Git data model

Essentially, Git is a content-addressable filesystem, Linus's one page explanation, correction: the SHA1 hash is NOT the hash of the compressed object.

Git from the Bottom Up by John Wiegley, discuss.

  • blob is content of file
$ git cat-file -p 74576250e3c3a901bf06832bd0e4ee5e00422115
# Shuo's notes
http://chenshuo.github.io/notes
  • tree has one or more tree/blob, it's Merkle tree.
    • blob are leaf nodes
    • tree are internal nodes
$ git cat-file -p 5d42664e3d812288b47795718d0e4faf26397bf9
100644 blob cde88fe0e10f265ed3cb2af0ea5422f607c1a37c    .gitignore
100644 blob 74576250e3c3a901bf06832bd0e4ee5e00422115    README.md
040000 tree eabff4ee0b30f5d6a644ce508ba7fe47dc563aa4    docs
100644 blob 020682e2399c75cf3ad9636964c7501f27a0e893    mkdocs.yml
  • commit:
    • has one tree
    • has one or more parent commit(s)
$ git cat-file -p 3f08891b366c750d4739241874cfb1dbef56c398
tree 5d42664e3d812288b47795718d0e4faf26397bf9
parent 955f683cae5d2514d1c788fce9206451e2ac3334
author Shuo Chen <chenshuo@chenshuo.com> 1484903215 -0800
committer Shuo Chen <chenshuo@chenshuo.com> 1484903215 -0800

update ssl.md

  • tag ???

  • Exceptions:

    • initial commit has no parent
    • empty file is empty blob
    • empty directory is empty tree

Pack file format

Delta

Pack index format