Git Internals

Transcript

1. Git Internals by @railsbros_andi Donnerstag, 21. Juni 12

2. History In April of 2005, Git was born Developed by

   Linus Torvalds for SCM of Linux “I’m an egotistical bastard, and I name all my projects after myself. First Linux, now git.” – Linus Git started out as a collection of lower level functions used in various combinations by shell and perl scripts. Donnerstag, 21. Juni 12

3. Donnerstag, 21. Juni 12

4. Git = Subversion + Magic Donnerstag, 21. Juni 12

5. Donnerstag, 21. Juni 12

6. Non-Linear Development is built to be worked on simultaneously by

   many people, having multiple branches developed by individual developers, being merged, branched and re- merged constantly Because of this, branching is incredibly cheap and merging is incredibly easy. Donnerstag, 21. Juni 12

7. Distributed Development Git is built to make distributed development simple.

   No repository is special or central in Git It works completely offline or with hundreds of remote repositories that can push to and/ or fetch from each other over several simple and standard protocols. Donnerstag, 21. Juni 12

8. Git Object Types The foundation of a Git repository Donnerstag,

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9. Git Object Types Git objects are the actual data of

   Git There are four main object types in Git Blob Tree Commit Tag Donnerstag, 21. Juni 12

10. Git Object Types Git objects are the actual data of

    Git There are four main object types in Git Blob Tree Commit Tag Important for understanding Donnerstag, 21. Juni 12

11. The Blob ./ Rakefile lib/ README simplegit.rb Working Directory Git

    Repository Donnerstag, 21. Juni 12

12. The Blob ./ Rakefile lib/ README simplegit.rb Working Directory Git

    Repository blob : a874b7 blob : a906cb blob : a0a60a Donnerstag, 21. Juni 12

13. The Tree ./ Rakefile lib/ README simplegit.rb Working Directory Git

    Repository blob : a874b7 blob : a906cb blob : a0a60a tree : 1a738d tree : fe8971 Donnerstag, 21. Juni 12

14. The Commit ./ Rakefile lib/ README simplegit.rb Working Directory Git

    Repository blob : a874b7 blob : a906cb blob : a0a60a tree : 1a738d tree : fe8971 commit : a11bef Donnerstag, 21. Juni 12

15. The Commit Contents pointer to a tree author commiter message

    parent commits Donnerstag, 21. Juni 12

16. The Commit Contents pointer to a tree author commiter message

    parent commits blob commit tree parent Donnerstag, 21. Juni 12

17. References are simple pointers/references to a particular commit for example

    branches blob commit master tree Donnerstag, 21. Juni 12

18. The Git Data Model a directed acyclic graph blob commit

    tag HEAD branch remote tree Donnerstag, 21. Juni 12

19. The Directory if you run git init you will find

    a .git directory in your current directory the .git directory holds all objects and references the .git is the whole repository Donnerstag, 21. Juni 12

20. Working Directory the working directory is the checkout it is

    a working copy, so it is not important if you switch branches, your working directory content will be changed without a checkout (an empty working directory) this is called a bare git repository Donnerstag, 21. Juni 12

21. Storing of commits How commits, trees and blobs are connected

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22. blob commit HEAD master tree tree tree blob blob .

    `-lib |-README `-example |-source | `-impl.rb `-example.rb Donnerstag, 21. Juni 12

23. blob commit HEAD master tree tree tree blob blob .

    `-lib |-README `-example |-source | `-impl.rb `-example.rb Donnerstag, 21. Juni 12

24. blob commit HEAD master tree tree tree blob blob .

    `-lib |-README `-example |-source | `-impl.rb `-example.rb Donnerstag, 21. Juni 12

25. blob commit HEAD master tree tree tree blob blob .

    `-lib |-README `-example |-source | `-impl.rb `-example.rb Donnerstag, 21. Juni 12

26. blob commit HEAD master tree tree tree blob blob .

    `-lib |-README `-example |-source | `-impl.rb `-example.rb Donnerstag, 21. Juni 12

27. blob commit HEAD master tree tree tree blob blob .

    `-lib |-README `-example |-source | `-impl.rb `-example.rb Donnerstag, 21. Juni 12

28. blob commit HEAD master tree tree tree blob blob .

