Git - Under the Bonnet

GIT under the bonnet

• Object Database
• SHA1
• DAG (Directed Acyclical Graph)
• Index

Object Types

blob

• store file data

tree

• ties one or more "blob" objects into a directory structure
• a tree object can refer to other tree objects, thus creating a directory hierarchy

commit

• ties such directory hierarchies together into a directed acyclic graph (DAG) of revisions
• each commit contains the object name of exactly one tree (snapshot of the tree)
• a commit refers to "parent" commit objects that describe the history of how we arrived at that directory hierarchy

tag

• symbolically identifies and can be used to sign other objects
• It contains
  • object name (SHA1, e.g. 232A...)
  • type of another object
  • a symbolic name (e.g. version 1.0.1)
  • optionally, a signature (PGP or GPG)

Directed Acyclic Graph (DAG)

Stored as a linked list Uses SHA1 as references One root (object without parents) Multiple parents allowed merge (2 parents) octopus merge (3 or more)

DAG and gitk

DAG and Git objects