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Deep dark-side of git: How git works internally

The document provides an overview of how Git, a distributed version control system created by Linus Torvalds, operates internally. It explains key concepts such as the content-addressable storage system, the roles of blobs, trees, and commits, and the efficient handling of version history using SHA-1 hashes. The text also highlights Git's strengths, challenges for new users, and the importance of commit messages for tracking changes.

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How GIT Works Internally SeongJae Park <sj38.park@gmail.com>
Nice To Meet You SeongJae Park sj38.park@gmail.com
Git DVCS(Distributed Version Control System) http://git-scm.com/images/logos/downloads/Git-Logo-2Color.png
Git DVCS(Distributed Version Control System) Made-by Linus Torvalds For Linux http://git-scm.com/images/logos/downloads/Git-Logo-2Color.png http://cdn.memegenerator.net/instances/400x/37078331.jpg
Git Many Projects Use Git Because It’s Awesome http://blog.appliedis.com/wp-content/uploads/2013/11/android1.png http://upload.wikimedia.org/wikipedia/en/4/40/Octocat,_a_Mascot_of_Github.jpg http://upload.wikimedia.org/wikipedia/commons/thumb/3/35/Tux.svg/512px-Tux.svg.png http://git-scm.com/images/logos/downloads/Git-Logo-2Color.png
Git Hard To Learn Confusing For CVCS Users Push? Pull? Fetch? Rebase? HEAD??? http://www.quickmeme.com/img/fd/fd09e17b3393b2ea1cd7e52af1ad7c77f3c2d7a83e9f47d4b90ba3af52dde329.jpg http://git-scm.com/images/logos/downloads/Git-Logo-2Color.png
Git: The Information Manager From Hell http://www.youblob.com/sites/default/files/styles/large/public/field/image/frontlego1.png?itok=XA5CXt84
Git: The Information Manager From Hell $ git log e83c516 commit e83c5163316f89bfbde7d9ab23ca2e25604af290 Author: Linus Torvalds <torvalds@ppc970.osdl.org> Date: Thu Apr 7 15:13:13 2005 -0700 Initial revision of "git", the information manager from hell http://www.youblob.com/sites/default/files/styles/large/public/field/image/frontlego1.png?itok=XA5CXt84
Git: The Information Manager From Hell That’s Why So Confusing And Hard To Learn $ git log e83c516 commit e83c5163316f89bfbde7d9ab23ca2e25604af290 Author: Linus Torvalds <torvalds@ppc970.osdl.org> Date: Thu Apr 7 15:13:13 2005 -0700 Initial revision of "git", the information manager from hell http://www.youblob.com/sites/default/files/styles/large/public/field/image/frontlego1.png?itok=XA5CXt84
This Time, We Will... See How Git Works From The Scratch https://lh4.googleusercontent.com/gBpfuABUjSNi2RagtJrGi8TW-pmtgak_0qtGOGubihvKH-5-umreO9C wJgjX2kaA9E7RkLwtEwiDnoMtOgm4iMJ0IWhvXlzlKL1kNVUYWuNa-gLRtRoyNjkVYg
This Time, We Will... See How Git Works From The Scratch Just For Fun ...Or To Be Friend Of Git https://lh4.googleusercontent.com/gBpfuABUjSNi2RagtJrGi8TW-pmtgak_0qtGOGubihvKH-5-umreO9C wJgjX2kaA9E7RkLwtEwiDnoMtOgm4iMJ0IWhvXlzlKL1kNVUYWuNa-gLRtRoyNjkVYg
This Time, We Will... See How Git Works From The Scratch Just For Fun ...Or To Be Friend Of Git Forget About The Complicated Commands This Time https://lh4.googleusercontent.com/gBpfuABUjSNi2RagtJrGi8TW-pmtgak_0qtGOGubihvKH-5-umreO9C wJgjX2kaA9E7RkLwtEwiDnoMtOgm4iMJ0IWhvXlzlKL1kNVUYWuNa-gLRtRoyNjkVYg
In Short, Git Is A Content-Addressable Storage System http://www.juliagiff.com/wp-content/uploads/2014/03/tld r_trollcat.jpg
In Short, Git Is A Content-Addressable Storage System Blob, Tree, Commit, Reference. That’s It =3 http://www.juliagiff.com/wp-content/uploads/2014/03/tld r_trollcat.jpg
Plumbers: Unsung Heroes Behind ● Git Looks Graceful Owing To Plumbing Commands Consisting Them http://cfile4.uf.tistory.com/image/182FF7244CFDDFB33CC999 http://cfile29.uf.tistory.com/image/18574F224CFDD89B163073
Plumbers: Unsung Heroes Behind ● Git Looks Graceful Owing To Plumbing Commands Consisting Them ○ The Wounded Foots Are What We Interested In http://cfile4.uf.tistory.com/image/182FF7244CFDDFB33CC999 http://cfile29.uf.tistory.com/image/18574F224CFDD89B163073
Again, From The Scratch VCS? Why? How?
Why VCS? Usual Life Of File FileA ver 0 FileB ver 0
Why VCS? Usual Life Of File FileA ver 0 FileB ver 1FileB ver 0
Why VCS? Usual Life Of File FileA ver 0 FileB ver 1
Why VCS? Usual Life Of File FileB ver 1 FileA ver 1FileA ver 0
Why VCS? Usual Life Of File FileB ver 1 FileA ver 1
Why VCS? Usual Life Of File FileB ver 2FileA ver 1FileB ver 1
Why VCS? Usual Life Of File FileB ver 2FileA ver 1
Why VCS? Usual Life Of File FileB ver 2FileA ver 1
We Need Version Control System VCS Would... Record Every Changes Safely, Efficiently
We Need Version Control System VCS Would... Record Every Changes Safely, Efficiently Able To Check Out Any Version
We Need Version Control System VCS Would... Record Every Changes Safely, Efficiently Able To Check Out Any Version Easy To Read History
Brute-force Idea Version Control Using File System
Brute-force Idea Rename / Backup Every Files Whenever Change Made
Brute-force Idea Rename / Backup Every Files Whenever Change Made $ ls foo.c
Brute-force Idea Rename / Backup Every Files Whenever Change Made $ ls foo.c foo_20140111.c
Brute-force Idea Rename / Backup Every Files Whenever Change Made $ ls foo.c foo_20140111.c foo_final.c
Brute-force Idea Rename / Backup Every Files Whenever Change Made $ ls foo.c foo_20140111.c foo_final.c foo_realfinal.c foo_planb.c foo_finalfinal.c
Brute-force Idea Rename / Backup Every Files Whenever Change Made $ ls foo.c foo_20140111.c foo_final.c foo_realfinal.c foo_planb.c foo_finalfinal.c
Brute-force Idea + History Isolation Keep Working / History Directory Seperately.
