[Question] Restoration from only delta snapshots without a full snapshot

[shreyas-s-rao]

Question:
Is there a valid use case for etcdbr to restore from a bucket which has only delta snapshots and no full snapshots? I ask this because in a recent PR I was working on, I saw the negative test for restoring from only delta snapshots when no full snapshot is present here.

I also see here in the code that restorer does not return error when it doesn't see a full snapshot during restoration.

I would like to discuss on whether we want etcdbr to support this use case, or can we remove this and only support cases where we mandatorily have full snapshots in the bucket? Since etcdbr is the agent who pushes these backups to the bucket in the first place, and etcdbr always pushes an initial full snapshot before pushing delta snapshots, I feel this use case might not be valid.

/cc @ashwani2k @unmarshall