Updated on 2024-07-30 GMT+08:00

Configuring Read Weights

This section describes how to adjust read/write weights of a primary instance and its read replicas. If one DDM instance is associated with multiple data nodes, you can configure read weights of the data nodes in batches.

Precautions

If a data node (associated DB instance) has no read replicas, you cannot configure a read/write weight for it.

Batch Configuring Read Weights for Multiple DB Instances

  1. Log in to the DDM console.
  2. On the Instances page, locate the DDM instance whose associated DB instances you want to configure read weights for.
  3. Click the instance name and go to the Basic Information page.
  4. In the navigation pane on the left, choose Data Nodes and click Configure Read Weight.

    Figure 1 Data Nodes

  5. Configure read weights for DB instances associated with the DDM instance

    In the displayed dialog box, you can click Synchronize to apply the read weight of the first DB instance to other instances. This operation requires that each of the DB instances has the same number of read replicas.

    Otherwise, you need to manually configure the read weight for each DB instance.

    • The read weight can be 0 to 100.
    • Read replicas of one of the DB instance handle all separated read requests by default. To re-assign read/write requests, you can configure read weights of the instance and its read replicas.
    • After the read weights are configured, the primary instance and its read replica will handle read requests according to the following formulas:
      • Primary instance: Read weight of primary instance/Total read weights of primary instance and read replica
      • Read replica: Read weight of read replica/Total read weights of primary instance and read replica

      For example, if an RDS for MySQL instance contains one primary instance and one read replica and read weights of the primary instance and its read replica are 20 and 80 respectively, they will process read requests in the ratio of 1:4. In other words, the primary instance processes 1/4 of read requests and the read replica processes 3/4. Write requests are automatically routed to the primary instance.

  6. After the read weight is configured, you can view the updated read weight in the data node list.

Configuring the Read Weight for a Single DB Instance

  1. Log in to the DDM console.
  2. On the Instances page, locate the DDM instance whose associated DB instance you want to configure a read weight for.
  3. Click the instance name and go to the Basic Information page.
  4. In the navigation pane on the left, choose Data Nodes.
  5. Locate the required instance and click Configure Read Weight in the Operation column.

    Figure 2 Configuring the read weight for a single DB instance
    • The read weight can be 0 to 100.
    • Read replicas of one of the DB instance handle all separated read requests by default. To re-assign read/write requests, you can configure read weights of the instance and its read replicas.
    • After the read weights are configured, the primary instance and its read replica will handle read requests according to the following formulas:
      • Primary instance: Read weight of primary instance/Total read weights of primary instance and read replica
      • Read replica: Read weight of read replica/Total read weights of primary instance and read replica

      For example, if an RDS for MySQL instance contains one primary instance and one read replica and read weights of the primary instance and its read replica are 20 and 80 respectively, they will process read requests in the ratio of 1:4. In other words, the primary instance processes 1/4 of read requests and the read replica processes 3/4. Write requests are automatically routed to the primary instance.

  6. After the read weight is configured, you can view the updated read weight in the data node list.