[mikesun]

I think there's some confusion at what distributed databases like Spanner, Cockroach, etc do:

- A given row of data is configured to have N replicas, e.g. 3, 5, etc, but N doesn't have to equal the actual size the database cluster. e.g. you can have a database cluster of 21 nodes with N being 3. N represents the "Raft cluster size" and the database is composed of many "Raft clusters" that are responsible for segments of the data space. You can horizontally scale the size of the database cluster by adding more nodes and thus more "Raft clusters"

- Raft/Paxos are used to ensure linearizable writes to those replicas through a leader

- Multi row/partition transactions are handled through a different kind consensus called atomic commit/2 phase commit that's orthogonal to Raft/Paxos consensus: https://timilearning.com/posts/mit-6.824/lecture-12-distribu...

- Systems like Spanner, Cockroach have higher write latencies because replicas in Raft cluster have to achieve quorum consensus, but reads latency can mostly not be affected by always reading from the leader of a cluster via things like leader leases.