Git Intermediate Workshop slides v1.3

OptionFactory
Git, beyond the basics
intermediate level workshop

About OptionFactory
Main activities
● Software development & consultancy
● Continuous Integration & Delivery
● Training & coaching
Key competences
● Java, Javascript, C++, Go, Erlang and more
● Secure Software Development Lifecycle
● Lean Software Development
● Re-engineering
Core domains
● High Availability and High Performance systems
● Application security
● Telcos, finance, insurance and security sensitive domains
● Startups, new markets and high uncertainty domains

Goals
If that doesn’t fix it, git.txt
contains the phone number of a
friend of mine who understands
git. Just wait through a few
minutes of “It’s really pretty
simple, just think of branches
as…” and eventually you’ll learn
the commands that will fix
everything.
HTTP://XKCD.COM/1597/
“

Goals (II)
No, improvising is wonderful.
But, the thing is that you cannot
improvise unless you know
exactly what you're doing.
Christopher Walken
“
”

Establishing a common base
● Participants’
○ background
○ VCS tools known
○ level of experience
○ expectations

Version control in 4 steps
● Do some work
● Checkin a “unit of work” (aka: transaction). Think “savegame”
● Repeat as much as you want
● Go back “in time” when something happens. Think “reload and try again”

Version control landscape
Git Mercurial (HG) SVN ClearCase
Model Distributed (clone) Distributed (clone) Centralized
(checkout)
Centralized
(checkout)
Transaction unit Commit Commit Commit File
Storage model Snapshot Delta Delta ?
Transaction id Hash Hash (local
sequence)
Global sequence Path + per-branch
sequence
Concurrency
model
Merge/Rebase
(graph)
Merge (graph) Merge on commit
(linear)
Pessimistic
locking + merge
(linear)
Rename / move
tracking
No (heuristic) Yes Yes Yes*

Centralized vs distributed (I)

Centralized vs Distributed (II)
Centralized Distributed
Instances Single, mandatory
Every istance is equal. “Central authority” is a
convention, not a necessity
Transaction id Centrally assigned Anyone must be able to assign it
The Truth™ One and only
“Luke, you're going to find that many of the truths we cling
to depend greatly on our own point of view.” _ Obi-Wan
Kenobi

Centralized vs Distributed (III)
Centralized Distributed
Isolation None, each transaction is “public” Many Sandboxes environments
Speed per
commit
Low, every transaction required
network communication
Fast, changes are on the local filesystem.
Conflicts Pain Manageable pain

Starting up
● setup your global git environment
git config --global user.name “Mario Rossi”
git config --global user.email “mrossi@example.com”
● initialize (i.e. create) your first repository
mkdir myfirstrepo
cd myfirstrepo
git init

Inside a commit
● parent id(s)
● timestamp
● author (& committer)
● content
○ filesystem state
NOT part of a commit (more on that later)
● branch
● tags

Creating a commit
● Create / edit files on your working copy (your local filesystem)
● Mark your changes for inclusion by copying them in the staging area
● Create a new commit, providing the missing (meta) data
● What goes in the commit comes from:
○ whatever you put in the staging area
○ your global git configuration (e.g. your name, email)
○ the git environment (e.g. the current date, the commit you started working from)
○ the commit message you specify

checkout/reset (file)
Checkout <file> Checkout <ref> -- <file> Reset <file>
Effect on graph
shape
None None None
Effect on
Staging Area
None Overwritten with version from graph Overwritten with version from
graph
Effect on
working copy
Overwrite with version from
staging area
Overwritten with version from graph None
Staging area
Working Copy Graph
add <file> com
m
it
reset<file>
checkout <ref> -- <file>
checkout <file>

Alternate (time)lines
● Creating alternate lines of work
○ branch
● Navigating the graph
○ checkout
○ reset
● “Crossing the streams” and other weird stuff
○ merging
○ rebasing
○ cherry-picking

