Git and GitHub at Washington University

An introduction to distributed version control for EFFECTIVE USE OF
GIT & GITHUB

Matthew.... @matthewmccull ‣Open source contributor ‣O'Reilly Git Video Co-instructor ‣Co-Author
of O'Reilly's Git book ‣5-year Git trainer ‣Instructor at GitHub

http://oreil.ly/ogitvid

http://amzn.to/oreillygit

[email protected] github.com/training @matthewmccull matthewmccullough

Version Control A refreshed approach to VCS

Open Source

bash scripts ☛ C code

is not a slightly better

Changelist Three stage thinking

Working Staging Repo add commit edit

‣shopping cart ‣put things in ‣take things out ‣purchase at
register

‣database transaction ‣update values ‣insert rows ‣delete rows ‣commit transaction

Working Staging Repo add commit edit

Typical SCMs use delta storage

CVS / Subversion / darcs / Mercurial

v1 v2 v3 v4 File A File B File C
File A File B File B File C v5 File A File B File B Δ Δ Δ Δ Δ Δ Δ

Checkin Checkin Checkin Checkin Checkin Checkin Checkin Checkin Checkin Checkin
Checkin Delta storage gets slower as the history of a ﬁle gets longer

Git uses DAG storage

Directed Acyclic Graph

Copy of the entire tree per checkin

cp -r srcfolder srcfolder.prev

File A File B File B File C v5 File A File B File B File A File A File C File C File C

hard link to existing identical blobs

File A File B File B File C v5 File A File B File B File A File A File C File C File C ß

zlib deﬂates each blob at commit

zlib deﬂates the entire repo

2100 MB became 205 MB Act I

Repo Creation Local and remote initialization simplicity

# Green field project $ git init newproject $ cd
newproject # ...start coding

or if you already have source code

# Legacy project tree $ cd existingproject $ git init
# Add all the code $ git add . $ git commit -m”Initial import”

‣Blob ‣Tree ‣Commit ‣Tag

tree tree: 7e8b1 web blob: 9ab16 index.html a10b3 tree blob:
8d162 logo.jpg blob: 51d22 draw.js 7e8b1 commit tree: a10b3 parent: nil author: Fird committer: Matthew message: Major refactoring of the web content. c67db blob <html> <body></body> </html> 9ab16 blob //Some more javascript var renderSize 51d22 blob 7D 8D B3 7F BD 12 9F E9 7B 78 9D 3F 5C A6 72 CB 8d162

Workspaces The power of simple branch toggling

Local Remote Upstream

# Creating a branch git branch <BRANCHNAME>

RELEASE_1.0 HEAD bug979branch commit c67db commit 9bd21 commit 1c2d7 commit
8c2d1 commit 1bdcd commit 2daa1

# Creating a branch git branch <BRANCHNAME> <REF>

RELEASE_1.0 HEAD bug979branch commit c67db commit 9bd21 commit 1c2d7 commit
8c2d1 commit 1bdcd commit 2daa1

What do cheap branches enable?

‣Experimentation ‣

‣Experimentation ‣Safe experimentation

Better reuse of units of work

Work Models Enabling different development styles

‣Branched by lifetime ‣ Product ‣ Integration ‣ Feature ‣
Story ‣ Idea

product integration feature story idea

product v1.0 integration story1 story2 v1.5 integration story3

Local Remote Upstream Integ Product Integ Product Integ Product

Local Remote Upstream Idea Story Feature Feature Feature Integ Product
Integ Product Integ Product

Central Repo C e n t r a l i
z e d

Blessed Repo D i c t a t o r
s h i p

Certiﬁed Repo Development Repo n t e g r a
t i o n M a n a g e d Continuous Integration Server

C u s t o m + P u b
l i c C o n t r i b Customized ☚ Private Public ☛ GitHub

Mirror Development Repo M i r r o r e
d Mirror Certiﬁed Repo

Client Apps GUIs and other front-ends

Remotes Bandwidth and geographic challenges

Local Remote Upstream

data from http://whygitisbetterthanx.com/#git-is-fast git svn Init git svn Status git
svn Diff git svn Tag git svn Log git svn Commit (Lg) git svn Commit (Sm) git c svn c Branch Speed

Local Remote Upstream commit fetch push clone clone clone push
pull pull pull

Commit Push Pull

Integration CI, scripting, and hooks

"This is so important, we can't entrust it to automation.
We need our top developer to supervise it."

continuous integration servers jenkins travis ci circleci buildhive

Summary The Git and GitHub ecosystem

[email protected] github.com/training @matthewmccull matthewmccullough Q&A

http://learn.github.com

http://teach.github.com

Git and GitHub at Washington University

Git and GitHub at Washington University

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