git

Lesson 1
 
 

LEARning goals

  1. Describe what a version control system is and list the main advantages of using it
  2. List the main advantages of git over other version control systems
  3. Understand the file status lifecycle

  • Version control system. Definition and history.

  • What is git and its advantages

  • File status life cycle. From untracked to committed.

OUTLINE

VERSION CONTROL SYSTEM (VCS)

Version control is a system that records changes to a file or set of files over time so that you can recall specific versions later.

Advantages of using a vcs

  • Revert files or the entire project back to a previous state

We can experiment with new code without worrying of messing around something..

..and we don't need to backup!

ADVANTAGES OF USING A VCS

  • Review changes made over time

We can read the history of a single file to understand how it evolved from the beginning

ADVANTAGES OF USING A VCS

  • See who last modified something that might be causing a problem... and blame him!

Type of VCS

Directory based "VCS"


Yay ?

Easy to use

Doesn't require any learning process

 

Nay

Extremely ineffective

Extremely difficult to collaborate

Impossible to track changes

No remote backups

Many other reasons

Local VCS


(rcs)

Yay

Allow to track changes in the files

 

Nay

Cannot be used to collaborate

No remote backups

 

Centralized VCS


(cvs, svn)

Yay

Allow collaboration

Access control

Central backup

 

Nay

Single point of failure

Painful merges

Requires internet connection

Decentralized VCS


(git, mercurial, bazaar, bitkeeper, darcs)

Yay

Every clone is a fork

Every clone is a backup

No connectivity issues

Fast. Really!

 

Nay

Not good for large binary files

Git is an open source, distributed version control system designed for speed and efficency

GIT




Git design goals

  • Speed
  • Simple design
  • Strong support for thousands of parallel branches
  • Fully distributed
  • Able to handle larges projects like Linux kernel effectively
  • Ensure integrity

Tracking Changes

(most VCS)

  • A basic version of the file is saved
  • Any modification to that file is saved separately
  • When we want to retrieve a specific version of the project, all the single modifications are applied to the basic file, for all the file in the repository

Advantages

Space efficient
 

Disadvantages

Time inefficient

Tracking Snapshots

(git)
  • A whole copy of a file is done when this is modified
  • When we want to retrieve a specific version of the project, we just copy to the tree structure corresponding to that version in the working directory

Advantages

Extremely time efficient

 

Disadvantages

Space "inefficient"

..but it's not a problem if we mostly track text based files

Git is a file system


Git thinks of its data more like a set of snapshots of a mini filesystem.

Git advantages

Nearly every operation is local

  • Operations are very fast
  • Every local repository is a backup
  • No need of internet connection to work
    (only needed to synchronize occasionally)

Git has integrity

  • Everything is checksummed
  • References are SHA-1



24b9da6552252987aa493b52f8696cd6d3b00373

Git doesn't delete

  • Git generally only adds data
  • If you mess up, you can usually recover your stuff
  • Recovery can be tricky though

The three states

  1. Modified
  2. Staged
  3. Committed

Workflow


The git directory

  • Located at .git/ (it's hidden)
  • Contains the entire history, i.e.,
    a copy of all the versions of all the files ever tracked by git and all the past folder tree structures
  • When we checkout we copy a set of files from this directory in the working directory
 

The working directory

  • The folder content we actually see in our file explorer
  • A single checkout from a Git repository

The Staging Area

  • Contained in a file
  • Tracks what will go into the next commit 
    AKA "the index"
 
 

File Status Lifecycle

The three states

  • Untracked means that git is not managing the file in any way 
  • Committed means that the data is safely stored in your local database.
  • Modified means that you have changed the file but have not committed it to your database yet.
  • Staged means that you have marked a modified file in its current version to go into your next commit snapshot.

What of these facts about git are true?

  • It's good in managing large binary files
  • Every clone of the repository is a backup
  • Requires internet connection to work
  • Every operation is fast

What is the staging area (the index)?

  • The folder that contains the whole git history

  • A file that tracks what will go into the next commit

  • The way git refers to the current working directory 

sanity check

List 3 advantages of using a VCS

LEARning goals

  1. Describe what a version control system is and list the main advantages of using it
  2. List the main advantages of git over other version control systems
  3. Understand the file status lifecycle

Now Git to work!


Resources

CreditS

This presentation was originally made by
Danilo Bargen

Revised by
Simone Gaiarin

The 3 slides on the Git definition are taken from the presentation " Introduction to Git" by Matthew McCullough



Git - Lesson 1

By Simone Gaiarin

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Git - Lesson 1

VCS, git, file status life cycle

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