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Not doing read locking is not a game-changer.

Firebird doesn't do read locking. Neither does Lotus Notes. Both have been around about 20 years.

Not doing read locking alone. Combine it with a planet-scale data storage system...

Postgres and Oracle?

PostgreSQL uses MVCC to ensure ACID compliance without read locks. Uncommitted concurrent transactions are isolated from each other.

Datomic.