PostgreSQL 9.6 scales well on a single node up to 4 CPU sockets. PostgreSQL scales well up to hundreds of active sessions, and up to thousands of connected sessions when using a session pool. Further scalability is achieved in each annual release.
PostgreSQL provides multi-node read scalability using the Hot Standby feature. Multi-node write scalability is under active development. The starting point for this is Bi-Directional Replication (discussed in Chapter 12, Replication and Upgrades).