Git - simple overview and architecture

Why Git is distributed? How the internals of Git works? Also a lot on Octocats :)

Transcript

1. Git- architecture The distributed source control management system Dulitha Wijewantha (Chan)
2. Why you know git?
4. What is Git? Distributed version control system What does that mean?
5. You get your own repo in your machine
6. Different from SVN 1. No VC server 2. All VC commands are local 3. Can have multiple remote repositories
7. NO Master Repo
8. In Details • .git directory • Git objects • Git index • Git branch • Git merge • Git rebase • Git refes • few advance stuff
9. .git directory • Used to hold everything regarding git • This folder is only present in the root of the repository • If you delete the .git folder - repository is deleted • Running a git commands affects the .git folder
10. How to create or obtain a Git Repo?
11. Clone Make git clone git@github.com: dulichan/product-emm.git git init
12. Git objects • blob • tree • commit • tag
13. blob • Bunch of bytes (source code, images, pdf etc) • A hash is generated per blob • A blob can be accessed using the hash
14. Helpful commands • git hash-object - used to add file to git datastore • git cat-file - used to view files in git using hash • git ls-files - used to view tree object
15. tree • represents a file system/ directory • links blobs and other trees • A hash is generated for tree • A tree can be viewed using the hash
16. Where does blobs and trees lie?
18. $ git cat-file -p master^{tree} 100644 blob a906cb2a4a904a152e80877d4088654daad0c859 README 100644 blob 8f94139338f9404f26296befa88755fc2598c289 Rakefile 040000 tree 99f1a6d12cb4b6f19c8655fca46c3ecf317074e0 lib
19. Time to Commit
20. commit • contains info of committer (username & email) • contains the hash of the tree object that represented the state of commit
21. • contains parent commit hash • contains a comment • a commit object is created from the index commit cont.
22. $ git cat-file -p d209165 tree 3ea4b675af6c7c1b8c398ab53a8a4d88c574610d parent 40063bbade778a59e2181a5f35493a080bfa7d66 author Nira <niranjan.karu@gmail.com> 1396417540 +0530 committer Nira <niranjan.karu@gmail.com> 1396417540 +0530 Modified driver.js
23. tags • used to name commit objects • contains name of tag • contains commit hash • contains a tag message
24. How to tag code? git tag -a v1.0 -m 'First Version'
25. git add
26. Git index • A staging area to add changes • Before committing - you have to place changes to the index
27. Git index cont. • content is stored temporarily in a binary file - .git/index • can be used to add partial parts of a file
29. It’s complicated. How do we find status? git status
30. Let’s checkout!
31. Checking out code • Checkout to working directory • Checkout branches, tags, commits, remotes • Checkout to commit to new branch
32. Now where? • .git directory • Git objects • Git index • Git branch • Git merge • Git rebase • Git refes • few advance stuff
33. Let’s branch
34. Branches • Default branch is master • branching makes a pointer to a commit • current branch = HEAD
36. Branches cont. git branch branch_name git checkout branch_name • branch is created making the current branch the parent
37. Branches cont. • located at .git/refs/heads • the filename is the name of the branch and file contains the hash of the most recent commit object
38. Branches cont. • Inexpensive to create since it’s a file creation locally • Branching strategies are there to simplify git branching workflows
39. It gets dirty!
40. git merge
41. Merging • one branch gets merged to another • Git will try it’s best to merge safely • flags to override behavior
42. Merging cont. git merge hotfix • merging can happen for branches • merge specified branch to current branch
43. Merging • In doubt Git will throw errors :) and make conflicts • When conflicts happen working directory is not safe to be commited.
44. don’t panic if you see this $ git merge abc Auto-merging index.html CONFLICT (content): Merge conflict in index.html Automatic merge failed; fix conflicts and then commit the result.
45. Git is your friend
46. Merge conflict resolution • git status to figure out what files have conflicts • Open up the files that has the conflict and navigate to the area that has <<<<<<< HEAD
47. <<<<<<< HEAD <div id="footer">contact : email.support@github.com</div> ======= <div id="footer"> please contact us at support@github.com </div> >>>>>>> iss53
48. Merge conflict resolution cont. • commit changes after resolving • commit message is included by default • Now the git commit objects will point to a git tree that has the resolved changes
49. Rebase
50. Rebasing • an option to base changes from a different branch. • Commits in one branch can be applied to another branch • Rebasing allows a linear commit history
51. Git rebase
52. Where is DVCS?
53. Refs and Remotes • online repo is called remote • local repo can have multiple remotes • found in .git/refs/remotes/ • local repo has all commits of all remotes
54. Refs and Remotes cont. git push origin master git pull origin master • set of commands present to work with remotes git fetch
55. Refs and Remotes cont. • how remotes, remote branches, local branches interact is called refspace. • refspace can be customized • refs are in .git/config file
56. Example :- .git/config [remote "dev"] url = git@github.com:wso2-dev/product-emm.git fetch = +refs/heads/*:refs/remotes/dev/* [branch "master"] remote = dev merge = refs/heads/master [remote "official"] url = git@github.com:wso2/product-emm.git fetch = +refs/heads/*:refs/remotes/official/* [remote "own"] url = git@github.com:dulichan/product-emm.git fetch = +refs/heads/*:refs/remotes/own/*
57. You are the central
58. Packfiles • Git packs blobs with zlib - upto 60% compression for text • Git stores data in git objects - blobs, trees, commits, tags • When storing blobs - previous data is intact and a new object is created if the content changes. ◦ Eg:- 14K file example • To be efficient Git packs the data in deltas. Git does this management automatically • To manually manage repacking - git gc
59. git gc
60. Credits • All the Octocats belong to Github <3 • Diagrams are from Git documentation
61. Thank You