Brute-force Idea + History Isolation Keep Working / History Directory Seperately. Better, But... $ find . -type f ./working/foo.c ./history/foo_20140111.c ./history/foo_final.c ./history/foo_realfinal.c ./history/foo_planb.c ./history/foo_finalfinal.c
TODOs From Version Control Using FS Use Storage Space-Efficiently
TODOs From Version Control Using FS Use Storage Space-Efficiently Easy History Searching
Mission #1: Store History Space-Efficiently
Basic Idea: Avoid Duplicated Objects
Basic Idea: Avoid Duplicated Objects Content-Addressable Storage System
Basic Idea: Avoid Duplicated Objects Content-Addressable Storage System Key: SHA-1 Hash Of Object’s Content Value: Compressed Content
Basic Idea: Avoid Duplicated Objects Content-Addressable Storage System Key: SHA-1 Hash Of Object’s Content Value: Compressed Content Same Content Never Saved Twice
Save / Load ‘homer’ $ mkdir simpsons; cd simpsons; git init Initialized empty Git repository in simpsons/.git/ $ echo ‘homer’ | git hash-object -w --stdin 4aa0bfa07f1680c50a1567ecc37bc3b6aa567b8f $
Save / Load ‘homer’ $ mkdir simpsons; cd simpsons; git init Initialized empty Git repository in simpsons/.git/ $ echo ‘homer’ | git hash-object -w --stdin 4aa0bfa07f1680c50a1567ecc37bc3b6aa567b8f $ find .git/objects/ -type f .git/objects/4a/a0bfa07f1680c50a1567ecc37bc3b6aa567b8f $
Save / Load ‘homer’ $ mkdir simpsons; cd simpsons; git init Initialized empty Git repository in simpsons/.git/ $ echo ‘homer’ | git hash-object -w --stdin 4aa0bfa07f1680c50a1567ecc37bc3b6aa567b8f $ find .git/objects/ -type f .git/objects/4a/a0bfa07f1680c50a1567ecc37bc3b6aa567b8f $ git cat-file -p 4aa0b homer $ git cat-file -t 4aa0b blob
What `hash-object -w` did hash_object_w(‘homern’)
What `hash-object -w` did hash_object_w(‘homern’) # Save compressed header + content at sha1 path def hash_object_w(content): header = ‘blob %d0’ % len(content) store = header + content sha1 = sha.new(store).hexdigest()
What `hash-object -w` did hash_object_w(‘homern’) # Save compressed header + content at sha1 path def hash_object_w(content): header = ‘blob %d0’ % len(content) store = header + content sha1 = sha.new(store).hexdigest() dir = ‘.git/objects/’ + sha1[0:2] + ‘/’ filename = sha1[2:]
What `hash-object -w` did hash_object_w(‘homern’) # Save compressed header + content at sha1 path def hash_object_w(content): header = ‘blob %d0’ % len(content) store = header + content sha1 = sha.new(store).hexdigest() dir = ‘.git/objects/’ + sha1[0:2] + ‘/’ filename = sha1[2:] open(dir + filename, ‘w’).write( zlib.compress(store))
Version Control Using Hash Value $ echo “bart” > son $ git hash-object -w son e00ddae83bdab443f4267426623aa34636c935f2 $
Version Control Using Hash Value $ echo “bart” > son $ git hash-object -w son e00ddae83bdab443f4267426623aa34636c935f2 $ echo “hugo” > son $ git hash-object -w son 8e1e2f09585e021c9727585af72e10871d7be7ce $
Version Control Using Hash Value $ echo “bart” > son $ git hash-object -w son e00ddae83bdab443f4267426623aa34636c935f2 $ echo “hugo” > son $ git hash-object -w son 8e1e2f09585e021c9727585af72e10871d7be7ce $ # Need former version, “bart” $ git cat-file -p e00dd > son $ cat son bart
TODOs From Version Control Using FS Use Storage Space-Efficiently Easy History Searching
Version Control Using Hash Value ● DONE ○ Efficient Space Usage ○ Safe Record / Checkout Of History https://www.sciencenews.org/sites/default/files/main/articles/sad_opener.jpg
Version Control Using Hash Value ● DONE ○ Efficient Space Usage ○ Safe Record / Checkout Of History ● TODO ○ Support Directory Structure ○ History Management ○ Better Reference Than Hash Value https://www.sciencenews.org/sites/default/files/main/articles/sad_opener.jpg
WAIT! Q: What If Small Changes Inside A Big File?
WAIT! Q: What If Small Changes Inside A Big File? $ du -h bigfile.c 188Kbigfile.c $ du -sh 408K. $ echo ‘/* small change */’ >> bigfile.c $ git commit -as -m “small change, big difference” $ du -sh 496K. $
WAIT! Q: What If Small Change Inside A Big File? A: Git Pick up Diff-Only If Necessary But, Don’t Forget To Keep It Small, Simple $ du -sh 496K. $ git gc Counting objects: 6, done. Delta compression using up to 4 threads. Compressing objects: 100% (4/4), done. Writing objects: 100% (6/6), done. Total 6 (delta 1), reused 0 (delta 0) $ du -sh 388K.
