Configuring the Delay Threshold and Routing Policy

After read/write splitting is enabled, you can configure the delay threshold and routing policy as required.

Table 1 Read/write splitting parameters

Parameter

Description

Delay Threshold

The maximum delay for data to be synchronized from primary DB instances to read replicas. To prevent data inconsistencies between primary DB instances and read replicas from lasting too long, if the delay of a read replica exceeds the configured threshold, read requests are not forwarded to the read replica regardless of the read weight distributed to it.

When read/write splitting is enabled, the default delay threshold is 30s and the default value range is 0-7,200s. It is recommended that the threshold be greater than or equal to 30s. Traffic is not allocated to read replicas whose delay exceeds the configured threshold.

Read Weight Distribution

When read/write splitting is enabled, the read weight of the primary DB instance is 0 by default. You can modify the read weights distributed to read replicas.

Read replicas with higher read weight distributions process more read requests. For example, if the read weights distributed to one primary DB instance and four read replicas are 0, 100, 200, 500, and 300, respectively, the primary DB instance does not process read requests (write requests are all automatically forwarded to the primary DB instance) while the four read replicas process read requests with a ratio of 1:2:5:3.

The system automatically distributes weights to read replicas, including read replicas created afterwards, according to their specifications based on the distribution rules listed in Rules for Distributing Weights.

Configuring Delay Threshold

  1. Log in to the management console.

  2. Click image1 in the upper left corner and select a region and a project.

  3. Click Service List. Under Database, click Relational Database Service. The RDS console is displayed.

  4. On the Instances page, click the target DB instance. The Basic Information page is displayed.

  5. In the navigation pane on the left, click Database Proxy.

  6. In the proxy information area, click image2 next to the Delay Threshold field.

Configuring Routing Policy in Single-Proxy Mode

  1. Log in to the management console.

  2. Click image3 in the upper left corner and select a region and a project.

  3. Click Service List. Under Database, click Relational Database Service. The RDS console is displayed.

  4. On the Instances page, click the target DB instance. The Basic Information page is displayed.

  5. In the navigation pane on the left, click Database Proxy.

  6. If proxy load balancing is not enabled, click Configure next to the Routing Policy field in the proxy information area. In the displayed dialog box, configure read weights for the primary instance and read replicas.

    Note

    • The system automatically distributes weights to read replicas, including read replicas created afterwards, according to the default distribution rules. If a read replica breaks down or is deleted, the weight is automatically removed. After the read replica recovers, the weight is automatically restored.

    • If the weight of a node is set to 0, read requests will not be routed to the node. If the weights of all nodes are set to 0, read requests will be randomly routed to these nodes.

  7. Click OK and view the weights on the Database Proxy page.

  8. If proxy load balancing is enabled, click Configure next to the Routing Policy field in the proxy information area. In the displayed dialog box, set required parameters.

    Select Load balancing as the routing policy. Read requests will be automatically distributed to read replicas based on the number of active connections to balance the load among these read replicas.

    Set Read Requests Accepted by Primary DB Instance:

    • Yes: Read requests can be routed to both the primary instance and read replicas, which increases the load of the primary instance to some extent. Configure this parameter based on your workload requirements.

    • No: To offload read pressure from the primary instance, read requests are only routed to read replicas.

  9. Click OK. On the Database Proxy page, view the result. You can select the instances for load balancing as required.