[cma256]

Node count doesn't matter. You could use an embedded database and encounter the same problem. There is some time T between when you acquire a lock and release it. Depending on the amount of contention in your system, this will have some affect on total throughput (i.e. Amdahl's law).

[justinclift]

How familiar are you with MVCC?

https://www.postgresql.org/docs/current/mvcc-intro.html

Asking because needing a lock for changing a row isn't the only approach that can be taken.

[senderista]

Almost all commercial MVCC implementations (including Postgres) use row locks. Very few use OCC even though it's arguably a more natural fit for MVCC. Pessimistic locking is simply more robust over varied workloads.