In scenarios with more reads but fewer writes, a single instance may not be able to handle the read load, which may even affect the business. To implement the auto-scaling of read capabilities and mitigate the pressure, you can create one or multiple read-only instances to sustain high numbers of database reads and increase the application throughput.
Prerequisites
The compatible database version is MySQL 5.7 or 8.0 (kernel version 3.1.2 or later).
Billing
Compute Billing Model
When the Instance Mode is set to provisioned resource: If the read-write instance under the cluster is subscribed on an annual or monthly basis, then the billing mode for the newly expanded provisioned resource read-only nodes will also be on a subscription basis. If the read-write instance under the cluster is billed on a pay-as-you-go basis, then the billing mode for the newly expanded provisioned resource read-only nodes will also be on a pay-as-you-go basis. If the cluster is expanded with new Serverless read-only nodes by enabling Serverless, or if the provisioned resource read-only nodes are converted to Serverless read-only nodes, then the billing mode for the new Serverless read-only nodes will be Serverless.
When the Instance Mode is Serverless: The billing mode for newly added read-only nodes in the cluster is Serverless.
Storage Billing Mode
As TDSQL-C for MySQL is billed by the actual storage used per hour, you don’t need to purchase storage space in advance. The storage of the read-only instance uses that of the entire cluster.
Adjusting read-only instance configuration
Region and AZ: Read-only instance needs to be deployed in the same AZ of a region where the read-write instance resides.
Database Compatibility: It must be the same as that of the read-write instance.
Specification: It may be different from that of the read-write instance and can be modified at any time. The read-only instance must have a specification not less than that of the read-write instance; otherwise, it may experience high latency and load.
Instance Name: It must contain less than 60 letters, digits, or symbols (-_.).
Network: It is the same as that of the read-write instance.
Project: It is the same as that of the read-write instance.
Monitoring and Alarm: It provides rich monitoring views of system performance indicators, such as memory utilization, QPS, TPS, and max connections.
Feature Limits
The number of read-only instances can be created: 15.
Database management: Databases can be neither created nor deleted.
Account management: Account creation, deletion, authorization, password modification of the account are not supported.
Creating Read-Only Instance