Mission #2: Store History Of Directories
tree Object Point Other Objects(Using Hash) With Name
tree Object Point Other Objects(Using Hash) With Name tree blob blob tree blob a113f2 mommy b8934 son c9240 pets d9b13 cat
tree Object Point Other Objects(Using Hash) With Name “A Root tree Object Is A Snapshot” tree blob blob tree blob a113f2 mommy b8934 son c9240 pets d9b13 cat I’m a snapshot
tree object $ mkdir pets; echo ‘snowball’ > pets/cat $ git update-index --add son pets/cat $ git write-tree 15ee76ed3e744b6796950d07f26283d033ea3ea7 $
tree object $ mkdir pets; echo ‘snowball’ > pets/cat $ git update-index --add son pets/cat $ git write-tree 15ee76ed3e744b6796950d07f26283d033ea3ea7 $ git cat-file -p 15ee7 040000 tree 85ab72cf1946dc56392718a1aafb3c6f66c02072 pets 100644 blob 8e1e2f09585e021c9727585af72e10871d7be7ce son $
tree object $ mkdir pets; echo ‘snowball’ > pets/cat $ git update-index --add son pets/cat $ git write-tree 15ee76ed3e744b6796950d07f26283d033ea3ea7 $ git cat-file -p 15ee7 040000 tree 85ab72cf1946dc56392718a1aafb3c6f66c02072 pets 100644 blob 8e1e2f09585e021c9727585af72e10871d7be7ce son $ git cat-file -p 85ab7 100644 blob 6a1f952e1baedcb3db93a3ea5e3389e5a87941e9 cat $ git cat-file -p 6a1f9 snowball $
Internal Data Structure tree blob tree 8e1e2 son 85ab7 pets
Internal Data Structure tree blob tree blob 6a1f9 cat 8e1e2 son 85ab7 pets
Version Control Using tree Object $ echo “bart” > son $ git update-index --add son $ git write-tree 661e6ad514a7f05c46c2931280cb78a339d34ee2 $
Version Control Using tree Object $ echo “bart” > son $ git update-index --add son $ git write-tree 661e6ad514a7f05c46c2931280cb78a339d34ee2 $ git cat-file -p 661e6 040000 tree 85ab72cf1946dc56392718a1aafb3c6f66c02072 pets 100644 blob e00ddae83bdab443f4267426623aa34636c935f2 son $
Version Control Using tree Object $ echo “bart” > son $ git update-index --add son $ git write-tree 661e6ad514a7f05c46c2931280cb78a339d34ee2 $ git cat-file -p 661e6 040000 tree 85ab72cf1946dc56392718a1aafb3c6f66c02072 pets 100644 blob e00ddae83bdab443f4267426623aa34636c935f2 son $ git cat-file -p e00dd bart $
Internal Data Structure tree blob tree blob 8e1e2 son 85ab7 pets 6a1f9 cat
Internal Data Structure tree blob tree blob tree blob e00dd son85ab7 pets 8e1e2 son 85ab7 pets 6a1f9 cat
Version Control Using Hash Value ● DONE ○ Efficient Space Usage ○ Safe Record / Checkout Of History ● TODO ○ Support Directory Structure ○ History Management ○ Better Reference Than Hash Value https://www.sciencenews.org/sites/default/files/main/articles/sad_opener.jpg
Version Control Using tree Object ● DONE ○ Efficient Space Usage ○ Safe Record / Checkout Of History ○ Support Directory Structure ● TODO ○ History Management ○ Better Reference Than Hash Value https://www.sciencenews.org/sites/default/files/main/articles/sad_opener.jpg
Mission #3: Commit Message
commit Object Describe Who / When / Why The Change Made http://modthink.com/wp-content/uploads/2013/05/WhoWhatWhenWhereWHY.jpg
commit Object Describe Who / When / Why The Change Made Point A tree Object With Information Above http://modthink.com/wp-content/uploads/2013/05/WhoWhatWhenWhereWHY.jpg
commit Object $ echo '1st commit' | git commit-tree 661e6 0ca7304ad6f5a40f8a26ba05b10b514ff2d8d8a0 $
commit Object $ echo '1st commit' | git commit-tree 661e6 0ca7304ad6f5a40f8a26ba05b10b514ff2d8d8a0 $ $ git cat-file -p d075c tree 661e6ad514a7f05c46c2931280cb78a339d34ee2 author SeongJae Park <s**@gmail.com> 1410527921 +0900 committer SeongJae Park <s**@gmail.com> 1410527921 +0900 1st commit $
commit Object $ echo '1st commit' | git commit-tree 661e6 0ca7304ad6f5a40f8a26ba05b10b514ff2d8d8a0 $ $ git cat-file -p d075c tree 661e6ad514a7f05c46c2931280cb78a339d34ee2 author SeongJae Park <s**@gmail.com> 1410527921 +0900 committer SeongJae Park <s**@gmail.com> 1410527921 +0900 1st commit $ Who When Why
Version Control Using commit Object $ echo '2nd commit' | git commit-tree 15ee7 -p 0ca73 003b5e66caa89a6228c7b4d91e0475e56bf1bdf6 $ $ git cat-file -p 003b5 tree 15ee76ed3e744b6796950d07f26283d033ea3ea7 parent 0ca7304ad6f5a40f8a26ba05b10b514ff2d8d8a0 author SeongJae Park <s**@gmail.com> 1410528231 +0900 committer SeongJae Park <s**@gmail.com> 1410528231 +0900 2nd commit $
Internal Data Structure That’s Why People Says, “A Commit is a snapshot” tree blob tree blob tree blob commit commit tree parent tree 85ab7 pets 8e1e2 son 85ab7 pets 6a1f9 cat e00dd son
Version Control Using tree Object ● DONE ○ Efficient Space Usage ○ Safe Record / Checkout Of History ○ Support Directory Structure ● TODO ○ History Management ○ Better Reference Than Hash Value https://www.sciencenews.org/sites/default/files/main/articles/sad_opener.jpg
Version Control Using commit Object ● DONE ○ Efficient Space Usage ○ Safe Record / Checkout Of History ○ Support Directory Structure ○ Manage History Well ● TODO ○ Better Reference Than Hash Value https://www.sciencenews.org/sites/default/files/main/articles/sad_opener.jpg
Mission #4: Human Readable Name
Git References File With Human-Readable Name
Git References File With Human-Readable Name Storing SHA-1 Value Of commit Object
Git References File With Human-Readable Name Storing SHA-1 Value Of commit Object Resides In .git/refs/
Git References Using echo $ echo "0ca7304ad6f5a40f8a26ba05b10b514ff2d8d8a0" > .git/refs/heads/first $
Git References Using echo $ echo "0ca7304ad6f5a40f8a26ba05b10b514ff2d8d8a0" > .git/refs/heads/first $ $ git log --pretty=oneline first 0ca7304ad6f5a40f8a26ba05b10b514ff2d8d8a0 1st commit $
Git References Using echo $ echo "0ca7304ad6f5a40f8a26ba05b10b514ff2d8d8a0" > .git/refs/heads/first $ $ git log --pretty=oneline first 0ca7304ad6f5a40f8a26ba05b10b514ff2d8d8a0 1st commit $ $ find .git/refs/heads -type f .git/refs/heads/first .git/refs/heads/master $
Git References Using update-ref $ git update-ref refs/heads/master 003b5 $ git log --pretty=oneline master 003b5e66caa89a6228c7b4d91e0475e56bf1bdf6 2nd commit 0ca7304ad6f5a40f8a26ba05b10b514ff2d8d8a0 1st commit $
Git References Using update-ref $ git update-ref refs/heads/master 003b5 $ git log --pretty=oneline master 003b5e66caa89a6228c7b4d91e0475e56bf1bdf6 2nd commit 0ca7304ad6f5a40f8a26ba05b10b514ff2d8d8a0 1st commit $ $ find .git/refs/heads -type f .git/refs/heads/first .git/refs/heads/master $
Git References Using update-ref $ git update-ref refs/heads/master 003b5 $ git log --pretty=oneline master 003b5e66caa89a6228c7b4d91e0475e56bf1bdf6 2nd commit 0ca7304ad6f5a40f8a26ba05b10b514ff2d8d8a0 1st commit $ $ find .git/refs/heads -type f .git/refs/heads/first .git/refs/heads/master $ $ cat .git/refs/heads/master 003b5e66caa89a6228c7b4d91e0475e56bf1bdf6
Internal Data Structure tree blob tree blob tree blob commit commit tree parent tree 85ab7 pets 8e1e2 son 85ab7 pets e00dd son 6a1f9 cat
Internal Data Structure tree blob tree blob tree blob commit commit tree parent tree refs/heads/ master refs/heads/ first 85ab7 pets 8e1e2 son 85ab7 pets e00dd son 6a1f9 cat
Version Control Using commit Object ● DONE ○ Efficient Space Usage ○ Safe Record / Checkout Of History ○ Support Directory Structure ○ Manage History Well ● TODO ○ Better Reference Than Hash Value https://www.sciencenews.org/sites/default/files/main/articles/sad_opener.jpg
Version Control Using Reference ● DONE ○ Efficient Space Usage ○ Safe Record / Checkout Of History ○ Support Directory Structure ○ Manage History Well ○ Easy To Remember Specific Snapshot ● TODO ○ ...cooperation? https://www.sciencenews.org/sites/default/files/main/articles/sad_opener.jpg
FAQ #1 How Git Make-up Working Directory?
