What Are the Differences Between the Storage Space and Backup Space of an RDS for PostgreSQL Primary/Standby Instance?

In an RDS for PostgreSQL primary/standby instance, the node accessed by applications is called the primary instance, and data on the primary instance is synchronized to the other node (called the standby instance) in real time. The standby instance acts as a failover target for the primary. If the primary instance fails, RDS for PostgreSQL promotes the standby instance to primary for high availability.

• Storage space

  Storage space of the standby instance is the same as that of the primary instance. Scaling up the storage space of the primary instance will also scale up that of the standby instance.

  Data on the primary instance may not be synchronized to the standby instance fast enough when there are a large number of data writes or a long replication delay. If this happens, the primary instance retains WAL logs for replication. WAL logs will be stacked and occupy storage space.

• Backup space

  Backup space is used to store automated backups, manual backups, and SQL audit logs. You can get a free backup space of the same size as your purchased storage space. If the free backup space is used up, the additional space will be billed. You can configure a custom backup policy to best fit your workloads' needs.

  To release backup space, see How Do I Clear RDS Backup Space?