Introducing Read Replicas

Introduction

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.

A read replica uses a single-node architecture (without a standby 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.

Functions

• Read replica specifications can be different from primary DB instance specifications.
  

  To prevent a read replica creation failure, long delay, and high load of the read replica, it is recommended that the specifications of the read replica be at least equal to those of the primary 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.

Constraints

• A maximum of five read replicas can be created for a DB instance.
• You can purchase read replicas only for your created primary DB instance.
• You cannot stop a read replica without stopping the primary instance. If you stop a primary instance, read replicas (if there are any) will also be stopped.
• All databases and tables in the primary instance are synchronized to read replicas. Data of the primary instance, standby instance, and read replicas is consistent.
• Read replicas do not support automated backups or manual backups. Read replicas do not provide binlogs.
• 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 or deletion.
• Read replicas do not support database account creation. Create database accounts on the primary DB instance. For details, see Creating a Database Account.

Creating and Managing a Read Replica

• Creating a Read Replica
• Managing a Read Replica