How Git Knows Current Commit? Answer: HEAD
How Git Knows Current Commit? Answer: HEAD HEAD Points reference Using ref format(Not SHA-1)
How Git Knows Current Commit? Answer: HEAD HEAD Points reference Using ref format (Not SHA-1) $ cat .git/HEAD ref: refs/heads/master
HEAD $ cat .git/HEAD ref: refs/heads/master $
HEAD $ cat .git/HEAD ref: refs/heads/master $ git branch first * master $
HEAD $ cat .git/HEAD ref: refs/heads/master $ git branch first * master $ $ git symbolic-ref HEAD refs/heads/first $ cat .git/HEAD ref: refs/heads/first $ git branch * first master
Internal Data Structure tree blob tree blob tree blob commit commit tree parent tree refs/heads/ master refs/heads/ first 85ab7 pets 8e1e2 son 85ab7 pets e00dd son 6a1f9 cat
Internal Data Structure tree blob tree blob tree blob commit commit tree parent tree refs/heads/ master refs/heads/ first .git/HEAD 85ab7 pets 8e1e2 son 85ab7 pets e00dd son 6a1f9 cat
FAQ #2 Cloned. Now Fetch Or Pull ?
Fetch / Pull Fetch Or Pull To Get Latest Code?
Fetch ● Just Fetch Remote Repository’s Objects And References To Local Git Internal Storage
Fetch ● Just Fetch Remote Repository’s Objects And References To Local Git Internal Storage ● If You Need The Changes On Your Working Directory,
Fetch ● Just Fetch Remote Repository’s Objects And References To Local Git Internal Storage ● If You Need The Changes On Your Working Directory, ○ Manually Merge Them Using git-merge Or, ○ Checkout
Fetch Refspec Describes Source / Destination $ cat .git/config | grep remote -A3 [remote "origin"] url = git://10.0.0.1/git/simpsons.git fetch = +refs/heads/*:refs/remotes/origin/* Source Destination
Fetch: Before url = git://10.0.0.1/git/simpsons.git fetch = +refs/heads/*:refs/remotes/origin/* tree blob tree blob a134f son 799cf pets 7cc07 cat tree blob 65464 son 799cf pets commit commit tree parent tree refs/ heads/ master .git/ HEAD git://10.0.0.1/git/simpsons.git tree blob tree blob a134f son 799cf pets 7cc07 cat commit tree refs/ heads/ master .git/ HEAD file:///home/sjpark/simpsons
Fetch: After url = git://10.0.0.1/git/simpsons.git fetch = +refs/heads/*:refs/remotes/origin/* tree blob tree blob a134f son 799cf pets 7cc07 cat tree blob 65464 son 799cf pets commit commit tree parent tree refs/ heads/ master .git/ HEAD git://10.0.0.1/git/simpsons.git tree blob tree blob a134f son 799cf pets 7cc07 cat tree blob 65464 son 799cf pets commit commit tree parent tree refs/ remotes/ origin/ master refs/ heads/ master .git/ HEAD file:///home/sjpark/simpsons
git merge origin/master tree blob tree blob a134f son 799cf pets 7cc07 cat tree blob 65464 son 799cf pets commit commit tree parent tree refs/ remotes/ origin/ master refs/ heads/ first .git/ HEAD tree blob tree blob a134f son 799cf pets 7cc07 cat tree blob 65464 son 799cf pets commit commit tree parent tree refs/ remotes/ origin/ master refs/ heads/ first .git/ HEAD
Pull Pull Is Just An Abbrev Of Fetch && Merge May Merge Conflict Occur… Pull Is Sufficient For Simple Project
Wrap-up
In Short, Git Is A Content-Addressable File System Blob, Tree, Commit, Reference. That’s It =3 http://www.juliagiff.com/wp-content/uploads/2014/03/tld r_trollcat.jpg
Thank you :) http://jeancharpentier.files.wordpress.com/2012/02/capture-plein-c3a9cran-01022012-230955.jpg
Slide-share http://www.slideshare.net/SeongJaePark1/dee p-darkside-ofgit Latest Version Of This Slide Would Be There
References http://git-scm.com/book http://www.youtube.com/watch?v=4XpnKHJAok8 http://en.wikipedia.org/wiki/The_Simpsons
This slide has been used for Samsung Open Source CONference 2014
This work by SeongJae Park is licensed under the Creative Commons Attribution-ShareAlike 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-sa/3.0/.

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Deep dark-side of git: How git works internally

  • 1.
    How GIT WorksInternally SeongJae Park <sj38.park@gmail.com>
  • 2.
    Nice To MeetYou SeongJae Park sj38.park@gmail.com
  • 3.
    Git DVCS(Distributed Version ControlSystem) http://git-scm.com/images/logos/downloads/Git-Logo-2Color.png
  • 4.
    Git DVCS(Distributed Version ControlSystem) Made-by Linus Torvalds For Linux http://git-scm.com/images/logos/downloads/Git-Logo-2Color.png http://cdn.memegenerator.net/instances/400x/37078331.jpg
  • 5.
