 Commit graph

A commit graph represents version-control commits as vertices and their parent relationships as directed edges. In Git, taking an edge from a child to each parent gives a directed acyclic graph: an existing version-control commit has fixed parents, and a newly created child cannot become its own ancestor.^[ref]

For example, if $B$ and $C$ both descend directly from $A$, and merge $M$ records parents $B,C$, its edges are $M\to B$, $M\to C$, $B\to A$ and $C\to A$. The merge retains both lines of ancestry. A version-control branch labels a selected tip; deleting that label does not by itself remove every reachable vertex. This graph supports ancestry tests and finding common bases for version-control merging.