SubGit default installation svn pre-commit hook git pre-receive hook git post-receive hook SubGit translation daemon Git Subversion Server
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 pre-commit post-commit data transfer translation scheduled revision added to SubGit translation queue revision installed git git commit created
19. SubGit asynchronous translation svn subgit pre-receive post-receive data transfer translation scheduled commit(s) added to SubGit translation queue references updated git svn revision created
20. SubGit asynchronous translation subgit git 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 t “Clean cut” migration Git adoption VCS transparency t SubGit smooth migration
24. Subversion<=>Git Translation • Branches and Tags • Deltas • Special properties • Merge tracking info • References • Trees • Special files • Commit parents
25. Branches and Tags overview /trunk /branches /branches/1.0.x /branches/1.1.x /tags /tags/1.0.0 --- r10 M /branches/1.0.x/file.txt master 1.1.x 1.0.x 1.0.0
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: • svn:ignore • svn:eol-style • svn:mime-type • files: • .gitignore • .gitattributes file.txt svn:eol-style=native .gitattributes * 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! :)