    Git Many Projects UseGit Because It’s Awesome http://blog.appliedis.com/wp-content/uploads/2013/11/android1.png http://upload.wikimedia.org/wikipedia/en/4/40/Octocat,_a_Mascot_of_Github.jpg http://upload.wikimedia.org/wikipedia/commons/thumb/3/35/Tux.svg/512px-Tux.svg.png http://git-scm.com/images/logos/downloads/Git-Logo-2Color.png
  • 6.
    Git Hard To Learn ConfusingFor CVCS Users Push? Pull? Fetch? Rebase? HEAD??? http://www.quickmeme.com/img/fd/fd09e17b3393b2ea1cd7e52af1ad7c77f3c2d7a83e9f47d4b90ba3af52dde329.jpg http://git-scm.com/images/logos/downloads/Git-Logo-2Color.png
  • 7.
    Git: The InformationManager From Hell http://www.youblob.com/sites/default/files/styles/large/public/field/image/frontlego1.png?itok=XA5CXt84
  • 8.
    Git: The InformationManager From Hell $ git log e83c516 commit e83c5163316f89bfbde7d9ab23ca2e25604af290 Author: Linus Torvalds <torvalds@ppc970.osdl.org> Date: Thu Apr 7 15:13:13 2005 -0700 Initial revision of "git", the information manager from hell http://www.youblob.com/sites/default/files/styles/large/public/field/image/frontlego1.png?itok=XA5CXt84
  • 9.
    Git: The InformationManager From Hell That’s Why So Confusing And Hard To Learn $ git log e83c516 commit e83c5163316f89bfbde7d9ab23ca2e25604af290 Author: Linus Torvalds <torvalds@ppc970.osdl.org> Date: Thu Apr 7 15:13:13 2005 -0700 Initial revision of "git", the information manager from hell http://www.youblob.com/sites/default/files/styles/large/public/field/image/frontlego1.png?itok=XA5CXt84
  • 10.
    This Time, WeWill... See How Git Works From The Scratch https://lh4.googleusercontent.com/gBpfuABUjSNi2RagtJrGi8TW-pmtgak_0qtGOGubihvKH-5-umreO9C wJgjX2kaA9E7RkLwtEwiDnoMtOgm4iMJ0IWhvXlzlKL1kNVUYWuNa-gLRtRoyNjkVYg
  • 11.
    This Time, WeWill... See How Git Works From The Scratch Just For Fun ...Or To Be Friend Of Git https://lh4.googleusercontent.com/gBpfuABUjSNi2RagtJrGi8TW-pmtgak_0qtGOGubihvKH-5-umreO9C wJgjX2kaA9E7RkLwtEwiDnoMtOgm4iMJ0IWhvXlzlKL1kNVUYWuNa-gLRtRoyNjkVYg
  • 12.
    This Time, WeWill... See How Git Works From The Scratch Just For Fun ...Or To Be Friend Of Git Forget About The Complicated Commands This Time https://lh4.googleusercontent.com/gBpfuABUjSNi2RagtJrGi8TW-pmtgak_0qtGOGubihvKH-5-umreO9C wJgjX2kaA9E7RkLwtEwiDnoMtOgm4iMJ0IWhvXlzlKL1kNVUYWuNa-gLRtRoyNjkVYg
  • 13.
    In Short, Git IsA Content-Addressable Storage System http://www.juliagiff.com/wp-content/uploads/2014/03/tld r_trollcat.jpg
  • 14.
    In Short, Git IsA Content-Addressable Storage System Blob, Tree, Commit, Reference. That’s It =3 http://www.juliagiff.com/wp-content/uploads/2014/03/tld r_trollcat.jpg
  • 15.
    Plumbers: Unsung HeroesBehind ● Git Looks Graceful Owing To Plumbing Commands Consisting Them http://cfile4.uf.tistory.com/image/182FF7244CFDDFB33CC999 http://cfile29.uf.tistory.com/image/18574F224CFDD89B163073
  • 16.
    Plumbers: Unsung HeroesBehind ● Git Looks Graceful Owing To Plumbing Commands Consisting Them ○ The Wounded Foots Are What We Interested In http://cfile4.uf.tistory.com/image/182FF7244CFDDFB33CC999 http://cfile29.uf.tistory.com/image/18574F224CFDD89B163073
  • 17.
    Again, From TheScratch VCS? Why? How?
  • 18.
    Why VCS? Usual LifeOf File FileA ver 0 FileB ver 0
  • 19.
    Why VCS? Usual LifeOf File FileA ver 0 FileB ver 1FileB ver 0
  • 20.
    Why VCS? Usual LifeOf File FileA ver 0 FileB ver 1
  • 21.
    Why VCS? Usual LifeOf File FileB ver 1 FileA ver 1FileA ver 0
  • 22.
    Why VCS? Usual LifeOf File FileB ver 1 FileA ver 1
  • 23.
    Why VCS? Usual LifeOf File FileB ver 2FileA ver 1FileB ver 1
  • 24.
    Why VCS? Usual LifeOf File FileB ver 2FileA ver 1
  • 25.
    Why VCS? Usual LifeOf File FileB ver 2FileA ver 1
  • 26.
    We Need VersionControl System VCS Would... Record Every Changes Safely, Efficiently
  • 27.
    We Need VersionControl System VCS Would... Record Every Changes Safely, Efficiently Able To Check Out Any Version
  • 28.
    We Need VersionControl System VCS Would... Record Every Changes Safely, Efficiently Able To Check Out Any Version Easy To Read History
  • 29.
  • 30.
    Brute-force Idea Rename /Backup Every Files Whenever Change Made
  • 31.
    Brute-force Idea Rename /Backup Every Files Whenever Change Made $ ls foo.c
  • 32.
    Brute-force Idea Rename /Backup Every Files Whenever Change Made $ ls foo.c foo_20140111.c
  • 33.
    Brute-force Idea Rename /Backup Every Files Whenever Change Made $ ls foo.c foo_20140111.c foo_final.c
  • 34.
    Brute-force Idea Rename /Backup Every Files Whenever Change Made $ ls foo.c foo_20140111.c foo_final.c foo_realfinal.c foo_planb.c foo_finalfinal.c
  • 35.
    Brute-force Idea Rename /Backup Every Files Whenever Change Made $ ls foo.c foo_20140111.c foo_final.c foo_realfinal.c foo_planb.c foo_finalfinal.c
  • 36.
    Brute-force Idea +History Isolation Keep Working / History Directory Seperately.
  • 37.
    Brute-force Idea +History Isolation Keep Working / History Directory Seperately. Better, But... $ find . -type f ./working/foo.c ./history/foo_20140111.c ./history/foo_final.c ./history/foo_realfinal.c ./history/foo_planb.c ./history/foo_finalfinal.c
  • 38.