    `-lib |-README `-example |-source | `-impl.rb `-example.rb Donnerstag, 21. Juni 12

29. blob commit HEAD master tree tree tree blob blob .

    `-lib |-README `-example |-source | `-impl.rb `-example.rb Donnerstag, 21. Juni 12

30. blob commit HEAD master tree tree tree blob blob .

    `-lib |-README `-example |-source | `-impl.rb `-example.rb $> modify impl.rb ..... $> git commit -a Donnerstag, 21. Juni 12

31. blob commit HEAD master tree tree tree blob blob commit

    tree tree tree blob . `-lib |-README `-example |-source | `-impl.rb `-example.rb Donnerstag, 21. Juni 12

32. blob commit HEAD master tree tree tree blob blob commit

    tree tree tree blob . `-lib |-README `-example |-source | `-impl.rb `-example.rb Donnerstag, 21. Juni 12

33. blob commit HEAD master tree tree tree blob blob commit

    tree tree tree blob . `-lib |-README `-example |-source | `-impl.rb `-example.rb Donnerstag, 21. Juni 12

34. blob commit HEAD master tree tree tree blob blob commit

    tree tree tree blob . `-lib |-README `-example |-source | `-impl.rb `-example.rb Donnerstag, 21. Juni 12

35. blob commit HEAD master tree tree tree blob blob commit

    tree tree tree blob . `-lib |-README `-example |-source | `-impl.rb `-example.rb $> modify README ... $> git commit -a Donnerstag, 21. Juni 12

36. . `-lib |-README `-example |-source | `-impl.rb `-example.rb blob commit

    tree tree tree blob blob commit tree tree tree blob HEAD master tree blob commit Donnerstag, 21. Juni 12

37. . `-lib |-README `-example |-source | `-impl.rb `-example.rb blob commit

    tree tree tree blob blob commit tree tree tree blob HEAD master tree blob commit Donnerstag, 21. Juni 12

38. Branching creating a new branch is simply writing a file

    in the .git/ refs/heads with the SHA-1 of the last commit for that branch ➡ Creating a branch is nothing more than just writing 40 characters to a file. DEMO Donnerstag, 21. Juni 12

39. Branching and Merging The Flow of merging branches Donnerstag, 21.

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40. C1 HEAD master C0 Donnerstag, 21. Juni 12

41. C1 HEAD master C0 $> git checkout -b feature Donnerstag,

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42. C1 HEAD master C0 feature Donnerstag, 21. Juni 12

43. C1 HEAD master C0 feature $> write some code ...

    $> git commit -a $> write more code ... $> git commit -a Donnerstag, 21. Juni 12

44. C1 HEAD master C0 feature C2 C3 Donnerstag, 21. Juni

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45. C1 HEAD master C0 feature C2 C3 HOTFIX ALERT Donnerstag,

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46. $> git checkout master $> fixing ... $> git commit

    -a $> git tag t1 C1 HEAD master C0 feature C2 C3 HOTFIX ALERT Donnerstag, 21. Juni 12

47. C1 HEAD master C0 feature C2 C3 C4 t1 Donnerstag,

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48. $> git checkout feature $> coding ... $> git commit

    -a C1 HEAD master C0 feature C2 C3 C4 t1 Donnerstag, 21. Juni 12

49. C1 HEAD master C0 feature C2 C3 C4 t1 C5

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50. $> git checkout master $> git merge feature C1 HEAD

    master C0 feature C2 C3 C4 t1 C5 Donnerstag, 21. Juni 12

51. C1 HEAD master C0 feature C2 C3 C4 t1 C5

    C6 Donnerstag, 21. Juni 12

52. C1 HEAD master C0 feature Donnerstag, 21. Juni 12

53. C1 HEAD master C0 feature $> write some code ...

    $> git commit -a $> write more code ... $> git commit -a $> write more code ... $> git commit -a Donnerstag, 21. Juni 12

