WORK IN PROGRESS
This page aims to introduce the concepts behind Git in a "Haskell way".
1 The DAG
3.1 Kinds of objects
3.2 The object store
All the different objects in Git - individual files, entire directory trees, commits and other things - are stored in a repository-wide central store. Each object is identified by computing a SHA-1 hash, which is a function of only the object's contents.
3.3 Garbage collection and git reflog
When objects are not reachable from any root (like a branch reference), they become dangling and are subject to garbage collection. However, garbage collection does not kick in immediately.
When making a mistake, it is often helpful to look at commit objects by date independent of whether they are reachable, in order to be able to restore them. You can use git reflog for that.