A Distributed Version Control System Dmitriy Iassenev GSC Game World 2011

1. Mercurial A Distributed Version Control System DmitriyIassenev GSC Game World 2011

2. Why Mercurial? Pros It has rich functionality It is easy to customize If you like Python It scales good Big files need to be handled carefully It has good GUI client – TortoiseHG It is easy to learn Non-progammers could have problems with it

3. Why Mercurial? Cons Every user has the whole repository User access rights problems – use subrepositories? Every user should have enough HDD space

4. Mercurialvs Subversion Pros Simpler for non-programmers Even better GUI client – TortoiseSVN (at the time we choose) Handle big files well without any additional effort Need less space on HDD Mixed revisions working copy Exclusive file lock

5. Mercurial vs Subversion Cons Centralized VCS No local commits No inter-repository commands Slower on most operations Complicated and restrictive merge and branch functionality In some use cases need even more space on HDD .svn folders Impossible to setup ignore filter for future folders Easier to loose your changes

6. Mercurial vsGit Pros Even more rich functionality Faster on Linux

7. Mercurial vsGit Cons Worse performance on Windows (2009 year measurements) You should “repack” your local repository to prevent performance degradation No good free GUI client for Windows at the time we choose – TortoiseGit? It is known to be more complicated for both programmers and non-programmers

8. How does Mercurial work? Local Repository and Working Copy commit update merge rebase

9. Local repository and Working Copy Merge 1 2 3

10. Local repository and Working Copy Rebase 1 2

11. Inter-repository communication clone pull After pull commands Update Fetch = update + merge + commit Rebase push push after commit option serve

12. Tags and Branches Tags Merge tags - .hgtags Branches Repository clones Markers Named branches Anonymous branches (several heads in a branch) Branch hierarchy doesn’t depend on folders structure (unlike Subversion)

13. Under the hood Deltas even for binaries Atomic transactions – only append to revlog Fast retrieval – snapshots File and folder renames Avoid case sensitive renames on case insensitive FSs Compression: deflate and bzip2 Concurrent access – lockless reading Minimizing disk seeks Hard links for cloning repositories locally

14. Recovering from errors Revert Rollback Undo the last commit Undo erroneous pull Backout Recovering from erroneous merge

15. Recovering from errors Rollback 1 2

16. Recovering from errors Backout 1 2

17. Recovering from erroneous merge 1 2 3 4

18. Hooks changegroup – we use it to detect when someone pushed to repository precommit – we use it to prevent case folding collisions

19. Extensions Modified Bigfiles Fetch Rebase Transplant Mercurial Queues (for Strip)

20. How we use Mercurial Multiplatform engine for video game and game itself (Win32, Win64, Xbox360, PS3) C++ for engine and game, C# for tools (.NET + WPF) Team: 11 programmers + 13 designers (up to 40 designers in a production stage) ~467k lines of code ~= 15Mb ~3.5M lines of code from various SDK and third party libraries which we build ~= 132Mb Working Copy: ~33.6k files and folders ~= 16.8Gb Local Repository (~0.4Gb) => 17.2Gb per user Full repository ~= 135Gb

21. Continuous Integration Workflow 2 Central repositories + Build station Programmers repository Build station repository Designers repository We plan to use Central repository for Testers

22. Continuous Integration Workflow on push to Programmers pull Build station from Programmers build binaries for all 16 projects configurations run tests commit to Build station repository on success or report failure otherwise pull from Designers push to Designers on push to Designers pull Programmers from Designers

23. Merge tool we use - Perforce p4merge

25. Questions? Feel free to email me at iassenev@gsc-game.com Online resources: “Mercurial: The Definitive Guide” by Bryan O'Sullivan - http://hgbook.red-bean.com/ Joel Spolsky Tutorial on Mercurial - http://hginit.com/