Kine (https://github.com/k3s-io/kine) is a shim or an external process (when not k3s) that translates the etcd api to enable compatibility with a database or alternative data store.
Kubernetes natively talks etcd, so this translation is what enables its usage with sqlite or another database, but it incurs an overhead.
I don't have specific numbers unfortunately since it was years ago I benchmarked Kine against etcd. But I had a better results with etcd both in cluster and single node.
