Git Internals and Git Rebasing

Git Objects & Refs
Git Rebasing - good practices

Transcript

1. git
2. • HEAD • config • description • hooks/ • index • info/ • objects/ • refs/
3. • HEAD • config • description • hooks/ • index • info/ • objects/ • refs/
4. Core parts • HEAD • index • objects/ • refs/
5. content-addressable fs
6. • git init • find .git/objects • find .git/objects -type f
7. hash-object • 40 character checksum SHA-1 hash • directory(2) + filename(38) • git hash-object ./file • echo “foo” | git hash-object -w —stdin
 # fetch input from stdin; write hash to git db • find .git/objects -type f
8. cat-file • git cat-file -p 8315faa98d6663204f4ca3b00526c530fd9e2bb4 • echo “test 1” > test • git hash-object -w test • echo “test 2” > test • git hash-object -w test • # restores “test 1”
 git cat-file -p 6f670c0fb53f9463760b7295fbb814e965fb20c8 > test
9. Tree Object • Git stores everything as blobs and trees • Trees => (UNIX directories) • Blobs => (inodes / file_contents)
10. • git update-index --add --cacheinfo 100644 <hash> test • git write-tree • git cat-file -p <hash>
11. Commit Objects • echo “commit message” | git commit- tree <hash> • echo “second message” | git commit- tree <hash> -p <prev_hash> • git log —stat <latest_hash>
12. This is what happens underneath during git-add & git-commit ? • Stores the blob for the files that have changed • Updates the index • Writes out trees • Writes commit objects (referencing top-level trees and commits that came immediately before them) • Updates Refs (upcoming slide)
13. hands on
14. Refs • .git/refs/heads/ • .git/regs/tags/ • git update-ref refs/heads/master <hash> • .git/HEAD => refs/heads/master • git update-ref refs/tags/v1.0 <hash> • cat .git/refs/remotes/origin/master
15. Recap • Git objects: • Blob • Tree • Commit • Tag
16. Recap • hash-object • cat-file • write-tree • update-index • read-tree • commit-tree • update-ref
17. Rebase
18. A-B-C (master) \ D (feat1)
19. A-B-C-E-F (master) \ D-G (feat1) Add some commits
20. A-B-C-E-F-H (master) \ / D-G (feat1) Merge feat1 to master git checkout master git merge feat1
21. A-B-C-E-F (master) \ D*-G*( (feat1) Rebase feat1 to master git checkout feat1 git rebase master
22. Rebase • Rebase is for maintaining a linear project history.
23. A-B-C-E-F (master) \ D-G (dev) \ H-I (feat1) One more branch & few more commits
24. What do we want?
25. • Import all commits so our development branch stays updated. • from `master` into `dev` and `feat1` branches • from `dev` into `feat1` • Preserve all commits of feature branch; merge it to development branch once it’s completed.
26. A-B-C-E-F (master) \ D-G (dev) \ H-I (feat1) From this
27. A-B-C-E-F (master) \ D-G (dev) \ H-I (feat1) We want this
28. git checkout master git branch --contains dev | xargs -n1 \ git rebase \ --committer-date-is-author-date \ --preserve-merges \ --onto master dev^
29. Now it’s safe to merge
30. A-B-C-E-F (master) \ D-G————K (dev) \ / H-I (feat1) merge feat1 to dev git checkout dev git merge --no-ff feat1 --no-ff ensures that a merge commit is created
31. Other Gotchas • When to rebase ? • When to merge ? • Always git pull with rebase • squash commits before pushing • Keep the number of commits as minimum as possible. • Add tags everywhere for all feature merges
32. Thank you Boopathi Rajaa boopathi.rajaa@flipkart.com