Git vs cvs ece2011

1

Git from a different (CVS/SVN) perspective

Christian Campo
EclipseCon Europe 2011

Confidential | Date | Other Information, if necessary
November 7, 2011 © 2002 IBM Corporation
Copyright © 2011 compeople AG, Made available under the Eclipse Public License v 1.0

Git vs CVS vs SVN

Git
• commits like db transactions
• commits linked in a hierarchy
• commits contains for a collection of files
• decentral repo
CVS
• commits are unrelated file diffs
• central repo

SVN
• commits are file diffs
• commit file diffs can be linked with a common revision
• central repo


Git Promises/Claims

 you get your own local repository
 you can commit even offline (in an airplane)
 branching is easy and no longer an unusual task but part of your
everyday workflow and its so much easier with Git
 you hated merging with CVS (SVN) ? you are going to love it with Git
 Git is fast and easy
 you cant run an open source project without Git


Git promises from the CVS angle

 you never wanted a local repository
 you hate toonly checkout a wholecommit in an airplane (modules)
• you can fly and therefore never repo with all projects
• you Internet now officially of the last 1-5
 you hate branches andhistory everywhere ? years
• isnt get the whole actually never create them yourself
• and even if you are offline, just write code for a change
• and all branches
• your release engineer does that
 you have a different definition of merge, if two people modify
• so now you should MERGE.
unrelated files thats NOcreate branches ? NO way
• branches isnt that like a fork ?
 Git is fast ! but not easy
 successful open source only requires Git....seriously ?
• no javadoc
• no unit tests
• no clean code
• no integration tests
• JUST Git ??


Git is giving words/things a new meaning

 commit does not mean everybody can see your code
 merge happens even if you edit unrelated files
 first commit THAN merge THAN possibly commit again ??
 and then....the merge commit is empty ? (has no diff)
 repository is not one central thing on the server but everyone has one
 branches on client and server can have different names
 its ok if two repos dont carry the same branches/tags


CVS Users Migration Steps

Step 1: Resistance


CVS has a real Synchronize

 Synchronize shows me the list of incoming and outgoing changes on
file level
 helps to not check in stuff that I dont intent to
 often people check incoming changes on a detailed level
 helps to understand what other people changed
 refactor stuff that seems wrong
 check typos :-)
 improves the quality of the code
 update is done step by step like kind of a to-do-list
 there is Synchronize in Git, but you can not incrementally update
(because of the concept of Git)


Things only CVS can do

 you can tag projects independant as you go
 you can tag single files later
 selectivly update only some projects
 NOT resolve conflicts when you update (i.e. a xx.launch file that you
changed)


CVS Usage is NOT problem free

 If you branch you almost never merge (because its so hard)
 it was always complicated to figure out what was changed for a certain
changeset ?
 A "changeset" are merely commits with the same message so it is easy
to amend a commit :-)
 did you ever tag before and after a commit to log the difference ?
 if you develop in HEAD and a version branch und later you have to copy
changesets from HEAD to the version branch


More CVS crap

 Refactoring (renaming a class) means loosing all your history
 Renaming a package, project means loosing all history of all objects in
that package/project
 If you delete a project it does not get deleted at your collegues
workspace committer unless you TELL him. (and he deletes it
manually)
 If you add a project your collegues wont find out until you TELL them.


And you come to Git...

 And people tell you....
the easiest way to use Git is the command line
 however the command line is way better than you expect
 it was created to actually work with it on a daily base


CVS User Migration Steps

Step 2: Euphoria

„Git is CVS without its problems, I have“


Pitfalls in Git

 you try to pull before you committed your changes
 you push .... EVERYTHING (including all local branches)
 you create a new project in the root of the Git Repository directory


Pitfalls in Git II

 Merge conflicts are a little more complicated
 CVS flags the conflict
 Git Pull actually puts a comment in the file (so that it doesnt compile)
 Rebases can be scary (rerunning commits on a different branch and
hoping that the commits also work there)
 Merge conflicts in the middle of a rebase even more
 You always have to update everything (no way to exclude a bundle or a
file)


More stuff...

 CVS users moving to Git think that Git is the solution to everything they
missed in CVS
 yes moving content between files means that Git still can keep track of
the history
 try to rename a bundle (just for fun) and then look at the proposed
commit (there is “git mv” though)
 you hear that the Git repo of the Eclipse platform was corrupted by a
single committer (Is Git the right move for me ?)


CVS User Migration Steps

Step 3: Realtity

Understanding what you can do


Where Git is better than CVS (the centerpiece)

 commits
 changes collected together in one metaobject called commit
 put more effort in creating a good commit
 amend a commit if wrong, dont just add a second (like in CVS)
 make smaller commits
 commits should be a "unit-of-work" useful by itself
 a good history is the key to using Git
 only Git commits truely show which modifications where committed
together
 there is no commit in CVS !!! Its just writing a collection of diffs..


Things only Git can do

 Pick some commits from one branch into another (cherrypicking)
 Revert commits
 Merge branches (and that actually works :-) )
 Rebase your local changes on top of the server master
 Work on commits in the past
 Tag them
 Branch from them
 Sign them
 Reset your workspace to that time in history
 If you manually undo the changes in a file it automagically shows the
file as unmodified.


Things only Git can do

 develop multiple features in parallel without checking-into-the-server-
repo
 stash your current work, while you do something else and then come
back to your work in progress
 commit only parts of the changes in a file
 freeze a state of your files before they are committed (staging area)


Git is confusing at times

 It uses names that CVS uses, but means something different
 commit, merge, repo
 local tracking branches can have a strategy
 git history can be confusing and complicated


Summary

 Dont treat Git as if it were CVS.
 Getting from CVS to Git
 requires you to "re-wire" your brain
 get used to a new way of doing things
 adapt your way of doing things to retain your workflow as much as
possible
 Symptoms are similar to learning any kind of new technology
 remember XML, Javascript, Objective-C, Modeling, XText, Tycho
 Git opens the door for better collaboration and contribution from
others


And...one more thing....

...you can commit in an airplane


Git vs cvs ece2011

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