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I learned that Git stores data as DAG at the very beginning when introduced to it. But I came to get clicked until I realized that it is not only a DAG but an immutable one. That is, existing nodes of the DAG are never changed once created. The only operation supported by the system is more or less: create. Also, using the plumbings to peek into the content of the objects and refs inside the .git helps a lot as well.

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Yeah, that's a very important point. Even changing the parent of a commit, that is, an edge in the graph, changes the hash of the commit. Therefore to change the parent (like in a rebase) you have to make a new commit, but the old commit doesn't go anywhere, you just can't see it because you have no reference to it any more.

Git will garbage collect these commits that can't be reached by any reference after a while, but usually that's long after you've forgotten they ever existed.

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