    TODOs From VersionControl Using FS Use Storage Space-Efficiently
  • 39.
    TODOs From VersionControl Using FS Use Storage Space-Efficiently Easy History Searching
  • 40.
    Mission #1: Store HistorySpace-Efficiently
  • 41.
    Basic Idea: AvoidDuplicated Objects
  • 42.
    Basic Idea: AvoidDuplicated Objects Content-Addressable Storage System
  • 43.
    Basic Idea: AvoidDuplicated Objects Content-Addressable Storage System Key: SHA-1 Hash Of Object’s Content Value: Compressed Content
  • 44.
    Basic Idea: AvoidDuplicated Objects Content-Addressable Storage System Key: SHA-1 Hash Of Object’s Content Value: Compressed Content Same Content Never Saved Twice
  • 45.
    Save / Load‘homer’ $ mkdir simpsons; cd simpsons; git init Initialized empty Git repository in simpsons/.git/ $ echo ‘homer’ | git hash-object -w --stdin 4aa0bfa07f1680c50a1567ecc37bc3b6aa567b8f $
  • 46.
    Save / Load‘homer’ $ mkdir simpsons; cd simpsons; git init Initialized empty Git repository in simpsons/.git/ $ echo ‘homer’ | git hash-object -w --stdin 4aa0bfa07f1680c50a1567ecc37bc3b6aa567b8f $ find .git/objects/ -type f .git/objects/4a/a0bfa07f1680c50a1567ecc37bc3b6aa567b8f $
  • 47.
    Save / Load‘homer’ $ mkdir simpsons; cd simpsons; git init Initialized empty Git repository in simpsons/.git/ $ echo ‘homer’ | git hash-object -w --stdin 4aa0bfa07f1680c50a1567ecc37bc3b6aa567b8f $ find .git/objects/ -type f .git/objects/4a/a0bfa07f1680c50a1567ecc37bc3b6aa567b8f $ git cat-file -p 4aa0b homer $ git cat-file -t 4aa0b blob
  • 48.
    What `hash-object -w`did hash_object_w(‘homern’)
  • 49.
    What `hash-object -w`did hash_object_w(‘homern’) # Save compressed header + content at sha1 path def hash_object_w(content): header = ‘blob %d0’ % len(content) store = header + content sha1 = sha.new(store).hexdigest()
  • 50.
    What `hash-object -w`did hash_object_w(‘homern’) # Save compressed header + content at sha1 path def hash_object_w(content): header = ‘blob %d0’ % len(content) store = header + content sha1 = sha.new(store).hexdigest() dir = ‘.git/objects/’ + sha1[0:2] + ‘/’ filename = sha1[2:]
  • 51.
    What `hash-object -w`did hash_object_w(‘homern’) # Save compressed header + content at sha1 path def hash_object_w(content): header = ‘blob %d0’ % len(content) store = header + content sha1 = sha.new(store).hexdigest() dir = ‘.git/objects/’ + sha1[0:2] + ‘/’ filename = sha1[2:] open(dir + filename, ‘w’).write( zlib.compress(store))
  • 52.
    Version Control UsingHash Value $ echo “bart” > son $ git hash-object -w son e00ddae83bdab443f4267426623aa34636c935f2 $
  • 53.
    Version Control UsingHash Value $ echo “bart” > son $ git hash-object -w son e00ddae83bdab443f4267426623aa34636c935f2 $ echo “hugo” > son $ git hash-object -w son 8e1e2f09585e021c9727585af72e10871d7be7ce $
  • 54.
    Version Control UsingHash Value $ echo “bart” > son $ git hash-object -w son e00ddae83bdab443f4267426623aa34636c935f2 $ echo “hugo” > son $ git hash-object -w son 8e1e2f09585e021c9727585af72e10871d7be7ce $ # Need former version, “bart” $ git cat-file -p e00dd > son $ cat son bart
  • 55.
    TODOs From VersionControl Using FS Use Storage Space-Efficiently Easy History Searching
  • 56.
    Version Control UsingHash Value ● DONE ○ Efficient Space Usage ○ Safe Record / Checkout Of History https://www.sciencenews.org/sites/default/files/main/articles/sad_opener.jpg
  • 57.
    Version Control UsingHash Value ● DONE ○ Efficient Space Usage ○ Safe Record / Checkout Of History ● TODO ○ Support Directory Structure ○ History Management ○ Better Reference Than Hash Value https://www.sciencenews.org/sites/default/files/main/articles/sad_opener.jpg
  • 58.
    WAIT! Q: What IfSmall Changes Inside A Big File?
  • 59.
    WAIT! Q: What IfSmall Changes Inside A Big File? $ du -h bigfile.c 188Kbigfile.c $ du -sh 408K. $ echo ‘/* small change */’ >> bigfile.c $ git commit -as -m “small change, big difference” $ du -sh 496K. $
  • 60.
    WAIT! Q: What IfSmall Change Inside A Big File? A: Git Pick up Diff-Only If Necessary But, Don’t Forget To Keep It Small, Simple $ du -sh 496K. $ git gc Counting objects: 6, done. Delta compression using up to 4 threads. Compressing objects: 100% (4/4), done. Writing objects: 100% (6/6), done. Total 6 (delta 1), reused 0 (delta 0) $ du -sh 388K.
  • 61.
  • 62.
    tree Object Point OtherObjects(Using Hash) With Name
  • 63.
    tree Object Point OtherObjects(Using Hash) With Name tree blob blob tree blob a113f2 mommy b8934 son c9240 pets d9b13 cat
  • 64.
    tree Object Point OtherObjects(Using Hash) With Name “A Root tree Object Is A Snapshot” tree blob blob tree blob a113f2 mommy b8934 son c9240 pets d9b13 cat I’m a snapshot
  • 65.
    tree object $ mkdirpets; echo ‘snowball’ > pets/cat $ git update-index --add son pets/cat $ git write-tree 15ee76ed3e744b6796950d07f26283d033ea3ea7 $
  • 66.
    tree object $ mkdirpets; echo ‘snowball’ > pets/cat $ git update-index --add son pets/cat $ git write-tree 15ee76ed3e744b6796950d07f26283d033ea3ea7 $ git cat-file -p 15ee7 040000 tree 85ab72cf1946dc56392718a1aafb3c6f66c02072 pets 100644 blob 8e1e2f09585e021c9727585af72e10871d7be7ce son $
  • 67.
    tree object $ mkdirpets; echo ‘snowball’ > pets/cat $ git update-index --add son pets/cat $ git write-tree 15ee76ed3e744b6796950d07f26283d033ea3ea7 $ git cat-file -p 15ee7 040000 tree 85ab72cf1946dc56392718a1aafb3c6f66c02072 pets 100644 blob 8e1e2f09585e021c9727585af72e10871d7be7ce son $ git cat-file -p 85ab7 100644 blob 6a1f952e1baedcb3db93a3ea5e3389e5a87941e9 cat $ git cat-file -p 6a1f9 snowball $
  • 68.
