Hot Standby (or read replicas) is the name for the PostgreSQL feature that allows us to connect to a standby node and execute read-only queries. Most importantly, Hot Standby allows us to run queries while the standby is being continuously updated through either file-based or streaming replication.
Hot Standby allows you to offload large or long running queries or parts of your read-only workload to the standby nodes. Should you need to switchover or failover to the standby node, your queries will keep executing during the promotion process to avoid any interruption of service.
You can add additional Hot Standby nodes to scale the read-only workload. There is no hard limit on the number of standby nodes, as long as you ensure enough server resources are available and parameters are set correctly – 10, 20, or more nodes are easily possible...