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

Introducing Read Replicas

Introduction

Currently, RDS for MySQL supports read replicas and read/write splitting.

To create read replicas billed on the yearly/monthly basis, contact customer service to apply for the required permissions.

In read-intensive scenarios, a single DB instance may be unable to handle the read pressure and service performance may be affected. To offload read pressure on the primary DB instance, you can create one or more read replicas in the same region as the primary instance. These read replicas can process a large number of read requests and increase application throughput.

Once read replicas are created, you can enable read/write splitting. Write requests are automatically routed to the primary DB instance and read requests are routed to read replicas by user-defined weights.

If read/write splitting is disabled, separately configure connection addresses for the primary DB instance and each read replica on your applications so that read requests are sent to read replicas and write requests are sent 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 MySQL 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 yearly/monthly or pay-per-use basis.

Functions

  • Read replica specifications can be different from primary DB instance specifications. It is recommended that the read replica specifications be greater than or equal to the primary DB instance specifications to prevent long delay and high load.
  • 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.

  • 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.
  • Read replicas do not support database creation and deletion.
  • Read replicas do not support database account creation.

Constraints

To create read replicas billed on the yearly/monthly basis, contact customer service to apply for the required permissions.

A maximum of five read replicas can be created for each primary DB instance. To create up to 10 read replicas for a primary DB instance, contact customer service to apply for the required permissions.

  • Read replicas cannot be recycled after they are deleted.

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