References & reachability
● A reference is just a named pointer to a commit in the graph
● Every commit, to be reachable, must be referenced:
○ directly (by a ref)
○ indirectly (by a reachable descendant, pointing to its parent)
● Bad parenting advisory:
○ Parent commits do not know about their children
○ You can’t navigate forward in time through the graph

references: Branches
● a “branch” identifies a sequence of commits, tracing a workflow
● “master” is by convention the project main line
● A branch points to a commit in the graph, and represents a pointer to such
commit. It is not directly related to working copy or staging area
● Any number of branches can point to the same commit, they are all
independent

references: HEAD
● HEAD is a special reference. It can either point to a commit or a branch,
and represents where we are in the graph
● The commit it points to (directly or indirectly) is used for comparison
against the staging area
● When HEAD points to a Branch reference, that branch is “current”, and will
move ahead on commit
● When HEAD points directly to a commit, we are in the “detached HEAD”
state
○ this is true even if there are branches referencing that same commit

references: Tags
● Lightweight Tags are similar to branches (a name attached to a specific
commit), but they are not meant to move
● Annotated Tags also contain an id, timestamp, author and a message on
top of that
● Therefore, annotated tags can be signed

Checkout/Reset/Revert (ref)
Checkout <ref> Reset <ref> Revert <ref>
Moves HEAD only “current” Branch “current” Branch
Effect on graph shape None potentially leaves back “dead”
nodes
Creates new node
Effect on Staging Area Fails if dirty* overwritten with --mixed (default)
or --hard
Fails if dirty
Effect on working
Copy
Fails if dirty overwritten only with --hard Attempts merge, fail if
not possible

Remotes, refs, tracking branches
● remotes: names pointer to a remote repository
○ origin is the one you cloned from (just another convention)
● remote branches
○ Remote references differ from branches (refs/heads references) mainly in that they’re
considered read-only. You can git checkout to one, but Git won’t point HEAD at one, so
you’ll never update it with a commit command. Git manages them as bookmarks to the last
known state of where those branches were on those servers.
● tracking branches
○ created once you checkout a remote branch
○ tracks your work on that branch to allow sync

Synchronization & collaboration
● clone
● push
● fetch
● pull (fetch+merge o fetch+rebase)

Collaborative workflow
● commit message
● approach
○ merge-based
○ rebase-based
○ not exclusive

http://zeroturnaround.com/wp-content/uploads/2016/02/Git-Cheat-Sheet.png

git as a service
● github, gitlab, bitbucket
● basic concepts mapping
● Authorization models
● “Fork” and “Pull Request” implementations
○ pull request
■ What’s that? “Please, take my changes”

security and workflow considerations
● Certificates
● Credentials storage

Resources
■ Good base: http://www.learnenough.com/git-tutorial
■ Visualizing Git Concepts with D3: https://onlywei.github.io/explain-git-with-d3/
■ Think like a git: http://think-like-a-git.net/epic.html
■ Cache your passwords: https://help.github.com/articles/caching-your-github-password-in-git/
■ Git-csm book, in particular:
● https://git-scm.com/book/en/v2/Git-Basics-Recording-Changes-to-the-Repository
● https://git-scm.com/book/en/v2/Git-Tools-Reset-Demystified
● https://git-scm.com/book/en/v2/Git-Basics-Git-Aliases
■ Some open source projects to visualize git graphs:
● https://github.com/FredrikNoren/ungit/blob/master/README.md
● https://github.com/Readify/GitViz
● https://github.com/Haacked/SeeGit
■ Always funny to watch: http://gource.io/
■ Git cheat sheet: http://zeroturnaround.com/rebellabs/git-commands-and-best-practices-cheat-sheet/
■ Interesting videos:
● Git For Ages 4 And Up: https://www.youtube.com/watch?v=1ffBJ4sVUb4
● Introduction to Git with Scott Chacon of GitHub: https://www.youtube.com/watch?v=ZDR433b0HJY

Git Intermediate Workshop slides v1.3

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