Git more done

git more done
Kwen Peterson
Senior Software Developer @ Raven
kwen.peterson@gmail.com
@kwenarik

"You're already in the top tier of developers just
by showing up here tonight. I don't know how
talented you are, how much experience you have,
but you showed up. You're putting yourself out
there because you care to improve. Thanks for
caring.“ – Scott Hanselman

Distributed
• One of the coolest features of any of the
Distributed VCSs, Git included, is that it isn‟t
centralized.
– This means that even if you're using a centralized
workflow, every user has what is essentially a full
backup of the main server, each of which could be
pushed up to replace the main server in the event of a
crash or corruption.
– There is basically no single point of failure with a
distributed VCS.

Git is Fast
• Git is extremely fast. Since all operations (except
for push and fetch) are local there is no network
latency involved to:
–
–
–
–
–

Perform a diff.
View file history.
Commit changes.
Merge branches.
Obtain any other revision of a file (not just the prior
committed revision).
– Switch branches.

Git is orders of
magnitude faster than SVN.
Operation

Git

SVN

Speed

Commit Files (A)

0.64

2.60

4x

Commit Images
(B)

1.53

24.70

16x

Diff Current

0.25

1.09

4x

Diff Recent

0.25

3.99

16x

Diff Tags

1.17

83.57

71x

Log (50)

0.01

0.38

31x

Log (All)

0.52

169.20

325x

Log (File)

0.60

82.84

138x

Update

0.90

2.82

3x

Blame

1.91

3.04

1x

Git is Small
• Git's repository and working directory sizes are extremely small
when compared to SVN.
– The Mozilla repository is reported to be almost 12 Gb stored across 240,000 files
in SVN.
– The exact same history is stored in Git using two files totaling just over 420 Mb.

• This means that SVN requires 30x the disk space to store the same
history!
– One of the reasons for the smaller repo size is that an SVN working directory
always contains two copies of each file: one for the user to actually work with and
another hidden in .svn/ to aid operations such as status, diff and commit.
– In contrast a Git working directory requires only one small index file that stores
about 100 bytes of data per tracked file. On projects with a large number of files
this can be a substantial difference in the disk space required per working copy.

Git is *
• GitHub
– 3 million+ users
– 5 million+ repositories
– THE place for open-source projects

• Merging & Branching are easy
– (unlike in many centralized systems)

The branch Dilemma
I have a 120 hour work package to do!
SVN:
– sit on 3 weeks worth of changes unversioned and then finally push 1
massive commit?
– push updates to trunk/branch as necessary and possibly break
functionality for anyone else working on project (but get to keep commit
history, and not have 1 massive commit)

Git:
– make daily commits to my local branch (full history, able to rollback to
intermediate stages!)
– merge in changes that others have pushed to the master branch at my
convenience
– hold off pushing to master until my code is fully polished and tested out,
minimizing impact on other developers

Code Reviews
• SVN
– Make a patch of uncommitted changes and send it
to another developer, and hope that they have an
SVN branch at the exact commit as yours to apply it
to.

•

Git
–

Push a copy of your local branch (and all its
commits) out to a remote branch on a repository,
where anyone can easily pull down a copy and build
your code, no matter where there current branch is.

git-svn
• “Git is the best SVN client out there.” – Keith
Dahlby
• Gives you ALL the local repository benefits of
git, while letting you treat your SVN repo as „just
another remote‟

Dictator & Lieutenants Workflow

Felix Baumgartner – Red Bull

Creating a Repository
• git init
– Creates an empty repository at current location

• git clone <url>
– Creates a local copy of an existing repository
– Examples:
• git clone http://github.com/jquery/jquery.git

Working with Remotes
• git remote add <name> <url>
– Maps a remote
– Example:
git remote kwen git://source/kwen-test.git

• git remote show <name>
– Displays a list of branches on the remote, any local
branches that track them, fetch URL, etc.

• git remote rm <name>
• git remote rename <old> <new>

Working with Branches
• git checkout <branch>
– Change to the specified local branch

• git branch <name> <remote>/<branch>
– Create a local branch that tracks the remote branch
– Example: git branch milestone3 kwen-test/milestone3

• git checkout –b <name> <remote>/<branch>
– Creates a new local branch and immediately checks it out
– Example: git co –b codereview kwen-test/milestone4

Dealing with Changes
• git st
– Shows you the status of currently modified files (tracked &
untracked)

• git add <file> (use a gui instead!)
– adds the specified file to the list of tracked changes

• git commit –m <message> (use a gui instead!)
– Commits all tracked changes to the current branch

• git reset HEAD –hard
– Reset current branch and lose ALL changes

• git stash <tag>
– Store all current changes away temporarily
– The tag is optional, and it will generate one for you if not provided

• git stash apply <tag>
– Reapply the last set of stashed changes onto
the current branch

Pushing and Pulling Changes
• git fetch <name>
– Gets the latest updates from the remote, but does NOT apply them
– Example: git fetch origin

• git pull <remote> <branch>
– Runs git fetch and then git merge
– If you are on a branch that already tracks a remote, you can just use git
pull, and it will merge any updates in the tracked remote branch into your
local branch.
– Can pass a --rebase parameter to rebase instead of merge

• git push <remote> <name>:<branch>
– Pushes the updates in my current local branch out to a remote branch
– Example: git push origin milestone3:milestone3

Git Trivia
1. Git push origin master:master
2. Git push origin +master:master

3. Git push origin –f master:master

Creating & Applying Patches
• git format-patch <branch>
– Creates patches for the diff between the current branch & <branch>
– Example: My local dev branch has updates that have not been
committed to origin/dev yet, but that I need to send to Wes.
Running git format-patch origin/dev creates patches for each of the
commits that are on my local dev branch that are not in origin/dev.