54. C1 HEAD master C0 feature C2 C3 C4 Donnerstag, 21.

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55. $> git checkout master $> git merge feature C1 HEAD

    master C0 feature C2 C3 C4 Donnerstag, 21. Juni 12

56. C1 HEAD master C0 feature C2 C3 C4 Donnerstag, 21.

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57. C1 HEAD master C0 feature C2 C3 C4 fast-forward Donnerstag,

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58. Remotes Remotes are pointers to branches in other peoples copies

    of the same repository often just one, named origin the master from the origin ist referenced by origin/master Donnerstag, 21. Juni 12

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60. $> git clone <some-repo> C0 master origin/master Donnerstag, 21. Juni

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61. C0 master origin/master Donnerstag, 21. Juni 12

62. C0 master origin/master $> coding ... $> git commit -a

    $> coding ... $> git commit -a Donnerstag, 21. Juni 12

63. C1 C0 C2 master origin/master Donnerstag, 21. Juni 12

64. C1 C0 C2 master origin/master $> git fetch Donnerstag, 21.

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65. C1 C0 C2 master origin/master CR1 CR3 CR4 CR2 origin/idea

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66. C1 C0 C2 master origin/master $> git checkout -b tryidea

    $> git merge origin/master --no-commit $> git merge origin/idea --no-commit $> git commit -a CR1 CR3 CR4 CR2 origin/idea Donnerstag, 21. Juni 12

67. C1 C0 C2 master origin/master CR1 CR3 CR4 CR2 origin/idea

    C3 tryidea Donnerstag, 21. Juni 12

68. C1 C0 C2 master origin/master CR1 CR3 CR4 CR2 origin/idea

    C3 tryidea $> git checkout master $> git merge tryidea $> git push orgin master Donnerstag, 21. Juni 12

69. C1 C0 C2 master origin/master CR1 CR3 CR4 CR2 origin/idea

    C3 Donnerstag, 21. Juni 12

70. Rebasing What is rebasing? Donnerstag, 21. Juni 12

71. C1 john/master master C0 R1 Donnerstag, 21. Juni 12

72. C1 john/master master C0 R1 $> git pull john master

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73. C1 john/master master C0 R1 C2 Donnerstag, 21. Juni 12

74. C1 john/master master C0 R1 $john> code ... commit $you>

    code ... commit $you> git pull john master C2 Donnerstag, 21. Juni 12

75. C1 john/master master C0 R1 C2 R2 C3 C4 Donnerstag,

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76. C1 john/master master C0 R1 C2 R2 C3 C4 Merge

    Commits Donnerstag, 21. Juni 12

77. C1 john/master master C0 R1 C2 R2 C3 C4 Merge

    Commits lets try the same scenario with rebasing Donnerstag, 21. Juni 12

78. C1 john/master master C0 R1 Donnerstag, 21. Juni 12

79. C1 john/master master C0 R1 $> git rebase john/master Donnerstag,

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80. C1 john/master master C0 R1 C2 C0:C1 Donnerstag, 21. Juni

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81. C1 john/master master C0 R1 C2 C0:C1 $john> code ...

    commit $you> code ... commit Donnerstag, 21. Juni 12

82. C1 john/master master C0 R1 C3 R2 C2 Donnerstag, 21.

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83. C1 john/master master C0 R1 C3 $> git rebase john/master

    R2 C2 Donnerstag, 21. Juni 12

84. C1 john/master C0 R1 R1:C2 R2 C2 master C5 C4

    C3 C2:C3 Donnerstag, 21. Juni 12

85. C1 john/master master C0 R1 C4 R2 C2 C1 john/master

    master C0 R1 C2 R2 C3 C4 fetch and merge rebase C5 C3 Donnerstag, 21. Juni 12

86. rebase instead of merge normally a pull is a fetch

    and a merge you can change it to be a fetch and a rebase git config branch.autosetuprebase always/never/local/ remote or you can call git pull --rebase Donnerstag, 21. Juni 12

87. Credits heavily based on Git Internals PDF by Scott Chacon

    from PeepCode (https:// peepcode.com/products/git-internals-pdf) and some own experience Donnerstag, 21. Juni 12

88. About Me Andi Bade – Galaxy Cats IT Consulting GmbH

    Twitter: @railsbros_andi Blog: thyphoon.github.com Mail: [email protected] Donnerstag, 21. Juni 12