    Internal Data Structure tree blobtree 8e1e2 son 85ab7 pets
  • 69.
    Internal Data Structure tree blobtree blob 6a1f9 cat 8e1e2 son 85ab7 pets
  • 70.
    Version Control Usingtree Object $ echo “bart” > son $ git update-index --add son $ git write-tree 661e6ad514a7f05c46c2931280cb78a339d34ee2 $
  • 71.
    Version Control Usingtree Object $ echo “bart” > son $ git update-index --add son $ git write-tree 661e6ad514a7f05c46c2931280cb78a339d34ee2 $ git cat-file -p 661e6 040000 tree 85ab72cf1946dc56392718a1aafb3c6f66c02072 pets 100644 blob e00ddae83bdab443f4267426623aa34636c935f2 son $
  • 72.
    Version Control Usingtree Object $ echo “bart” > son $ git update-index --add son $ git write-tree 661e6ad514a7f05c46c2931280cb78a339d34ee2 $ git cat-file -p 661e6 040000 tree 85ab72cf1946dc56392718a1aafb3c6f66c02072 pets 100644 blob e00ddae83bdab443f4267426623aa34636c935f2 son $ git cat-file -p e00dd bart $
  • 73.
    Internal Data Structure tree blobtree blob 8e1e2 son 85ab7 pets 6a1f9 cat
  • 74.
    Internal Data Structure tree blobtree blob tree blob e00dd son85ab7 pets 8e1e2 son 85ab7 pets 6a1f9 cat
  • 75.
    Version Control UsingHash Value ● DONE ○ Efficient Space Usage ○ Safe Record / Checkout Of History ● TODO ○ Support Directory Structure ○ History Management ○ Better Reference Than Hash Value https://www.sciencenews.org/sites/default/files/main/articles/sad_opener.jpg
  • 76.
    Version Control Usingtree Object ● DONE ○ Efficient Space Usage ○ Safe Record / Checkout Of History ○ Support Directory Structure ● TODO ○ History Management ○ Better Reference Than Hash Value https://www.sciencenews.org/sites/default/files/main/articles/sad_opener.jpg
  • 77.
  • 78.
    commit Object Describe Who/ When / Why The Change Made http://modthink.com/wp-content/uploads/2013/05/WhoWhatWhenWhereWHY.jpg
  • 79.
    commit Object Describe Who/ When / Why The Change Made Point A tree Object With Information Above http://modthink.com/wp-content/uploads/2013/05/WhoWhatWhenWhereWHY.jpg
  • 80.
    commit Object $ echo'1st commit' | git commit-tree 661e6 0ca7304ad6f5a40f8a26ba05b10b514ff2d8d8a0 $
  • 81.
    commit Object $ echo'1st commit' | git commit-tree 661e6 0ca7304ad6f5a40f8a26ba05b10b514ff2d8d8a0 $ $ git cat-file -p d075c tree 661e6ad514a7f05c46c2931280cb78a339d34ee2 author SeongJae Park <s**@gmail.com> 1410527921 +0900 committer SeongJae Park <s**@gmail.com> 1410527921 +0900 1st commit $
  • 82.
    commit Object $ echo'1st commit' | git commit-tree 661e6 0ca7304ad6f5a40f8a26ba05b10b514ff2d8d8a0 $ $ git cat-file -p d075c tree 661e6ad514a7f05c46c2931280cb78a339d34ee2 author SeongJae Park <s**@gmail.com> 1410527921 +0900 committer SeongJae Park <s**@gmail.com> 1410527921 +0900 1st commit $ Who When Why
  • 83.
    Version Control Usingcommit Object $ echo '2nd commit' | git commit-tree 15ee7 -p 0ca73 003b5e66caa89a6228c7b4d91e0475e56bf1bdf6 $ $ git cat-file -p 003b5 tree 15ee76ed3e744b6796950d07f26283d033ea3ea7 parent 0ca7304ad6f5a40f8a26ba05b10b514ff2d8d8a0 author SeongJae Park <s**@gmail.com> 1410528231 +0900 committer SeongJae Park <s**@gmail.com> 1410528231 +0900 2nd commit $
  • 84.
    Internal Data Structure That’sWhy People Says, “A Commit is a snapshot” tree blob tree blob tree blob commit commit tree parent tree 85ab7 pets 8e1e2 son 85ab7 pets 6a1f9 cat e00dd son
  • 85.
    Version Control Usingtree Object ● DONE ○ Efficient Space Usage ○ Safe Record / Checkout Of History ○ Support Directory Structure ● TODO ○ History Management ○ Better Reference Than Hash Value https://www.sciencenews.org/sites/default/files/main/articles/sad_opener.jpg
  • 86.
    Version Control Usingcommit Object ● DONE ○ Efficient Space Usage ○ Safe Record / Checkout Of History ○ Support Directory Structure ○ Manage History Well ● TODO ○ Better Reference Than Hash Value https://www.sciencenews.org/sites/default/files/main/articles/sad_opener.jpg
  • 87.
  • 88.
    Git References File WithHuman-Readable Name
  • 89.
    Git References File WithHuman-Readable Name Storing SHA-1 Value Of commit Object
  • 90.
    Git References File WithHuman-Readable Name Storing SHA-1 Value Of commit Object Resides In .git/refs/
  • 91.
    Git References Usingecho $ echo "0ca7304ad6f5a40f8a26ba05b10b514ff2d8d8a0" > .git/refs/heads/first $
  • 92.
    Git References Usingecho $ echo "0ca7304ad6f5a40f8a26ba05b10b514ff2d8d8a0" > .git/refs/heads/first $ $ git log --pretty=oneline first 0ca7304ad6f5a40f8a26ba05b10b514ff2d8d8a0 1st commit $
  • 93.
    Git References Usingecho $ echo "0ca7304ad6f5a40f8a26ba05b10b514ff2d8d8a0" > .git/refs/heads/first $ $ git log --pretty=oneline first 0ca7304ad6f5a40f8a26ba05b10b514ff2d8d8a0 1st commit $ $ find .git/refs/heads -type f .git/refs/heads/first .git/refs/heads/master $
  • 94.
