Requirements and tips for configuring replication

This page provides information about working with read replicas.

For information about how to configure a read replica, see Creating read replicas.

Read replicas

Read replicas are Cloud SQL instances that replicate from a Cloud SQL primary instance. Read replicas are read-only. You cannot write to them. You use a replica to offload read requests anc analytics traffic from the primary.

For information about how to configure a read replica, see Creating Read Replicas.

Quick reference for Cloud SQL read replica topics

Topic Discussion
High availability Read replicas neither provide high availability nor offer it.
Failover A primary instance cannot failover to a read replica, and read replicas are unable to failover in any way during an outage.
Maintenance windows Maintenance windows cannot be set on read replicas and they do not share maintenance windows with the primary instance. Maintenance can occur at any time on the read replica. Maintenance occurs on read replicas at a different time than on the primary instance.
Disruptive upgrades Read replicas can experience a disruptive upgrade at any time.
Performance When you create a read replica, it does not impact the performance or availability of the primary instance.
Multiple read replicas You can create multiple read replicas for a single primary instance.
Load balancing Cloud SQL does not provide load balancing between replicas.
Settings The settings of the primary instance are propagated to the replica, including the password for the postgres user and changes to the user table.
Machine types Read replicas can be a different machine type (or tier) than the primary instance. Read replicas can have more CPUs and memory than the primary instance, but they cannot have less.
Regions Read replicas must be in the same region as the primary instance.
User tables You cannot make changes to the user table on the replica. All user changes must be done on the primary instance.
Backups You cannot configure backups on the replica.
Restoring the primary instance You cannot restore the primary of a replica while the replica exists. Before restoring an instance from a backup, you must promote or delete all of its replicas.
Deleting the primary instance Before you can delete a primary instance, you must promote all of its read replicas to stand-alone instances or delete the read replicas.
Creating a replica of a replica You cannot create a replica of a replica.
Stopping a replica You cannot stop a replica. You can restart, delete, or disable replication on it, but you cannot stop it as you can a primary instance.


  • A read replica is charged at the same rate as a standard Cloud SQL instance. There is no charge for the data replication.

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