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Create and use read-only replicas

PostgreSQL® read-only replicas provide a great way to reduce the load on the primary server by enabling read-only queries to be performed against the replica. It's also a good way to optimise query response times across different geographical locations since, with Aiven, the replica can be placed in different regions or even different cloud providers.

note

If your service is running a business-* or premium-* plan, you have standby nodes available in a high availability setup. These support read-only queries to reduce the effect of slow queries on the primary node.

Create a replica​

To set up a remote replica:

  1. Log in to the Aiven Console.
  2. Select the PostgreSQL instance for which you want to create a remote replica.
  3. In the Overview page of your service, select Create replica.
  4. Enter a name for the remote replica and select the cloud provider, region, and Aiven for PostgreSQL service plan that you want to use, then select Create.

The read-only replica is created and added to the list of services in your project. The Overview page of the replica indicates the name of the primary service for the replica.

Read-only replicas can be manually promoted to become the master database if the need arises. For more complex high availability and failover scenarios check the related documentation.

tip

You can promote a read-replica to master using the API endpoint to delete the service integration and passing the integration_id of the replica service.

Deleting the integration that comes with integration_type of value read_replica will lead to the service to no longer be a read-replica, hence becoming the master.

Use a replica​

To use a read only replica:

  1. Log in to the Aiven Console and select your PostgreSQL service.

  2. In the Overview page, copy the Replica URI an use it to connect via psql:

    psql POSTGRESQL_REPLICA_URI

Identify replica status​

To check whether you are connected to a primary or replica node, run the following command within a psql terminal already connected to a database:

SELECT * FROM pg_is_in_recovery();

If the above command returns TRUE if you are connected to the replica, and FALSE if you are connected to the primary server.

warning

Aiven for PostgreSQL uses asynchronous replication and so a small lag is expected. When running an INSERT operation on the primary node, a minimal delay (usually less than a second) can be expected for the change to be propagated to the replica and to be visible there.

Read-replica for disaster recovery​

High availability enables data distribution across availability zones within a single region. To do this without a default multi-region service with node allocation spanning multiple regions:

  1. Establish a high-availability Aiven for PostgreSQL service within a single region.
  2. Configure a remote read-only replica in a different region or even on an alternate cloud platform.

As a result, you introduce an additional node in the distinct region/cloud. Since this node does not work as a hot standby node, you might want to promote it manually to the primary role, which makes it operate as an independent standalone service.