    Git References Usingupdate-ref $ git update-ref refs/heads/master 003b5 $ git log --pretty=oneline master 003b5e66caa89a6228c7b4d91e0475e56bf1bdf6 2nd commit 0ca7304ad6f5a40f8a26ba05b10b514ff2d8d8a0 1st commit $
  • 95.
    Git References Usingupdate-ref $ git update-ref refs/heads/master 003b5 $ git log --pretty=oneline master 003b5e66caa89a6228c7b4d91e0475e56bf1bdf6 2nd commit 0ca7304ad6f5a40f8a26ba05b10b514ff2d8d8a0 1st commit $ $ find .git/refs/heads -type f .git/refs/heads/first .git/refs/heads/master $
  • 96.
    Git References Usingupdate-ref $ git update-ref refs/heads/master 003b5 $ git log --pretty=oneline master 003b5e66caa89a6228c7b4d91e0475e56bf1bdf6 2nd commit 0ca7304ad6f5a40f8a26ba05b10b514ff2d8d8a0 1st commit $ $ find .git/refs/heads -type f .git/refs/heads/first .git/refs/heads/master $ $ cat .git/refs/heads/master 003b5e66caa89a6228c7b4d91e0475e56bf1bdf6
  • 97.
    Internal Data Structure tree blobtree blob tree blob commit commit tree parent tree 85ab7 pets 8e1e2 son 85ab7 pets e00dd son 6a1f9 cat
  • 98.
    Internal Data Structure tree blobtree blob tree blob commit commit tree parent tree refs/heads/ master refs/heads/ first 85ab7 pets 8e1e2 son 85ab7 pets e00dd son 6a1f9 cat
  • 99.
    Version Control Usingcommit Object ● DONE ○ Efficient Space Usage ○ Safe Record / Checkout Of History ○ Support Directory Structure ○ Manage History Well ● TODO ○ Better Reference Than Hash Value https://www.sciencenews.org/sites/default/files/main/articles/sad_opener.jpg
  • 100.
    Version Control UsingReference ● DONE ○ Efficient Space Usage ○ Safe Record / Checkout Of History ○ Support Directory Structure ○ Manage History Well ○ Easy To Remember Specific Snapshot ● TODO ○ ...cooperation? https://www.sciencenews.org/sites/default/files/main/articles/sad_opener.jpg
  • 101.
    FAQ #1 How GitMake-up Working Directory?
  • 102.
    How Git KnowsCurrent Commit? Answer: HEAD
  • 103.
    How Git KnowsCurrent Commit? Answer: HEAD HEAD Points reference Using ref format(Not SHA-1)
  • 104.
    How Git KnowsCurrent Commit? Answer: HEAD HEAD Points reference Using ref format (Not SHA-1) $ cat .git/HEAD ref: refs/heads/master
  • 105.
    HEAD $ cat .git/HEAD ref:refs/heads/master $
  • 106.
    HEAD $ cat .git/HEAD ref:refs/heads/master $ git branch first * master $
  • 107.
    HEAD $ cat .git/HEAD ref:refs/heads/master $ git branch first * master $ $ git symbolic-ref HEAD refs/heads/first $ cat .git/HEAD ref: refs/heads/first $ git branch * first master
  • 108.
    Internal Data Structure tree blobtree blob tree blob commit commit tree parent tree refs/heads/ master refs/heads/ first 85ab7 pets 8e1e2 son 85ab7 pets e00dd son 6a1f9 cat
  • 109.
    Internal Data Structure tree blobtree blob tree blob commit commit tree parent tree refs/heads/ master refs/heads/ first .git/HEAD 85ab7 pets 8e1e2 son 85ab7 pets e00dd son 6a1f9 cat
  • 110.
    FAQ #2 Cloned. NowFetch Or Pull ?
  • 111.
    Fetch / Pull FetchOr Pull To Get Latest Code?
  • 112.
    Fetch ● Just FetchRemote Repository’s Objects And References To Local Git Internal Storage
  • 113.
    Fetch ● Just FetchRemote Repository’s Objects And References To Local Git Internal Storage ● If You Need The Changes On Your Working Directory,
  • 114.
    Fetch ● Just FetchRemote Repository’s Objects And References To Local Git Internal Storage ● If You Need The Changes On Your Working Directory, ○ Manually Merge Them Using git-merge Or, ○ Checkout
  • 115.
    Fetch Refspec Describes Source/ Destination $ cat .git/config | grep remote -A3 [remote "origin"] url = git://10.0.0.1/git/simpsons.git fetch = +refs/heads/*:refs/remotes/origin/* Source Destination
  • 116.
    Fetch: Before url =git://10.0.0.1/git/simpsons.git fetch = +refs/heads/*:refs/remotes/origin/* tree blob tree blob a134f son 799cf pets 7cc07 cat tree blob 65464 son 799cf pets commit commit tree parent tree refs/ heads/ master .git/ HEAD git://10.0.0.1/git/simpsons.git tree blob tree blob a134f son 799cf pets 7cc07 cat commit tree refs/ heads/ master .git/ HEAD file:///home/sjpark/simpsons
  • 117.
    Fetch: After url =git://10.0.0.1/git/simpsons.git fetch = +refs/heads/*:refs/remotes/origin/* tree blob tree blob a134f son 799cf pets 7cc07 cat tree blob 65464 son 799cf pets commit commit tree parent tree refs/ heads/ master .git/ HEAD git://10.0.0.1/git/simpsons.git tree blob tree blob a134f son 799cf pets 7cc07 cat tree blob 65464 son 799cf pets commit commit tree parent tree refs/ remotes/ origin/ master refs/ heads/ master .git/ HEAD file:///home/sjpark/simpsons
  • 118.
    git merge origin/master tree blobtree blob a134f son 799cf pets 7cc07 cat tree blob 65464 son 799cf pets commit commit tree parent tree refs/ remotes/ origin/ master refs/ heads/ first .git/ HEAD tree blob tree blob a134f son 799cf pets 7cc07 cat tree blob 65464 son 799cf pets commit commit tree parent tree refs/ remotes/ origin/ master refs/ heads/ first .git/ HEAD
  • 119.
    Pull Pull Is JustAn Abbrev Of Fetch && Merge May Merge Conflict Occur… Pull Is Sufficient For Simple Project
  • 120.
  • 121.
    In Short, Git IsA Content-Addressable File System Blob, Tree, Commit, Reference. That’s It =3 http://www.juliagiff.com/wp-content/uploads/2014/03/tld r_trollcat.jpg
  • 122.
  • 123.
  • 124.
  • 125.
    This slide hasbeen used for Samsung Open Source CONference 2014
  • 126.
    This work bySeongJae Park is licensed under the Creative Commons Attribution-ShareAlike 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-sa/3.0/.