A PostgreSQL instance

A Cluster is a single, complete, running, PostgreSQL server (IE: cluster of databases)

• One PostgreSQL Server
• Listening on one port (may be multiple addresses)
• One set of data files (including tablespaces)
• One set of Write Ahead Log

Operations done on a Cluster:

• Initialization (initdb)
• Start / Stop the cluster
• File-level Backup / Restores
• Streaming Replication

Objects defined at Cluster level

• Users / Roles
• Tablespaces
• Databases