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Updated at: Apr 02, 2022 GMT+08:00

Introducing Read Replicas


Only RDS for SQL Server 2017 Enterprise Edition supports read replicas.

In read-intensive scenarios, a single DB instance may be unable to handle the read pressure and service performance may be affected. To expand the DB instance read ability to offload read pressure on the database, you can create one or more read replicas in a region. These read replicas can process a large number of read requests and increase application throughput. You need to separately configure connection addresses of the primary DB instance and each read replica on your applications so that all read requests can be sent to read replicas and write requests to the primary DB instance.

A read replica uses a single-node architecture (without a slave node). Changes to the primary DB instance are also automatically synchronized to all associated read replicas through the native SQL Server replication function. The synchronization is not affected by network latency. Read replicas and the primary DB instance must be in the same region but can be in different AZs.

Billing Standards

Read replicas are billed on a pay-per-use basis.


  • Specifications of read replicas can be different from those of the primary DB instance, and can be changed at any time.
  • You do not need to maintain separate database accounts or databases. They are synchronized from the primary DB instance.
  • Read replicas support system performance monitoring.

    RDS provides up to 20 monitoring metrics, including storage space, IOPS, the number of database connections, CPU usage, and network traffic. You can view these metrics to learn about the load on DB instances.

  • You can bind EIPs to read replicas and unbind EIPs from read replicas.
  • Permission modifications to the primary DB instance are automatically synchronized to the standby DB instance and read replicas.
  • Read replicas do not support automated backups or manual backups.
  • Read replicas do not support restoration from backups to new, existing, or original read replicas.
  • Data cannot be migrated to read replicas.


A maximum of five read replicas can be created for each primary DB instance.

Creating and Managing a Read Replica

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