Git Internals

Git Internals Keynote for @colognerb

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
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4. Git = Subversion + Magic Donnerstag, 21. Juni 12
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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, 21. Juni 12
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 Donnerstag, 21. Juni 12
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. Juni 12
40. C1 HEAD master C0 Donnerstag, 21. Juni 12
41. C1 HEAD master C0 $> git checkout -b feature Donnerstag, 21. Juni 12
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 12
45. C1 HEAD master C0 feature C2 C3 HOTFIX ALERT Donnerstag, 21. Juni 12
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, 21. Juni 12
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 Donnerstag, 21. Juni 12
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. Juni 12
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. Juni 12
57. C1 HEAD master C0 feature C2 C3 C4 fast-forward Donnerstag, 21. Juni 12
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 12
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. Juni 12
65. C1 C0 C2 master origin/master CR1 CR3 CR4 CR2 origin/idea Donnerstag, 21. Juni 12
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 Donnerstag, 21. Juni 12
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, 21. Juni 12
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, 21. Juni 12
80. C1 john/master master C0 R1 C2 C0:C1 Donnerstag, 21. Juni 12
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. Juni 12
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: andi@galaxycats.com Donnerstag, 21. Juni 12