• git format-patch -#
– Same as above, except this method simply takes the last X
commits and creates patches for them.
– Example: git format-patch -3 (creates patches for the last 3 commits
you made on this branch)

• git am -3 –s –i <file or folder>
– Apply the specified patches to the current branch
– Example: git am -3 –s –i patches/* (applies all the patches located
in my patches folder)

Copy/Paste a commit locally
• Git cherry-pick <hash>
– Copies the changeset for the given commit onto the
current branch
– (Great way to apply a hotfix to multiple different
branches.)

*

Bug, or…

https://twitter.com/pardel/status/372750244963819522/photo/1

https://twitter.com/GeorgeTakei/status/385913390377750528/photo/1

Common git branching strategy
• 3 core branches: master, dev, release
– Master is “the truth” and should always be in a stable,
fully-functional state. This is where new topic/feature
branches are cloned from. (nightly builds)
– Dev is where integration testing happens. This is
where topic branches are pushed and tested PRIOR
to being signed off on as stable enough to go to
master. (continuous integration, test environment)
– Release is where the last live build lives. This exists
so that if an absolutely critical issue arises, we can
make the fix here and release the build, being
confident that the ONLY change going out is the
critical bug fix.

Rebase vs. Merge (1)
• Merging brings two lines of development
together while preserving the ancestry of each
commit history.
• In contrast, rebasing unifies the lines of
development by re-writing changes from the
source branch so that they appear as children of
the destination branch – effectively pretending
that those commits were written on top of the
destination branch all along.

• Rebase requires the commits on the source
branch to be re-written, which changes their
content and their SHAS.
• Merging is better if you only have one (or few
trusted) commiter(s) and you don‟t care much
about reading your history.
• Rebasing makes you sure that your commits go
on top of the „public‟ branch.

31

• git merge <branch>
– Merge changes in the specified branch onto the current branch
– If you run into merge conflicts, the current branch is called local, and the
branch you are merging in is referred to as remote.

• git rebase <remote>/<branch>
– Base the current branch you are on off the specified remote branch
– Takes the specified branch as the base, and then applies any changes
you have in your local branch on top of that. For conflicts, the current
branch is called remote, and the branch you are rebasing off of is treated
as local.
– Example: git rebase origin/master

Merge
• Pros
– Simple to use and understand
– The commits on the source branch remain separate from
other branch commits, provided you don‟t perform a fastforward merge. (This separation can be useful in the case
of feature branches, where you might want to take a
feature and merge it into another branch later.)
– Existing commits on the source branch are unchanged and
remain valid; it doesn‟t matter if they‟ve been shared.
• Cons
– If the need to merge arises simply because multiple people
are working on the same branch in parallel, the merges
don‟t serve any useful historical purpose & create clutter.

Rebase
• Pros
– Simplifies your history.
– Is the most intuitive and clutter-free way to combine
commits from multiple developers in a shared branch.

• Cons
– Slightly more complex, conflicts require resolution on
a per commit basis.
– Rewriting of history has ramifications if you‟ve
previously pushed those commits elsewhere.

Golden Rule of Rebasing

• NEVER EVER rebase a branch
that you pushed, or that you
pulled from another person.

37

Interactive Rebase (Squash)
• git rebase –i HEAD~3
– pick f392171 Added new feature X
– pick ba9dd9a Added new elements to page design
– pick df71a27 Updated CSS for new elements

• Change to:
– pick f392171 Added new feature X
– squash ba9dd9a Added new elements to page
design
– squash df71a27 Updated CSS for new elements

Reflog, Detached Heads, Submodules
• Git reflog – „restore points‟ for everything you do!
• Git reset –hard <hash>
• Detached Head – Tracking a specific commit,
not a branch!
• Submodules – Shared „child‟ git repository
(notorious for detached HEAD issues…)

Resources
• Recommended
– http://rogerdudler.github.io/git-guide/
– http://www.slideshare.net/lemiorhan/git-branchingmodel?utm_source=slideshow&utm_medium=ssemail&utm_campaign=wee
kly_digest

• Comparison vs. SVN
–
–
–
–

http://whygitisbetterthanx.com/
http://git-scm.com/course/svn.html
https://git.wiki.kernel.org/index.php/GitSvnComparison
http://zurb.com/article/597/the-one-critical-reason-we-switched-from-

• Git Clients
– https://code.google.com/p/gitextensions/
– http://sourcetreeapp.com/
– https://github.com/dahlbyk/posh-git

Kwen Peterson
• http://tinyurl.com/rsdcc13
– https://github.com/Kwen/sdcc2013
– http://speakerrate.com/talks/27811-git-more-done
– http://www.slideshare.net/KwenPeterson/git-moredone

•
•
•
•

@kwenarik
#sdcc2013
plus.google.com/+KwenPeterson
kwen.peterson@gmail.com
https://github.com/Kwen

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