Using Git For Development. Shantanu Pavgi, UAB IT Research Computing

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1 Using Git For Development Shantanu Pavgi, UAB IT Research Computing

2 Outline Version control system Git Branching and Merging Workflows Advantages

3 Version Control System (VCS) Recording changes to files and maintaing associated metadata Copy or tar command with timestamps Types Centralized Distributed

4 Centralized vs Distributed VCS Reference:

5 Git Git is a free & open source, distributed version control system designed to handle everything from small to very large projects with speed and efficiency. Tool for maintaining your work history Used by: Linux Kernel Android Ruby on Rails Reference:

6 Advantages Works off-line Fast Easy or cheap branching Public and private work histories Rewrite or curate history before making it public Repositories can talk to each other Flexibility in workflows

7 Commits Tracks content and not files working directory staging area git repository Allows you to stage changes add Each commit is a complete snapshot of all staged files Unique 40 character hash for each commit checkout commit Local operations

8 Commits Snapshot Committer s name and address Parent commits Commit message

9 Branching Branch: Line of development master branch is the default Create branches to have isolated lines of development A 'head' is a named reference to a commit object - e.g. branches and tags. A repository can contain any number of heads, however it points to only one 'head' at a time. This 'current head' is called HEAD.

10 Branching Branch: Line of development master branch is the default Create branches to have isolated lines of development A 'head' is a named reference to a commit object - e.g. branches and tags. A repository can contain any number of heads, however it points to only one 'head' at a time. This 'current head' is called HEAD.

11 Branching HEAD *master f32dc5 abc123 9ff2b8 2bc3d4 e26a2f (root) 7f3bcd 123abc ticket-4 time

12 Merging HEAD f32dc5 abc123 *master 9ff2b8 2bc3d4 e26a2f def234 (root) 7f3bcd 123abc ticket-4 time

13 Branching and Merging Allows switching contexts Diverge from main line of development or stable code in a clean manner Separate space for experimentation and bug fixes Local - private commit history Rewrite or curate history before publishing it or merging into other branches

14 Workflows Distributed model and cheap branching allows numerous types of workflows Push model: Centralized repository type Pull model: Integration manager type git workflows --help Read more in ProGit book

15 Workflow: Solo commit checkout Shantanu s Repo

16 Workflow: Solo commit checkout Shantanu s Repo pull push Official or Public Repo

17 Workflow: Centralized commit pull checkout Shantanu s Repo push commit checkout John s Repo pull push Official or Public Repo

18 Workflow: Integration Manager

19 Workflow: Integration Manager commit pull checkout Shantanu s Repo push commit checkout pull John s Repo pull Official or Public Repo

20 Workflow: Integration Manager commit pull checkout Shantanu s Repo push commit checkout pull pull John s Repo pull Official or Public pull Repo commit Curtis s Repo pull checkout

21 Learn More Subversion folks: svn.html git man pages

22 MOTD Use Git Works off-line Personal logbook Curate and publish history Flexibility in workflows UABgrid docs:

23 Additional Information

24 Git Installation Linux Package managers Source Windows Mac: Source Homebrew:

25 Add-on tools Access control: gitosis and gitolite GUI: gitk Display branch name is shell:

26 Rewriting History Remove sensitive data from repository Rewrite commits - commit messages, committer names, timestamps and committed files Rewriting changes commit hash DON T rewrite commits of published history unless absolutely necessary Commands: rebase and filter-branch

27 Distributed repository model Curtis s Private Repo on laptop Curtis s Published Repo on Cheaha Official Repo git.uabgrid John s Published Repo on Cheaha Shantanu s Published Repo on Cheaha Shantanu s Private Repo on Cheaha

28 Git Objects Reference:

29 Repository Size and Packfiles Each commit is a complete snapshot Packs up several blob objects Creates index file(s) and pack file(s) Latest commit includes a complete copy Older commits contain deltas git gc - cleanup and optimization References:

30 Git with large files Limitations: Compression Checksums Deltas Memory - few hundred MB - tracks content/files without checking it in

31 Git with binary files Configurable with external diff tool Create a new type according to file extension Configure diff tool for the new type Details:

32 Best Practices Work in a private and non-tracking local branch Granular commits - easier to squash commits together than split commits Fetch and merge Create ticket or issue specific branches

33 Git or Mercurial Google s analysis: Answer to Google s analysis: Speed and size:

34 Language Git: C and Perl Mercurial: Python Syntax Branches Community Git or Mercurial

35 git SSH http(s) Transport protocols

36 Community Support irc://irc.freenode.net/git

37 Acknowledgments David Shealy John-Paul Robinson Bill Bradley Mike Hanby Poornima Pochana, Thomas Anthony

38 Questions???

Revision Control. An Introduction Using Git 1/15

Revision Control. An Introduction Using Git 1/15 Revision Control An Introduction Using Git 1/15 Overview 1. What is revision control? 2. 30,000 foot view 3. Software - git and gitk 4. Setting up your own repository on onyx 2/15 What is version control?