REUTERS / Eric Gaillard

Understanding GIT

Tadeusz Balcer12/5/2016

Centralized Version Control System (CVCS) (SVN, Perforce)

Source: https://git-scm.com/book/en/v2/book/01-introduction/images/centralized.png

Distributed Version Control System (DVCS) (GIT, Mercurial)

Source: https://git-scm.com/book/en/v2/book/01-introduction/images/distributed.png

Typical CVCS - differences

GIT – stream of snapshots.

GIT features

• Snapshot, not differences• Nearly every operation is local (no need network connection to work)• GIT has integrity (SHA-1 checksums)• Generally only adds data (It is hard to get the system to do anything that is not undoable)• Three states of files (commited, modified, staged)

The Three States

Source: https://git-scm.com/book/en/v2/book/01-introduction/images/areas.png

REUTERS / Edgar Su

Creating commit is like saving your game before you battle the boss.

Commit object

• pointer to the snapshot of content• author’s name and email• message• pointer to commit or commits that directly came before this commit (zero, one or many)

Commit object

Source: https://git-scm.com/book/en/v2/book/03-git-branching/images/commit-and-tree.png

Commit object

Source: https://git-scm.com/book/en/v2/book/03-git-branching/images/commits-and-parents.png

REUTERS / Mario Anzuoni

Merge vs rebase

Branch

3-way merge algorithm

1. Find a suitable merge base B - a version of the file that is an ancestor of both of the new versions (X and Y), and usually the most recent such base (although there are cases where it will have to go back further, which is one of the features of gits default recursive merge)

2. Perform diffs of X with B and Y with B.3. Walk through the change blocks identified in the two diffs. If both

sides introduce the same change in the same spot, accept either one; if one introduces a change and the other leaves that region alone, introduce the change in the final; if both introduce changes in a spot, but they don't match, mark a conflict to be resolved manually.

Merging

Merging

Merge conflicts

Merge conflicts (merge.conflictstyle=diff3)

Remote branches

Source: https://git-scm.com/book/en/v2/book/03-git-branching/images/remote-branches-2.png

Remote branches

Source: https://git-scm.com/book/en/v2/book/03-git-branching/images/remote-branches-3.png

Remote branches

Source: https://git-scm.com/book/en/v2/book/03-git-branching/images/remote-branches-5.png

Distributed workflows

Source: https://git-scm.com/book/en/v2/book/05-distributed-git/images/integration-manager.png

Rebase

Source: https://git-scm.com/book/en/v2/book/03-git-branching/images/basic-rebase-3.png

Fast-Forward

Source: https://git-scm.com/book/en/v2/book/03-git-branching/images/basic-rebase-4.png

Rebase

Source: https://git-scm.com/book/en/v2/book/03-git-branching/images/interesting-rebase-1.png

Rebase

Source: https://git-scm.com/book/en/v2/book/03-git-branching/images/interesting-rebase-2.png

Cherry-pick

Source: http://image.slidesharecdn.com/git-getreadytouseit-140228043813-phpapp02/95/git-get-ready-to-use-it-65-638.jpg?cb=1393562489

Resources

https://sivapremv.wordpress.com/2015/01/21/git-version-control-an-interesting-infographic-view/http://code.snipcademy.com/tutorials/git/fundamentals/three-states-areashttps://git-scm.com/book/en/v2/Getting-Started-Git-Basicshttps://www.quora.com/How-does-Git-merge-work